Teach-In Electronics by Lee Yuan

Teach-In 2011

7($&+ ,1 $ %52$' %$6(' ,1752'8&7,21 72 (/(&7521,&6 0ARTª ª)NTRODUCTIONªTOªSIGNALSªINª ELECTRONICªCIRCUITSªANDªSYSTEMS By Mike and Richard Tooley

% "%'). THIS NEW 5FBDI *O SERIES BY INTRODUCING THE SIGNALS USED TO CONVEY INFORMATION IN ELECTRONIC CIRCUITS AND THE UNITS THAT WE USE TO MEASURE THE QUANTITIES IN ELECTRONIC CIRCUITS 7E CONCLUDE THIS PART BY LOOKING AT SOME SIMPLE ELECTRONIC CIRCUITS THAT YOU CAN BUILD AND TEST USING #IRCUIT 7IZARD SOFTWARE SEE PAGES AND

3IGNALSªINªELECTRONICªCIRCUITSª ANDªSYSTEMS

4HIS ÚRST PART OF OUR 4EACH )N SERIES WILL PROVIDE YOU WITH AN INTRODUC TION TO THE SIGNALS THAT CONVEY JO GPSNBUJPO IN ELECTRONIC CIRCUITS 7E WILL ALSO INTRODUCE YOU TO SOME OF THE UNITS THAT ARE USED WHEN MEASURING ELECTRICAL QUANTITIES SUCH AS CUR RENT VOLTAGE AND FREQUENCY 9OU WILL LEARN ABOUT THE DIFFERENCE BETWEEN ANALOGUE AND DIGITAL SIGNALS AND HOW

TO RECOGNISE SIGNALS FROM THE SHAPE OF THEIR WAVEFORMS "EING ABLE TO lREADm AND INTERPRET A CIRCUIT DIAGRAM OR lSCHEMATICm IS AN ESSENTIAL SKILL REQUIRED OF EVERY ELEC TRONIC TECHNICIAN AND ENGINEER -ANY DIFFERENT PARTS AND DEVICES ARE USED IN ELECTRONIC CIRCUITS AND IT IS IMPORTANT THAT YOU SHOULD BE ABLE TO RECOGNISE THEM BOTH FROM THE SYMBOLS THAT WE USE TO REPRESENT THEM IN THEORETICAL CIRCUIT DIAGRAMS AND ALSO FROM THEIR PHYSICAL APPEARANCE

,EARN 3IGNALSªANDªSIGNALªCONVERSION

)N ALL FORMS OF COMMUNICATION SIG NALS ARE USED TO CONVEY INFORMATION 4HE SIGNALS THAT WE USE IN EVERYDAY LIFE CAN TAKE MANY FORMS INCLUDING ÛASHING LIGHTS SHOUTING WAVING OUR HANDS SHAKING OUR HEADS AND OTH

ERS FORMS OF lBODY LANGUAGEm )N FACT LIFE WOULD BE VERY DIFÚCULT WITHOUT SIGNALS q THINK ABOUT DRIVING A CAR OR MOTORBIKE IN HEAVY TRAFÚCØ )N THIS SECTION WE WILL LOOK AT HOW SIGNALS ARE USED IN ELECTRONICS HOW THEY CAN BE CONVERTED FROM ONE FORM TO ANOTHER AND HOW THEY ARE MEASURED )N ELECTRONICS SIGNALS CAN TAKE MANY FORMS INCLUDING CHANGES IN VOLTAGE LEVELS PULSES OF CURRENT AND SEQUENCES OF BINARY CODED DIGITS OR CJUT 3IGNALS THAT VARY CONTINUOUSLY IN LEVEL ARE REFERRED TO AS ANALOGUE SIG NALS WHILE THOSE THAT USE DISCRETE IE ÚXED LEVELS ARE REFERRED TO AS DIGITAL SIGNALS 3OME TYPICAL ANALOGUE AND DIGITAL SIGNALS ARE SHOWN IN &IG .OTICE HOW THE DIGITAL SIGNAL EXISTS ONLY AS A SERIES OF DISCRETE VOLTAGE LEVELS WHILE THE ANALOGUE SIGNAL VARIES CONTINUOUSLY FROM ONE VOLTAGE LEVEL TO ANOTHER

Everyday Practical Electronics, November 2010

Teach-In 2011 3IGNALS CAN ALSO BE QUITE EASILY CONVERTED FROM ONE FORM TO ANOTHER &OR EXAMPLE THE SIGNAL FROM THE STAGE MICROPHONE AT A LIVE RADIO BROADCAST WILL BE AN ANALOGUE SIGNAL AT THE POINT AT WHICH THE ORIGINAL SOUND IS PRODUCED IE ON STAGE !FTER APPROPRIATE PROCESSING WHICH MIGHT INVOLVE AMPLIÚCATION AND OR REMOVAL OF NOISE AND OTHER UNWANTED SOUNDS IT MIGHT THEN BE CONVERTED TO A DIGITAL SIGNAL FOR RADIO TRANSMIS SION AND THEN CONVERTED BACK TO AN ANALOGUE SIGNAL BEFORE BEING AMPLI ÚED AND SENT TO THE LOUDSPEAKER AT THE POINT OF RECEPTION ! DEVICE THAT CONVERTS AN ANALOGUE SIGNAL TO DIGITAL FORMAT IS CALLED AN BOBMPHVF UP EJHJUBM DPOWFSUFS !$# WHILE ONE THAT CONVERTS A DIGITAL SIGNAL TO ANALOGUE IS REFERRED TO AS A EJHJUBM UP BOBMPHVF DPOWFSUFS $!# !N ELECTRONIC SYSTEM THAT USES BOTH ANALOGUE AND DIGITAL SIGNALS IS SHOWN IN &IG

'JH 5ZQJDBM BOBMPHVF BOE EJHJUBM TJHOBMT

%LECTRONICªUNITS

! NUMBER OF UNITS ARE COMMONLY USED IN ELECTRONICS SO WE SHALL START BY INTRODUCING SOME OF THEM ,ATER WE WILL BE PUT THESE UNITS TO USE WHEN WE SOLVE SOME SIMPLE CIRCUIT PROBLEMS BUT SINCE ITmS IMPORTANT TO GET TO KNOW THESE UNITS AND ALSO TO BE ABLE TO RECOGNISE THEIR ABBREVIATIONS AND SYMBOLS WE HAVE SUMMARISED THEM IN 4ABLE

0LEASE NOTEØ

&REQUENCY AND BIT RATE ARE VERY SIMILAR 4HEY BOTH INDICATE THE SPEED AT WHICH A SIGNAL IS TRANSMITTED BUT BIT RATE IS USED FOR DIGITAL SIGNALS WHILE FRE QUENCY IS USED WITH ANALOGUE SIGNALS

'JH "O FMFDUSPOJD TZTUFN UIBU VTFT CPUI BOBMPHVF BOE EJHJUBM TJHOBMT

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Everyday Practical Electronics, November 2010

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Teach-In 2011 0LEASE NOTEØ

4O AVOID CONFUSION BETWEEN THE SYMBOLS AND THE ABBREVIATIONS THAT WE USE FOR UNITS THE FORMER ARE NORMALLY DISPLAYED IN ITALIC FONT &OR EXAMPLE A CAPITAL LETTER 6 IS USED AS BOTH THE ABBREVIATION FOR VOLTAGE AND FOR ITS UNIT SYMBOL THE 6OLT 7HEN USED AS A SYM BOL IN A FORMULA IT IS CONVENTIONALLY SHOWN IN ITALIC AS 7 AND WHEN USED AS SHORTHAND FOR VOLTS IT IS SHOWN IN NORMAL NON ITALIC FONT AS l6m

-ULTIPLESªANDª SUB MULTIPLESª

5NFORTUNATELY BECAUSE THE NUMBERS CAN BE VERY LARGE OR VERY SMALL MANY OF THE ELECTRONIC UNITS CAN BE CUMBER SOME FOR EVERYDAY USE &OR EXAMPLE THE VOLTAGE PRESENT AT THE ANTENNA OF A MOBILE PHONE COULD BE AS LITTLE AS ONE TEN MILLIONTH OF A VOLT OR 6 #ONVERSELY THE RESISTANCE SEEN AT THE INPUT OF AN AUDIO AMPLIÚER STAGE COULD BE MORE THAN ONE HUNDRED THOUSAND OHMS OR : 4O MAKE LIFE A LOT EASIER WE USE A STANDARD RANGE OF MULTIPLES AND SUB MULTIPLES 4HESE USE A PREÚX LETTER IN ORDER TO ADD A MULTIPLIER TO THE QUOTED VALUE AS SHOWN IN 4ABLE

0LEASE NOTEØ

%XPONENT NOTATION IS OFTEN USEFUL WHEN PERFORMING CALCULATIONS USING VERY LARGE OR VERY SMALL NUMBERS 9OU CAN USE EXPONENT NOTATION BY PRESSING THE EXPONENT % OR ENGINEERING %.' BUTTON ON YOUR CALCULATOR

#ONVERTINGªTO FROMªMULTIPLESª ANDªSUB MULTIPLES

#ONVERTING TO AND FROM MULTIPLES AND SUB MULTIPLES IS ACTUALLY QUITE EASY AS THE FOLLOWING EXAMPLES SHOW

%XAMPLE $POWFSU )[ UP L)[ 4O DO THIS YOU JUST NEED TO MOVE THE DECIMAL POINT UISFF PLACES TO THE MFGU 4HIS IS THE SAME AS DIVIDING BY BECAUSE THERE ARE (Z IN K(Z -OVING THE DECIMAL POINT THREE PLACES TO THE LEFT TELLS US THAT (Z K(Z K(Z %XAMPLE $POWFSU : UP .: 4O DO THIS YOU NEED TO MOVE THE DECIMAL POINT TJY PLACES TO THE MFGU 4HIS IS THE SAME AS DIVIDING BY BE CAUSE THERE ARE : IN -: -OVING THE DECIMAL POINT SIX PLACES TO THE LEFT TELLS US THAT : -:

0LEASE NOTEØ

-ULTIPLYING BY IS EQUIVALENT TO MOVING THE DECIMAL POINT THREE PLACES TO THE RIGHT WHILE DIVIDING BY IS EQUIVALENT TO MOVING THE DECIMAL POINT THREE PLACES TO THE LEFT 3IMILARLY MULTIPLYING BY IS EQUIVALENT TO MOVING THE DECIMAL POINT SIX PLACES TO THE RIGHT WHILE DIVIDING BY IS EQUIVALENT TO MOVING THE DECIMAL POINT SIX PLACES TO THE LEFT

7AVEFORMSªANDªWAVEFORMª MEASUREMENT

! GRAPH SHOWING THE VARIATION OF VOLTAGE OR CURRENT PRESENT IN A CIRCUIT

%XAMPLE $POWFSU 7 UP N7 4O DO THIS YOU NEED TO MOVE THE DECI MAL POINT UISFF PLACES TO THE SJHIU 4HIS IS THE SAME AS MULTIPLYING BY BECAUSE THERE ARE M6 IN 6 -OVING THE DECIMAL POINT THREE PLACES TO THE RIGHT TELLS US THAT 6 M6 %XAMPLE $POWFSU LCQT UP .CQT 4O DO THIS YOU NEED TO MOVE THE DECI MAL POINT UISFF PLACES TO THE MFGU 4HIS IS THE SAME AS DIVIDING BY BECAUSE THERE ARE KBPS IN -BPS -OVING THE DECIMAL POINT THREE PLACES TO THE LEFT TELLS US THAT KBPS -BPS

'JH 4PNF DPNNPO XBWFGPSNT 4ABLE 3OMEªCOMMONªMULTIPLESªANDªSUB MULTIPLES

Multiple

Exponent notation Prefix

u1,000,000,000

u1,000,000

Abbreviation

Example

Giga

1.2GHz (1,200 million Hertz)

Mega

2.2M: (2.2 million Ohms)

u1,000

Kilo

4kbs (4,000 bits per second)

None

none

220: (220 Ohms)

Milli

45mV (0.045 Volts)

Micro

33PA (0.000033 Amps)

Nano

450nW (0.00000045 Watts)

Everyday Practical Electronics, November 2010

Teach-In 2011 IS KNOWN AS A WAVEFORM 7AVEFORMS SHOW US HOW VOLTAGE OR CURRENT SIG NALS VARY WITH TIME 4HERE ARE MANY COMMON TYPES OF WAVEFORM ENCOUN TERED IN ELECTRONIC CIRCUITS INCLUDING TJOF OR SINUSOIDAL TRVBSF USJBOHMF SBNQ OR TBXUPPUI WHICH MAY BE EITHER POSITIVE OR NEGATIVE GOING AND QVMTF #OMPLEX WAVEFORMS LIKE SPEECH AND MUSIC USUALLY COMPRISE MANY DIFFERENT SIGNAL COMPONENTS AT DIFFER ENT FREQUENCIES 0ULSE WAVEFORMS ARE OFTEN CATEGORISED AS EITHER REPETITIVE OR NON REPETITIVE THE FORMER COMPRISES A PATTERN OF PULSES THAT REPEATS REGU LARLY WHILE THE LATTER COMPRISES PULSES WHICH EACH CONSTITUTE A UNIQUE EVENT 3OME COMMON WAVEFORMS ARE SHOWN IN &IG &REQUENCY 4HE FREQUENCY OF A REPETITIVE WAVE FORM IS THE NUMBER OF CYCLES OF THE WAVEFORM WHICH OCCUR IN UNIT TIME IE ONE SECOND &REQUENCY IS EXPRESSED IN (ERTZ (Z AND A FREQUENCY OF (Z IS EQUIVALENT TO ONE CYCLE PER SECOND (ENCE IF A VOLTAGE HAS A FREQUENCY OF (Z CYCLES OF IT WILL OCCUR IN EVERY SECOND 0ERIODIC TIME 4HE PERIODIC TIME OR PERIOD OF A WAVEFORM IS THE TIME TAKEN FOR ONE COMPLETE CYCLE OF THE WAVE SEE &IG 4HE RELATIONSHIP BETWEEN PERIODIC TIME AND FREQUENCY IS THUS U G OR G U WHERE U IS THE PERIODIC TIME IN S AND G IS THE FREQUENCY IN (Z

'JH 0OF DZDMF PG B TJOFXBWF WPMUBHF TIPXJOH JUT QFSJPEJD UJNF

%XAMPLE " XBWFGPSN IBT B GSFRVFODZ PG )[ 8IBU JT UIF QFSJPEJD UJNF PG UIF XBWFGPSN (ERE WE MUST USE THE RELATIONSHIP U G WHERE G (Z (ENCE U S OR MS %XAMPLE " XBWFGPSN IBT B QFSJPEJD UJNF PG NT 8IBU JT JUT GSFRVFODZ (ERE WE MUST USE THE RELATIONSHIP G U WHERE U MS OR S (ENCE G (Z !MPLITUDE 4HE AMPLITUDE OR QFBL WBMVF OF A WAVEFORM IS A MEASURE OF THE EXTENT OF ITS VOLTAGE OR CURRENT EXCURSION FROM THE RESTING VALUE USUALLY ZERO 4HE QFBL UP QFBL VALUE FOR A WAVE WHICH IS SYMMETRICAL ABOUT ITS RESTING VALUE IS TWICE ITS PEAK VALUE SEE &IG 4HESE UNITS ARE USUALLY MORE CONVEN IENT TO USE WHEN TAKING MEASUREMENTS FROM A WAVEFORM DISPLAY

0ULSEªWAVEFORMS

7HEN DESCRIBING RECTANGULAR AND PULSE WAVEFORMS WE USE A DIFFERENT SET OF PARAMETERS SEE &IG 4HESE INCLUDE /N TIME TON 4HIS IS THE TIME FOR WHICH THE PULSE IS PRESENT AT ITS MAXIMUM AMPLITUDE 4HIS IS SOMETIMES REFERRED TO AS THE lNBSL UJNFm .OTE THAT WHEN A PULSE IS NOT PER FECTLY RECTANGULAR IE WHEN IT TAKES SOME TIME TO CHANGE FROM ONE LEVEL TO THE OTHER WE DEÚNE THE OFF TIME AS THE TIME FOR WHICH THE PULSE AMPLITUDE REMAINS ABOVE OF ITS MAXI MUM VALUE /FF TIME T/&& 4HIS IS THE TIME FOR WHICH THE PULSE IS NOT PRESENT IE ZERO VOLTAGE OR CURRENT 4HIS IS SOMETIMES REFERRED TO AS THE lTQBDF UJNFm

Everyday Practical Electronics, November 2010

.OTE THAT WHEN A PULSE IS NOT PER FECTLY RECTANGULAR AND TAKES SOME TIME TO CHANGE FROM ONE LEVEL TO AN OTHER WE DEÚNE THE OFF TIME AS THE TIME FOR WHICH THE PULSE AMPLITUDE FALLS BELOW OF ITS MAXIMUM VALUE 0ULSE PERIOD T 4HIS IS THE TIME FOR ONE COMPLETE CYCLE OF A REPETITIVE PULSE WAVEFORM 4HE PERIODIC TIME IS THUS EQUAL TO THE SUM OF THE ON AND OFF TIMES BUT ONCE AGAIN NOTE THAT THIS IS ONLY VALID IF THE PULSE TRAIN IS REPETITIVE AND IS MEAN INGLESS IF THE PULSES OCCUR AT RANDOM INTERVALS 7HEN A PULSE TRAIN IS NOT PERFECTLY RECTANGULAR THE PULSE PERIOD IS MEAS URED AT THE AMPLITUDE POINTS

'JH 0OF DZDMF PG B TJOFXBWF WPMU BHF TIPXJOH JUT QFBL BOE QFBL UP QFBL WBMVFT 0ULSE REPETITION FREQUENCY PRF 4HE PULSE REPETITION FREQUENCY PRF IS THE RECIPROCAL OF THE PULSE PERIOD (ENCE QSG U U/. U/&& -ARK TO SPACE RATIO 4HE MARK TO SPACE RATIO OF A PULSE WAVE IS SIMPLY THE RATIO OF THE ON TO OFF TIMES (ENCE

'JH " QVMTF XBWFGPSN TIPXJOH mPOn BOE mPGGn UJNFT

Teach-In 2011 .BSL UP TQBDF SBUJP U/. U/&& .OTE THAT FOR A PERFECT SQUARE WAVE THE MARK TO SPACE RATIO WILL BE BECAUSE U/. U/&& $UTY CYCLE 4HE DUTY CYCLE OF A PULSE WAVE IS THE RATIO OF THE ON TIME TO THE ON PLUS OFF TIME AND IS USUALLY EXPRESSED AS A PERCENTAGE (ENCE %VUZ DZDMF U/. U/. U/&& Â¯ U/. U Â¯

'JH 4PNF UZQJDBM DFMMT BOE CBUUFSJFT VTFE JO FMFDUSPOJD FRVJQNFOU

&OR A PERFECT SQUARE WAVE THE DUTY CYCLE WILL BE

#ELLS ÂªBATTERIESÂªANDÂªPOWERÂª SUPPLIES

#ELLS AND BATTERIES PROVIDE THE POWER FOR A WIDE RANGE OF PORTABLE AND HAND HELD ELECTRONIC EQUIPMENT 4HERE ARE TWO BASIC TYPES OF CELL QSJNBSZ AND TFDPOEBSZ 0RIMARY CELLS PRODUCE ELECTRICAL ENERGY AT THE EXPENSE OF THE CHEMI CALS FROM WHICH THEY ARE MADE AND ONCE THESE CHEMICALS ARE USED UP NO MORE ELECTRICITY CAN BE OBTAINED FROM THE CELL !N EXAMPLE OF A PRIMARY CELL IS AN ORDINARY 6 !! ALKALINE BATTERY )N SECONDARY CELLS THE CHEMICAL ACTION IS REVERSIBLE 4HIS MEANS THAT THE CHEMICAL ENERGY IS CONVERTED INTO ELECTRICAL ENERGY WHEN THE CELL IS DISCHARGED WHEREAS ELECTRICAL ENERGY IS CONVERTED INTO CHEMI CAL ENERGY WHEN THE CELL IS BEING CHARGED !N EXAMPLE OF A SECONDARY CELL IS A 6 !! NICKEL CADMIUM .I#AD BATTERY )N ORDER TO PRODUCE A BATTERY IN DIVIDUAL CELLS ARE USUALLY CONNECTED IN SERIES WITH ONE ANOTHER AS SHOWN IN &IG 4HE VOLTAGE PRODUCED BY A BATTERY WITH N CELLS WILL BE O TIMES THE VOLTAGE OF ONE INDIVIDUAL CELL ASSUM ING THAT ALL OF THE CELLS ARE IDENTICAL &URTHERMORE EACH CELL IN THE BATTERY WILL SUPPLY THE SAME CURRENT 3ERIES CONNECTED CELLS ARE OFTEN USED TO FORM BATTERIES &OR EXAMPLE THE POPULAR 00 00 AND 00 BATTERIES ARE MADE FROM SIX lLAYEREDm 6 PRIMARY ALKALINE CELLS WHICH ARE EFFECTIVELY CONNECTED IN SERIES ! 6 CAR BAT TERY ON THE OTHER HAND USES SIX 6 LEAD ACID SECONDARY CELLS CONNECTED IN SERIES 7HERE AN ELECTRONIC CIRCUIT DERIVES ITS POWER FROM AN !# MAINS SUPPLY

'JH 4ZNCPMT GPS DFMMT BOE CBUUFSJFT WE SOMETIMES SHOW THE SUPPLY AS A BOX WITH TWO TERMINALS ONE MARKED POSITIVE AND ONE MARKED NEGATIVE 4REATING THE POWER SUPPLY AS A SEPARATE UNIT HELPS KEEP THE CIRCUIT SIMPLE )F THE POWER SUPPLY FAILS WE CAN SIMPLY

'JH 4FSJFT BSSBOHFNFOU PG DFMMT REPLACE THE ENTIRE UNIT IN MUCH THE SAME WAY AS WE WOULD REPLACE A SET OF EXHAUSTED BATTERIES

'JH " UZQJDBM QPXFS TVQQMZ

'JH " CMPDL TDIFNBUJD SFQSFTFOUBUJPO PG UIF QPXFS TVQQMZ JO 'JH

Everyday Practical Electronics, November 2010

Teach-In 2011 ! TYPICAL POWER SUPPLY WHICH HAS AN !# MAINS INPUT AND $# OUTPUT IS SHOWN IN &IG &IG SHOWS HOW WE CAN REPRESENT THE POWER SUP PLY USING A SIMPLE CMPDL TDIFNBUJD EJBHSBN .OTE THAT WE HAVE NOT SHOWN ANY SWITCHES FUSES OR INDICATORS IN THIS DIAGRAMØ

0LEASE NOTEØ 7E REFER TO THE OUTPUT VOLTAGE PRO DUCED BY A BATTERY OR A POWER SUPPLY AS AN ELECTROMOTIVE FORCE %-& %LEC TROMOTIVE FORCE IS MEASURED IN VOLTS 6 )N CONTRAST WE REFER TO THE VOLTAGE DROP ACROSS AN ELECTRONIC COMPONENT

SUCH AS A RESISTOR OR CAPACITOR AS A POTENTIAL DIFFERENCE PD 0OTENTIAL DIFFERENCE IS ALSO MEASURED IN VOLTS 6 4HE BEST WAY TO DISTINGUISH BE TWEEN %-& AND PD IS TO REMEMBER THAT %-& IS THE lCAUSEm AND PD IS THE lEFFECTm

#HECKªnª(OWªDOªYOUªTHINKªYOUªAREªDOING 3HORT ANSWER QUESTIONS

A M6 B K(Z

%XPLAIN THE DIFFERENCE BE TWEEN ANALOGUE AND DIGITAL SIGNALS

C ! D -(Z

,IST THE UNITS USED FOR EACH OF THE FOLLOWING ELECTRICAL QUANTITIES

E K: F N7

A CURRENT

D KBPS

B POTENTIAL C POWER D RESISTANCE E FREQUENCY F BIT RATE %XPLAIN WHAT IS MEANT BY EACH OF THE FOLLOWING ABBREVIATIONS

!N AMPLIÚER REQUIRES AN INPUT SIGNAL OF 6 %XPRESS THIS IN M6 !N !$# OPERATES AT A BIT RATE OF KBPS %XPRESS THIS IN -BPS ! CURRENT OF ! ÛOWS IN A RESISTOR %XPRESS THIS IN M!

! RADIO SIGNAL HAS A FRE QUENCY OF -(Z %XPRESS THIS IN K(Z ! PORTABLE #$ PLAYER USES A BATTERY WHICH HAS FOUR 6 CELLS CONNECTED IN SERIES 7HAT %-& DOES THIS BATTERY SUPPLY %XPLAIN THE DIFFERENCE BETWEEN %-& AND PD %XPLAIN THE DIFFERENCE BE TWEEN PRIMARY CELLS AND SECONDARY CELLS

,ONG ANSWER QUESTIONS

D #AN YOU SUGGEST ANY AD &IG BELOW SHOWS AN ELEC VANTAGES AND OR TRONIC SYSTEM THAT USES BOTH ANALOGUE DISADVANTAGES OF AND DIGITAL SIGNALS 4AKE A CAREFUL THE SYSTEM LOOK AT THE DIAGRAM AND SEE IF YOU CAN UNDERSTAND HOW IT WORKS BEFORE & I G SHOWS A WAVE ANSWERING THE FOLLOWING QUESTIONS FORM DIAGRAM A %XPLAIN THE PURPOSE OF THE SYSTEM A 7HAT TYPE B !T WHICH POINTS ! " # ETC OF WAVEFORM IS DO THE SIGNALS EXIST IN DIGITAL FORM 'JH 4FF 2VFTUJPO SHOWN AND AT WHICH POINTS DO THEY EXIST IN B 7HAT IS THE AMPLITUDE OF THE ANALOGUE FORM D 7HAT IS THE REPETITION FRE WAVEFORM QUENCY OF THE WAVEFORM C 7HAT FORM DO THE SIGNALS HAVE C 7HAT IS THE PERIOD OF THE WAVE WHEN THEY ARE PRESENT IN THE WIRELESS E 7HAT IS THE MARK TO SPACE FORM RADIO LINK RATIO OF THE WAVEFORM

'JH 4FF 2VFTUJPO

Everyday Practical Electronics, November 2010

Teach-In 2011

"UILDªnª4HEª#IRCUITª7IZARDªWAY

.% OF THE PROBLEMS WITH ELEC TRONICS IS SIMPLY THE AMOUNT OF KIT THAT YOU NEED TO GET STARTED %VEN A BASIC STARTER SET UP COULD RUN IN TO HUNDREDS OF POUNDS SOLDERING IRON HAND TOOLS CIRCUIT BOARD WIRES LEADS COMPONENTS TEST EQUIPMENT q IT ALL ADDS UPØ 4HEREFORE THE l"UILDm SECTION OF OUR 4EACH )N SERIES IS GOING TO FOCUS AROUND USING #IRCUIT 7IZARD A REALLY GREAT PIECE OF CIRCUIT SIMULATION SOFT WARE THAT RUNS ON YOUR 7INDOWS 0# )N THIS WAY YOUmLL HAVE ACCESS TO LITERALLY THOUSANDS OF COMPONENTS A FULL RANGE OF lVIRTUAL TEST EQUIPMENTm ALONG WITH REAL TIME SIMULATION AND TOOLS TO HELP YOU ACTUALLY VISUAL ISE THE OPERATION OF YOUR CIRCUITS 4HEREmS ALSO THE ABILITY TO BUILD BREADBOARD CIRCUITS AND CONVERT YOUR CIRCUITS INTO A PRINTED CIRCUIT BOARD 0#" DESIGN THAT CAN THEN BE MANUFACTURED 7E REALLY FEEL THAT ITmS THE IDEAL WAY TO GET STARTED WITH ELECTRONICS SO MUCH SO THAT WITH THE NEXT ISSUE OF &1& WE WILL GIVE AWAY A GSFF #$ 2/- CONTAINING A lDEMOm VERSION OF THE #IRCUIT 7IZARD

3IMULATION

3TUDENTS OF ELECTRONICS ARE OFTEN CONFUSED BY THE FACT THAT YOU CANmT ACTUALLY SEE WHATmS GOING ON INSIDE A CIRCUIT )N A MECHANICAL MACHINE ITmS EASY TO SEE THINGS MOVING AND WORKING BUT WE HAVE NONE OF THESE VISUAL CLUES WHEN WORKING ON AN ELECTRONIC CIRCUIT #OMPUTER SIMULATION NEATLY OVER COMES THIS PROBLEM BY PROVIDING A VISUAL REPRESENTATION OF WHATmS GOING ON UNDER THE SURFACE 4HIS MIGHT IN CLUDE THE ÛOW OF CURRENT IN WIRES THE VOLTAGE AT VARIOUS POINTS IN A CIRCUIT OR THE CHARGE PRESENT IN A CAPACITOR )N INDUSTRY THE USE OF SOFTWARE FOR SIMULATION DESIGN AND MANUFACTURE OF ELECTRONIC PRODUCTS IS THE NORM )N DEED BEING ABLE TO MAKE EFFECTIVE USE OF SOFTWARE TOOLS IS NOW A KEY SKILL FOR ANY ASPIRING ELECTRONIC ENGINEER OR HOBBYIST ! STANDARD LICENCE FOR #IRCUIT 7IZARD COSTS AROUND | AND CAN BE PURCHASED FROM THE EDITORIAL OFÚCE OF %0% q SEE THE 5+ SHOP ON OUR WEBSITE WWW EPEMAG COM &URTHER INFORMA TION CAN BE FOUND ON THE .EW 7AVE #ONCEPTS WEBSITE WWW NEW WAVE CONCEPTS COM 4HE DEVELOPER ALSO OF FERS AN EVALUATION COPY OF THE SOFTWARE

'JH $JSDVJU 8J[BSE TDSFFOTIPU TIPXJOH UIF VTF PG mWJSUVBM JOTUSVNFOUTn THAT WILL OPERATE FOR DAYS ALTHOUGH IT DOES HAVE SOME LIMITATIONS APPLIED SUCH AS ONLY BEING ABLE TO SIMULATE THE INCLUDED SAMPLE CIRCUITS AND NO ABILITY TO SAVE YOUR CREATIONS THIS IS

THE SOFTWARE THAT WILL BE GSFF WITH &1& NEXT MONTH (OWEVER IF YOUmRE SERI OUS ABOUT ELECTRONICS AND WANT TO FOL LOW OUR SERIES THEN A COPY OF #IRCUIT 7IZARD IS A REALLY SOUND INVESTMENT

'JH " DBQBDJUPS DIBSHJOH DJSDVJU TIPXJOH DIBSHF CVJMEJOH VQ PO UIF QMBUFT WPMUBHF MFWFMT BOE B HSBQIJDBM QMPU PG WPMUBHF BHBJOTU UJNF

Everyday Practical Electronics, November 2010

Teach-In 2011

'JH " MPHJD CBTFE FMFDUSPOJD EJDF JO mMPHJD WJFXn TIPXJOH EJHJUBM TJHOBM MFWFMT BU FBDI QPJOU JO UIF DJSDVJU )N THIS INSTALMENT WEmRE GOING TO LOOK AT INSTALLING AND GETTING STARTED WITH #IRCUIT 7IZARD )N FUTURE MONTHS WE WILL BE USING THE SOFTWARE TO IN VESTIGATE THE THEORY AND CIRCUITS THAT YOU WILL MEET IN l,EARNm 7EmLL ALSO DEVELOP ELECTRONIC DEVICES AND USE #IRCUIT 7IZARD TO DESIGN AND PRODUCE 0#"S SO THAT YOU CAN MAKE THE REAL THINGØ

)NSTALLATION

)NSTALLATION OF #IRCUIT 7IZARD IS VERY STRAIGHTFORWARD AND ITmS A SURPRISINGLY SMALL INSTALLATION FOR WHAT IS SUCH A POWERFUL PIECE OF SOFTWARE /UR INSTALL PROCESS TOOK NO MORE THAN QUARTER OF AN HOUR FROM START TO ÚNISH $URING THE INSTALLATION PROCESS YOUmLL BE ASKED TO ENTER A LICENCE KEY WHICH WILL BE SUP PLIED WITH YOUR INSTALL DISC 7HEN YOU RUN #IRCUIT 7IZARD FOR THE ÚRST TIME YOU WILL BE ASKED TO OBTAIN A RELEASE CODE WHICH CAN BE DONE OVER THE lPHONE OR VIA THE DEVELOPERmS WEB SITE WHERE THE RELEASE CODE IS THEN SUB SEQUENTLY E MAILED TO YOU 4HIS NEEDS TO BE DONE WITHIN A DAY WINDOW OR THE SOFTWARE WILL CEASE TO LOAD

&IRSTªLOOKS

4HE USER INTERFACE IS BOTH CLEAN AND INTUITIVE 4HE MAIN WHITE DRAWING AREA ÚLLS MOST OF THE SCREEN WITH THE STANDARD 7INDOWS MENUS AND TOOLBAR ACROSS THE TOP ! TABBED PANE ON THE RIGHT HAND SIDE OF THE SCREEN PRESENTS A l'ETTING 3TARTEDm MENU WHERE YOU CAN ACCESS VARIOUS SAMPLES TUTORIALS AND GAIN HELP

#LICKING THE l'ALLERYm TAB EXPOSES AN EXTENSIVE LIBRARY OF COMPONENTS AND TEST EQUIPMENT 4ABS ON THE FAR LEFT OF THE SCREEN ALLOW YOU TO SEE YOUR CIRCUIT IN VARIOUS DIFFERENT lVIEWSm 4HESE ARE DESIGNED TO HELP YOU SEE WHATmS ACTUALLY GOING ON IN YOUR CIR CUITS BY COLOURING AND OR ANIMATING THE CIRCUIT DIAGRAM TO SHOW VOLTAGES CURRENTS 4HIS IS A REALLY NIFTY FEATURE AL LOWING YOU TO ACTUALLY SEE ELECTRON ICS IN ACTION 4HERE ARE A NUMBER OF PRESET VIEWS OR YOU CAN CREATE YOUR OWN TO SUIT !LONG THE BOTTOM OF THE SCREEN A ROW OF TABS ALLOWS YOU TO CHANGE BETWEEN DIFFERENT PAGES OF YOUR DESIGN l$RAWINGm IS WHERE YOU WOULD AC TUALLY ENTER AND SIMULATE A CIRCUIT l0#" ,AYOUTm IS WHERE YOU WOULD PRODUCE A 0#" DESIGN AS WELL AS WORKING WITH VIRTUAL TEST EQUIPMENT AND BREADBOARDS &INALLY l"ILL OF -ATERIALSm GENERATES AN INVENTORY COSTING OF THE COMPONENTS USED IN YOUR CIRCUIT

&INDINGªYOURªWAYªAROUND

"Y FAR THE BEST WAY TO GET STARTED WITH #IRCUIT 7IZARD IS TO FOLLOW THE GUIDED TOUR SCREEN VIDEOS AND EX PERIMENT WITH THE SAMPLE CIRCUITS PROVIDED !LL OF THESE ARE DIRECTLY ACCESSIBLE FROM THE l'ETTING 3TARTEDm PAGE IN THE RIGHT HAND PANE CLICK ON

'JH $JSDVJU 8J[BSEnT (BMMFSZ PG DPNQPOFOUT BOE UFTU FRVJQNFOU

Everyday Practical Electronics, November 2010

Teach-In 2011 4HEª#IRCUITª7IZARDªWAY THE l!SSISTANTm TAB IF THE CIRCUIT GALLERY VIEW IS SHOWN 4HE SCREEN VIDEOS EXPLAIN THE BASIC OPERATION OF THE SOFTWARE BUT LACK SOUND WITH ONLY WRITTEN DESCRIPTIONS APPEARING ON THE SCREEN THIS DOES MAKE FOR SLOW PROGRESS )F YOUmRE A CON ÚDENT COMPUTER USER YOU MAY WANT TO JUST JUMP STRAIGHT IN AND EXPLORE OVER ÚFTY SAMPLE CIRCUITS THAT ARE INCLUDED AND GET TO KNOW THE SOFTWARE HANDS ON

SOME SIMPLE CIRCUITS THAT WILL BE UN DERPINNED BY THE THEORY COVERED IN OUR l,EARNm SECTION 5NTIL THEN YOU MIGHT LIKE TO GET YOURSELF A COPY OF #IRCUIT 7IZARD AND HAVE A PLAYØ )F YOUmRE RE ALLY KEEN TO GET STUCK IN CHECK OUT OUR 5FBDI *O WEBSITE AT WWW TOOLEY CO UK TEACH IN WHERE YOU CAN DOWNLOAD SOME FURTHER EXAMPLES

'JH " UZQJDBM CFODI PTDJMMPTDPQF

)NVESTIGATE

!6%&/2-3 ARE USUALLY DIS PLAYED USING AN INSTRUMENT CALLED AN OSCILLOSCOPE 9OU WILL LEARN MORE ABOUT THIS INSTRUMENT LATER IN THE SERIES /SCILLOSCOPES CAN BE STAND ALONE TEST INSTRUMENTS SEE &IG OR THEY CAN BE VIRTUAL INSTRUMENTS THAT USE A 0#mS IN BUILT SIGNAL PROCESSING CAPABILITIES EG THE ANALOGUE TO DIGITAL CONVERTER IN A 0# SOUND CARD &IG SHOWS A TYPICAL VIRTUAL IN STRUMENT DISPLAY OBTAINED BY USING A SOUNDCARD OSCILLOSCOPE PROGRAM 4HE PROGRAM RECEIVES ITS DATA FROM THE COMPUTERmS SOUND CARD WITH A SAMPLING RATE OF K(Z AND A RESOLUTION OF BITS 4HE DATA SOURCE CAN BE SELECTED BY THE 0#mS OWN SOUND CARD CONTROLS EG MICROPHONE LINE INPUT OR WAVE 4HE FREQUENCY RANGE OF THE INSTRUMENT DEPENDS ON THE PERFORMANCE OF THE COMPUTERmS SOUND CARD BUT IS TYPICALLY ACCURATE OVER THE RANGE (Z TO K(Z

4HE OSCILLOSCOPE ALSO CONTAINS A SIMPLE SIGNAL GENERATOR PRODUCING SINE SQUARE TRIANGLE AND SAWTOOTH WAVEFORMS IN THE FREQUENCY RANGE FROM TO K(Z 4HESE SIGNALS ARE AVAILABLE AT THE SPEAKER OUTPUT OF THE SOUND CARD 4AKE A CAREFUL LOOK AT &IG AND USE IT TO ANSWER THE FOLLOWING QUESTIONS A 7HAT TYPE OF WAVEFORM IS SHOWN B 7HAT TOTAL TIME INTERVAL IS DIS PLAYED ON THE SCREEN (INT LOOK AT THE HORIZONTAL SCALE C 7HAT SETTINGS ARE USED FOR THE VERTICAL AND HORIZONTAL SCALES ON THE OSCILLOSCOPE DISPLAY D 7HAT IS THE GREATEST POSITIVE VOLT AGE PRESENT IN THE WAVEFORM SAMPLE E 7HAT IS THE GREATEST NEGATIVE VOLT AGE PRESENT IN THE WAVEFORM SAMPLE F 7HAT IS THE OVERALL PEAK PEAK VOLTAGE OF THE WAVEFORM

'JH $JSDVJU 8J[BSE QSPWJEFT B HPPE TFMFDUJPO PG TUBSUFS NBUFSJBMT 4HE SAMPLE CIRCUITS ARE SPLIT BY COM PLEXITY INTO THREE FOLDERS SIMPLE BASIC AND ADVANCED %ACH OF THESE IS THEN FURTHER DIVIDED INTO SUB CATEGORIES WHICH REALLY SHOWCASE THE EXTENSIVE FEATURES OF THE SOFTWARE 4HE SAMPLE CIRCUITS ARE EXCELLENT AND CONTAIN INSTRUCTIONS ON HOW TO TEST OUT THE CIR CUIT q THEYmRE ALSO REALLY EDUCATIONAL SO YOU MIGHT EVEN LEARN SOMETHING ABOUT ELECTRONICS AS YOU DISCOVER THE SOFTWARE TOOØ )N NEXT MONTHmS INSTALMENT WEmLL BE SHOWING YOU HOW TO ENTER AND TEST

'JH 4FF UIF *OWFTUJHBUF RVFTUJPOT

Everyday Practical Electronics, November 2010

Teach-In 2011

!MAZE

!NSWERSÂªTOÂª1UESTIONS !NALOGUE SIGNALS VARY CON TINUOUSLY IN VOLTAGE AND CURRENT WHILST DIGITAL SIGNALS CAN ONLY EXIST IN DISCRETE LEVELS OF VOLTAGE OR CURRENT A !MPERE B 6OLT C 7ATT D /HM E (ERTZ F BITS PER SECOND A MILLIVOLT B KILOHERTZ C MICROAMP D MEGAHERTZ E KILOHM F NANOWATT G KILOBITS PER SECOND M6 -BPS M! K(Z 6 %-& IS USED TO DESCRIBE THE OUTPUT VOLTAGE PRODUCED BY A BATTERY OR POWER SUPPLY 0OTENTIAL DIFFERENCE IS USED TO DESCRIBE THE

$OWNLOAD A COPY OF THE 3OUNDCARD /SCILLOSCOPE SOFTWARE AND INVESTIGATE THE OPERATION OF THE PROGRAM USING SOME TYPICAL SIGNALS APPLIED TO THE MICROPHONE OR AUXILIARY INPUTS OF A 0# 4HE SOFTWARE IS AVAILABLE FROM #HRISTIAN :EITNITZmS WEBSITE HTTP WWW ZEITNITZ DE #HRISTIAN SCOPE?EN

VOLTAGE DROP THAT APPEARS ACROSS A COM PONENT SUCH AS A RESISTOR OR CAPACITOR 0RIMARY CELLS PRODUCE ELEC TRICAL ENERGY FROM A NON REVERSIBLE CHEMICAL REACTION AND MUST BE DIS POSED OF WHEN EXHAUSTED 3ECONDARY CELLS MAKE USE OF A REVERSIBLE CHEMI CAL REACTION AND CAN BE RECHARGED AND USED AGAIN

.EXTÂªMONTH

)N NEXT MONTHmS 5FBDI *O WE SHALL BE LOOKING AT RESISTORS AND CA PACITORS %XAMPLES OF THESE TWO PASSIVE COMPONENTS ARE FOUND IN ALMOST EVERY ELECTRONIC CIRCUIT &URTHERMORE WHEN USED TOGETHER THESE TWO COMPONENTS FORM THE BASIS OF A WIDE RANGE OF ELEC TRONIC TIMING AND DELAY CIRCUITS 7E SHALL BE INVESTIGATING THE BE HAVIOUR OF THESE CIRCUITS USING #IRCUIT 7IZARD

A 7IRELESS DATA LINK BETWEEN COMPUTER SYSTEMS B ! DIGITAL " ANALOGUE # ANALOGUE $ ANALOGUE % ANALOGUE & DIGITAL C 3INEWAVE RADIO FREQUENCY WITH SUPERIMPOSED MODULATED SIGNAL INFORMATION D $ISADVANTAGES LACK OF SECURITY COM PARED WITH SYSTEMS LINKED BY CABLE MAY SUFFER FROM INTERFERENCE TO FROM OTHER NEARBY WIRELESS SYSTEMS !DVAN TAGES SIMPLE TO INSTALL DOES NOT NEED PERMANENT CABLING

For more information, links and other resources please check out our Teach-In website at:

A PULSE WAVE B 6 C MS D (Z E

www.tooley.co.uk/ teach-in

Technobots

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cc n A me o i at co uc Wel www.technobotsonline.com Ed

Shop callers welcome: Technobots Ltd, 60 Rumbridge Street, Totton, Hampshire SO40 9DS Tel: 023 8086 4891

Everyday Practical Electronics, November 2010

worldmags

Teach-In 2011

7($&+ ,1 $ %52$' %$6(' ,1752'8&7,21 72 (/(&7521,&6 0ARTª ª2ESISTORS ªCAPACITORS ª TIMINGªANDªDELAYªCIRCUITS By Mike and Richard Tooley

/URª4EACH )NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROAD BASEDªINTRODUCTIONªTOªELECTRONICS ª7EªHAVEªª ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ ª4HESEªINCLUDEª%DEXCELª"4%#ª,EVELª ªAWARDS ªASªWELLªASªELECTRONICSªUNITSª OFªTHEªNEWª$IPLOMAªINª%NGINEERINGª ALSOªATª,EVELª ª4HEªSERIESªWILLªALSOªPROVIDEªTHEªMOREªEXPERIENCEDªREADERª WITHªANªOPPORTUNITYªTOª@BRUSHªUP ªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIAR ª %ACHªPARTªOFªOURª4EACH )NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGS ª,EARN ª#HECK ª"UILD ª)NVESTIGATEªANDª !MAZE ª,EARNªWILLªTEACHªYOUªTHEªTHEORY ª#HECKªWILLªHELPªYOUªTOªCHECKªYOURªUNDERSTANDING ªANDª"UILDªWILLªGIVEª YOUªANªOPPORTUNITYªTOªBUILDªANDªTESTªSIMPLEªELECTRONICªCIRCUITS ª)NVESTIGATEªWILLªPROVIDEªYOUªWITHªAªCHALLENGEª WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNING ªANDªlNALLYª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTOR ªª )NªLASTªMONTH SªINSTALMENT ª,EARNªPROVIDEDªYOUªWITHªANªINTRODUCTIONªTOªTHEªSIGNALSªTHATªCONVEYªª INFORMATIONªINªELECTRONICªCIRCUITSªANDªTHEªUNITS ªMULTIPLESªANDªSUB MULTIPLESªTHATªAREªUSEDªWHENªMEASURINGª ELECTRICALªQUANTITIES ª"UILDªFEATUREDªANªINTRODUCTIONªTOª#IRCUITª7IZARD ªSHOWINGªYOUªHOWªTOªINSTALLªTHEªSOFT WAREªANDªUSEªAªVIRTUALªTESTªINSTRUMENTªWHILEªOURªPRACTICALªSECTIONS ª)NVESTIGATEªANDª!MAZE ªPROVIDEDªYOUª WITHªANªOPPORTUNITYªTOªGETªTOªGRIPSªWITHªANªOSCILLOSCOPEªBASEDªONªAª0#ªSOUNDCARD

. THIS PART OF 4EACH )N WE WILL INTRODUCE YOU TO RESISTORS CAPACI TORS TIMING AND DELAY CIRCUITS 7E WILL ALSO USE #IRCUIT 7IZARD TO INVES TIGATE /HMmS ,AW AS WELL AS ÚNDING OUT WHAT HAPPENS IN A CIRCUIT WHEN A CAPACITOR IS CHARGED AND DISCHARGED

2ESISTORS

,EARN

&ROM LAST MONTHmS 4EACH )N YOU SHOULD RECALL THAT VOLTAGE IS SPECI ÚED IN VOLTS 6 CURRENT IN AMPS ! AND RESISTANCE IN OHMS : ! POTENTIAL DIFFERENCE OF 6 WILL

APPEAR ACROSS A RESISTANCE OF : WHEN A CURRENT OF ! ÛOWS IN IT 2ESISTANCE CAN BE THOUGHT OF AS AN OPPOSITION TO THE ÛOW OF ELECTRIC CURRENT 4HE AMOUNT OF CURRENT THAT WILL ÛOW IN A CIRCUIT WHEN A GIVEN ELECTROMOTIVE FORCE %-& IS APPLIED TO IT IS INVERSELY PROPORTIONAL TO ITS RESISTANCE )N OTHER WORDS THE LARGER THE RESISTANCE THE GREATER THE OPPOSI TION TO CURRENT ÛOW WHEN AN %-& IS APPLIED

* AND RESISTANCE 3 IN A CIRCUIT SEE &IG IS

/HM SªLAW

7 * ¯ 3 ¯ 6 .OTE THAT M! IS THE SAME AS !

/HMmS LAW TELLS US THAT THE RELA TIONSHIP BETWEEN VOLTAGE 7 CURRENT

7 * ¯ 3 WHERE 7 IS THE VOLTAGE IN 6 * IS THE CURRENT IN ! AND 3 IS THE RESIST ANCE IN : %XAMPLE ! CURRENT OF M! ÛOWS IN A : RESISTOR 7HAT POTENTIAL DIFFERENCE APPEARS ACROSS THE RESISTOR &ROM /HMmS ,AW

Everyday Practical Electronics, December 2010

worldmags

Teach-In 2011

'JH 7BSJPVT UZQFT PG SFTJTUPS JODMVEJOH ÜYFE QSFTFU BOE WBSJBCMF UZQFT %XAMPLE 7HAT CURRENT WILL ÛOW WHEN A : RESISTOR IS CONNECTED TO A 6 BATTERY

4YPESªOFªRESISTOR

6ARIOUS TYPES OF ÚXED PRESET AND VARIABLE RESISTOR ARE FOUND IN ELEC TRONIC CIRCUITS INCLUDING CARBON ÚLM 2EARRANGING THE FORMULA TO MAKE * METAL ÚLM AND WIREWOUND TYPES SEE THE SUBJECT GIVES &IG 2ESISTORS HAVE A WIDE VARIETY OF APPLICATIONS IN ELECTRONIC CIRCUITS 9 WHERE THEY ARE USED FOR DETERMINING , $ P$ THE VOLTAGES AND CURRENTS IN CIRCUITS 5 AS lLOADSm TO CONSUME POWER AND IN %XAMPLE PRESET AND VARIABLE FORM FOR MAKING ! CURRENT OF M! ÛOWS IN A RE ADJUSTMENTS FOR EXAMPLE VOLUME SISTOR WHEN IT IS CONNECTED TO A 6 AND TONE CONTROLS POWER SUPPLY 7HAT IS THE VALUE OF 4HE TERMS POTENTIOMETER AND THE RESISTANCE VARIABLE RESISTOR ARE OFTEN USED INTERCHANGEABLY (OWEVER STRICTLY 2EARRANGING THE FORMULA TO MAKE SPEAKING PRESET AND VARIABLE RESIS 3 THE SUBJECT GIVES TORS HAVE ONLY TWO TERMINALS WHILE POTENTIOMETERS EITHER PRESET OR 9 5 :: N:: ROTARY TYPES HAVE THREE TERMINALS , .OTE ALSO THAT A PRESET OR VARIABLE .OTE THAT M! IS THE SAME AS POTENTIOMETER CAN BE USED AS A VARI ABLE RESISTOR BY SIMPLY IGNORING ONE ! OF ITS END TERMINALS OR BY CONNECTING ITS MOVING CONTACT TO ONE OF ITS OUTER TERMINALS 4YPICAL CIRCUIT SYMBOLS FOR VARIOUS TYPES OF RESISTOR ARE SHOWN IN &IG 4HE SPECIÚCATIONS FOR A RESISTOR USUALLY INCLUDE THE VALUE OF RESISTANCE EXPRESSED IN : K: OR -: THE ACCURACY OR TOLER ANCE OF THE MARKED VALUE QUOTED AS THE MAXIMUM 'JH " TJNQMF DJSDVJU JO XIJDI B CBUUFSZ TVQQMJFT PERMISSIBLE PERCENTAGE DEVIATION FROM THE MARKED DVSSFOU UP B SFTJTUPS

Everyday Practical Electronics, December 2010

'JH $JSDVJU TZNCPMT VTFE GPS SFTJTUPST

worldmags

Teach-In 2011 VALUE AND THE POWER RATING WHICH MUST BE EQUAL TO OR GREATER THAN THE MAXIMUM EXPECTED POWER DIS SIPATION

4ABLEÂª Âª4HEÂª% Âª% ÂªANDÂª% ÂªSERIESÂªOFÂªPREFERREDÂªRESISTORÂªVALUES

Series of preferred values

&IXEDÂªRESISTORS

&IXED RESISTORS ARE AVAILABLE IN SEVERAL SERIES OF lPREFERREDm VALUES SEE 4ABLE 4HE NUMBER OF VALUES PROVIDED WITH EACH SERIES IE AND IS DETERMINED BY THE TOLER ANCE INVOLVED )N ORDER TO COVER THE FULL RANGE OF RESISTANCE VALUES USING RESISTORS HAV ING A Â&#x2030; TOLERANCE IT IS NECESSARY TO PROVIDE SIX BASIC VALUES KNOWN AS THE % SERIES -ORE VALUES ARE REQUIRED IN A SERIES THAT OFFERS A TOLERANCE OF Â&#x2030; AND CONSEQUENTLY THE % SERIES PROVIDES TWELVE BASIC VALUES 4HE % SERIES FOR RESISTORS OF Â&#x2030; TOLERANCE PROVIDES BASIC VALUES AND AS WITH THE % AND % SERIES DECADE MULTIPLES IE Â¯ Â¯ Â¯ Â¯ K Â¯ K Â¯ K AND Â¯ - OF THE BASIC SERIES ! FURTHER SERIES % PROVIDES FOR RESIS TORS WITH A TOLERANCE OF Â&#x2030; #ARBON AND METAL OXIDE RESISTORS ARE NORMALLY MARKED WITH COLOUR CODES THAT INDICATE THEIR VALUE AND TOLER ANCE 3EE &IG AND &IG FOR THE COLOUR CODES

1.0, 1.5, 2.2, 3.3, 4.7, 6.8

E12

1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2

E24

1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1

2ELATIONSHIP BETWEEN VOLTAGE CURRENT AND POWER 4HE POWER 1 DISSIPATED IN A RE SISTOR IS EQUIVALENT TO THE PRODUCT OF VOLTAGE 7 AND CURRENT * 4HUS 1 *7 WHERE 1 IS THE POWER IN 7 * IS THE CURRENT IN ! AND 7 IS THE VOLT AGE IN 6 7E CAN COMBINE THIS RELATIONSHIP WITH THE /HMmS LAW EQUATION THAT WE MET EARLIER IN ORDER TO ARRIVE AT THE FOLLOWING USEFUL EXPRESSIONS

'JH 'PVS CBOE SFTJTUPS DPMPVS DPEF

Values available

, u ,5

, 5

AND

9 u9 5

9 5

%XAMPLE 7HAT POWER IS DISSIPATED IN A RE SISTOR OF K: WHEN A VOLTAGE OF 6 APPEARS ACROSS IT 5SING THE PREVIOUS FORMULA GIVES

9 5

'JH 'JWF CBOE SFTJTUPS DPMPVS DPEF

10%

Everyday Practical Electronics, December 2010

worldmags

Teach-In 2011

'JH 7BSJPVT UZQFT PG DBQBDJUPS JODMVEJOH ÜYFE QSFTFU BOE WBSJBCMF UZQFT

#APACITORS

#APACITORS STORE ENERGY IN THE FORM OF AN ELECTRIC ÚELD 7HEN A POTENTIAL DIFFERENCE IS APPLIED TO TWO CONDUCT ING PLATES AN ELECTRIC CHARGE WILL AP PEAR ON THE PLATES AND AN ELECTRIC ÚELD WILL APPEAR BETWEEN THE PLATES 4HE ÚELD CAN BE CONCENTRATED INTENSIÚED BY PLACING AN INSULATING MATERIAL SUCH AS POLYESTER ÚLM MICA OR A CERAMIC MATERIAL BETWEEN THE PLATES 4HIS MA TERIAL IS KNOWN AS A DIELECTRIC AND ITS ELECTRICAL PROPERTIES HELP TO INCREASE THE CAPACITANCE OF THE COMPONENT SEE &IG #APACITORS PROVIDE US WITH A MEANS OF STORING AND CONSERVING ELECTRIC

CHARGE 4HEY ARE WIDELY USED IN POWER SUPPLIES WHERE THEY ACT AS lRESERVOIRSm FOR CHARGE AND ALSO IN MANY TIMING AND WAVE SHAPING CIRCUITS #APACITORS WILL PASS ALTERNATING CURRENTS BUT THEY WILL lBLOCKm DIRECT CURRENT ONCE CHARGED 4HEY ARE THUS USED FOR COUPLING SIGNALS WHICH ARE !# IN AND OUT OF AMPLIÚER STAGES 4HE SPECIÚCATIONS FOR A CAPACITOR USUALLY INCLUDE THE VALUE OF CAPACI TANCE EXPRESSED IN & & N& OR P& THE ACCURACY OR TOLERANCE OF THE MARKED VALUE QUOTED AS THE MAXIMUM PER MISSIBLE PERCENTAGE DEVIATION FROM THE MARKED VALUE THE VOLTAGE RATING WHICH MUST BE EQUAL TO OR GREATER

'JH #BTJD BSSBOHFNFOU PG B QBSBMMFM QMBUF DBQBDJUPS

Everyday Practical Electronics, December 2010

THAN THE MAXIMUM EXPECTED VOLTAGE APPLIED TO THE CAPACITOR #APACITORS ARE USUALLY AVAILABLE WITH VALUES IN THE % SERIES SEE 4ABLE

0LEASE NOTEØ

,ARGE VALUE CAPACITORS OFTEN USE A CHEMICAL DIELECTRIC MATERIAL AND THEY REQUIRE THE APPLICATION OF A $# POLARISINGª VOLTAGE IN ORDER TO WORK

'JH 4ZNCPMT VTFE GPS DBQBDJUPST

worldmags

Teach-In 2011 PROPERLY 4HIS VOLTAGE MUST BE APPLIED WITH THE CORRECT POLARITY INVARIABLY THIS IS CLEARLY MARKED ON THE CASE OF THE CAPACITOR WITH A POSITIVE SIGN OR NEGATIVE q SIGN OR A COLOURED STRIPE OR OTHER MARKING &AILURE TO OBSERVE THE CORRECT POLARITY CAN RESULT IN OVER HEATING LEAKAGE AND EVEN A RISK OF EXPLOSIONØ

OF CAPACITANCE $ AND THE SQUARE OF THE APPLIED VOLTAGE 7 4HUS TO STORE A LARGE AMOUNT OF ENERGY WE NEED A CORRESPONDINGLY LARGER VALUE OF CA PACITANCE FOR A GIVEN VALUE OF CHARGING VOLTAGE 4HE FOLLOWING RELATIONSHIP APPLIES

2ELATIONSHIP BETWEEN CHARGE VOLTAGE AND CAPACITANCE 4HE QUANTITY OF ELECTRIC CHARGE 2 THAT CAN BE STORED IN THE ELECTRIC ÚELD BETWEEN THE CAPACITOR PLATES IS PROPOR TIONAL TO THE APPLIED VOLTAGE 7 AND THE CAPACITANCE $ OF THE CAPACITOR

WHERE $ IS THE VALUE OF CAPACITANCE IN & 7 IS THE CAPACITOR VOLTAGE AND 8 IS THE STORED ENERGY IN JOULES

4HUS

%XAMPLE $ETERMINE THE CHARGE STORED IN A & CAPACITOR WHEN IT IS CHARGED TO A POTENTIAL OF 6 4HE STORED ENERGY WILL BE GIVEN BY

4 & 9 WHERE 2 IS THE CHARGE IN COULOMBS $ IS THE CAPACITANCE IN FARADS AND 7 IS THE POTENTIAL DIFFERENCE IN VOLTS %XAMPLE $ETERMINE THE CHARGE STORED IN A & CAPACITOR WHEN IT IS CHARGED TO A POTENTIAL OF 6 4HE CHARGE STORED WILL BE GIVEN BY

4 & 9 î î

î î

P& P&

%NERGYªSTORAGE

8 $ 7

: ò & 9 ò î î

î î î - 0LEASE NOTEØ

4HE ENERGY STORED IN A CAPACITOR IS PROPORTIONAL TO THE SQUARE OF THE PO TENTIAL DIFFERENCE BETWEEN ITS PLATES 4HUS IF THE POTENTIAL DIFFERENCE IS DOUBLED THE ENERGY STORED WILL IN CREASE BY A FACTOR OF FOUR ,IKEWISE IF THE POTENTIAL DIFFERENCE INCREASES BY A FACTOR OF TEN THE STORED ENERGY WILL INCREASE BY A FACTOR OF

0LEASE NOTEØ

! CHARGED CAPACITOR ACTS AS A RESER VOIR FOR CHARGE AND THE STORED ENERGY CAN BE PUT TO GOOD USE SOME TIME LATER 4HE AMOUNT OF ENERGY STORED IN A CAPACITOR DEPENDS ON THE PRODUCT

! CHARGED CAPACITOR CAN REMAIN IN A PARTIALLY CHARGED STATE FOR A VERY LONG TIME IF THERE IS NO PATH FOR THE STORED CHARGE TO DRAIN AWAY )TmS THEREFORE IMPORTANT TO AVOID WORKING ON A CIR CUIT THAT USES LARGE VALUE CAPACITORS

PARTICULARLY IF THEY ARE HIGH VOLTAGE TYPES UNTIL YOU ARE CERTAIN THAT THE CAPACITORS ARE FULLY DISCHARGED 3OME CIRCUITS INCORPORATE lBLEEDm RESISTORS TO SAFELY DISCHARGE LARGE VALUE CAPACITORS WHEN THE EQUIPMENT IN WHICH THEY ARE USED HAS BEEN SWITCHED OFF

# 2ªCIRCUITSª CHARGEªANDª DISCHARGE

%ARLIER WE MENTIONED THAT A CA PACITOR IS A DEVICE FOR STORING ELECTRIC CHARGE 4HIS CHARGE CAN BE STORED IN A CAPACITOR BY CONNECTING IT TO A BATTERY OR POWER SUPPLY VIA A SERIES RESISTOR WHICH SUPPLIES CURRENT FOR CHARGING ,ATER THE STORED CHARGE CAN BE DRAINED AWAY BY CONNECTING A RESISTOR IN PARAL LEL WITH THE CAPACITOR !FTER A PERIOD OF TIME THERE WILL THEN BE NO CHARGE REMAINING IN THE CAPACITOR 4HE TIME THAT IT TAKES TO CHARGE AND DISCHARGE A CAPACITOR DEPENDS ON THE VALUES OF CAPACITANCE AND RESISTANCE AND THIS MAKES CAPACITORS IDEAL FOR USE IN TIMING AND DELAY CIRCUITS "ECAUSE THIS IS SO IMPORTANT ITmS WORTH LOOKING AT THIS IN A LITTLE MORE DETAIL 3IMPLE CHARGING AND DISCHARGING ARRANGEMENTS ARE SHOWN IN &IG )N THE CHARGING ARRANGEMENT SHOWN IN &IG A THE CAPACITOR IS INITIALLY UNCHARGED AND CURRENT WILL FLOW AND CHARGE WILL BUILD UP INSIDE THE CAPACITOR QUICKLY AT ÚRST AND THEN MORE SLOWLY !S THE CAPACITOR BECOMES CHARGED THE CAPACITOR VOLTAGE 7# WILL INCREASE UNTIL IT EVENTUALLY BECOMES CLOSE BUT NEVER QUITE EQUAL TO THE VOLTAGE OF THE SUPPLY 73 !T THAT POINT WHEN 7# IS APPROXIMATELY EQUAL TO 73 WE SAY THAT THE CAPACITOR IS FULLY CHARGED

'JH " DBQBDJUPS DIBSHJOH EJTDIBSHJOH BSSBOHFNFOU

Everyday Practical Electronics, December 2010

worldmags

Teach-In 2011

Virtually fully discharged

'JH (SBQI PG DBQBDJUPS WPMUBHF BHBJOTU UJNF GPS UIF 'JH (SBQI PG DBQBDJUPS WPMUBHF BHBJOTU UJNF GPS UIF DIBSHJOH DJSDVJU EJTDIBSHJOH DJSDVJU ! GRAPH SHOWING HOW THE CAPACITOR VOLTAGE 7# INCREASES WITH TIME IS SHOWN IN &IG 4HIS GRAPH IS KNOWN AS AN EXPONENTIALÂŞGROWTH CURVE 4HE SPEED AT WHICH THE CAPACITOR BECOMES CHARGED DEPENDS ON THE TIME CONSTANT 5 OF THE CIRCUIT 4HIS IS THE PRODUCT OF THE CAPACITANCE $ AND THE CHARGING RESISTANCE 3 (ENCE 5 $ ÂŻ 3 WHERE $ IS THE VALUE OF CAPACITANCE IN & 3 IS THE RESISTANCE IN : AND 5 IS THE TIME CONSTANT IN SECONDS 9OU MIGHT NOW BE WONDERING HOW LONG IT TAKES TO GVMMZ CHARGE THE CAPACI TOR 4HE TRUE ANSWER IS THAT THE CAPACI TOR VOLTAGE NEVER QUITE REACHES THE SUP PLY VOLTAGE EVEN IF YOU WAIT FOR A WFSZ LONG TIME (OWEVER IT DOES GET CLOSER AND CLOSER TO IT AND FOR THIS REASON WE SAY THAT THE CAPACITOR IS FULLY CHARGED AFTER A TIME INTERVAL EQUAL TO Ă&#x161;VE TIMES THE TIME CONSTANT 5 OR $3 )N THE DISCHARGING ARRANGEMENT SHOWN IN &IG B THE CAPACITOR IS INITIALLY FULLY CHARGED AND CURRENT WILL Ă&#x203A;OW WHILE THE CHARGE INSIDE THE CAPACITOR DECAYS AWAY !S THE CAPACITOR BECOMES DISCHARGED THE CAPACITOR VOLTAGE 7# WILL DECREASE UNTIL IT EVENTUALLY BECOMES CLOSE BUT NEVER QUITE EQUAL TO ZERO 6 !T THAT POINT WHEN 7# IS APPROXIMATELY EQUAL TO 6 WE SAY THAT THE CAPACITOR IS FULLY DISCHARGED ! GRAPH SHOWING HOW THE CAPACITOR VOLTAGE 7# DECREASES WITH TIME IS SHOWN IN &IG 4HIS GRAPH IS KNOWN AS AN EXPONENTIALÂŞDECAY CURVE

/NCE AGAIN THE SPEED AT WHICH THE CAPACITOR BECOMES DISCHARGED DEPENDS ON THE TIMEÂŞCONSTANT 5 OF THE CIRCUIT &OR OUR DISCHARGING CIRCUIT THE TIME CONSTANT IS ALSO GIVEN BY 5 $ ÂŻ 3 !S BEFORE YOU MIGHT NOW BE WONDER ING HOW LONG IT TAKES TO GVMMZ DISCHARGE THE CAPACITOR 4HE TRUE ANSWER IS THAT THE CAPACITOR VOLTAGE NEVER QUITE REACH ES 6 EVEN IF YOU WAIT FOR A VERY LONG TIME (OWEVER IT DOES GET CLOSER AND CLOSER TO 6 AND FOR THIS REASON WE SAY THAT THE CAPACITOR IS FULLY DISCHARGED AFTER A TIME INTERVAL EQUAL TO Ă&#x161;VE TIMES THE TIME CONSTANT 5 OR $3 %XAMPLE ! $ 3 CIRCUIT CONSISTS OF $ Â?& AND 3 -: A 7HAT IS THE TIME CONSTANT OF THE CIRCUIT B )F THE CAPACITOR IS INITIALLY UN CHARGED HOW LONG WILL IT TAKE TO FULLY CHARGE THE CAPACITOR A 4HE TIME CONSTANT IS GIVEN BY 5 $3 Â?& ÂŻ -: SECONDS .OTE THAT IF WE WORK IN Â?& AND -: THE TIME CONSTANT WILL BE EXPRESSED DIRECTLY IN SECONDS B 4HE CAPACITOR WILL BE APPROXI MATELY FULLY CHARGED AFTER 5 OR ÂŻ OR SECONDS

Everyday Practical Electronics, December 2010

0LEASE NOTEĂ&#x2DC;

4HE VOLTAGE ACROSS THE PLATES OF A CHARGING CAPACITOR GROWS EXPONENTIALLY NOT LINEARLYĂ&#x2DC; AT A RATE DETERMINED BY THE TIME CONSTANT OF THE CIRCUIT #ON VERSELY THE VOLTAGE ACROSS THE PLATES OF A DISCHARGING CAPACITOR DECAYS EXPONEN TIALLY NOT LINEARLYĂ&#x2DC; AT A RATE DETERMINED BY THE TIME CONSTANT OF THE CIRCUIT

Circuit Wizard A Standard or Professional version of Circuit Wizard can be purchased from the editorial ofďŹ ce of EPE â&#x20AC;&#x201C; see CD-ROMs for Electronics page and the UK shop on our website (www. epemag.com) for a â&#x20AC;&#x2DC;special offerâ&#x20AC;&#x2122;. Further information can be found on the New Wave Concepts website; www.new-wave-concepts.com.The developer also offers an evaluation copy of the software that will operate for 30 days, although it does have some limitations applied, such as only being able to simulate the included sample circuits and no ability to save your creations, this is the software that is free with EPE this month. However, if youâ&#x20AC;&#x2122;re serious about electronics and want to follow our series, then a full copy of Circuit Wizard is a really sound investment.

worldmags

Teach-In 2011

#HECKªnª(OWªDOªYOUªTHINKªYOUªAREªDOING %XPLAIN BRIEÛY WHAT IS MEANT BY RESISTANCE 7HAT UNITS ARE USED FOR RESISTANCE AND WHAT SYMBOL IS USED TO DENOTE THESE UNITS %XPLAIN BRIEÛY WHAT IS MEANT BY CAPACITANCE 7HAT UNITS ARE USED FOR CAPACITANCE AND WHAT SYMBOL IS USED TO DENOTE THESE UNITS ! CURRENT OF ! ÛOWS IN A : RESISTOR 7HAT POTENTIAL DIFFERENCE APPEARS ACROSS THE RESISTOR 7HAT CURRENT WILL ÛOW WHEN A : RESISTOR IS CONNECTED TO A 6 BATTERY ! CURRENT OF M! ÛOWS IN A RESISTOR WHEN IT IS CONNECTED TO A 6 POWER SUPPLY 7HAT IS THE VALUE OF THE RESISTANCE

! CHARGE OF # IS HELD IN A N& CAPACITOR 7HAT POTENTIAL AP PEARS ACROSS THE PLATES OF THE CAPACITOR ! CHARGE OF # IS TO BE PLACED ON THE PLATES OF A CAPACITOR OF N& 7HAT VOLTAGE IS NEEDED TO DO THIS ! RESISTANCE OF K: IS CON NECTED TO A CAPACITOR OF & 7HAT IS THE TIME CONSTANT OF THIS CIRCUIT AND HOW LONG WILL IT TAKE FOR THE CAPACITOR TO BECOME APPROXIMATELY FULLY CHARGED 7HAT COMPONENTS ARE REPRE SENTED BY THE CIRCUIT SYMBOLS SHOWN IN &IG 7HAT TYPE OF COMPONENT IS SHOWN IN &IG

'JH 4FF RVFTUJPO ! RESISTOR IS MARKED WITH THE FOL ! VOLTAGE DROP OF 6 APPEARS ACROSS A : RESISTOR 7HAT POWER IS LOWING COLOURED BANDS BROWN BLACK ORANGE SILVER 7HAT IS THE VALUE OF THE DISSIPATED IN THE RESISTOR RESISTOR AND WHAT IS ITS TOLERANCE ! RESISTOR IS RATED AT : ! RESISTOR OF : AT IS 7 7HAT IS THE MAXIMUM VOLT AGE THAT CAN BE SAFELY APPLIED TO THIS REQUIRED 7HAT SHOULD BE THE COLOUR CODE FOR THIS COMPONENT RESISTOR ! & CAPACITOR IS CHARGED TO A POTENTIAL OF 6 7HAT CHARGE IS PRESENT 'JH 4FF RVFTUJPO

For more information, links and other resources please check out our Teach-In website at:

www.tooley.co.uk/ teach-in 56

ªª"UILDªn

. 4()3 MONTHmS l,EARNm SECTION WEmVE INTRODUCED YOU TO THE BASICS OF RESISTORS AND CAPACITORS !LMOST ALL ELECTRONIC CIRCUITS WILL CONTAIN ONE OR BOTH OF THESE TYPES OF COMPONENTS SO ITmS REALLY IMPORTANT THAT WE UNDERSTAND WHAT THEY DO AND HOW THEY WORK %LECTRONICS TEXT BOOKS OFTEN HAVE LENGTHY AND CONFUSING EXPLANATIONS WITH LOTS OF MATHEMATICAL FORMULAE (OWEVER THE BEST WAY TO REALLY GET TO GRIPS WITH WHATmS GOING ON IS TO EXPERIMENT WITH SOME SIMPLE CIR CUITS 7E ARE GOING TO LOOK AT A FEW OF THE SAMPLE CIRCUITS INCLUDED WITH #IRCUIT 7IZARD AS WELL AS GIVING YOU SOME NEW CIRCUITS TO ENTER AND TRY OUT FOR YOURSELF

/HM Sª,AWªINªPRACTICE

4O START WITH WEmLL HAVE A LOOK AT /HMmS ,AW IN PRACTICE /PEN THE l/HMmS ,AWm SAMPLE CIRCUIT FROM THE !SSISTANT PANEL ON THE RIGHT HAND SIDE OF THE SCREEN BY SELECTING l3AMPLE #IRCUITSm THEN l%LEMENTARY #IRCUITSm AND SCROLLING DOWN TO THE l%LECTRICAL 4HEORYm SECTION 4HE CIRCUIT SEE &IG IS ABOUT AS SIMPLE AS IT COMES WITH A POWER SOURCE A 6 00 BATTERY AND A VARIABLE RESISTOR 7E ALSO HAVE TWO MULTIMETERS ONE TO SHOW THE VOLT AGE ACROSS THE RESISTOR AND ONE TO SHOW THE CURRENT ÛOWING THROUGH IT

3IMULATION

0RESS THE PLAY BUTTON FOUND ON THE TOOLBAR TO ACTIVATE THE SIMULA TION 9OU SHOULD SEE VALUES APPEAR ING ON THE MULTIMETERS .OW TRY CHANGING THE VALUE OF THE VARIABLE RESISTOR 62 BY CLICKING ON THE END OF THE SHAFT q THE MOUSE POINTER WILL CHANGE TO A POINTED ÚNGER WHEN YOUmRE IN THE RIGHT PLACE 9OUmLL THEN BE PRESENTED WITH A VIRTUAL KNOB THAT YOU CAN TURN TO THE DESIRED VALUE .OTICE THAT AS YOU INCREASE THE RESISTANCE THE CURRENT FLOWING THROUGH IT REDUCES AND WJDF WFSTB .OTE THAT THE READINGS FOR CURRENT ARE IN MILLIAMPS M! 4O TRY OUT THE THEORY THAT WE INTRO DUCED CHECK THE VALUES FOR VOLTAGE AND CURRENT WHEN THE VARIABLE RESIS TOR IS AT AND K AND CHECK THAT THEY OBEY /HMmS LAW

Everyday Practical Electronics, December 2010

worldmags

Teach-In 2011

ªªªªªªª4HEª#IRCUITª7IZARDªWAY

worldmags

CIRCUIT ALONG WITH AN OSCILLOSCOPE SHOWING THE VOLTAGE ACROSS A & CAPACITOR # 3TART SIMULATING THE CIRCUIT AND KEEP AN EYE ON THE lDOTm ON THE OSCIL LOSCOPE SCREEN 7ATCH HOW IT RISES AS THE CAPACITOR CHARGES /NCE THE TRACE HAS LEVELLED OFF ÛICK THE SWITCH TO START DISCHARGING THE CAPACITOR AND AGAIN WATCH THE OSCILLOSCOPE SCREEN TO SEE HOW THE VOLTAGE FALLS WITH TIME

#IRCUITªDIAGRAM

'JH 5IF 0INnT -BX TBNQMF DJSDVJU

#APACITORSªINªACTION

.OW WEmLL TAKE A LOOK AT CAPACITORS IN ACTION /PEN l#APACITOR #HARGINGm BY SELECTING 3AMPLE #IRCUITS THEN

"ASIC #IRCUITS IN THE !SSISTANT SEE &IG 7HEN THE ÚLE OPENS IT WILL START OFF IN l0#" ,AYOUTm VIEW WHICH SHOWS A VIRTUAL REPRESENTATION OF THE

'JH 5IF DBQBDJUPS DIBSHJOH TBNQMF DJSDVJU

Everyday Practical Electronics, December 2010

4O SEE THE SCHEMATIC LAYOUT FOR THE CIRCUIT SWITCH TO THE l#IRCUIT $IAGRAMm VIEW USING THE TABS ON THE BOTTOM OF THE SCREEN 3TART THE SIMU LATION AGAIN AND CONTROL THE SWITCH TO ALLOW THE CAPACITOR TO CHARGE AND DISCHARGE 4HE VOLTAGE ACROSS THE CAPACITOR IS THEN PLOTTED ON THE GRAPH IN REAL TIME #IRCUIT 7IZARD ALSO DEMONSTRATES THE CHARGE BUILDING UP ON THE PLATES OF THE CAPACITOR WITH BLUE RED lPLUSSESm AND lMINUSESm )N l,EARNm WE SHOWED HOW TO CALCU LATE THE TIME PERIOD USING THE FORMULA 5 $3 WHICH IS WHEN THE VOLTAGE ACROSS THE CAPACITOR HAS REACHED OF THE SUPPLY VOLTAGE AROUND 6 IN THIS CASE /NCE YOU HAVE A NICE LOOKING PLOT FOR CHARGING AND DISCHARGING PRINT OUT YOUR GRAPH SEE &IG #ALCULATE THE TIME CONSTANT FOR THE CIRCUIT USING THE VALUES OF $ AND 3 AND THEN USING A RULER DRAW A VERTICAL LINE UP FROM THAT VALUE ON THE GRAPH FROM THE POINT AT WHICH IT STARTED TO CHARGE AND READ OFF THE VOLTAGE AT THIS POINT $OES IT AGREE WITH WHAT YOU WOULD EXPECT 4HE LAST SAMPLE CIRCUIT THAT WEmLL LOOK AT IS A PRACTI CAL APPLICATION OF CHARGING A CAPACITOR /PEN l4RANSISTOR 4IMERm FROM l3AMPLE #IRCUITSm FOUND UNDER l"ASIC #IRCUITSm l'ENERALm 4HE CIRCUIT USES A CAPACITOR TO CREATE A TIME DELAY BEFORE THE BULB IS IL LUMINATED )T DOES THIS BY USING A PAIR OF TRANSISTORS ACTING LIKE A SWITCH 7EmLL BE LOOKING AT TRANSISTORS IN MORE DETAIL IN SUBSEQUENT 4EACH )N EDITIONS

worldmags

Teach-In 2011

ªª4HEª#IRCUITª7IZARDªWAY

!MAZE #APACITORS NORMALLY COME IN VERY SMALL VALUES &OR EXAMPLE A P& CA PACITOR HAS A VALUE OF FARADS q THATmS A PRETTY SMALL NUMBERØ )N FACT A ONE FARAD CAPACITOR IS ENOR MOUS RELATIVELY SPEAKING 7HATmS THE LARGEST VALUE CAPACITOR THAT YOU CAN ÚND 4RY LOOKING AT HOW CAPACITORS ARE USED IN SOME OF THE MOST ELABORATE CAR AUDIO SYSTEMS AS THEY CAN BE VERY BIGØ

'JH (SBQI PG DBQBDJUPS WPMUBHF QMPUUFE BHBJOTU UJNF XIJDI TIPXT ÜSTU DIBSHF BOE UIFO EJTDIBSHF 3TART THE SIMULATION AND TEST THE CIRCUITmS OPERATION !S THE CAPACITOR CHARGES THE VOLTAGE ACROSS IT INCREASES /NCE THE VOLTAGE REACHES A CERTAIN VALUE THE TRANSISTORS lTURN ONm ALLOW ING CURRENT TO ÛOW FROM THE POSITIVE OF THE BATTERY THROUGH THE BULB TO GROUND 6 AND THEREFORE LIGHTING IT 4HE LONGER IT TAKES FOR THE CAPACITOR TO CHARGE THE LONGER THE DELAY WILL BE

BEFORE THE BULB LIGHTS 4HE CAPACITOR CHARGES THROUGH THE VARIABLE RESISTOR 62 4HEREFORE BY CHANGING THE VALUE OF THE RESISTOR WE CAN CHANGE HOW FAST THE CAPACITOR CHARGES AND HENCE SET THE DELAY )TmS A BIT LIKE TURN ING A TAP TO CHANGE HOW FAST YOU ÚLL UP A BUCKET OF WATER 4RY SETTING THE VARIABLE RESISTOR SO THAT THERE IS A TWO SECOND DELAY BEFORE THE BULB LIGHTS

'JH " TFMFDUJPO PG DBQBDJUPST UIBU QSPWJEF TPNF FYUSFNFMZ MBSHF WBMVFT PG DBQBDJUBODF

!NSWERSªTOª1UESTIONS 3EE PAGE /HM :

)NVESTIGATE

3EE PAGE &ARAD & 6

4HE DATA SHOWN IN 4ABLE WAS OBTAINED DURING AN EXPERIMENT ON A $ 3 CIRCUIT 5SE THIS DATA TO PLOT A GRAPH SHOWING HOW THE CAPACITOR VOLTAGE VARIES WITH TIME AND THEN USE THE GRAPH TO ANSWER THE FOLLOWING QUESTIONS )S THE CAPACITOR BEING CHARGED OR DISCHARGED

ª)F THE VALUE OF 3 IS -: DETERMINE THE VALUE OF $

ª&ROM THE GRAPH ESTIMATE THE TIME CONSTANT OF THE $ 3 CIRCUIT (INT 4AKE A LOOK AT &IG Ø

ª(OW MUCH ENERGY IS STORED IN THE CAPACITOR AT THE START OF THE EXPERIMENT AND WHERE DOES THIS ENERGY GO

! : ª 7 6 ª M# 6 6 S S

4ABLEª ªª4ABLEªOFªRESULTSªFORªTHEªEXPERIMENTALª# 2ªCIRCUIT

Time (s) Capacitor Voltage (V)

A BATTERY B PRESET CAPA CITOR C ELECTROLYTIC CAPACITOR D LIGHT DEPENDENT RESISTOR ,$2 E VARIABLE POTENTIOMETER 6ARIABLE CAPACITOR K:

15.0

7.4

3.6

1.8

0.9

0.4

0.2

2ED BLACK GREEN BLACK RED

.EXT MONTHØ

)N NEXT MONTHmS 4EACH )N WE SHALL BE LOOKING AT DIODES AND POWER SUPPLIES

Everyday Practical Electronics, December 2010

HandsOn Technology http://www.handsontec.com

ISP to ICP Programming Bridge: HT-ICP200 In-Circuit-Programming (ICP) for P89LPC900 Series of 8051 Flash Controllers. ICP uses a serial shift protocol that requires 5 pins to program: PCL, PDA, Reset, VDD and VSS. ICP is different from ISP (In System Programming) because it is done completely by the microcontroller’s hardware and does not require a boot loader. Program whole series of P89LPC900 µController from NXP Semiconductors…

USB-RS232 Interface Card: HT-MP213 A compact solution for missing ports… Thanks to a special integrated circuit from Silicon Laboratories, computer peripherals with an RS232 interface are easily connected to a USB port. This simple solution is ideal if a peripheral does not have a USB port, your notebook PC has no free RS232 port available, or none at all !

Classic P89C51 Development/Programmer Board: HT-MC-02 HT-MC-02 is an ideal platform for small to medium scale embedded systems development and quick 8051 embedded design prototyping. HT-MC-02 can be used as stand-alone 8051 C Flash programmer or as a development, prototyping, industry and educational platform.

For professional, hobbyists…

worldmags

Teach-In 2011

7($&+ ,1 $ %52$' %$6(' ,1752'8&7,21 72 (/(&7521,&6 0ARTÂª Âª$IODESÂªANDÂª0OWERÂª 3UPPLIES By Mike and Richard Tooley

/URÂª4EACH )NÂªSERIESÂªISÂªDESIGNEDÂªTOÂªPROVIDEÂªYOUÂªWITHÂªAÂªBROAD BASEDÂªINTRODUCTIONÂªTOÂªELECTRONICS Âª7EÂªHAVEÂªÂª ATTEMPTEDÂªTOÂªPROVIDEÂªCOVERAGEÂªOFÂªTHREEÂªOFÂªTHEÂªMOSTÂªIMPORTANTÂªELECTRONICSÂªUNITSÂªTHATÂªAREÂªCURRENTLYÂªSTUDIEDÂªINÂª MANYÂªSCHOOLSÂªANDÂªCOLLEGESÂªINÂªTHEÂª5+ Âª4HESEÂªINCLUDEÂª%DEXCELÂª"4%#Âª,EVELÂª ÂªAWARDS ÂªASÂªWELLÂªASÂªELECTRONICSÂªUNITSÂª OFÂªTHEÂªNEWÂª$IPLOMAÂªINÂª%NGINEERINGÂª ALSOÂªATÂª,EVELÂª Âª4HEÂªSERIESÂªWILLÂªALSOÂªPROVIDEÂªTHEÂªMOREÂªEXPERIENCEDÂªREADERÂª WITHÂªANÂªOPPORTUNITYÂªTOÂª@BRUSHÂªUP ÂªONÂªSPECIlCÂªTOPICSÂªWITHÂªWHICHÂªHEÂªORÂªSHEÂªMAYÂªBEÂªLESSÂªFAMILIAR Âª %ACHÂªPARTÂªOFÂªOURÂª4EACH )NÂªSERIESÂªISÂªORGANISEDÂªUNDERÂªlVEÂªMAINÂªHEADINGS Âª,EARN Âª#HECK Âª"UILD Âª)NVESTIGATEÂªANDÂª !MAZE Âª,EARNÂªWILLÂªTEACHÂªYOUÂªTHEÂªTHEORY Âª#HECKÂªWILLÂªHELPÂªYOUÂªTOÂªCHECKÂªYOURÂªUNDERSTANDING ÂªANDÂª"UILDÂªWILLÂªGIVEÂª YOUÂªANÂªOPPORTUNITYÂªTOÂªBUILDÂªANDÂªTESTÂªSIMPLEÂªELECTRONICÂªCIRCUITS Âª)NVESTIGATEÂªWILLÂªPROVIDEÂªYOUÂªWITHÂªAÂªCHALLENGE Âª WHICHÂªWILLÂªALLOWÂªYOUÂªTOÂªFURTHERÂªEXTENDÂªYOURÂªLEARNING ÂªANDÂªlNALLY Âª!MAZEÂªWILLÂªSHOWÂªYOUÂªTHEÂª@WOWÂªFACTOR ÂªÂª

.Âª 4()3 OUR THIRD INSTALLMENT OF 5FBDI *O WE SHALL BE INTRO DUCING YOU TO A COMPONENT THAT ACTS RATHER LIKE A ONE WAY STREET q THE DIODE 7E SHALL BE USING #IRCUIT 7IZ ARD TO INVESTIGATE HOW DIFFERENT TYPES OF DIODE CONDUCT WHEN A VOLTAGE IS APPLIED TO THEM )NVESTIGATE PROVIDES YOU WITH AN OPPORTUNITY TO DELVE INTO THE OPERATION OF A SIMPLE $# POWER SUPPLY WHILE !MAZE EXPLORES SOME EXCITING DEVELOPMENTS IN LIGHT EMIT TING DIODE ,%$ TECHNOLOGY

$IODES

,EARN

! DIODE IS AN ELECTRONIC COMPONENT THAT ALLOWS CURRENT TO Ã&#x203A;OW IN ONE DIREC TION BUT NOT IN THE OTHER )N EFFECT IT ACTS AS A lONE WAY STREETm FOR CURRENT Ã&#x203A;OW WHICH LEADS TO SOME USEFUL APPLICATIONS

INCLUDING CONVERTING ALTERNATING CURRENT !# TO DIRECT CURRENT $# ! DIODE IS FORMED FROM A JUNCTION OF O TYPE AND Q TYPE SEMICONDUCTOR MATERIALS 4HE RESULTING DEVICE OFFERS AN EXTREMELY LOW RESISTANCE TO CURRENT Ã&#x203A;OW IN ONE DIRECTION AND AN EXTREMELY HIGH RESISTANCE TO CURRENT Ã&#x203A;OW IN THE OTHER .OTE THAT AN lIDEALm DIODE WOULD CONDUCT PERFECTLY IN ONE DIRECTION AND NOT AT ALL IN THE OTHER DIRECTION

'JH %JPEF DPOTUSVDUJPO

#ONNECTIONS ARE MADE TO EACH SIDE OF THE DIODE 4HE CONNECTION TO THE Q TYPE MATERIAL IS REFERRED TO AS THE ANODE A WHILE THAT TO THE O TYPE MATERIAL IS CALLED THE CATHODEÂª K AS SHOWN IN &IG

&ORWARDÂªANDÂªREVERSEÂªBIAS )F THE ANODE OF A DIODE IS MADE POSITIVE WITH RESPECT TO THE CATHODE AND PROVIDED THAT THE RELATIVELY SMALL CONDUCTION THRESHOLD VOLTAGE IS EXCEEDED THE DIODE WILL FREELY PASS CURRENT 4HIS CONDITION IS SHOWN IN &IG A AND IT IS REFERRED TO AS FORWARDÂªBIAS #ONVERSELY WHEN THE CATHODE OF A DIODE IS MADE POSITIVE WITH RESPECT TO THE ANODE THE DIODE WILL CEASE TO CONDUCT 4HIS CONDITION IS SHOWN IN &IG B AND IT IS REFERRED TO AS REVERSEÂª BIAS )N THE REVERSE BIASED CONDITION THE DIODE PASSES A NEGLIGIBLE

Everyday Practical Electronics, January 2011

worldmags

Teach-In 2011

'JH 5ZQJDBM WPMUBHF DVSSFOU DIBSBDUFSJTUJDT GPS UZQJDBM TJMJDPO BOE HFSNBOJVN EJPEFT /PUF UIF EJGGFSFOU TDBMFT GPS QPTJUJWF BOE OFHBUJWF WPMUBHF VALUES OF REVERSE VOLTAGE AND LARGE VALUES OF FORWARD CURRENT CONSISTENCY OF CHARACTERISTICS IS OF SECONDARY IMPORTANCE IN SUCH APPLICATIONS 3EMICONDUCTOR DIODES ARE ALSO AVAILABLE CONNECTED IN A FOUR DIODE BRIDGE CONÚGURATION FOR USE AS A RECTIÚER IN AN !# POWER SUPPLY &IG SHOWS A SE LECTION OF VARIOUS DIODE TYPES WHILE &IG SHOWS THE SYMBOLS THAT ARE USED TO REPRESENT THEM IN ELECTRONIC CIRCUIT SCHEMATICS 'JH 'PSXBSE BOE SFWFSTF DPOOFD UJPOT GPS B EJPEF AMOUNT OF CURRENT AND BEHAVES LIKE AN INSULATOR

$IODEªCHARACTERISTICS

4YPICAL * 7 CHARACTERISTICS FOR GERMA NIUM AND SILICON DIODES ARE SHOWN IN &IG )F YOU TAKE A CAREFUL LOOK AT THESE GRAPHS YOU WILL SEE THAT THE APPROXIMATE FORWARD CONDUCTION VOLTAGE FOR A GERMA NIUM DIODE IS 6 WHILE THE VOLTAGE FOR A SILICON DIODE IS APPROXIMATELY 6

$IODEªTYPES

$IODES ARE OFTEN DIVIDED INTO SIGNAL OR RECTIÚER TYPES ACCORDING TO THEIR PRINCI PAL ÚELD OF APPLICATION 3IGNALªDIODES RE QUIRE CONSISTENT FORWARD CHARACTERISTICS WITH LOW FORWARD VOLTAGE DROP 2ECTIlERª DIODES NEED TO BE ABLE TO COPE WITH HIGH

Everyday Practical Electronics, January 2011

'JH 7BSJPVT UZQFT PG EJPEF JODMVEJOH SFDUJÜFS TXJUDIJOH BOE MJHIU FNJUUJOH UZQFT

worldmags

Teach-In 2011

'JH 4ZNCPMT VTFE UP SFQSFTFOU WBSJPVT UZQFT PG EJPEF BOE B CSJEHF SFDUJÜFS

'JH " TJNQMF IBMG XBWF SFDUJÜFS

'JH *NQSPWFE GVMM XBWF CSJEHF SFDUJÜFS

2ECTIlERS

4HE MOST COMMON APPLICATION FOR A DIODE IS THAT OF CHANGING ALTERNATING CURRENT !# INTO DIRECT CURRENT $# &IG SHOWS A SIMPLE HALF WAVE RECTI ÚER POWER SUPPLY IN WHICH THE DIODE PASSES CURRENT WHEN THE INCOMING VOLT AGE IS POSITIVE BUT BLOCKS CURRENT ÛOW WHEN IT IS NEGATIVE )N ORDER TO MAIN TAIN A CONSTANT VOLTAGE AT THE OUTPUT A RESERVOIR CAPACITOR IS CONNECTED ACROSS THE $# OUTPUT TERMINALS 4HIS CAPACITOR IS CHARGED ON POSITIVE HALF CYCLES AND DISCHARGES ON NEGATIVE HALF CYCLES AS SHOWN IN &IG !N IMPROVED FULL WAVE POWER SUP PLY THAT USES A BRIDGE RECTIÚER IS SHOWN IN &IG )N THIS CIRCUIT ONLY TWO OF THE FOUR DIODES OF THE BRIDGE CONDUCT AT ANY ONE TIME EITHER $ AND $ OR $ AND $ DEPENDING ON THE POLARITY OF THE INPUT VOLTAGE

4RANSFORMERS

'JH 7PMUBHF XBWFGPSNT GPS UIF IBMG XBWF SFDUJÜFS

0OWER SUPPLIES REQUIRE SOME MEANS OF ISOLATING AND STEPPING DOWN THE !# MAINS SUPPLY BEFORE THE RECTIÚER AND RESERVOIR CAPACITOR 4HIS IS ACHIEVED WITH THE USE OF A STEP DOWN TRANSFORMER AS

Everyday Practical Electronics, January 2011

worldmags

Teach-In 2011 SHOWN IN &IG 4HE PRIMARY AND SEC ONDARY WINDINGS OF THE TRANSFORMER ARE WOUND ON THE SAME LAMINATED STEEL CORE 7HEN CURRENT ÛOWS IN THE PRIMARY WIND ING IT CREATES AN ALTERNATING MAGNETIC ÛUX THAT IS COUPLED TIGHTLY INTO THE SECONDARY WINDING 4HIS IN TURN INDUCES AN %-& IN THE SECONDARY WINDING 4HE RELATIONSHIP BETWEEN THE PRIMARY AND SECONDARY TURNS AND VOLTAGES IS AS FOLLOWS

93 96

,IGHT EMITTINGªDIODES

13 16

,IGHT EMITTING DIODES ,%$ CAN BE USED AS GENERAL PURPOSE INDICATORS #OMPARED WITH CONVENTIONAL ÚLAMENT LAMPS THEY OPERATE FROM SIGNIÚCANTLY SMALLER VOLTAGES AND CURRENTS 4HEY ARE ALSO VERY MUCH MORE RELIABLE THAN ÚLA MENT LAMPS -OST ,%$S WILL PROVIDE A REASONABLE LEVEL OF LIGHT OUTPUT WHEN A FORWARD CURRENT OF AS LITTLE AS M! TO M! AT A FORWARD CONDUCTION VOLTAGE OF AROUND 6 ! TYPICAL ,%$ INDICATOR CIRCUIT IS SHOWN IN &IG 4HE ÚXED RESISTOR 3 IS USED TO SET THE FORWARD CURRENT OF THE ,%$ IN THIS CASE ABOUT M! 4HE VALUE OF THE RESISTOR MAY BE CALCULATED FROM THE FORMULA

(a) Transformer symbol, voltages and turns

WHERE 70 AND 73 ARE THE PRIMARY AND SECONDARY VOLTAGES WHILE /P AND /S ARE THE PRIMARY AND SECONDARY TURNS .OTE ALSO THAT THE TURNS RATIO FOR A TRANSFORMER IS USUALLY QUOTED AS /P /S 3O FOR EX AMPLE A TRANSFORMER WITH PRIMARY TURNS AND SECONDARY TURNS WOULD HAVE A TURNS RATIO OF

WHERE 7G IS THE FORWARD VOLTAGE DROP FOR THE ,%$ TYPICALLY AROUND 6 7 IS THE SUPPLY VOLTAGE AND * IS THE FORWARD CURRENT

:ENERªDIODES

:ENER DIODES ARE SILICON DIODES THAT UNLIKE NORMAL DIODES EXHIBIT AN ABRUPT REVERSE BREAKDOWN AT RELATIVELY LOW VOLT AGES FOR EXAMPLE 6 6 OR 6 4HE CIRCUIT SYMBOL FOR A :ENER DIODE WAS SHOWN EARLIER IN &IG WHILE A TYPICAL :ENER DIODE CHARACTERISTIC CURVE IS SHOWN IN &IG 7HEN A :ENER DIODE IS UNDERGOING REVERSE BREAKDOWN AND PROVIDED ITS MAXIMUM RATINGS ARE NOT EXCEEDED THE

9 9I ,

(b) A typical transformer

0LEASE NOTEØ 'JH " USBOTGPSNFS VOLTAGE APPEARING ACROSS IT WILL REMAIN SUBSTANTIALLY CONSTANT REGARDLESS OF THE CURRENT ÛOWING 4HIS PROPERTY MAKES A :ENER DIODE IDEAL FOR USE AS A VOLTAGE REGULATOR AS SHOWN IN &IG

4HE LARGE VALUE RESERVOIR CAPACITOR IN A POWER SUPPLY CAN OFTEN REMAIN IN A PARTIALLY CHARGED STATE LONG AFTER THE SUPPLY HAS BEEN SWITCHED OFF OR DISCON NECTED "ECAUSE OF THIS IT IS IMPORTANT TO EXERCISE GREAT CARE WHEN WORKING ON POWER SUPPLY CIRCUITSØ

'JH " TJNQMF ;FOFS EJPEF WPMUBHF SFHVMBUPS

'JH " UZQJDBM TFU PG ;FOFS EJPEF DIBSBDUFSJTUJDT

Everyday Practical Electronics, January 2011

'JH " UZQJDBM -&% JOEJDBUPS

worldmags

Teach-In 2011

#HECKªnª(OWªDOªYOUªTHINKª YOUªAREªDOING

3KETCH THE CIRCUIT SYMBOL FOR A DIODE AND LABEL THE ANODE AND CATHODE CONNECTIONS 7HAT IS A THE FORWARD RESISTANCE AND B THE REVERSE RESISTANCE OF AN lIDEALm DIODE 7HICH OF THE DIODES SHOWN IN &IG IS CONDUCTING

'JH 4FF RVFTUJPO 3TATE THE FORWARD CONDUCTION VOLTAGE FOR A A GERMA NIUM DIODE AND B A SILICON DIODE %XPLAIN BRIEÛY HOW A RECTIÚER OPERATES %XPLAIN WHY A RESERVOIR CAPACITOR IS NEEDED IN A POWER SUPPLY

. 4()3 MONTHmS l"UILDm WE ARE GOING TO TRY OUT SOME OF THE DIODE THEORY THAT WE DISCUSSED EARLIER 4O START WITH WEmLL CARRY OUT SOME SIMPLE EXPERIMENTS WITH ORDINARY SILICON DIODES TO SEE HOW THEY REALLY WORK )N l,EARNm WE SAW HOW A DIODE ACTS LIKE A ONE WAY VALVE (OWEVER BY USING A REALLY HIGH REVERSE VOLTAGE WE CAN MAKE A DIODE BREAK DOWN AND LET THROUGH CURRENT lBACK WARDSm 7E ALSO KNOW THAT IT TAKES A LITTLE VOLTAGE TO lOPEN UPm A DIODE AND MAKE IT START LETTING CURRENT ÛOW THROUGH IT 3O LETmS TRY THIS OUTØ

'JH 5FTUJOH B TJMJDPO EJPEF VTJOH GPSXBSE CJBT

$IODEªTESTªCIRCUIT

%NTER THE CIRCUIT SHOWN IN &IG 9OUmLL ÚND THE DIODE IN THE l$ISCRETE SEMICONDUC TORSm FOLDER THE INPUT VOLTAGE IN l0OWER 3UP PLIESm AND THE METERS IN l6IRTUAL )NSTRUMENTSm "Y DEFAULT #IRCUIT 7IZARD WILL GIVE YOU AN

)DENTIFY EACH OF THE DIODE SYMBOLS SHOWN IN &IG

'JH 4FF RVFTUJPO

! TRANSFORMER HAS PRIMARY TURNS AND SEC ONDARY TURNS $ETERMINE THE SECONDARY OUTPUT VOLTAGE IF THE PRIMARY IS SUPPLIED FROM A 6 !# MAINS SUPPLY

'JH 4FMFDUJOH UIF NPEFM GPS B EJPEF

Everyday Practical Electronics, January 2011

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Teach-In 2011

ªª"UILDªnª4HEª#IRCUITª7IZARDªWAY

'JH &YDFM HSBQI PG SFTVMUT GPS / JO GPSXBSE CJBT lIDEALm DIODE !S WE WANT TO SEE HOW A REAL DIODE MIGHT WORK YOU NEED TO SELECT A MODEL 4O DO THIS DOUBLE CLICK THE DIODE SYMBOL AND SELECT l . m FROM THE l-ODELm DROP DOWN LIST SEE &IG 4HE . IS A STANDARD SILICON RECTIÚER DIODE AND IS VERY COM MONLY USED

4EST

7HAT WE HAVE HERE IS A REALLY SIMPLE CIRCUIT q PROBABLY NOT ONE THAT YOUmD USE IN REAL LIFE (OWEVER IT LETS US SEE HOW MUCH CURRENT THE DIODE PASSES DEPENDING ON WHAT VOLTAGE WE PUT ACROSS IT 4O CARRY OUT OUR TEST WHAT WEmLL DO IS SLOWLY INCREASE THE VOLTAGE ACROSS THE DIODE AND SEE WHAT CURRENT ÛOWS THROUGH IT 4HIS WILL TELL US IF THE DIODE IS CONDUCTING &IRST TRY STARTING THE SIMULATION BY HITTING THE PLAY BUTTON ON THE TOP BAR 5SE THE SLIDER TO VARY THE INPUT VOLT AGE AND WATCH THE EFFECT 9OUmLL ONLY NEED TO INCREASE THE VOLTAGE TO ABOUT 6 AT WHICH POINT THE DIODE SHOULD BE CONDUCTING NICELY AND YOU SHOULD SEE A LARGE VALUE FOR THE CURRENT 9OU MIGHT ÚND IT EASIER TO SET THE LIMIT FOR THE INPUT VOLTAGE TO 6 ITmS SET

'JH $JSDVJU GPS EJPEF UFTUJOH JO SFWFSTF CJBT

AT 6 BY DEFAULT q THIS WILL ALSO HELP YOU WITH THE NEXT BITØ 9OU CAN DO THIS BY DOUBLE CLICKING THE COMPONENT AND CHANGING THE 6 TO 6 (OPEFULLY YOU SHOULD NOTICE THAT IT DOESNmT SIMPLY START LETTING A LARGE CUR RENT PASS IMMEDIATELY q IT TAKES A LITTLE VOLTAGE ACROSS IT TO REALLY lOPEN IT UPm ) ALWAYS LIKE TO THINK OF A DIODE LIKE A SPRUNG ONE WAY GATE ITmS EASY TO GET THROUGH IT IN THE RIGHT DIRECTION BUT YOU NEED TO PUT A LITTLE PRESSURE AGAINST IT IN ORDER TO GET THROUGH

4AKINGªREADINGS

.OW LETmS GET A LITTLE MORE SCIENTIÚC ABOUT THINGS AND TAKE SOME READINGS 7E CAN THEN DRAW UP A GRAPH OF OUR RESULTS TO SEE WHATmS GOING ON 3TARTING FROM 6 AND STEPPING UP IN 6 M6 STEPS INCREASE THE VOLTAGE AND RECORD THE CURRENT ÛOWING THROUGH THE DIODE /NCE YOUmVE GOT A FULL SET OF RESULTS YOU CAN USE THEM TO DRAW A GRAPH 4AKE CARE TO MAKE SURE THAT ALL OF YOUR CURRENT READINGS ARE IN THE SAME UNITS WHEN YOU PLOT YOUR GRAPHØ !N EXAMPLE USING -ICROSOFT %XCEL IS SHOW IN &IG !S YOU HAVE FOUND ONCE WE GET TO AROUND 6 THE DIODE STARTS TO LET CURRENT THROUGH AND THIS IS WHAT WEmD EXPECT FOR A SILICON DIODE 3O FAR WEmVE BEEN USING THE DIODE lTHE RIGHT WAY ROUNDm IN WHAT WE CALL FORWARDªBIAS .OW WEmLL SEE WHAT HAPPENS WHEN WE TURN THE DIODE AROUND SO THATmS ITmS IN REVERSEª BIAS OR lBACKWARDSm 'JH &YDFM HSBQI GPS / JO SFWFSTF CJBT

Everyday Practical Electronics, January 2011

!LTER YOUR CIRCUIT TO THAT SHOWN IN &IG .OTICE THAT AS WELL AS THE DIODE ORIENTATION CHANGING THE TOP LIMIT ON THE INPUT VOLTAGE HAS BEEN INCREASED TO 6 3TART THE SIMULATION AND TRY EXPERIMENTING WITH THE INPUT VOLTAGE 9OU SHOULD ÚND THAT ITmS REALLY HARD TO GET A DIODE TO CONDUCT IN REVERSE BIASØ 'OING BACK TO THE IDEA OF A DIODE AS A ONE WAY GATE IF YOU REALLY WANTED TO GET THROUGH IT THE WRONG WAY YOU WOULD BE ABLE TO DO IT BUT YOUmD HAVE TO WORK REALLY HARD TO FORCE IT OPEN 4HEREFORE ITmS NOT STRICTLY TRUE THAT A STANDARD DIODE ONLY LETS CURRENT THROUGH IN ONE DIRECTIONØ (OWEVER IN PRACTICE IF YOU WERE USING A DIODE IN A LOW VOLT AGE CIRCUIT IT IS UNLIKELY THAT A REVERSE VOLTAGE WOULD EVER BE HIGH ENOUGH TO BREAK IT DOWN 2ECORD VALUES FOR THE VOLTAGE AND CUR RENT GOING UP IN STEPS OF 6 AND GRAPH YOUR RESULTS 4IP YOUmLL ALSO NEED TO GO TO 6 TO GET YOUR ÚNAL READINGØ 9OU SHOULD OBTAIN SOMETHING THAT LOOKS LIKE THE GRAPH SHOWN IN &IG

)RU \ FRS\ RXU RI &L :L]D UFXLW VHH & UG ² ' 52 SDJH 0 V

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Teach-In 2011

ªªªªªªª4HEª#IRCUITª7IZARDªWAY

'JH &YDFM HSBQI TIPXJOH / DIBSBDUFSJTUJDT JO CPUI GPSXBSE BOE SFWFSTF CJBT 3EMICONDUCTOR MANUFACTURERS OFTEN PRODUCE A GRAPH OF THE CHARACTERISTICS OF THEIR DIODES SIMILAR TO THOSE THAT YOUmVE CREATED (OWEVER THEY USU ALLY RECORD THE VOLTAGES AND CURRENTS IN REVERSE BIAS AS NEGATIVE AND SHOW THEM BOTH ON ONE GRAPH 4RY THIS WITH YOUR RESULTS AND SEE IF YOU CAN PRODUCE A MANUFACTURER LIKE GRAPH FOR THE . 4AKE A LOOK AT OURS WHICH WEmVE SHOWN IN &IG 3O WEmVE SEEN HOW A STANDARD DI ODE LETS CURRENT THROUGH IN A FORWARD DIRECTION ONCE THERE IS A SMALL VOLTAGE ACROSS IT BUT NORMALLY BLOCKS CURRENT IN A REVERSE DIRECTION UNLESS WE APPLY A REALLY LARGE VOLTAGE

:ENERªDIODES

$IODES ARE A REALLY USEFUL DEVICE TO HELP US CONTROL WHERE CURRENT ÛOWS IN A CIRCUIT AND ARE ESSENTIAL WHEN IT COMES TO CONVERTING ALTERNATING CUR RENT !# TO DIRECT CURRENT $# WE CALL THIS VOLTAGE RECTIlCATION (OWEVER AS YOU MET IN THE l,EARNm SECTION THERE

IS ALSO ANOTHER TYPE OF DIODE THAT HAS A SPECIAL AND RATHER USEFUL FEATURE WHEN IT COMES TO REVERSE BIAS 4HESE ARE CALLED :ENER DIODES "ASICALLY WHEN WE MANUFACTURE A :ENER DIODE WE CAN ENGINEER IT SO THAT WE KNOW AT EXACTLY WHAT VOLTAGE IT WILL BREAKDOWN IN REVERSE BIAS AND CONDUCT 9OU CAN PURCHASE A FULL RANGE OF :ENER DIODES WITH DIFFERENT SPECIÚED VOLTAGES 3O LETmS TRY OUR PREVIOUS DIODE EX PERIMENTS BUT WITH SOME :ENER DIODES INSTEAD OF ORDINARY SILICON DIODES !LTER YOUR REVERSE BIAS DIODE CIRCUIT SHOWN IN &IG BY CHANGING THE DIODE TO A :ENER DIODE q SEE &IG 7E NEED TO SPECIFY THE :ENER VOLTAGE OF THE DIODE AND WE DO THIS IN THE SAME WAY AS WE SELECTED THE DIODE MODEL PREVIOUSLY BY DOUBLE CLICKING THE :ENER DIODE AND SELECTING A VOLTAGE FROM THE l-ODELm DROP DOWN LIST SEE &IG 4O START WITH SELECT 6 6 THEN SLOWLY INCREASE THE VOLTAGE ACROSS THE DIODE TAKING READINGS EVERY 6 UNTIL THE CURRENT REACHES AROUND M!

'JH 4FMFDUJOH UIF ;FOFS EJPEF NPEFM

'JH ;FOFS EJPEF UFTU DJSDVJU .OW REPEAT THIS FOR SOME MORE :ENER VOLTAGE VALUES (EREmS OUR RESULTS FOR THREE :ENER DIODES 6 6 6 6 AND 6 6 )F YOU CARRIED OUT YOUR EXPERIMENTS ACCURATELY YOU SHOULD BE ABLE TO PRO DUCE A GRAPH SIMILAR TO THAT SHOWN IN &IG .OTICE THAT THE CURRENT RAPIDLY INCREASES THROUGH THE DIODE ONCE IT REACHES THE :ENER VOLTAGE OF THE DIODE 4HIS CAN BE EXTREMELY USEFUL IN ELECTRONIC CIRCUITS 7E OFTEN USE :ENER DIODES TO GIVE US EXACT REFERENCE VOLTAGES AND TO REGULATE VOLTAGES DOWN TO A SPECIÚC VALUE

For more information, links and other resources please check out our Teach-In website at:

www.tooley.co.uk/ teach-in

'JH $IBSBDUFSJTUJDT GPS UISFF EJGGFSFOU ;FOFS EJPEFT

Everyday Practical Electronics, January 2011

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Teach-In 2011

!MAZE !NSWERSªTOª1UESTIONS 3EE &IG A A ZERO B INÚNITE $ AND $ A 6 B 6 3EE PAGE 3EE PAGE A PHOTODIODE B :ENER DIODE C LIGHT EMITTING DIODE ,%$ 6

!S YOUmVE SEEN ,%$S ARE A TYPE OF DIODE THAT EMITS LIGHT WHEN THE DEVICE IS FORWARD BIASED AND PASSING CURRENT ,%$S HAVE BEEN AROUND IN VARIOUS FORMS FOR QUITE A LONG TIME AND SO YOU WILL ALREADY BE FAMILIAR WITH THEM AND HOW THEY ARE USED ,%$S OFFER SOME NOTABLE ADVANTAGES WHEN COMPARED WITH ÚLA MENT LAMPS AND ÛUORESCENT DISPLAYS p 4HEY ARE EXTREMELY RELIABLE AND THEY CAN OPERATE FOR MANY TENS OR EVEN HUNDREDS OF THOUSANDS OF HOURS IF USED AT THEIR RATED CURRENT p 4HEY ARE IMPERVIOUS TO HEAT COLD SHOCK AND VIBRATION p 4HEY ARE VERY EFÚCIENT AND PRODUCE VERY LITTLE HEAT SO RUN COOL p 4HEY OPERATE FROM LOW VOLTAGE AND CURRENT AND CAN BE EASILY INTERFACED TO ELECTRONIC CIRCUITS p 4HEY ARE RUGGED BECAUSE NO BREAK ABLE GLASS IS USED IN THEIR CONSTRUCTION

)NVESTIGATE &IG SHOWS THE CIRCUIT OF A POWER SUPPLY 3TUDY THE CIRCUIT CAREFULLY LOOK BACK AT WHAT WE DID IN 0ART AND THEN ANSWER EACH OF THE FOLLOWING QUESTIONS 7HAT TYPE OF RECTIÚER IS USED IN THE POWER SUPPLY 7HAT IS THE TURNS RATIO OF THE TRANSFORMER

7HAT !# VOLTAGE WILL APPEAR AT THE INPUT OF THE BRIDGE RECTIÚER )F THE ,%$ HAS A FORWARD VOLTAGE OF 6 WHAT CURRENT IS SUPPLIED TO IT 7HAT POWER WILL BE DISSIPATED IN THE :ENER DIODE

'JH 4FF *OWFTUJHBUF

Everyday Practical Electronics, January 2011

'JH "O FBSMZ QSPUPUZQF 0-&% EJTQMBZ QIPUP DPVSUFTZ PG . & )BSSJT

'OINGªORGANIC

2ECENT ADVANCES IN SEMICONDUCTOR TECHNOLOGY HAVE SEEN THE INTRODUCTION OF WHITE lHIGH BRIGHTNESSm ,%$S THAT CAN BE USED IN GROUPS OR ARRAYS TO REPLACE LAMPS USED IN DOMESTIC LIGHTING APPLICA TIONS $EVELOPED BY +ODAK IN THE S ORGANIC LIGHT EMITTING DIODES /,%$ SEEM POISED TO OUST THE ,#$ DISPLAY JUST AS ,#$ TECHNOLOGY HAS ECLIPSED THE #24 /,%$ PANELS ARE THINNER CRISPER BRIGHTER AND MORE ENERGY EFÚCIENT THAN THEIR ,%$ COUNTERPARTS !N /,%$ PANEL CONSISTS OF A LAYER OF ORGANIC LIGHT EMITTING MATERIAL SAND WICHED BETWEEN TWO CONDUCTORS AN ANODE AND A CATHODE 4HE RESULTING DEVICE IS ABOUT TIMES THINNER THAN A HUMAN HAIR AND IT EMITS LIGHT WHEN AN ELECTRIC CURRENT IS PASSED THROUGH IT 4HEREmS NO NEED FOR A BACKLIGHT BECAUSE THE ORGANIC MATERIAL EMITS ITS OWN LIGHT WHEN CHARGED 4HE ABSENCE OF A BACKLIGHT MEANS THAT /,%$ DISPLAYS CAN BE EXTREMELY THIN &OR EXAMPLE THE 3ONY 8%, IS ONLY MM THICK AND 3ONYmS PROTOTYPE INCH /,%$ 46 USES A PANEL WHICH HAS A THICKNESS OF AS LITTLE AS MMØ )N THE SAME WAY THAT INKS ARE SPRAYED ONTO PAPER DURING PRINTING /,%$S CAN BE SPRAYED ONTO SUBSTRATES USING INKJET TECHNOLOGY 4HIS REDUCES THE COST OF MANUFACTURING AND ALLOWS DISPLAYS TO BE PRINTED ONTO VERY LARGE ÚLMS THAT CAN BE USED IN GIANT SCREENS AND ELECTRONIC BILLBOARDS 3O IF YOU FANCY A INCH 46 DISPLAY THAT ROLLS UP FOR STORAGE OR IF YOU THINK IT MIGHT BE USEFUL TO HAVE A DISPLAY BUILT INTO YOUR CLOTHING YOU MIGHT NOT HAVE TO WAIT TOO LONGØ

.EXT MONTHØ

)N PART NEXT MONTHmS 4EACH )N WE WILL LOOK AT TRANSISTORS

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Teach-In 2011

7($&+ ,1 $ %52$' %$6(' ,1752'8&7,21 72 (/(&7521,&6 0ARTª ª4RANSISTORS By Mike and Richard Tooley

/URª4EACH )NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROAD BASEDªINTRODUCTIONªTOªELECTRONICS ª7EªHAVEª ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ ª4HESEªINCLUDEª%DEXCELª"4%#ª,EVELª ªAWARDS ªASªWELLªASªELECTRONICSª UNITSªOFªTHEªNEWª$IPLOMAªINª%NGINEERINGª ALSOªATª,EVELª ª4HEªSERIESªWILLªALSOªPROVIDEªTHEªMOREªEXPERIENCEDª READERªWITHªANªOPPORTUNITYªTOª@BRUSHªUP ªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIAR ª %ACHªPARTªOFªOURª4EACH )NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGS ª,EARN ª#HECK ª"UILD ª)NVESTIGATEªANDª !MAZE ª,EARNªWILLªTEACHªYOUªTHEªTHEORY ª#HECKªWILLªHELPªYOUªTOªCHECKªYOURªUNDERSTANDING ªANDª"UILDªWILLªGIVEª YOUªANªOPPORTUNITYªTOªBUILDªANDªTESTªSIMPLEªELECTRONICªCIRCUITS ª)NVESTIGATEªWILLªPROVIDEªYOUªWITHªAªCHALLENGEª WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNING ªANDªlNALLY ª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTOR ªª

. PART FOUR OF 5FBDI *O WE WILL INTRODUCE YOU TO A COM PONENT THAT CAN ACT AS BOTH AN AMPLIÚER AND A SWITCH /RIGINALLY CALLED A lTRANSFER RESISTORm THE UBIQ UITOUS TRANSISTOR IS FOUND IN ALMOST EVERY ELECTRONIC CIRCUIT EITHER AS A DISCRETE COMPONENT OR AS PART OF AN INTEGRATED CIRCUIT 7E WILL USE #IRCUIT 7IZARD TO IN VESTIGATE THE OPERATION OF A TRANSIS TOR AS A DEVICE FOR AMPLIFYING AND SWITCHING CURRENT 9OU WILL ALSO BE ABLE TO CONSTRUCT AND TEST A SIMPLE LIGHT ÛASHER THAT USES LIGHT EMITTING DIODES ,%$ &INALLY IN !MAZE WE TAKE THIS ONE STEP FURTHER BY SHOW ING YOU HOW TO DESIGN A PRINTED CIRCUIT BOARD 0#" LAYOUT FOR THE ,%$ ÛASHERØ 46

,EARN 4RANSISTORS 4HERE ARE SEVERAL DIFFERENT TYPES OF TRANSISTOR BUT FOR CONVENIENCE THEY ARE OFTEN DIVIDED INTO TWO MAIN CATEGORIES BIPOLARªJUNCTIONªTRANSIS TORSª "*4 AND lELD EFFECTªTRANSISTORSª &%4 !LTHOUGH THE PRINCIPLE ON WHICH THEY OPERATE IS DIFFERENT THEY ARE OFTEN USED IN SIMILAR APPLICA TIONS AND BECAUSE OF THIS WE WILL FOCUS OUR ATTENTION ON "*4 RATHER THAN &%4 DEVICES ! SELECTION OF DIFFERENT TYPES OF TRANSISTOR INCLUD ING "*4 AND &%4 DEVICES IS SHOWN IN &IG "IPOLAR JUNCTION TRANSISTORS ARE MADE OF /1/ OR 1/1 JUNCTIONS OF SILICON 3I 4HE JUNCTIONS ARE

EXTREMELY SMALL AND THEY ARE PRO DUCED IN A SINGLE SLICE OF SILICON BY DIFFUSING IMPURITIES THROUGH A PHOTOGRAPHICALLY REDUCED MASK 3IMPLIFIED REPRESENTATIONS OF /1/ AND 1/1 TRANSISTORS ARE SHOWN TOGETHER WITH THEIR SYM BOLS IN &IG 4HE CONNECTIONS TO THE SEMICONDUCTOR MATERIAL ARE LABELLED COLLECTORª C BASE B AND EMITTERª E !N IMPORTANT POINT TO NOTE IS THAT BOTH TYPES OF TRANSISTOR CONSIST OF TWO DIODE 1 / JUNCTIONS BACK TO BACK (OWEVER ITmS IMPORTANT TO REALISE THAT THE MIDDLE LAYER THE 1 TYPE BASE REGION IN AN /1/ TRANSIS TOR OR THE / TYPE BASE REGION IN THE 1/1 TRANSISTOR IS MADE EXTREMELY NARROW AND THIS ALLOWS CHARGE

Everyday Practical Electronics, February 2011

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Teach-In 2011 TYPICALLY TIMES GREATER THAN THAT ÛOWING IN THE BASE 4HE EQUATION THAT RELATES CURRENT ÛOW IN THE COLLECTOR BASE AND EMIT TER CURRENTS IS

IE = IB + IC WHERE *% IS THE EMITTER CURRENT *" IS THE BASE CURRENT AND *# IS THE COLLECTOR CURRENT ALL EXPRESSED IN THE SAME UNITS

'JH " TFMFDUJPO PG EJGGFSFOU #+5 BOE '&5 EFWJDFT

'JH CFMPX 4ZNCPMT TJNQMJÜFE NPEFMT BOE DPOTUSVDUJPO PG .0. BOE 0.0 CJQPMBS KVODUJPO USBOTJTUPST

CARRIERS TO PASS ACROSS IT RATHER THAN ENTER OR EXIT AT THE BASE 4HUS THE MAIN CURRENT ÛOW IN A TRANSISTOR IS FROM COLLECTOR TO EMITTER IN THE CASE OF A /1/ TRANSISTOR OR FROM EMITTER TO COLLECTOR IN THE CASE OF A 1/1 TRANSISTOR AS SHOWN IN &IG AND &IG &IG AND &IG RESPECTIVELY SHOW THE NORMAL VOLTAGES APPLIED TO /1/ AND 1/1 TRANSISTORS AND THE CURRENT ÛOW WITHIN THE DEVICE )T IS IMPORTANT TO NOTE FROM THIS THAT THE BASE EMITTER JUNCTION IS FORWARD BIASED AND THE COLLECTOR BASE JUNC TION IS REVERSE BIASED "ECAUSE THE BASE REGION IS MADE VERY NARROW CHARGE CARRIERS ARE SWEPT ACROSS IT AND ONLY A RELATIVELY SMALL NUMBER APPEAR AT THE BASE 4O PUT THIS INTO CONTEXT THE CUR RENT ÛOWING IN THE EMITTER CIRCUIT IS

'JH 'MPX PG DVSSFOU JO BO .0. USBOTJTUPS

Everyday Practical Electronics, February 2011

'JH 'MPX PG DVSSFOU JO B 0.0 USBOTJTUPS

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Teach-In 2011 4ABLEª ª#HARACTERISTICSªOFªTHEªTHREEª"*4ªCIRCUITªCONlGURATIONS

0LEASE NOTEØ 4HE DIRECTION OF CONVENTIONAL CUR RENT ÛOW IS FROM COLLECTOR TO EMITTER IN THE CASE OF AN /1/ TRANSISTOR AND EMITTER TO COLLECTOR IN THE CASE OF A 1/1 TRANSISTOR )N BOTH CASES THE AMOUNT OF CURRENT ÛOWING FROM COLLECTOR TO EMITTER IS DETERMINED BY THE AMOUNT OF CURRENT ÛOWING INTO THE BASE

Parameter 3DUDPHWHU

Common emitter &RPPRQ HPLWWHU

7\SLFDO DSSOLFDWLRQV

*HQHUDO SXUSRVH DPSOLILHU VWDJHV

9ROWDJH JDLQ &XUUHQW JDLQ 3RZHU JDLQ ,QSXW UHVLVWDQFH 2XWSXW UHVLVWDQFH 3KDVH VKLIW

0HGLXP KLJK +LJK 9HU\ KLJK 0HGLXP Nȍ 0HGLXP KLJK Nȍ

0LEASE NOTEØ 4HERE ARE MANY DIFFERENT TYPES OF TRANSISTOR )N THIS INSTALMENT OF 4EACH )N WE ARE JUST LOOKING AT ONE OF THE MOST COMMON TYPES THE BIPOLAR JUNCTION TRANSISTOR "*4 &IG SHOWS SYMBOLS FOR SOME OF THE OTHER LESS COMMON TYPES THAT YOU MIGHT COME ACROSS

8QLW\ +LJK +LJK +LJK Nȍ /RZ ȍ ,QSXW DQG RXWSXW VWDJHV ZKHUH QR YROWDJH JDLQ LV QHHGHG

Common base &RPPRQ EDVH

+LJK 8QLW\ +LJK /RZ ȍ +LJK Nȍ

5DGLR IUHTXHQF\ DPSOLILHUV

4HE VALUE OF *% CAN BE CALCULATED BY RE ARRANGING THE EQUATION *% *" *# TO MAKE *# THE SUBJECT AS FOLLOWS *# *% q *# q M! .OTE THAT ! IS THE SAME AS M!

"*4ªCIRCUITªCONlGURATIONS

%XAMPLEª ! TRANSISTOR OPERATES WITH A COLLEC TOR CURRENT OF M! AND AN EMITTER CURRENT OF M! $ETERMINE THE VALUE OF BASE CURRENT 4HE VALUE OF *% CAN BE CALCULATED BY RE ARRANGING THE EQUATION *% *" *# TO MAKE *" THE SUBJECT AS FOLLOWS

*" *% q *# (ENCE

*" q M! %XAMPLEª 'JH 4ZNCPMT VTFE GPS PUIFS UZQFT PG USBOTJTUPS

Common collector &RPPRQ FROOHFWRU

! TRANSISTOR OPERATES WITH *% M! AND *" ! $ETERMINE THE VALUE OF *#

2EGARDLESS OF WHETHER A "*4 IS AN /1/ OR 1/1 TYPE THREE BASIC CIRCUIT CONÚGURATIONS ARE USED AND ALL TRANSISTOR BNQMJÜFS STAGES ARE BASED ON ONE OF THESE 4HE THREE CIRCUITS ARE BASED ON WHICH ONE OF THE THREE TRANSISTOR CONNECTIONS IS MADE COMMON TO BOTH THE INPUT AND THE OUTPUT )N THE CASE OF "*4S THE CONÚGURATIONS ARE KNOWN AS COM MONªEMITTER COMMONªCOLLECTOR OR EMITTERªFOLLOWER AND COMMONªBASE SEE &IG .OTE THAT WE HAVE INCLUDED A RESIS TOR KNOWN AS A LOAD MARKED 3- IN &IG WHICH CONVERTS THE OUTPUT

'JH #JQPMBS KVODUJPO USBOTJTUPS #+5 DJSDVJU DPOÜHVSBUJPOT

Everyday Practical Electronics, February 2011

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Teach-In 2011 CURRENT TAKEN FROM THE COLLECTOR OR EMITTER INTO A CORRESPONDING VOLT AGE WHICH APPEARS AT THE OUTPUT 4HE THREE CIRCUIT CONFIGURATIONS EXHIBIT QUITE DIFFERENT PERFORMANCE CHARACTERISTICS AS LISTED IN 4ABLE 4YPICAL VALUES HAVE BEEN INCLUDED IN BRACKETS

#URRENTªGAIN "*4S ARE PRIMARILY CURRENT AM PLIFYING DEVICES IN WHICH A SMALL CURRENT AT THE BASE B INÛUENCES A MUCH LARGER CURRENT AT THE COLLECTOR C 4HERE IS A DIRECT RELATIONSHIP BETWEEN THESE TWO CURRENTS &OR EX AMPLE DOUBLING THE CURRENT APPLIED TO THE BASE WILL CAUSE THE COLLECTOR CURRENT TO DOUBLE AND SO ON )N THE CASE OF THE COMMON EMITTER MODE WHERE THE INPUT IS CONNECTED TO THE BASE AND THE OUTPUT IS TAKEN FROM THE COLLECTOR THE CURRENT GAIN IS THE RATIO OF COLLECTOR CURRENT TO BASE CURRENT (ENCE #URRENT GAIN

,&# ,%"

4O UNDERSTAND THIS IMPORTANT EFFECT TAKE A LOOK AT &IG 4HIS

SHOWS A TRANSISTOR WITH A CURRENT GAIN OF OPERATING IN COMMON EMITTER CONÚGURATION WITH THREE DIF FERENT VALUES OF BASE CURRENT APPLIED )N &IG A THERE IS NO BASE CUR RENT SO THEREmS ALSO NO COLLECTOR CUR RENT )N &IG B THE BASE CURRENT HAS INCREASED TO M! ! AND THIS HAS CAUSED THE COLLECTOR CURRENT TO INCREASE FROM ZERO TO M! ! FURTHER INCREASE IN BASE CURRENT FROM M! TO M! ! CAUSES THE COLLECTOR CURRENT TO INCREASE BY A FURTHER M! TO M! 7E COULD NOW PLOT A GRAPH OF THESE RESULTS SO THAT WE CAN PREDICT THE COLLECTOR CURRENT FOR ANY GIVEN VALUE OF BASE CURRENT .OT SURPRIS INGLY THIS GRAPH WHICH IS KNOWN AS A TRANSFERªCHARACTERISTIC BECAUSE IT SHOWS INPUT PLOTTED AGAINST OUTPUT TAKES THE FORM OF A STRAIGHT LINE AS SHOWN IN &IG

%XAMPLEª ! TRANSISTOR OPERATES WITH A COL LECTOR CURRENT OF M! AND A BASE CURRENT OF ! 7HAT IS THE COMMON EMITTER CURRENT GAIN OF THE TRANSISTOR

5SING THE RELATIONSHIP

,&# #URRENT GAIN GIVES ,%" #URRENT GAIN

%XAMPLEª ! "*4 HAS A COMMON EMITTER CURRENT GAIN OF )F THE TRANSISTOR OP ERATES WITH A COLLECTOR CURRENT OF M! DETERMINE THE VALUE OF BASE CURRENT 2EARRANGING THE CURRENT GAIN FOR MULA TO MAKE *# THE SUBJECT GIVES

,,%"%

,& FXUUHQW JDLQ

FROM WHICH

,%%"

P$ RU ȝ$

"IAS 7HEN WE USE A "*4 TO AMPLIFY SIGNALS SUCH AS SPEECH OR MUSIC WE NEED TO ENSURE THAT THE TRANSIS TOR IS ALWAYS CONDUCTING AN AMOUNT OF STANDING COLLECTOR CURRENT 7E ACHIEVE THIS BY APPLYING A BIAS

'JH UPQ MFGU $VSSFOU ÝPX JO B TJNQMF #+5 DPNNPO FNJUUFS BNQMJÜFS 'JH CFMPX 0VUQVU DVSSFOU QMPUUFE BHBJOTU JOQVU DVSSFOU GPS UIF #+5 JO 'JH 'JH CFMPX MFGU " TJNQMF DPNNPO FNJUUFS BNQMJÜFS DJSDVJU

Everyday Practical Electronics, February 2011

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Teach-In 2011 CURRENT TO THE BASE OF THE TRANSIS TOR 4HIS MEANS THAT A STATIC VALUE OF COLLECTOR CURRENT WILL ÛOW EVEN WHEN THERE IS NO SIGNAL PRESENT 4HE COLLECTOR CURRENT CAN THEN INCREASE ABOVE OR DECREASE BELOW THIS STAND ING VALUE OF CURRENT DEPENDING UPON THE POLARITY OF THE INPUT SIGNAL )F THIS SOUNDS A LITTLE COMPLICATED TAKE A LOOK AT THE SIMPLE COMMON EMIT TER AMPLIÚER CIRCUIT SHOWN IN &IG 4HE SIGNAL WHICH IS !# IS COU PLED INTO THE AMPLIÚER VIA CAPACITOR # AND OUT OF THE AMPLIÚER VIA # 4HESE TWO CAPACITORS HELP TO ISOLATE THE TRANSISTOR STAGE SO THAT THE $# VOLTAGES AND CURRENTS INSIDE IT ARE UN AFFECTED BY WHATEVER IS CONNECTED TO THE INPUT AND OUTPUT TERMINALS 4HE BIAS CURRENT WHICH ÛOWS ALL THE TIME IS JOINED BY THE SIGNAL CURRENT BEFORE ENTERING THE BASE OF THE TRANSISTOR )N A SIMILAR MANNER THE TRAN SISTORmS COLLECTOR CURRENT HAS TWO COMPONENTS A $# VALUE RESULTING FROM THE STEADY BIAS CURRENT AND AN !# CURRENT SUPERIMPOSED ON IT RESULTING FROM THE AMPLIÚED SIGNAL CURRENT 4HESE CURRENTS JOIN TOGETHER AND ÛOW THROUGH THE COLLECTORªLOAD 2 ACROSS WHICH THE OUTPUT VOLTAGE IS DEVELOPED .OTE THAT THE OUTPUT VOLTAGE HAS THE SAME SHAPE AS THE INPUT VOLTAGE BUT IS INVERTED OR TURNED THROUGH

.OW LETmS SEE IF WE CAN CALCULATE THE BASE AND COLLECTOR VOLTAGES AND CURRENTS WHEN NO SIGNAL IS PRESENTØ &IG SHOWS THE AMPLIÚER CIRCUIT REDRAWN OMITTING THE INPUT AND OUT PUT COUPLING CAPACITORS AS THEY WILL HAVE NO EFFECT ON THE $# CONDITIONS WITHIN THE AMPLIÚER 4HE TRANSISTOR IS A SILICON TYPE AND AS WE MENTIONED EARLIER THE DEVICE CONSISTS OF TWO 1 / JUNCTIONS 4HE COLLECTOR BASE JUNCTION IS REVERSE BIASED WHILE THE BASE EMITTER JUNC TION IS FORWARD BIASED !S A RESULT THE VOLTAGE DROP BE TWEEN THE BASE AND EMITTER WILL BE THE SAME AS THE FORWARD VOLTAGE DROP FOR ANY CONDUCTING SILICON DIODE OR APPROXIMATELY 6 4HE VOLTAGE DROP ACROSS RESISTOR 2 WILL THUS BE q 6 OR 6 AND THE CURRENT ÛOWING IN IT THE BASE BIAS CURRENT CAN BE CALCULATED USING /HMmS LAW

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P$ P$

)F THE TRANSISTOR HAS A CURRENT GAIN OF WE CAN NOW ÚND THE STATIC VALUE OF COLLECTOR CURRENT USING

,&%# &XUUHQW JDLQ u , %

9//

u 9 9

&INALLY THE VOLTAGE DROP BETWEEN THE COLLECTOR AND EMITTER CAN BE CAL CULATED FROM

9#%&( &( 9 9/

9 9

.OW LETmS SUPERIMPOSE A SIGNAL CURRENT ONTO THE BIAS AND SEE WHAT HAPPENS TO THE COLLECTOR CURRENT 4O DO THIS WE CAN USE THE TRANSFER CHARACTERISTIC THAT WE MET EARLIER 4HE NO SIGNAL OR QUIESCENT CONDI TION WHEN THE BASE CURRENT IS M! AND COLLECTOR CURRENT IS M! IS MARKED AS THE OPERATINGª POINT ON &IG WHICH ALSO SHOWS THE EFFECT OF SUPERIMPOSING A SIGNAL WHICH HAS A PEAK VALUE OF M! ON THE STEADY BIAS CURRENT $UE TO THE SIGNAL THE BASE CURRENT WILL SWING UP TO M! ON POSITIVE PEAKS AND DOWN TO M! ON NEGA TIVE PEAKS )N RESPONSE TO THIS THE COLLECTOR CURRENT WILL SWING UP TO M! AND DOWN TO M! 4HIS WILL HAVE THE EFFECT OF PRODUCING AN OUT PUT VOLTAGE CHANGE DROPPED ACROSS 3- OF 6 PEAK TO PEAK

0LEASE NOTEØ

u P$ P$ 7E CAN NOW DETERMINE THE VOLT AGE DROPPED ACROSS THE COLLECTOR LOAD 2

4HE OPTIMUM VALUE OF COLLECTOR EMITTER VOLTAGE FOR THE COMMON EMITTER AMPLIÚER CIRCUIT SHOWN IN &IG IS EXACTLY HALF THAT OF THE

'JH #JBT DBMDVMBUJPOT GPS UIF TJNQMF DPNNPO FNJUUFS BNQMJÜFS DJSDVJU 'JH SJHIU 4VQFSJNQPTJOH BO JOQVU TJHOBM PO UIF CJBT DVSSFOU JO 'JH

Everyday Practical Electronics, February 2011

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Teach-In 2011

'JH "O JNQSPWFE DPNNPO FNJUUFS BNQMJÜFS

'JH " TJNQMF USBOTJTUPS TXJUDI 'JH " GVSUIFS JNQSPWFE DPNNPO FNJUUFS BNQMJÜFS

SUPPLY 4HIS ENSURES THAT THE VOLTAGE AT THE COLLECTOR OF THE TRANSISTOR IE THE OUTPUT SIGNAL CAN SWING EVENLY UP TO 6 AND DOWN TO 6 WHEN THE SIGNAL IS APPLIED RETURNING BACK TO 6 WHEN THE SIGNAL IS NO LONGER PRESENT

)MPROVEDªAMPLIlERªSTAGES )N ORDER TO STABILISE THE OPERATING CONDITIONS FOR AN AMPLIÚER STAGE AND COMPENSATE FOR VARIATIONS IN TRANSIS TOR PARAMETERS BASE BIAS CURRENT FOR THE TRANSISTOR CAN BE DERIVED FROM THE VOLTAGE AT THE COLLECTOR SEE &IG 4HIS VOLTAGE IS DEPENDANT ON THE COL LECTOR CURRENT THAT IN TURN DEPENDS UPON THE BASE CURRENT ! NEGATIVEª FEEDBACK LOOP THUS EXISTS IN WHICH THERE IS A DEGREE OF SELF REGULATION )F THE COLLECTOR CUR RENT INCREASES THE COLLECTOR VOLTAGE

WILL FALL AND THE BASE CURRENT WILL BE REDUCED 4HE REDUCTION IN BASE CURRENT WILL PRODUCE A CORRESPOND ING REDUCTION IN COLLECTOR CURRENT TO OFFSET THE ORIGINAL CHANGE #ON VERSELY IF THE COLLECTOR CURRENT FALLS THE COLLECTOR VOLTAGE WILL RISE AND THE BASE CURRENT WILL INCREASE 4HIS IN TURN WILL PRODUCE A CORRESPOND ING INCREASE IN COLLECTOR CURRENT TO COMPENSATE FOR THE ORIGINAL CHANGE &IG SHOWS A FURTHER IMPROVE MENT IN WHICH $# NEGATIVE FEEDBACK IS USED TO STABILISE THE STAGE AND COM PENSATE FOR VARIATIONS IN TRANSISTOR PARAMETERS COMPONENT VALUES AND TEMPERATURE CHANGES 2ESISTORS 2 AND 2 FORM A POTENTIAL DIVIDER THAT DETERMINES THE $# BASE POTENTIAL 7" 4HE BASE EMITTER VOLTAGE 7"% IS THE DIFFERENCE BETWEEN THE POTENTIALS

Everyday Practical Electronics, February 2011

PRESENT AT THE BASE 7" AND EMITTER 7% 4HE POTENTIAL AT THE EMITTER IS GOVERNED BY THE EMITTER CURRENT *% )F THIS CURRENT INCREASES THE EMIT TER VOLTAGE 7% WILL INCREASE AND AS A CONSEQUENCE 7"% WILL FALL 4HIS IN TURN PRODUCES A REDUCTION IN EMIT TER CURRENT WHICH LARGELY OFFSETS THE ORIGINAL CHANGE #ONVERSELY IF THE EMITTER CURRENT 7% DECREASES THE EMITTER VOLTAGE 7"% WILL INCREASE REMEMBER THAT 7" REMAINS CONSTANT 4HE INCREASE IN BIAS RESULTS IN AN INCREASE IN EMITTER CURRENT COMPENSATING FOR THE ORIGINAL CHANGE

4HEªTRANSISTORªASªAªSWITCH #ONVENTIONAL ELECTROMECHANICAL SWITCHES CAN ONLY OPERATE AT VERY LOW SPEEDS 4RANSISTORS ON THE OTHER HAND CAN SWITCH CURRENT MANY MIL LIONS OF TIMES FASTER AND WITHOUT ANY WEAR OR DETERIORATION &IG 51

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Teach-In 2011 SHOWS A SIMPLE TRANSISTOR SWITCHING CIRCUIT IN WHICH THE CURRENT IS BEING SWITCHED ON AND OFF IN THE LOAD 3, )N &IG A NO BASE CURRENT IS AP PLIED TO THE TRANSISTOR AND THE TRANSISTOR IS IN THE lOFFm STATE )N THIS CONDITION NO COLLECTOR CURRENT ÛOWS AND SIMILARLY NO CURRENT ÛOWS IN 3, )N &IG B A BASE CURRENT OF M! IS APPLIED TO THE TRANSISTOR FROM A 6 SOURCE !S BEFORE IF WE ASSUME THAT THE TRANSISTOR HAS A CURRENT GAIN OF THE COLLECTOR CURRENT SHOULD BE M! TIMES THE BASE CURRENT (OWEVER THIS IS NOT POSSIBLE BECAUSE THE COLLECTOR CURRENT CAN NEVER BE MORE THAN M! DETERMINED BY THE 6 SUPPLY AND THE RESISTANCE OF THE LOAD )N THIS CONDITION THE TRANSISTOR IS SAID TO BE SATURATED AND NO MORE COLLECTOR CURRENT WILL ÛOW REGARDLESS OF HOW MUCH MORE BASE CURRENT IS SUPPLIED 4RANSISTORS USED IN SWITCHING CIR CUITS ARE NORMALLY OPERATED UNDER SATURATION CONDITIONS 4HIS MEANS THAT THE COLLECTOR VOLTAGE WILL EITHER BE THE SAME AS THE SUPPLY VOLTAGE IN THE lOFFm STATE OR VERY CLOSE TO 6 IN THE lONm STATE ,ATER IN THIS INSTAL MENT OF 4EACH )N YOU WILL BE BUILD ING AND TESTING AN lASTABLEm CIRCUIT THAT USES TWO TRANSISTORS OPERATING AS SATURATED SWITCHES

Circuit Wizard A Standard or Professional version of Circuit Wizard can be purchased from the editorial ofﬁce of EPE – see CDROMs for Electronics page and the UK shop on our website (www.epemag. com) for a ‘special offer’. Further information can be found on the New Wave Concepts website; www.new-wave-concepts.com. The developer also offers an evaluation copy of the software that will operate for 30 days, although it does have some limitations applied, such as only being able to simulate the included sample circuits and no ability to save your creations. However, if you’re serious about electronics and want to follow our series, then a full copy of Circuit Wizard is a really sound investment.

#HECKªnª(OWªDOªYOUªTHINKªYOUªAREªDOING 3KETCH THE CIRCUIT SYMBOL FOR A AN /1/ "*4 AND B A 1/1 "*4 AND LABEL THE CONNECTIONS

3KETCH THE CIRCUIT OF A SIMPLE COMMON EMITTER AMPLIÚER ,ABEL YOUR DIAGRAM

7HEN USED AS A SIMPLE COM MON EMITTER AMPLIÚER WHAT VOLT AGE WOULD YOU EXPECT TO MEASURE BETWEEN THE BASE AND EMITTER OF A SILICON TRANSISTOR %XPLAIN YOUR ANSWER

%XPLAIN WHY CAPACITORS ARE NEEDED AT THE INPUT AND OUTPUT OF A SIMPLE "*4 AMPLIÚER

! TRANSISTOR OPERATES WITH A COLLECTOR CURRENT OF M! AND A BASE CURRENT OF ! 7HAT WILL THE EMITTER CURRENT BE 7HAT WILL THE COMMON EMIT TER CURRENT GAIN BE FOR THE "*4 IN 1UESTION

%XPLAIN WHY BIAS IS NEEDED IN A TRANSISTOR AMPLIÚER 3KETCH THE CIRCUIT OF A SIMPLE TRANSISTOR SWITCH %XPLAIN HOW THE CIRCUIT OPERATES For more information, links and other resources please check out our Teach-In website at:

www.tooley.co.uk/ teach-in

ªª"UILDªnª4HEª#IRCUITª7IZARDªWAY

/ YOUmVE HEARD THE THEORY ABOUT TRANSISTORS q NOW LETmS TRY IT OUT IN #IRCUIT 7IZARD 7EmLL START OFF BY EXPLORING A COUPLE OF REALLY SIMPLE TRANSISTOR CIRCUITS TO SEE HOW THEY FUNCTION 9OU CAN ÚND TRANSISTORS IN THE l$ISCRETE 3EMICONDUCTORSm FOLDER IN THE GALLERY 9OUmLL NOTICE THAT THERE ARE LOTS OF DIFFERENT TYPES OF TRANSISTORS TO CHOOSE INCLUDING STANDARD BIPOLAR AND ÚELD EFFECT TYPES !S WELL AS HAVING DIFFERENT TYPES OF TRANSISTOR EACH CAN BE SET TO ONE OF A LARGE SELECTION OF DIFFERENT MODELS FOR THAT TYPE 4HERE ARE LITERALLY THOUSANDS OF DIFFERENT MODELS OF TRANSISTORS ON THE MARKET ALL WITH DIFFERENT SHAPES SIZES AND CHARACTERISTICS )TmS IMPORTANT THAT WHEN YOUmRE DESIGNING CIRCUITS THAT YOU

CHOOSE ONE THATmS RIGHT FOR THE JOB 7EmLL SEE WHAT DIFFERENCE IT MAKES BY TRYING OUT A CIRCUIT WITH TWO DIFFERENT TRANSISTOR MODELS 3TART OFF BY RECREATING THE CIRCUIT SHOWN IN &IG USING AN /1/ TRANSISTOR /NCE YOUmVE DRAGGED THE TRANSISTOR ON TO YOUR CIRCUIT DOUBLE CLICK THE SYMBOL AND SELECT "# " FROM THE MODEL DROP DOWN 4HE AMMETERS CAN BE FOUND IN THE lVIRTUAL INSTRUMENTSm FOLDER -AKE SURE THAT YOU GET THEM THE RIGHT WAY ROUND LOOK FOR THE POSITIVE SYMBOL OR YOUmLL GET A NEGATIVE CURRENT READING /NE OF THE NEAT FEATURES IN #IRCUIT 7IZARD IS THAT YOU CAN POP VOLTMETERS AND AMMETERS INTO YOUR CIRCUIT DESIGNS SO THAT YOU CAN TAKE READ INGS AND SEE WHATmS GOING ON IN YOUR CIRCUIT WITH EASE

Everyday Practical Electronics, February 2011

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Teach-In 2011

ªª4HEª#IRCUITª7IZARDªWAY .OW RUN THE CIRCUIT AND ÛICK THE SWITCH .OT THE MOST INTERESTING OF CIRCUITS BUT IT DOES SHOW US SOME KEY FEATURES OF A TRANSISTORmS OPERA TION 9OU MIGHT ALSO LIKE TO SWITCH TO THE l#URRENT &LOWm VIEW TO SEE A VISUALISATION OF THE CURRENT MOVING AROUND THE CIRCUIT ,EAVE THE SWITCH CLOSED ON FOR THE MOMENT AND TAKE

READINGS FOR *# AND *" AND SEEING IF IT MATCHES UP TO YOUR READING FOR *% 4HE NUMBER OF TIMES BIGGER THE LOAD CURRENT IS THAN THE INPUT CURRENT USED TO CONTROL THE TRANSISTOR IS CALLED THE GAIN 7E CAN CALCULATE THE GAIN FOR OUR TRANSISTOR USING THE FORMULA #URRENT GAIN ,&#

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A LOOK AT THE THREE AMMETER READINGS .OTICE THAT THERE IS A SMALL AMOUNT OF CURRENT ÛOWING INTO THE BASE OF THE TRANSISTOR BUT THEREmS A MUCH LARGER CURRENT ÛOWING INTO THE COLLECTOR AND THROUGH TO THE EMITTER )N CURRENT ÛOW VIEW YOU CAN SEE THAT THE RIGHT HAND LOOP OF THE CIRCUIT IS MUCH THICKER 4HIS DEMONSTRATES HOW WE CAN USE TRANSISTORS TO CONTROL A MUCH LARGER CURRENT FROM A RELATIVELY SMALL ONE 4HE NEXT THING TO NOTICE IS THAT THE CURRENT ÛOWING OUT OF THE EMITTER IS EQUAL TO THE CURRENT ÛOWING INTO THE COLLECTOR PLUS THE CURRENT ÛOWING IN TO THE BASE 7E CAN WRITE THIS US ING THE FORMULA THAT WE MET BEFORE

*% *" *# $OUBLE CHECK THIS PROVES TRUE FOR YOUR CIRCUIT BY ADDING YOUR

'JH 5SBOTJTUPSJTFE NPUPS DPOUSPM DJSDVJU

5SE THIS FORMULA TO HELP YOU CALCULATE THE GAIN FOR THE CIRCUIT 2EMEMBER TO USE *$ NOT *& q ITmS A VERY COMMON MISTAKEØ .OW WEmVE PROVED A BIT OF THE ORY IN ACTION LETmS SEE SOME REAL CIRCUITS THAT USE TRANSISTORS 7E DISCUSSED IN ,EARN THAT TRANSIS TORS CAN BE USED AS A SWITCH OR AN AMPLIFIER q SO HEREmS AN EXAMPLE OF EACH

4RANSISTORªSWITCHINGªCIRCUIT %NTER AND SIMULATE THE TRANSISTOR SWITCHING CIRCUIT SHOWN IN &IG 4HIS CIRCUIT USES A TIMER CHIP WEmLL BE LOOKING AT THESE IN DETAIL A LITTLE LATER IN THE SERIES TO PULSE A $# MOTOR 4HE PROBLEM WE HAVE IS THAT ALTHOUGH THE IS A CLEVER LITTLE CHIP ITmS A BIT PUNY AND NOT CAPABLE

Everyday Practical Electronics, February 2011

OF DIRECTLY POWERING A LARGE LOAD LIKE A MOTOR 4HE MOST IT COULD HANDLE IS ÛASH ING AN ,%$ q SO THE QUESTION IS HOW CAN WE USE IT TO CONTROL SOMETHING MUCH MORE POWERFUL 7ELL THE AN SWER IS BY USING A TRANSISTOR 7HAT WE DO IS USE A REALLY SMALL CURRENT COMING OUT OF THE TO CONTROL A

MUCH LARGER CURRENT SUPPLIED TO THE MOTOR ,OOKING AT THE CIRCUITS YOU CAN SEE THAT PIN THE OUTPUT OF THE IS GOING TO THE BASE OF THE TRAN SISTOR (ENCE WHEN THE OUTPUT IS HIGH A LITTLE CURRENT ÛOWS INTO THE BASE OF THE TRANSISTOR AND lTURNS IT ONm 4HIS ALLOWS CURRENT TO ÛOW DOWN FROM THE SUPPLY THROUGH THE MOTOR AND DOWN TO GROUND )N THIS CASE THE TRANSISTOR IS USED AS A SWITCH WITH THE TRANSISTOR EITHER BEING COMPLETELY lONm OR lOFFm 7HEN YOUmVE ENTERED THE CIR CUIT INTO #IRCUIT 7IZARD CHANGE THE VIEW TO l6OLTAGE ,EVELSm LEFT HAND TABS SEE &IG AND LOOK CAREFULLY AT THE CURRENTS IN THE CIRCUIT ESPECIALLY AROUND THE TRANSISTOR

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Teach-In 2011

ªª4HEª#IRCUITª7IZARDªWAY ONE PROBE RED TO THE OUTPUT AND ONE BLUE ON TO THE INPUT JUST AFTER THE FUNCTION GENERATOR !S YOU PLACE MORE PROBES IT WILL AUTOMATI CALLY GIVE THEN A NEW COLOUR SO THAT YOU CAN IDENTIFY THEM LATER ON !S YOU PLACE YOUR ÚRST PROBE YOU SHOULD NOTICE THAT A GRAPH WILL APPEAR ALONG THE BOTTOM OF THE SCREEN 4HIS IS GREAT FOR ALLOWING YOU TO MONITOR HOW VOLTAGES AROUND YOUR CIRCUIT CHANGE OVER TIME "EFORE YOU HIT lSIMULATEm DOUBLE CLICK ON THE GRAPH AND CHANGE THE GRAPH PROPERTIES TO THOSE SHOWN IN &IG 4HIS WILL SET THE MINIMUM AND MAXIMUM VOLTAGES SHOWN ON THE GRAPH SEE &IG AND THE TIME SCALE TO GIVE YOU A NICE LOOKING TRACE FROM THE CIRCUIT 'JH 5SBOTJTUPSJTFE NPUPS DPOUSPM DJSDVJU TJNVMBUFE JO m7PMUBHF -FWFMTn WJFX

4RANSISTORªAMPLIlERªCIRCUIT )N THE NEXT CIRCUIT WE ARE GOING TO SEE A TRANSISTOR OPERATING AS AN AMPLIÚER 4HIS WILL ALSO INTRODUCE US TO SOME OF THE GRAPHING FACILITIES IN CIRCUIT WIZARD 3TART OFF BY ENTERING THE CIRCUIT SHOWN IN &IG INTO #IRCUIT 7IZARD -AKE SURE THAT YOU DONmT CONFUSE VOLTAGE RAILS FOUND IN l0OWER 3UP PLIESm AND A TERMINAL FOUND IN l#ONNECTORSm 4O LABEL THE LATTER JUST DOUBLE CLICK ON THEM AND ENTER A NAME BUT NOTE THAT NAMING A TER MINAL l 6m OR l 6m DOES NOT TURN IT IN TO A VOLTAGE RAILØ -AKE SURE THAT YOU CHANGE DEFAULT VALUES FOR THE COMPONENTS AND FUNCTION GENERATOR TO MATCH THE DIAGRAM GIVEN

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/NCE YOU HAVE THE CIRCUIT MADE UP YOUmLL NEED TO ADD SOME PROBES $O THIS BY CLICKING ON THE PROBE l!DD 0ROBEm BUTTON ON THE TOOLBAR SEE &IG THEN DROPPING THE PROBE WHERE YOU WOULD LIKE IT TO GO !DD

.OW SIMULATE THE CIRCUIT AND KEEP AN EYE ON THE GRAPH 9OU SHOULD SEE TWO SINUSOIDAL WAVES TRACED OUT SEE &IG 4HE ÚRST BLUE LINE IS THE INPUT q IT HAS A RE ALLY SMALL AMPLITUDE YOU CAN BARELY

'JH (SBQI QSPQFSUJFT EJBMPHVF GPS UIF USBOTJTUPS BNQMJÜFS DJSDVJU

Everyday Practical Electronics, February 2011

worldmags

Teach-In 2011

ªª4HEª#IRCUITª7IZARDªWAY SEE IT RISING ABOVE DIPPING BELOW THE AXIS 4HE RED LINE HOWEVER IS A MUCH LARGER VERSION OF THE BLUE LINE 4HIS IS THE AMPLIÚED OUTPUT SIGNAL )T HAS A MUCH HIGHER AMPLITUDE THAN THE INPUT SIGNAL )N THIS CIRCUIT THE TRANSISTOR ACTS AS AN AMPLIÚER 4HE TRANSISTOR IS BEING PROGRESSIVELY SATURATED BY THE SMALL SIGNAL INPUT AND SO THE OUTPUT VARIES COINCIDENTLY TO THE INPUT )TmS ACTING A BIT LIKE A TAP BEING OPENED AND CLOSED TO CONTROL THE ÛOW OF CURRENT IN THE OUTPUT

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!STABLEªOSCILLATORªCIRCUIT .OW WEmRE GOING TO STEP THINGS UP A LITTLE AND ENTER ANOTHER USEFUL REAL WORLD CIRCUIT INTO #IRCUIT 7IZARD 4HE CIRCUIT SHOWN IN &IG IS A SIMPLE CIRCUIT THAT ÛASHES TWO ,%$S ALTERNATELY 4O GIVE IT ITS CORRECT NAME ITmS AN ASTABLEª OSCILLATOR CIRCUIT BECAUSE IT TURNS ON AND OFF CONTINUOUSLY )T USES A PAIR OF TRANSISTORS THAT CONTROL THE CHARGING AND DISCHARGING OF TWO CAPACITORS ALTERNATELY q A LITTLE LIKE A SEE SAW %NTER THE CIRCUIT SHOWN IN &IG MAKING SURE THAT YOU GET ALL OF THE COMPONENT VALUES CORRECT AND THEN HIT THE PLAY BUTTON ON THE TOP BAR TO START THE SIMULATION $ID IT WORK 4RY OUT THE DIFFERENT DISPLAY STYLES BY CLICKING THE TABS ALONG THE LEFT OF THE SCREEN THE lCURRENT ÛOWm DISPLAY SEE &IG WORKS REALLY WELL SHOWING HOW THE CURRENT IS ÛOWING AROUND THE CIRCUIT WITH THE COLOUR SHOWING THE VOLTAGE SEE SAWING ON EITHER SIDE OF THE CIRCUIT AND THE CHARGES BUILDING DIMINISH ING ON THE CAPACITORS &INALLY SAVE YOUR CIRCUIT AS WEmLL BE USING THEM TO CONSTRUCT A PRINTED CIRCUIT BOARD LAYOUT LATER ON

Everyday Practical Electronics, February 2011

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'JH 5SBOTJTUPS BTUBCMF PTDJMMBUPS JO DVSSFOU ÝPX EJTQMBZ TUZMF

worldmags

Teach-In 2011

)NVESTIGATE

!MAZE 3O FAR IN 4EACH )N WEmVE BEEN USING #IRCUIT 7IZARD TO SIMULATE A VARIETY OF SIMPLE ELECTRONIC CIRCUITS SO THAT WE CAN BETTER UNDERSTAND HOW THEY WORK (OWEVER YOU MAY BE WONDERING HOW WE GET FROM SOME THING THAT LOOKS NICE ON A COMPUTER SCREEN TO SOMETHING THAT WE CAN ACTUALLY BUILD AND USE 7ELL #IRCUIT 7IZARD HAS A SUPERB SET OF TOOLS TO HELPS US DO JUST THAT ,OAD UP THE TRANSISTOR ASTABLE CIRCUIT THAT YOU MADE IN OUR l"UILDm TUTORIAL 4HEN CLICK ON THE l#ONVERT TO 0#" ,AYOUTm BUTTON ON THE TOOLBAR SEE &IG 4HIS WILL INITIATE A SIMPLE WIZARD THAT LETS YOU CONVERT A CIRCUIT DESIGN INTO A PRINTED CIRCUIT BOARD 0#"

'JH 4FF RVFTUJPOT CFMPX

4HE CIRCUIT OF A SIMPLE AUDIO AM PLIÚER IS SHOWN IN &IG 3TUDY THE CIRCUIT CAREFULLY LOOK BACK AT WHAT WE DID IN 4EACH )N 0ART TO 0ART AND THEN SEE IF YOU CAN ANSWER EACH OF THE FOLLOWING QUESTIONS 7HAT TYPE OF TRANSISTOR IS A 42 AND B 42 7HAT OPERATING MODE IS USED FOR A 42 AND B 42 7HAT TYPE OF DIODE IS $ AND WHAT VOLTAGE WOULD YOU EXPECT TO MEASURE ACROSS IT

'JH $POWFSU UP 1$# CVUUPO

4HE MAINS OPERATED POWER SUP PLY FOR THE AMPLIÚER IS RATED AT 7 7ILL THIS BE SUFÚCIENT %XPLAIN YOUR ANSWER 7HAT TYPE OF CAPACITOR IS # AND WHAT SHOULD ITS RATED WORKING VOLTAGE BE 7HAT COLOUR CODE SHOULD APPEAR ON A 2 B 2 AND C 2 )F A POTENTIAL DROP OF 6 AP PEARS ACROSS 2 WHAT CURRENT WILL BE ÛOWING IN IT 7HAT IS THE TIME CONSTANT OF THE SERIES CIRCUIT FORMED BY # AND 2

'JH 4FMFDUJOH 1$# UZQF

Everyday Practical Electronics, February 2011

worldmags

Teach-In 2011 !NSWERSÂŞTOÂŞ1UESTIONS 3EE &IG 6 AS THIS IS THE USUAL FORWARD VOLTAGE FOR A CONDUCTING 1 / JUNCTION M! 3EE &IG 3EE PAGE 'JH $IFDLJOH PVU UIF XPSLJOH BTUBCMF DJSDVJU

DESIGN THAT YOU CAN THEN TEST lVIRTU ALLYm AND OR CREATE ARTWORK TO PRODUCE THE 0#" FOR REAL 3TEP THROUGH THE WIZARD BY CLICKING l.EXTm WEmLL LEAVE THE DEFAULT SETTING FOR THE MOMENT 9OU WILL THEN BE ASKED TO CHOOSE A 0#" LAYOUT q SELECT l3INGLE 3IDED .ORMAL 4RACKSm SEE &IG &INALLY CLICK ON THE l#ONVERTm BUTTON THEN SIT BACK CROSS YOUR Ă&#x161;NGERS AND LET #IRCUIT 7IZARD WORK ITmS MAGICĂ&#x2DC; )F ALL GOES WELL YOU SHOULD SEE THE COM PONENTS BEING PLACED ON TO THE CIRCUIT BOARD AND THEN THE TRACKS AUTOMATICALLY ROUTED RIGHT BEFORE YOUR EYES 7HEN ITmS COMPLETED CONVERTING YOUR CIRCUIT IT WILL POP UP A WINDOW TELLING YOU HOW SUCCESSFUL ITmS BEEN

O (3( D L F 6SH IHU 2I

worldmags

HOPEFULLY IT WILL REPORT THAT OF THE CONNECTIONS HAVE BEEN MADE #LICK ON /+ AND ADMIRE YOUR 0#" DESIGN #IRCUIT 7IZARD GIVES YOU A REALLY NICE l2EAL 7ORLDm VIEW OF WHAT YOUR PRODUCED CIRCUIT WOULD LOOK LIKE .OW TRY SOME OF THE OTHER VIEWS ALONG THE LEFT 4HERE ARE A NUMBER OF THINGS THAT YOU CAN NOW DO WITH YOUR DESIGN )F YOU WANT TO GO AHEAD AND PRODUCE YOUR CIRCUIT YOU CAN EASILY PRINT OUT YOUR ARTWORK MASK TO USE !LTERNA TIVELY YOU CAN TRY OUT YOUR 0#" AND TEST IT VIRTUALLY *UST AS IN REAL LIFE YOU NEED A BATTERY TO OPERATE THE CIRCUIT 'RAB ONE FROM THE l/FF "OARD #OMPONENTSm l0OWER 3UPPLIESm FOLDER IN THE GALLERY )N THIS

3EE PAGE 3EE PAGE CASE YOUmLL NEED A 6 00 ALTERNA TIVELY YOU COULD USE THE VIRTUAL POWER SUPPLY FROM l6IRTUAL 4EST %QUIPMENTm #ONNECT UP YOUR BATTERY AS SHOWN IN &IG AND TEST YOUR 0#" BY STARTING THE SIMULATION %XPERIMENT WITH THE VIRTUAL MULTI METER TO CHECK SOME OF THE VOLTAGES AROUND THE CIRCUIT 4HE DISPLAY STYLES ALSO WORK WITH A 0#" SO TRY SOME OF THESE OUT TOO

.EXT MONTHĂ&#x2DC; )N NEXT MONTHmS 4EACH )N WE WILL LOOK AT INTEGRATED CIRCUITS )#S AND OPERATIONAL AMPLIĂ&#x161;ERS OP AMPS

&,5&8,7 :,=$5'

Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard â&#x20AC;&#x201C; which is on special offer from EPE â&#x20AC;&#x201C; and Professional. By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ďŹ nish â&#x20AC;&#x201C; even including on-screen testing of the PCB prior to construction!

Circuit diagram design with component library (500 components * Standard, 1500 components Professional) Virtual instruments (4 Standard, 7 Professional) * On-screen animation *

Layout * PCB Interactive PCB layout simulation * Automatic PCB routing * Gerber export *

Special EPE Offer - Standard version only. EPE is offering readers a 10% discount on Cicuit Wizard Standard software if purchased before 31 Jan, 2011. This is the software used in our Teach-In 2011 series. Standard (EPE Special Offer) ÂŁ59.99 ÂŁ53.99 inc. VAT

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Teach-In 2011

TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS By Mike and Richard Tooley

! ! "# $ % & $' ( ) * ! +

$ , ( )- %

. /

! $ ! 0 ( * ' 1* & * 2 3 ( * ' 1 1 * &

! % * * 2 3 . ! /4

NTEGRATED circuits (ICs) comprise large numbers of transistors and other components built on a single small slice of silicon.

built in a package thatâ&#x20AC;&#x2122;s smaller

as inductors and capacitors (dif circuit form) and other components that need to be externally accessible are then connected as external â&#x20AC;&#x2DC;discreteâ&#x20AC;&#x2122; components. In this instalment of Teach-In 2011

the most common types of integrated

op amp). In Build

Circuit Wizard to simulate a variety

while Investigate challenges you to explain the operation of a simple

Amaze we shall look back at the technology that we used before integrated circuits became available.

( Used in a huge variety of different

are probably the most common and versatile form of analogue integrated circuit. Fig. 5.1 shows the ubiquitous !"#

5.2 shows whatâ&#x20AC;&#x2122;s inside the 8-pin dual-in-line package.

Fig.5.1. The famous 741 operational

Everyday Practical Electronics, March 2011

Teach-In 2011 You can think of an operational

$ %& '

Op amp

+ , output and no common connection. / % $0& % $3& % 0

$3&

$0& #679 : #679 ; $0& $inverting input& :

$3& % $noninverting& & ' * <

;

>?@ >#+@

! " # 7@; 7@; + " appear if we decided to include them. Note

B = common connection

; the common rail in our $ " #

Fig.5.2. Internal circuit of the 741 operational

Everyday Practical Electronics, March 2011

Teach-In 2011

relative to this rail.

Gain Before we take a look at some of the characteristics of operational

One of the most important of these is

$gainâ&#x20AC;&#x2122; % as simple as possible we will use an $ = &

+ + is much easier to work with than the

+ H M + +

$ % & /

% $ & (Rin + +; $ & %

(Rout + +; $ & % %

$ & ; Gain is simply the ratio of what : the ratio of output voltage to input P

V Av = out Vin where Av Vout Vin voltages respectively. :

as the ratio of output current to input P

Ai =

I out I in

where Ai Iout Iin current respectively. 50

%& ' # # "

output power to input power. As a P

Ap =

Pout Pin

where Ap Pout Pin voltages respectively. / P

Pout = I out Ă&#x2014; Vout and and Pin = I in Ă&#x2014; Vin Combining these relationships gives:

Ap =

I outVout = Ai Ă&#x2014; Av I inVin

input of 4mV. Determine the value of

Solution Now:

Av =

Vout Vin

Av =

2 2 Ă&#x2014; 103 = = 500 4 Ă&#x2014; 10â&#x2C6;&#x2019;3 4

of 2M: X

+7 @

[

Solution

Input resistance

input resistance

to input current:

Vin I in

Now:

Rin = P

where Rin is the input resistance (in ; Vin is the input voltage (in volts) Iin is the input current (in amps).

Output resistance

output resistance of an ampli Q circuit output voltage to short-circuit P

Rout =

Example 1

Example 2

power gain

product of the current gain voltage gain.

Rin =

is the short-circuit output current (in amps).

Vout(oc) I out(sc)

where Rout is the output resistance ; Vout(oc) is the open-circuit ; Iout(sc)

I in =

Vin I in

Vin 50 Ă&#x2014; 10â&#x2C6;&#x2019;3 = = Rin 2 Ă&#x2014; 106

Ă&#x2014;

= 25 Ă&#x2014; 10â&#x2C6;&#x2019;9 A = 25 nA nA Please note!

\= operate.

characteristics

]

Everyday Practical Electronics, March 2011

Teach-In 2011 that we would associate with an ‘ideal’

bandwidth of making the closed-loop gains equal to 10,000, 1,000, 100, and 10. Table 5.2 summarises these results. You should also note that the (gain × bandwidth) product for this 6 Hz (ie, 1MHz). We can determine the bandwidth

(a) The voltage gain should be as large as possible, so that a large output voltage will be produced by a small input voltage (b) The input resistance should be as large as possible, so that only a small input current will be taken from the signal source (c) The output resistance should be as low as possible, so as not to limit the output current and power delivered by

voltage gain is set to a particular value by constructing a line and noting the i n ter c ep t p oi n t on th e r es p on s e c u r v e.

Please note! The product of gain and bandwidth -

(d) Bandwidth should be as wide as possible so as not to limit the fre

stant. Thus an increase in gain can only be achieved at the expense of bandwidth, and vice versa .

Fortunately, the characteristics of most

Please note! When negative feedback is applied

close to those of an ‘ideal’ operational

Table 5.2. Relationship between voltage gain and

Table 5.1. Ideal and typical characteristics

Parameter

Ideal

Typical

Voltage gain

Very high

100,000

Input resistance

Very high

100MΩ

Output resistance

Very low

20Ω

Bandwidth

Very wide

2MHz

with a gain-bandwidth product of 1MHz

Voltage gain (AV)

Bandwidth

DC to 1MHz

DC to 100kHz

100

DC to 10kHz

1000

DC to 1kHz

10000

DC to 100 Hz

100000

DC to 10 Hz

Gain and bandwidth It is important to note that the product of gain and bandwidth is a constant for any particular opera increase in gain can only be achieved at the expense of bandwidth, and vice versa . In practice, we control the gain (and bandwidth) of an operational of negative feedback . Figure 5.6 shows the relationship between voltage gain and bandwidth

Fig.5.6. Frequency response curves for

reduced and the bandwidth is in creased. When positive feedback is

gain increases and the bandwidth is reduced. In most cases this will result in instability and oscillation.

The three basic configurations

R =

(note that the axes use logarithmic, rather than linear scales). The openloop voltage gain (ie, that obtained with no external feedback applied) is 100,000 and the bandwidth obtained in this condition is a mere 10Hz. The effect of applying increasing amounts of negative feedback (and consequent ly reducing the gain to a more manage able amount) is that the bandwidth increases in direct proportion.

are shown in Fig.5.7. As mentioned earlier, supply rails have been omit ted from these diagrams for clarity but are assumed to be symmetrical about 0V. The voltage gain for the inverting

Frequency response

The minus sign in the voltage gain expression is included to indicate in version (ie, a positive input voltage will

The frequency response curves in Fig.5.6 show the effect on the

Everyday Practical Electronics, March 2011

produce a negative output voltage, and vice versa ). To preserve symmetry and minimise offset voltage, a third resis tor is often included in series with the non-inverting input. The value of this resistor should be equivalent to the par allel combination of R IN and R F. Hence:

The voltage gain for the non-invert

AV =

Vout R =1 + F Vin RIN

Finally, the voltage gain for the dif

Vout R =− F Vin RIN

given by the expression:

by the expression:

AV =−

RF × RIN RF + RIN

is given by the expression:

AV =

Vout V R = out = F Vin V2 − V1 RIN 51

Teach-In 2011 Where V 1 and V 2 are the voltages at the input resistance ( R IN ) connected to inverting and non-inverting inputs respectively.

Where C2 is in Farads and ohms.

R 2 is in

Example 3

Limit capacitor

is to be designed to the following -

scribed previously have used direct coupling and thus have frequency response characteristics that extend to DC. This, of course, is undesirable for many applications, particularly where a wanted AC signal may be superimposed on an unwanted DC voltage level. In such cases a capacitor of ap propriate value may be inserted in series with the input, as shown below. The value of this capacitor should be chosen so that its reac tance is very much smaller than the input resistance at the lower applied input frequency. We can also use a capacitor to re strict the upper frequency response of is connected as part of the feedback path. Indeed, by selecting appropri ate values of capacitor, the frequency response of an inverting operational

1 0.159 = 2π C1R1 C1R1

Where C1 is in farads and ohms.

Solution To make things a little easier, we can break the problem down into manage able parts. We shall base our circuit

lower cut-off frequencies, as shown in the Fig.5.8. The nominal input resistance is the same as the value for R 1. Thus:

R1 = 10 kΩ kΩ Provided the upper frequency re sponse it not limited by the gain × bandwidth product, the upper cut-off frequency will be determined by the feedback capacitance, C2, and feed back resistance, R 2, such that:

R 1 is in

f1=

1 0.159 = 2π C 2R 2 C 2R 2

To determine the value of R 2 we can make use of the formula for mid-band voltage gain:

AV = R2/R1 Thus:

sR2 = Av × R1 = 20 × 10 kΩ kΩ = 200 kΩ kΩ

both the low and the high frequency response

tailored to suit individual require ments (see Fig.5.8 and Fig.5.9). The lower cut-off frequency is determined by the value of the input capacitance, C1, and input resistance, R 1. The lower cut-off frequency is given by:

f1=

Voltage gain = 20 Input resistance (at mid-band) = 10k ? Lower cut-off frequency = 100Hz Upper cut-off frequency = 10kHz Devise a circuit to satisfy the above

Everyday Practical Electronics, March 2011

Teach-In 2011 To determine the value of C1 we will use the formula for the low frequency cut-off:

0.159 f1= C1R1 From which:

C1 = =

0.159 0.159 = = = 0.159 ×10 F =159 nF f 1R1 100 × 10 × 103 1 × 10

0.159 = 0.159 ×10−6 F =159nF 6 1 × 10

Finally, to determine the value of C2 we will use the formula for high frequency cut-off:

f2=

0.159 C 2R2

From which:

C2 = =

0.159 0.159 0.159 = = = 0.159 ×10 F =159 pF 3 3 2 ×10 1 ×109 f 2 R 2 10 ×10 ×100

0.159

21 ×109

= 0.159 ×0.5 ×10−9 F =180 pF

in Fig. 5.10. Fig.5.11. A voltage follower

Other applications As well as their application as a general purpose amplifying device, of other uses. We shall conclude this month’s Learn by taking a brief look at two of these, voltage followers and comparators . A voltage follower using an operation circuit is essentially a non-inverting

Fig.5.12. Typical input and output waveforms for a voltage follower

Fig.5.13. A comparator

is fed back to the input. The result is an The output voltage produced by the ‘unity’), a very high input resistance and a very high output resistance. This stage is often referred to as a buffer and is used for matching a high-impedance circuit to a low-impedance circuit. Typical input and output waveforms for a voltage follower are shown in Fig.5.12. Notice how the input and output waveforms are both in-phase (they rise and fall together) and that they are identical in amplitude. A comparator using an operational no negative feedback has been ap plied, this circuit uses the maximum

the maximum possible value (equal to the positive supply rail voltage) whenever the voltage present at the non-inverting input exceeds that present at the inverting input. Con versely, the output voltage produced to the minimum possible value (equal to the negative supply rail voltage) whenever the voltage present at the inverting input exceeds that present at the non-inverting input. -

Everyday Practical Electronics, March 2011

Fig.5.14. Typical input and output waveforms for a comparator

Teach-In 2011 Typical input and output wave forms for a comparator are shown in Fig.5.14. Notice how the output is either +15V or –15V depending on the relative polarity of the two inputs.

The Circuit Wizard way

OW we’ve heard the theory, let’s use Circuit W izard to try out some practical operational am really neat way to explore this kind of theory because students often

Check –

prototyping boards. This might be due to needing dual rail power supplies, or the fact that

How do you think you are doing?

the schematic diagram into a ‘real life’ circuit where incorrect layout can cause confusing results! Fortu nately, we can do away with these problems when investigating these devices using Circuit W izard. So let’s look at a simple operational am -

5.1. Sketch the circuit symbol for of the connections.

5.2. Sketch an equivalent circuit and output resistances. Label your drawing .

5.3. List four desirable characteris .

5.4.

put of 1.5V when an input of 7.5mV is present. Determine the value of the voltage gain.

5.5. of 50 and a current gain of 2,000. W hat power gain does the ampli

5.6. Sketch the circuit of an invert

and identify the components that determine the voltage gain of the

. 5.7. An inverting operational ampli gain of –15, an input resistance of 5k ? , and a frequency response ex tending from 20Hz to 10kHz. Devise a circuit and specify all component values required.

circuit you are entering – so make sure that you double check! Fortunately, it’s really easy to change this; just right-click the op amp and click ‘arrange’ then ‘mir ror’ (see Fig.5.15). It is important to note that by ‘mirroring’ the op amp, the supply connections re main unchanged, ie the positive supply at the top and negative at the bottom.

W ith the foregoing in mind, enter the circuit shown in Fig.5.16. In this circuit we have a 2V variable input voltage connected to our invert ing input, with our non-inverting input connected to ground (0V). Recalling what we learned earlier,

Please note! W hen capturing a schematic based on operational am plifiers it is im portant to double check the orien tation of the two signal input pins. By default, Circuit W izard will draw an operational am plifier with the non-inverting in put (labelled ‘+’) at the top and the non-inverting in put (labelled ‘−‘) at the bottom. This may or may not be the same as the

the correct orientation of inverting and non-inverting inputs

For more information, links and other resources please check out our Teach-In website at:

www.tooley.co.uk/ teach-in

Everyday Practical Electronics, March 2011

Teach-In 2011

generator and adding some probes, as shown in Fig.5.17. The waveform dis play in Fig.5.18 shows how the signal

we know that the basic principle of the difference in voltage between the two inputs. vided by the circuit shown in Fig. 5.16 is determined by the gain, which will depend on the arrangement and values of the resistors in the circuit. We learnt that we can calculate the gain of an

Comparator

the formula:

The inverting input is a simple poten tial divider that sets the voltage to half of the supply voltage, in this case 5V. The non-inverting input is connected

R Voltage gain = − F RIN

In our second circuit we’ll inves

‘compares’ two input voltages and -

to a potentiometer; effectively a vari able potential divider. This allows us to control the voltage to this input. In practical circuits this might be replaced with a potential divider in volving a resistive input device, such as a light dependent resistor (LDR) or thermistor (we’ll be looking at a circuit using an LDR next). Some circuits even use two variable inputs to be com pared – for example a line following robot might compare the inputs from two LDRs to determine its orientation on a line. Enter the comparator circuit shown in Fig.5.19 and experiment with the circuit by changing the potentiometer and observing the input/output volt

or ‘voltage level’ views to analyse the operation of the circuit. By changing the potentiometer you are changing the voltage at the non-inverting input. The inverting input is held at a constant voltage of about 5V. When the non-inverting input volt age is higher than the inverting input, back resistors the gain is very large, and therefore the output swings to the maximum voltage possible; the supply In our circuit, R F (R2) is 2.5k ? and R IN (R1) is 500 ? . Use the formula above to prove that the gain of this circuit is –5. In simple terms, this means that we should expect our output voltage to be –5 times larger than the input voltage. Note the minus sign; the output will be inverted, as its name suggests. Now set the input voltage to 1V and run the simulation. We would expect the output voltage to be −5 × 1V = −5V. Now experiment with changing the in put voltage and monitoring the output voltage. You should see that the gain holds true whatever the input voltage up until the output reaches the supply voltage. At this point, the output volt age will remain constant, even with increased input voltage. Whereas this

Fig.5.18. Waveform graph produced by the modi -

is shown in blue and the output in red

Fig.5.19. A simple circuit to demonstrate comparator

used in audio circuits this can cause clipping of the waveform, which can distort the sound. Modify your circuit by replacing the variable input voltage with a function

Everyday Practical Electronics, March 2011

Teach-In 2011 The Circuit Wizard way

! "# $ !

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an oscillator circuit Fig.5.22(right). Changing simulation

Everyday Practical Electronics, March 2011

Teach-In 2011

Fig.5.23(above). Suggested graph parameters Fig.5.24(right). Typical waveforms produced by the oscillator circuit If your computer is a bit on the slow side, opt for less until you get a nice looking trace (see Fig.5.22). You will also need to adjust the scale on your graph; Fig.5.23 shows some suggested values that will give you a graph like that shown in Fig.5.24. The rest is for you to investigateâ&#x20AC;Ś so how does it do it? The blue trace/probe in Fig. 5.24 should give you some clues!

Amaze

Before we could use transistors in electronic circuits, we had to use valves. These looked a bit like light bulbs. They needed lots of space, lots of power and often produced a lot of heat (they had to be heated up internally before they could work). This Answers to Questions made designing simple circuits quite complicated â&#x20AC;&#x201C; not only did we need a low-voltage high-current heater sup5.1. See Fig.5.3 ply, but we also needed a high voltage supply of around 200V or more. 5.2. See Fig.5.5 When transistors came along, they revolutionised electronics, making 5.3. See page 51 it possible to have small, complex circuits that operated from low volt5.4. 200 age. Today, we can make transistors so % %

5.5. 100,000 of them on an area the size of your 5.6. See Fig.5.7(a) The current generation of microprocessors are manufactured using a process 5.7. See Fig.5.8 with R1 = 5k:, thatâ&#x20AC;&#x2122;s capable of producing individual R2 = 75k:, C1 = 1.59ÎźF, transistors 1,000 times smaller than the C2 = 212pF diameter of a human hair. That means that the inFig.5.25. Valves from the 1940s and 1950s com- d i v i d u a l pared with transistors from the 1960s and 1970s s e m i c o n ductor layers might only have a few tens or hundreds of atoms. In fact, the latest technology is capable of producing transistors that are less than 25nm across â&#x20AC;&#x201C; thatâ&#x20AC;&#x2122;s a mere 0.000025mm!

Everyday Practical Electronics, March 2011

Circuit Wizard A Standard or Professional version of Circuit Wizard can be purchased from the editorial ofďŹ ce of EPE â&#x20AC;&#x201C; see CD-ROMs for Electronics page and the UK shop on our website (www. epemag.com). Further information can be found on the New Wave Concepts website; www.new-wave-concepts.com. The developer also offers an evaluation copy of the software that will operate for 30 days, although it does have some limitations applied, such as only being able to simulate the included sample circuits and no ability to save your creations.

Next month!

In next monthâ&#x20AC;&#x2122;s Teach-In we will be investigating logic circuits.

Fig.5.26. This 1970s semiconductor memory device contains the equivalent of more than 65,000 individual transistors. The latest chips have more than 100 million devices in the same space!

Teach-In 2011

TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS Part 6: Logic circuits By Mike and Richard Tooley

Our Teach-In series is designed to provide you with a broad-based introduction to electronics. We have attempted to provide coverage of three of the most important electronics units that are currently studied in many schools and colleges in the UK. These include Edexcel BTEC Level 2 awards, as well as electronics units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced READERÂŞWITHÂŞANÂŞOPPORTUNITYÂŞTOÂŞ@BRUSHÂŞUP ÂŞONÂŞSPECIlCÂŞTOPICSÂŞWITHÂŞWHICHÂŞHEÂŞORÂŞSHEÂŞMAYÂŞBEÂŞLESSÂŞFAMILIAR ÂŞ %ACHÂŞPARTÂŞOFÂŞOURÂŞ4EACH )NÂŞSERIESÂŞISÂŞORGANISEDÂŞUNDERÂŞlVEÂŞMAINÂŞHEADINGS ÂŞ,EARN ÂŞ#HECK ÂŞ"UILD ÂŞ)NVESTIGATEÂŞANDÂŞ !MAZE ÂŞ,EARNÂŞWILLÂŞTEACHÂŞYOUÂŞTHEÂŞTHEORY ÂŞ#HECKÂŞWILLÂŞHELPÂŞYOUÂŞTOÂŞCHECKÂŞYOURÂŞUNDERSTANDING ÂŞANDÂŞ"UILDÂŞWILLÂŞGIVEÂŞ you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge WHICHÂŞWILLÂŞALLOWÂŞYOUÂŞTOÂŞFURTHERÂŞEXTENDÂŞYOURÂŞLEARNING ÂŞANDÂŞlNALLY ÂŞ!MAZEÂŞWILLÂŞSHOWÂŞYOUÂŞTHEÂŞ@WOWÂŞFACTOR ÂŞÂŞ

N THIS instalment of Teach-In we introduce the basic building blocks of digital circuits. We explain the operation of each of the most common types of logic gate and show how they can be combined together in order to solve more complex logic problems. We also introduce bistable circuits and show how they can be used to remember a momentary event. We shall be using Circuit Wizard to investigate each of the basic logic gates before moving on to explore some applications. Finally, in Amaze we look at how recent advances in technology have provided us with digital circuits that are capable of operation at speeds that are increasingly fast.

Learn

Digital logic

Logic circuits are the basic building blocks of digital circuits and systems. Logic circuits have inputs and outputs that can only exist in one of two discrete states, variously known as â&#x20AC;&#x2DC;onâ&#x20AC;&#x2122; and â&#x20AC;&#x2DC;offâ&#x20AC;&#x2122;, â&#x20AC;&#x2DC;highâ&#x20AC;&#x2122; and â&#x20AC;&#x2DC;lowâ&#x20AC;&#x2122;, or â&#x20AC;&#x2DC;1â&#x20AC;&#x2122; and â&#x20AC;&#x2DC;0â&#x20AC;&#x2122;. Logic circuits usually have several inputs and one or more outputs. At any instant of time, the state of the inputs will determine the state of the output, according to the logic function provided by the circuit. If this is beginning to sound a little complicated, letâ&#x20AC;&#x2122;s look at a couple of simple logic functions that can be SATISĂ&#x161;ED USING NOTHING MORE THAN A

couple of switches and a lamp and battery. Consider the circuit shown in Fig.6.1. In this circuit, a battery is connected to a lamp via two switches, A and B. It should be obvious that the lamp will only operate when both of the switches are closed (ie, both A AND B are closed). Letâ&#x20AC;&#x2122;s look at the operation of the circuit in a little more detail. Since there are two switches (A and B) and there are two possible states for each switch (open or closed), there is a total of four possible conditions for the circuit. We have summarised these states in Fig.6.2. Note that the two states (ie, open or closed) are mutually exclusive

Everyday Practical Electronics, April 2011

Teach-In 2011

Fig.6.2. Possible states for the circuit of Fig.6.1 Fig.6.1. AND switch and lamp logic

Fig.6.3 (right). Truth table for the AND switch and lamp logic

Fig.6.5. Possible states for the circuit of Fig. 6.4 Fig.6.4. OR switch and lamp logic

and that the switches cannot exist in any other state than completely open or completely closed. Because of this, we can represent the state of the switches using the binary digits, 0 and 1, where an open switch is represented by 0 and a closed switch by a 1. Furthermore, if we assume that ‘no light’ is represented by a 0 and ‘light on’ is represented by a 1, we can rewrite Fig.6.2 in the form of a truth table, as shown in Fig.6.3. Another circuit with two switches is shown in Fig.6.4. This circuit differs from that shown in Fig.6.1 by virtue of the fact that the two switches are connected in parallel rather than in series. In this case, the lamp will operate when either of the two switches is closed (in other words, when A OR B is closed). As before, there is a total of four possible conditions for the circuit. We can summarise these conditions in Fig.6.5. Once again, adopting the convention that an open switch can be represented by 0 and a closed switch by 1, we can rewrite the truth table in terms of the binary states, as shown in Fig.6.6. Everyday Practical Electronics, April 2011

Fig.6.6 (right). Truth table for the OR switch and lamp logic

The basic logic functions can be combined to produce circuits that satisfy a more complex logical operation. For example, Fig.6.7 shows a simple switching circuit in which the lamp will operate when switch A AND either switch B OR switch C is closed. The truth table for this arrangement is shown in Fig.6.8.

Logic gates Logic gates are building blocks that are designed to produce the

basic logic functions, AND, OR, NOT, etc. These circuits are designed to be interconnected into larger, more complex, logic circuit arrangements. Each gate type has its own symbol and we have shown both the British Standard (BS) symbol together with the more universally accepted American Standard (MIL/ANSI) symbol. Note that, while inverters and buffers each have only one input, exclusive-OR gates have two inputs and the other basic gates

Fig.6.7. Simple switching circuit using AND and OR logic Fig.6.8 (right). Truth table for the simple switching circuit shown in Fig.6.7

Teach-In 2011

Fig.6.10. Logic gates with inverted outputs

Fig.6.11 (above). Majority vote logic circuit

Fig.6.9. Logic gate symbols and truth tables

(eg, AND, OR, NAND and NOR) are commonly available with up to eight inputs. Some of the logic gates shown in Fig.6.9 have inverted outputs. These gates are the NOT, NAND, NOR, and Exclusive-NOR and the small circle at the output of the gate (see Fig.6.10a) indicates this inversion. It is important to note that the output of an inverted gate (eg, NOR) is identical to that of the same (ie, non-inverted) function with its output connected to an inverter (or NOT gate) as shown in Fig.6.10b). The logical function of a logic gate can also be described using Boolean notation. In this type of notation, the 46

Fig.6.12 (right). Truth table for the majority vote logic circuit

OR function is represented by a ‘+’ SYMBOL THE !.$ FUNCTION BY A lpm sign, and the NOT function by an overscore or ‘/’. Thus the output, Y, of an OR gate with inputs A and B can be represented by the Boolean algebraic expression: Y=A+B Similarly, the output of an AND gate can be shown as: 9 ! p " 7E SHALL NOW BRIEÛY SUMMARISE the logic functions of each of the basic logic gates that we met earlier in Fig.6.9:

Buffers Buffers do not affect the logical state of a digital signal (ie, a logic 1 input results in a logic 1 output, and a logic 0 input results in a logic 0 output). Buffers are normally used to provide extra current drive at the output, but can also be used to regularise the logic levels present at an interface. The Boolean expression for the output, Y, of a buffer with an input, X, is Y = X.

Everyday Practical Electronics, April 2011

Teach-In 2011 Boolean expression for the output, Y, of an exclusive-NOR gate with inputs, A and B, is 9 ! p " " p !

Combinational logic

Fig.6.13. An exclusive-OR gate produced from AND, OR and NOT gates

Inverters Inverters are used to complement the logical state (ie, a logic 1 input results in a logic 0 output and vice versa). Inverters also provide extra current drive and, like buffers, are used in interfacing applications where they provide a means of regularising logic levels present at the input or output of a digital system. The Boolean expression for the output, Y, of an inverter with an input, X, is Y = /X.

AND gates AND gates will only produce a logic 1 output when all inputs are simultaneously at logic 1. Any other input combination results in a logic 0 output. The Boolean expression for the output, Y, of an AND gate WITH INPUTS ! AND " IS 9 ! p "

OR gates OR gates will produce a logic 1 output whenever any one, or more inputs are at logic 1. Putting this another way, an OR gate will only produce a logic 0 output whenever all of its inputs are simultaneously at logic 0. The Boolean expression for the output, Y, of an OR gate with inputs, A and B, is Y = A + B.

NAND gates NAND (ie, NOT-AND) gates will only produce a logic 0 output when all inputs are simultaneously at logic 1. Any other input combination will produce a logic 1 output. A NAND gate, therefore, is nothing more than an AND gate with its Everyday Practical Electronics, April 2011

output inverted! The circle shown at the output denotes this inversion. The Boolean expression for the output, Y, of a NAND gate with inputs, ! AND " IS 9 ! p "

NOR gates NOR (ie, NOT-OR) gates will only produce a logic 1 output when all inputs are simultaneously at logic 0. Any other input combination will produce a logic 0 output. A NOR gate, therefore, is simply an OR gate with its output inverted. A circle is again used to indicate inversion. The Boolean expression for the output, Y, of a NOR gate with inputs, A and B, is Y = A + B.

Exclusive-OR gates Exclusive-OR gates will produce a logic 1 output whenever either one of the two inputs is at logic 1 and the other is at logic 0. ExclusiveOR gates produce a logic 0 output whenever both inputs have the same logical state (ie, when both are at logic 0 or both are at logic 1). The Boolean expression for the output, Y, of an exclusive-OR gate WITH INPUTS ! AND " IS 9 ! p " " p !

Exclusive-NOR gates Exclusive-NOR gates will produce a logic 0 output whenever either one of the two inputs is at logic 1 and the other is at logic 0. ExclusiveNOR gates produce a logic 1 output whenever both inputs have the same logical state (ie, when both are at logic 0 or both are at logic 1). The

The basic logic gates can be combined together to solve more complex logic functions. This is made possible by adopting a standard range of logic levels (ie, voltage levels used to represent the logic 1 and logic 0 states) so that the output of one logic circuit is compatible with the input of another. As an example, letâ&#x20AC;&#x2122;s assume that we require a logic circuit that will produce a logic 1 output whenever two, or more, of its three inputs are at logic 1. This circuit (shown in Fig.6.11) is often referred to as a majority vote circuit, and its truth table is shown in Fig.6.12. Note that the outputs of the three two-input AND gates are fed to the three inputs of the OR gate, and that the output of the OR gate will become logic 1 whenever any one or more of the two-input AND gates detects a condition in which two of the inputs are simultaneously at logic 1. As a further example, consider how we might combine several of the basic logic gates (AND, OR and NOT) in order to realise the exclusive-OR function. In order to solve this problem, consider the Boolean expression for the exclusive-OR function that we met earlier: 9 ! p " " p ! /A and /B can be obtained by simply inverting A and B respecTIVELY 4HEN ! p " AND " p ! CAN be obtained using two two-input AND gates. Finally, these two can be applied to a two-input OR gate in order to obtain the required LOGIC FUNCTION ! p " " p ! The complete solution is shown in Fig.6.13. 47

Teach-In 2011 Bistables Bistable circuits provide us with a means of remembering a transient logic condition. For example, the logic that controls a lift must remember that the lift has been called in response to a push-button that only requires momentary operation. As its name suggests, the output of a bistable (or Ă?JQ Ă?PQ) circuit has two stables states (logic 0 or logic 1). Once set, the output of a bistable will remain at logic 1 or logic FOR AN INDEĂ&#x161;NITE PERIOD OR UNTIL the bistable is reset. A bistable thus forms a simple form of memory, remaining in its latched state (either set or reset) until a signal is applied to it to change its state (or until the supply is disconnected). The simplest form of bistable is the R-S bistable. This device has two inputs, SET and RESET, and complementary outputs, Q and Q. A logic 1 applied to the SET input will cause the Q output to become (or remain at) logic 1, while a logic 1 applied to the RESET input will cause the Q output

Two simple forms of R-S bistable based on cross-coupled logic gates are shown in Fig.6.14. Fig.6.14(a) is based on two cross-coupled two-input NAND gates, while Fig.6.14(b) is based on two cross-coupled two-input NOR gates.

D-type bistable

'JH 4JNQMF 3 4 CJTUBCMFT B CBTFE PO /"/% HBUFT BOE C CBTFE PO /03 HBUFT

to become (or remain at) logic 0. In either case, the bistable will remain in its SET or RESET state until an input is applied in such a sense as to change the state. Note also that the Q and Q outputs always have opposite logical states. Thus, when the Q output is at logic 1 the Q output will be at logic 0, and WJDF versa.

Unfortunately, the simple cross-coupled logic gate bistable has a number of serious shortcomings (consider what would happen if a logic 1 was simultaneously present on both the SET and RESET inputs!) and practical forms of bistable make use of much improved purpose-designed logic circuits, such as D-type and J-K bistables. The D-type bistable has two inputs: D (standing variously for data or de lay) and CLOCK (CLK). The data input (logic 0 or logic 1) is clocked into the bistable such that the output state only changes when the clock changes state. Operation is thus said to be synchronous. Additional subsidiary inputs (which are invariably active low) are provided, which can be used to directly set or reset the bistable. These are usually called PRESET (PR) and CLEAR (CLR). D-type bistables are used both as latches (a simple form of memory) and as binary dividers. The simple circuit arrangement in Fig.6.15, together with the timing diagram shown in Fig. 6.16 illustrate the operation of D-type bistables.

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'JH 5JNJOH EJBHSBN GPS UIF % UZQF CJTUBCMF

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Everyday Practical Electronics, April 2011

Teach-In 2011 J-K bistables J-K bistables (see Fig.6.17) have two clocked inputs (J and K), two direct inputs (PRESET and CLEAR), a CLOCK (CK) input, and outputs (Q and Q). As with R-S bistables, the two outputs are complementary (ie, when one is 0 the other is 1, and vice versa). Similarly, the PRESET and CLEAR inputs are invariably both active low (ie, a 0 on the PRESET input will set the Q output to 1, Fig.6.19. Circuit for a four-stage binary counter using J-K bistables whereas a 0 on the CLEAR input will set the Q output to 0). Fig.6.18 summarises the input and corresponding output states of a J-K bistable

(ie, Q is reset

Fig.6.20. Timing diagram for the four-stage binary counter of Fig.6.19

(ie, Q is reset

for various input states. J-K bistables are the most soPHISTICATED AND Ă&#x203A;EXIBLE OF THE BISTABLE TYPES AND THEY CAN BE CONĂ&#x161;GURED IN VARIOUS WAYS INCLUDING BINARY dividers, shift registers, and latches. The circuit arrangement of a four-stage binary counter, based on J-K bistables, is shown in Fig.6.19. The timing diagram for this circuit is shown in Fig.6.20. Each stage successively divides the clock input signal by a factor of two. Note that a logic 1 input is transferred to the respective Q-output on the falling edge of the clock pulse, and all J and K inputs must be taken to logic 1 to enable binary counting.

Practical logic circuits

whatever state it was before, while

Fig.6.18. J-K bistable operation

Everyday Practical Electronics, April 2011

You should now have a basic grasp of the theory of logic circuits, but what we havenâ&#x20AC;&#x2122;t done yet is give you an idea of what these devices look like and how they appear in practical logic circuits. So, letâ&#x20AC;&#x2122;s end this monthâ&#x20AC;&#x2122;s Learn BY SHOWING YOU TWO EXAMPLES OF MODERN LOGIC CIRCUITS 4HE Ă&#x161;RST OF THESE IS A DUAL $ TYPE BISTABLE WHILE THE SECOND IS A & QUAD TWO INPUT .!.$ GATE 49

Teach-In 2011 The 4013 dual D-type bistable is supplied in various packages, including the dual-in-line (DIL) package shown in Fig.6.21. This device uses standard complementary metal oxide semiconductor (CMOS) technology, and its pin connections are shown in Fig.6.22. Note that pin 14 and pin 7 supply power to both of the D-type bistables. The 74F08 quad two-input NAND gate is also available in several different packages. We have shown the small integrated circuit (SOIC) package in Fig.6.23. This package is ideal for surface mounting rather than through-hole mounting used with the DIL package that we met before. The 74F08 contains four independent NAND gates and uses ‘fast’ transistortransistor logic (TTL). The pin connection diagram for the chip is shown in Fig.6.24. As with the 4013, the supply connections (pin 14 and pin 7) are common to all four of the internal logic gates.

Please note! Some logic devices, particularly CMOS types, are static-sensitive and special precautions are needed when handling and transporting them.

Circuit Wizard A Standard or Professional version of Circuit Wizard can be purchased from the editorial ofﬁce of EPE – see CD-ROMs for Electronics page and the UK shop on our website (www. epemag.com). Further information can be found on the New Wave Concepts website; www.new-wave-concepts.com. The developer also offers an evaluation copy of the software that will operate for 30 days, although it does have some limitations applied, such as only being able to simulate the included sample circuits and no ability to save your creations.

Fig.6.21. A 4013 dual D-type bistable in a plastic dual-in-line (DIL) package. This chip was manufactured in 1992

Fig.6.23. A 74F08 quad two-input NAND gate in a small surface-mount package (SOIC). This chip was manufactured in 2001

Fig.6.24. Pin connections for the 74F08 quad two-input NAND gate IC

Check – How do you think you are doing? 6.1. Identify each of the logic symbols shown in Fig.6.25 6.2. Draw the truth table for the logic gate arrangement shown in Fig. 6.26. 6.3. Show how three two-input AND gates can be connected together to form a four-input AND gate.

Fig.6.26. See Question 2

6.4. State the Boolean logic expression for the output of each of the gate arrangements shown in Fig.6.27 – opposite. 6.5. Devise a logic gate arrangement that provides an output described by the truth table shown in Fig.6.28.

Fig.6.25. See Question 1

Fig.6.22. Pin connections for the 4013 dual D-type bistable IC

Fig.6.28. See Question 5

Everyday Practical Electronics, April 2011

Teach-In 2011

Build â&#x20AC;&#x201C; The Circuit Wizard way

OUâ&#x20AC;&#x2122;VE learnt the theory about logic gates, so now letâ&#x20AC;&#x2122;s try it out using Circuit Wizard. Anyone whoâ&#x20AC;&#x2122;s experimented or prototyped with discrete logic circuits before will be all too familiar with hopelessly prodding a logic probe into an incomprehensible â&#x20AC;&#x2DC;ratâ&#x20AC;&#x2122;s nestâ&#x20AC;&#x2122; of breadboard and link wires. Fortunately, nowadays we can do all this and more using software packages before we commit any copper to PCB. Circuit Wizard really does have a few aces up its sleeve when it comes to working with logic. First, you can work directly with the logic gates themselves and let it worry about the chip packages (see later on), as well as a number of dedicated inputs/outputs and simulation schemes that bring the circuits to life and visually convey whatâ&#x20AC;&#x2122;s

Fig.6.27. See Question 4

Everyday Practical Electronics, April 2011

really going on in the circuit. In this instalment of Build weâ&#x20AC;&#x2122;ll be trying out some logic gates to see how they operate, as well as experimenting with some real life applications.

Gate numbers

When you add a gate to the drawing area you should notice that it will automatically number your gate in accordance with the corresponding IC required. As each IC contains a number of gates, an Opening the gates ALPHABETICAL SUFĂ&#x161;X WILL BE ADDED TO Circuit Wizard includes a the chip reference (eg, IC1a) to show large range of logic devices in which has been allocated. Once the both CMOS and TTL versions total number of gates has exceeded (note that the extent of the that of the IC, Circuit Wizard will logic devices may depend on the automatically include a new chip, and so on. You are able to change which gate has been allocated within the chip. This can be useful when it comes to generating the MOST EFĂ&#x161;CIENT 0#" LAYOUT However, the automatic allocation works great for most users. Circuit WizFig.6.29. Changing logic families for a logic gate ard will also add power version of Circuit Wizard that connections â&#x20AC;&#x2DC;in the backgroundâ&#x20AC;&#x2122;, you are running). so that these are accounted for in The first thing that you may net lists when moving on to PCB notice is that in the Gallery generation. (right-hand panel) you can acThe best way to understand the cess standard and Schmitt varieoperation of the basic gates is to ties of gates in the â&#x20AC;&#x2DC;Logic Gatesâ&#x20AC;&#x2122; drop one on to the drawing area, folder, as well as each family of add inputs and outputs and see chip separately in the â&#x20AC;&#x2DC;Integrated how the output changes in reCircuitsâ&#x20AC;&#x2122; folder. We can only assponse to changes in the inputs. sume that this is for the purpose Circuit Wizard has some really of providing quick access to the useful input toggles and output more common gates. indicators which can be found at By default, 4000 series ICs the top of the â&#x20AC;&#x2DC;Logic Gatesâ&#x20AC;&#x2122; folder will be used. However, you are (see Fig.6.30). able to select the family of gate Switching to the â&#x20AC;&#x2DC;Logic Viewâ&#x20AC;&#x2122; by selecting the appropriate (click on the vertical tab on the left model in the properties context of the drawing area) is a particularly box; see Fig. 6.29 (double-click useful way to analyse any logic the component to access this). This default behaviour can also be altered in the softwareâ&#x20AC;&#x2122;s setting if required. Fig.6.30. A simple arrangement to test an AND gate

Teach-In 2011

Build â&#x20AC;&#x201C; The Circuit Wizard way circuit. This view uses both colour coding as well as 1s and 0s at the inputs/outputs of each pin to show the logic state. This can really help you see whatâ&#x20AC;&#x2122;s going on around the circuit. One important thing to note about the logic indicators and the â&#x20AC;&#x2DC;Logic Levelâ&#x20AC;&#x2122; view is that the logic high state is indicated by red, and the logic low by green. This might seem a little counterintuitive to some people â&#x20AC;&#x201C; the author included!

Give it a try Experiment with some of the basic gates; AND, OR, NAND, XOR and NOT. Draw up a truth table for each gate and check that this matches what youâ&#x20AC;&#x2122;ve seen in Learn. Alternatively, weâ&#x20AC;&#x2122;ve developed an interactive logic gate worksheet (see Fig.6.31). This can be downloaded from the Teach-In 2011 website; www.tooley.co.uk/teach-in â&#x20AC;&#x201C; follow the link to Circuit Wizard downloads. Print out the worksheet and complete the truth tables by simulating them on screen. Logic circuits usually contain a number of different gates and can get very complicated. DeSIGNERS CAN SPEND A LONG TIME TRYING TO Ă&#x161;GURE OUT the simplest arrangement of gates to perform the logical function thatâ&#x20AC;&#x2122;s required. However, with the widespread use and availability of microprocessors, complex combinational logic circuits are becoming a thing of the past. Have a go at entering and testing the logic circuit shown in Fig.6.32, and produce a truth table. Could the function of this circuit have been reproduced with fewer gates? If you think about actually producing the circuit above you would need three logic ICs and two of the ICs would only have one gate used in THEM /BVIOUSLY THIS IS A PRETTY INEFĂ&#x161;CIENT WAY to do things. Fortunately, logic designers came up with a great idea; what if we could use just a single gate and wire them in such a way to act like the other gates? In this way, you would only need to buy one type of IC. It turns out that the NAND gate is the ideal candidate for this as you can produce all of the other gates using them â&#x20AC;&#x201C; we call them â&#x20AC;&#x2DC;NAND equivalentsâ&#x20AC;&#x2122;. Fig.6.33 shows the NAND equivalent for an AND gate. Enter the circuit in to Circuit Wizard and verify that the combination acts just like an AND gate. In this case, the first gate is a straight forward NAND and the second 52

Fig.6.31. A view of our logic gate worksheet, which can be downloaded from: www.tooley.co.uk/teach-in

Fig.6.32. A combinational logic circuit

Fig.6.33. An AND gate made using NAND gates (in other words, a â&#x20AC;&#x2DC;NAND equivalentâ&#x20AC;&#x2122; of an AND gate

gate acts as a NOT gate. Hence, the result is â&#x20AC;&#x2DC;NOT NANDâ&#x20AC;&#x2122; or AND. 7HY NOT SEE IF YOU CAN Ă&#x161;GURE OUT THE .!.$ EQUIVALENTS for the other gates. You can also download our NAND Gate Equivalent simulator (Fig.6.34) from the Teach-In website, which includes a number of other equivalents for you to explore. Everyday Practical Electronics, April 2011

Teach-In 2011

Fig.6.33. Download our NAND gate

equivalent simulator from: www. tooley.co.uk/teach-in

Fig.6.35. Intruder alarm circuit. When one of the ‘links’ is broken, the alarm sounds

Intruder alarm Now we’ll look at a real-life application of a simple logic circuit. Fig.6.35 shows an intruder alarm circuit. When any one of the links (simulated by push-to-break buttons) is broken, the alarm is activated. Enter the circuit and try it out for yourself! Advanced readers might like to see if they can adapt the circuit to latch the alarm on once a link has been broken.

Fig.6.36. Four-bit ripple counter using J-K bistables

Ripple counter Another area of logic design is sometimes described as sequential logic. Often this involves counting and/or timing. Fig.6.36 shows what is commonly known as a ripple counter or cascade counter. It produces a binary count using a series of J-K bistables or ‘flip-flops’. Enter the circuit and look closely at its operation. The ‘Logic View’ is excellent for this kind of circuit, and you should be able to see how the logic high ‘ripples’ along the flip-flops in order to generate a four-bit binary counting sequence. Everyday Practical Electronics, April 2011

The world’s fastest microprocessor resulted from an investment of $1.5 billion, and operates at a speed of 5.2GHz (courtesy of International Business Machines Corp.)

Teach-In 2011

Build â&#x20AC;&#x201C; The Circuit Wizard way Decade counter A binary count could be really useful for lots of applications. Apart from possibly a few computer nerds, not all that many people can easily read a binary number! Therefore, if we need to display a number to a consumer we need to convert this to a displayable number. This can be easily achieved with a 74LS47 sevensegment display decoder, a driver chip and a seven-segment LED display (common anode). The chip decodes the fourbit lines of the binary count and outputs a number on the seven-segment LED display by turning on/off the appropriate

Fig.6.37. A decade (ie, 0-9) counter circuit using J-K bistables and a sevensegment display

lines. Amend your ripple counter circuit as shown in Fig.6.37. The NAND gate is used to reset the

flip-flops when the count reaches 9, the highest single-digit number that can be displayed.

Investigate A block schematic diagram of a logic system used in a large aircraft is shown in Fig.6.38.

The system is designed to alert THE Ă&#x203A;IGHT CREW BY GENERATING VISible and audible warnings that one

Fig.6.38. A block schematic of a logic system used in an aircraft

or more of the aircraftâ&#x20AC;&#x2122;s undercarriage doors remain open when the AIRCRAFT IS IN NORMAL Ă&#x203A;IGHT 4HE Ă&#x161;VE DOOR SWITCHES PROVIDE logic 1 signals when the respective door is open and logic 0 when closed. All of the warning indicators are â&#x20AC;&#x2DC;active lowâ&#x20AC;&#x2122; and require a logic 0 to produce a visible or audible output. Study the circuit carefully and then see if you can answer each of the following questions: 1. What logic level appears at points X, Y and Z with all of the doors closed? 2. What logic level appears at points X, Y and Z with the left wing door open and all other doors closed? 3. What logic level appears at points X, Y and Z with the nose door open and all other doors closed? 4. When any one or more of the doors opens, the audible warning

Everyday Practical Electronics, April 2011

Teach-In 2011

Answers to Check questions 6.1. (a) Three input OR gate B 4WO INPUT .!.$ GATE C )NVERTER OR ./4 GATE D $ TYPE BISTABLE OR $ TYPE Ă&#x203A;IP Ă&#x203A;OP 2. See Fig. 6.40

Fig.6.41. Answer to Question 3

3. See Fig. 6.41 A ! p " B ! " C ! p "

Fig.6.40. Answer to Question 2 Fig.6.42. Answer to Question 5

5. See Fig. 6.42 should sound and remain operatING UNTIL THE Ă&#x203A;IGHT CREW CANCELS the alarm by means of the RESET BUTTON 7HAT DEVICE SHOULD BE USED FOR )# AND SHOW HOW SHOULD IT BE CONNECTED

Amaze 4HE TIME THAT IT TAKES FOR A DIGITAL signal to travel from the input(s) of a LOGIC GATE TO PRODUCE A CHANGE IN THE output is usually extremely small AND MEASURED IN MICROSECONDS Â?S NANOSECONDS NS OR PICOSECONDS (ps). This time (often referred to as propagation delay) has a major imPACT IN DETERMINING THE MAXIMUM SPEED AT WHICH A PARTICULAR LOGIC CIRCUIT WILL OPERATE 3TANDARD LOGIC GATES WILL HAPPILY OPERATE AT SWITCHING SPEEDS OF UP

Fig.6.39. IBMâ&#x20AC;&#x2122;s new zEnterprise System mainframe (courtesy of International

SUCH AS THE LATEST GENERATION OF MICROPROCESSORS WHICH NEED CLOCK RATES THAT ARE VERY MUCH HIGHER THAN THIS 4HE HIGHEST CLOCK SPEED MICROPROCESSOR CURRENTLY SOLD COMMERCIALLY IS FOUND INSIDE )"-mS Z%NTERPRISE MAINFRAME COMPUTER 4HIS DEVICE WAS INTRODUCED IN *ULY AND ITS CORES RUN CONTINUOUSLY AT A SPEED OF '(Z OR TIMES A SECOND .OW THAT MAY SOUND FAST BUT FUTURE TECHNOLOGY BASED ON SUPERCONDUCTING LOGIC PROMISES TO OFFER SPEEDS THAT ARE PREDICTED TO BE around 100 times faster than this. 3O AS THE OLD SAYING GOES lYOU AINmT SEEN NOTHING YETĂ&#x2DC;m

Business Machines Corporation)

Next month!

TO ABOUT Ă&#x161;FTY MILLION OPERATIONS PER SECOND BUT EVEN THIS IS INSUFĂ&#x161;CIENT FOR USE IN HIGH SPEED APPLICATIONS

)N NEXT MONTHmS Teach-In WE SHALL BE LOOKING AT TIMERS AND PULSE generators.

CIRCUIT WIZARD

Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard and Professional. By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ďŹ nish â&#x20AC;&#x201C; even including on-screen testing of the PCB prior to construction!

Circuit diagram design with component library (500 components * Standard, 1500 components Professional) Virtual instruments (4 Standard, 7 Professional) * On-screen animation *

Layout * PCB Interactive PCB layout simulation * Automatic PCB routing * Gerber export *

This is the software used in our Teach-In 2011 series. Standard ÂŁ61.25 inc. VAT Professional ÂŁ91.90 inc. VAT See Direct Book Service â&#x20AC;&#x201C; pages 75-77 in this issue

Everyday Practical Electronics, April 2011

Teach-In 2011

TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS Part 7: Timer circuits By Mike and Richard Tooley

N THIS instalment of Teach-In, we will bring together several important ideas and concepts that weâ&#x20AC;&#x2122;ve already met in the earlier parts. At the same time, we will introduce you to a highly versatile integrated circuit (IC), the 555 timer. Using this IC, we will show you how you can quickly and easily design circuits that will produce time delays from a few hundred nanoseconds to several hundred seconds, and square wave pulses of known frequency, period and duty cycle. Build and Investigate will extend this further with a detailed look at some practical timer and pulse generator circuits. Finally, in Amaze we look at ways in which

we measure time with a very high degree of accuracy.

Learn

The 555 timer

The 555 timer is, without doubt, one of the most versatile integrated circuit chips ever produced. Not only is it a neat mixture of analogue and digital circuitry, but its applications are virtually limitless in the world of digital pulse generation. The chip also makes an excellent case study for beginners because it brings together a number of important concepts and techniques. The standard 555 timer is supplied in a standard 8-pin dual-in-line (DIL) package with the pinout shown in Fig.7.1.

Fig.7.1. Pinout connections for a standard 555 timer IC

To begin to understand how timer circuits operate, it is worth spending a few moments studying the internal circuitry of the 555 timer, see Fig.7.2. Essentially, the chip comprises two operational ampliĂ&#x161;ERS USED AS COMPARATORS TOGETHER with an R-S bistable. In addition, AN INVERTING TRANSISTOR AMPLIĂ&#x161;ER IS incorporated so that an appreciable current can be delivered to a load.

Everyday Practical Electronics, May 2011

Teach-In 2011 Sinking and sourcing Unlike the standard logic devices that we met last month, the 555 timer can both sink and source current. It’s worth taking a little time to explain what we mean by these two terms:

s When sourcing current, the 555’s output (pin 3) is in the high state, AND CURRENT WILL THEN ÛOW out of the output pin into the load and down to 0V, as shown in Fig.7.3(a). s When sinking current, the 555’s output (pin 3) is in the low state, in WHICH CASE CURRENT WILL ÛOW FROM the positive supply (+Vcc) through the load and into the output (pin 3), as shown in Fig.7.3(b).

Fig.7.3. Loads connected to the output of a 555 timer: (a) current sourced by the timer when the output is high, (b) current sunk by the timer when the output is low

Fig.7.2. Internal schematic arrangement of the standard 555 timer Feature A

C D E

Table 7.1: Main features of the 555 timer IC Function A potential divider comprising R1, R2 and R3 connected in series. Since all three resistors have the same values the input voltage (VCC) will be divided into thirds, i.e. one third of VCC will appear at the junction of R2 and R3 while two thirds of VCC will appear at the junction of R1 and R2. Two operational amplifiers connected as comparators. The operational amplifiers are used to examine the voltages at the threshold and trigger inputs and compare these with the fixed voltages from the potential divider (two thirds and one third of VCC respectively). An R-S bistable stage. This stage can be either set or reset depending upon the output from the comparator stage. An external reset input is also provided. An open-collector transistor switch. This stage is used to discharge an external capacitor by effectively shorting it out whenever the base of the transistor is driven positive. An inverting power amplifier. This stage is capable of sourcing and sinking enough current (well over 100mA in the case of a standard 555 device) to drive a small relay or another low-resistance load connected to the output.

Everyday Practical Electronics, May 2011

Returning to Fig.7.2, the single transistor switch, TR1, is provided as a means of rapidly discharging an external timing capacitor. Because the series chain of resistors, comprising R1, R2 and R3, all have identical values, the supply voltage (VCC) is divided equally across the three resistors. The voltage at the noninverting input of IC1 is one-third of the supply voltage (VCC), while that at the inverting input of IC2 is two-thirds of the supply voltage (V CC ). Thus, if VCC is 9V, 3V will appear across each resistor and the upper comparator will have 6V applied to its inverting input, while the lower comparator will have 3V at its non-inverting input.

The 555 family The standard 555 timer is housed in an 8-pin DIL package and operates from supply rail voltages of between 4.5V and 15V. This, of course, encompasses 45

Teach-In 2011 the normal range for TTL devices (5V Âą5%) and thus the device is ideally suited for use with TTL circuitry. The following versions of the standard 555 timer are commonly available:

Low power 555 The low power 555 timer is a CMOS version that is both pin and function compatible with its standard counterpart. By virtue of its CMOS technology, the device operates over a somewhat wider range of supply voltages (2V to 18V) and consumes minimal operating current (120PA typical for an 18V supply). Note that, by virtue of the low-power CMOS technology employed, the device does not have the same output current drive as that possessed by its standard counterparts. However, it can supply up to two standard TTL loads.

556 dual timer The 556 is a dual version of the standard 555 timer housed in a 14pin DIL package. The two devices may be used entirely independently and share the same electrical characteristics as the standard 555.

Low power 556 The low power 556 is a dual version of the low power CMOS 555 timer contained in a 14-pin DIL package. The two devices may again be used entirely independently and share the same electrical characteristics as the low power CMOS 555.

Please note! Low power timers use CMOS technology and should be handled using anti-static precautions.

Monostable pulse generator Fig. 7.4 shows a standard 555 timer operating as a monostable pulse generator. The term â&#x20AC;&#x2DC;monostableâ&#x20AC;&#x2122; refers to the fact that the output has only one stable state, and it will always return to this state after a period of time spent in the opposite state. The monostable timing period (ie, the time for which the output is high) is initiated by a falling edge trigger pulse applied to the trigger input (pin 2). When this falling edge trigger pulse is received and falls below one third of the supply voltage, the output of IC2 goes high and the bistable will be placed in the set state. The inverted Q output (ie, Q) of the bistable then goes low, the internal transistor TR1 is placed in the off (non-conducting) state and the output voltage (pin 3) goes high. The capacitor, C, then charges through the series resistor, R, until the voltage at the threshold input reaches two thirds of the supply voltage (Vcc). At this point, the output of the upper comparator changes state and the bistable is reset. The inverted Q output (ie, Q) then goes high, TR1 is driven into CONDUCTION AND THE Ă&#x161;NAL OUTPUT

'JH " UJNFS JO NPOPTUBCMF DPOĂ&#x153;HVSBUJPO

goes low. The device then remains in the inactive state until another falling trigger pulse is received.

Output waveform The output waveform produced by the circuit of Fig.7.4 is shown in Fig.7.5. The waveform has the following properties: Time for which output is high:

ton = 1.1 C R Recommended trigger pulse width:

t tr <

t on 4

Where ton and ttr are in seconds, C is in farads and R is in ohms. The period of the 555 monostable output can be changed very easily by simply altering the values of the timing resistor, R, and/or timing capacitor, C. Doubling the value of R will double the timing period. Similarly, doubling the value of C will double the timing period.

Please note! The usual range of values for capacitance and resistance in a monostable timer are 470pF to 470PF and 1k: to 3.3M: respectively. Outside this range operation is less predictable.

Example 1 Now letâ&#x20AC;&#x2122;s work through a simple design example. For this we shall

Fig.7.5. Waveforms for monostable operation

Everyday Practical Electronics, May 2011

Teach-In 2011

Fig.7.7 (above). Circuit diagram for a 60 second timer (see Example 2) Fig.7.6. (left) Graph for determining values of C, ton and R for a 555 operating in monostable mode. The red line shows how a 10ms pulse will be produced when C = 100nF and R = 91k: (see Example 1)

assume that we need a circuit that will produce a 10ms pulse when a negative-going trigger pulse is applied to it. Using the circuit shown in Fig. 7.4, the value of monostable timing period can be calculated from the formula:

ton = 1.1 C R We need to choose an appropriate value for C that is in the range stated earlier. Since we require a fairly modest time period, we will choose a mid-range value for C. This should help to ensure that the value of R is neither too small nor too large. A value of 100nF should be appropriate and should also be easy to obtain. Making R the subject of the formula and substituting for C = 100nF gives:

t on 10ms ms = = 1.1C 1.1×100nF nF =

10×10-3 110×10-9

Everyday Practical Electronics, May 2011

From which:

10 R= ×106 = 0.091×106 : 110 or 9.1 1 kk:: Alternatively, the graph shown in Fig.7.6 can be used.

Example 2 Next, we shall design a timer circuit that will produce a +5V output for a period of 60s when a ‘start’ button is operated. The time period is to be aborted when a ‘stop’ button is operated. For the purposes of this example we shall assume that the ‘start’ and ‘stop’ buttons both have normally-open (NO) actions. The value of monostable timing period can be calculated from the formula:

ton = 1.1 C R We need to choose an appropriate value for C that is in the range stated earlier. Since we require a fairly long time period we will choose a relatively large value of C

in order to avoid making the value of R too high. A value of 100PF should be appropriate and should also be easy to obtain. Making R the subject of the formula, and substituting for C = 100PF gives:

R= =

t on 60s = = 1.1C 1.1×100ȝF

60 110×10-6

From which:

60 ×106 = 0.545×106 : 110 or 545 kk: :

In practice 560k: (the nearest preferred value) would be adequate. The ‘start’ button needs to be connected between pin 2 and ground, while the ‘stop’ button needs to be connected between pin 4 and ground. Each of the inputs requires 47

Teach-In 2011 a â&#x20AC;&#x2DC;pull-upâ&#x20AC;&#x2122; resistor to ensure that the input is taken high when the switch is not being operated. The precise value of the â&#x20AC;&#x2DC;pull-upâ&#x20AC;&#x2122; resistor is unimportant, and a value of 10k: will be perfectly adequate in this application. The complete circuit of the 60s timer is shown in Fig.7.7.

Astable pulse generator How the standard 555 can be conĂ&#x161;GURED AS AN astable pulse generator, is shown in Fig.7.8. In order to understand how this circuit operates, assume that the output (pin 3) is initially high and that TR1 is in the non-conducting state. The capacitor, C, will begin to charge with current supplied by series resistors, R1 and R2.

When the voltage at the threshold input (pin 6) exceeds two thirds of the supply voltage, the output of the upper comparator, IC1, will change state and the bistable will become reset, due to the voltage transition that appears at R. This, in turn, will make the Q output go high, turning TR1 on and saturating it at the same time. Due to the inverting action of THE BUFFER )# SEE &IG THE Ă&#x161;NAL output (pin 3) will go low. The capacitor, C, will now disCHARGE WITH CURRENT Ă&#x203A;OWING THROUGH R2 into the collector of TR1. At a certain point, the voltage appearing at the trigger input (pin 2) will have fallen back to one third of the supply voltage, at which point the lower comparator will change state and the voltage transition at S (Fig.7.2) will return the bistable to its original set condition. The inverted Q output then goes low, TR1 switches off (no longer conducting), and the output (pin 3) goes high. Thereafter, the entire charge/discharge cycle is REPEATED INDEĂ&#x161;NITELY The output waveform produced by the circuit of Fig.7.8 is shown in Fig.7.9. The waveform has the following properties:

Time for which output is low:

toff = 0.693 C R2 Period of output waveform:

t = ton + toff = 0.693 C (R1 + 2R2) Pulse repetition frequency:

p.r.f. =

1.44 C R 1 +2R 2

Mark-to-space ratio:

t on R 1 +R 2 = t off R2 Duty cycle:

t on R +R = 1 2 Ă&#x2014;100% t on +t off R 1 +2R 2

Time for which output is high: 'JH BTUBCMF DPOĂ&#x153;HVSBUJPO

ton = 0.693 C (R1 + R2)

Fig.7.9. Waveforms for astable operation

'JH (SBQI GPS EFUFSNJOJOH WBMVFT PG $ Q S G BOE 32 for a 555 operating in astable mode XIFSF 32 31 JF GPS TRVBSF XBWF PQFSBUJPO 5IF SFE MJOF TIPXT IPX B )[ TRVBSF XBWF XJMM CF QSPEVDFE XIFO $ O' BOE 3 L: TFF &YBNQMF

Everyday Practical Electronics, May 2011

Teach-In 2011 Where t is in seconds, C is in farads, R1 and R2 are in ohms.

t on R 1 + R 2 R+ R 2 = = = =2 t off R2 R 1

be a problem if we need to produce a precise square wave in which ton = toff. However, by making R 2 very much larger than R1, the timer can be made to produce a reasonably symmetrical square wave output. (Note, that the minimum recommended value for R2 is 1k: – see Please note!).

In this case, the duty cycle will be given by:

If R2 >> R1, the expressions for p.r.f. and duty cycle simplify to:

When R1 = R2, the duty cycle of the astable output from the timer can be found by letting R = R1 = R2. In this condition:

t on R + R2 = 1 ×100% = ×100% 0.72 t on + t off R 1 + 2R 2 R + 2R p.r.f. = CR 2 R+R t on R2 = ×100% u 100% R + 2R t on + t off 2R 2 1 u 100% 2

Thus:

t on 2R = ×100% t on +t off 3R

2 3

2 = ×100% = 67% 3 The p.r.f. of the 555 astable output can be changed very easily by simply altering the values of R1, R2, and C. The required values of C, R1 and R2 for any required p.r.f. and duty cycle can be determined from the formulae shown earlier. Alternatively, the graph shown in Fig.7.10 can be used when R1 and R2 are equal in value (corresponding to a 67% duty cycle).

Please note! The usual range of values for capacitance and resistance in an astable timer are 10nF to 470PF for C, and 1k: to 1M: for R 1 and R 2. As for the monostable circuit, operation is less predictable outside this range.

Square wave generators Because the high time (ton) is always greater than the low time (toff), the mark-to-space ratio produced by a 555 timer can never be made equal to (or less than) unity. This could Everyday Practical Electronics, May 2011

R= =

0.48 = p.r.f.×C

0.48 p.r.f.×1×10-6

Hence:

480×103 1043 = = 4.8 48k: kȍ = 4.8×10 k 100

Example 4

50%

Now let’s design a 5V 50Hz square wave generator using a 555 timer. Using the circuit shown in Fig.7.11, when R2 >> R1, the value of p.r.f. can be calculated from:

p.r.f. =

Example 3 Let’s design a pulse generator that will produce a p.r.f. of 10Hz with a 67% duty cycle (ie, the output will be high for one third of the time and low for two thirds of the time). Using the circuit that we met in Fig.7.8, the value of p.r.f. can be calculated from:

p.r.f. =

the formula, and substituting for C = 1PF gives:

1.44 C R 1 +2R 2

0.72 CR 2

We shall use the minimum recommended value for R1 (ie, 10k:) and ensure that the value of R2 that we calculate from the formula is at least ten times larger, in order to satisfy the criteria that R2 should be very much larger than R1. When selecting the value for C, we need to choose a value that will keep the value of R2 relatively

3INCE THE SPECIÚED DUTY CYCLE IS 67%, we can make R1 equal to R2. Hence, if R = R1 = R2 we obtain the following relationship:

p.r.f. =

1.44 1.44 0.48 = = C R+2R 3CR CR

We need to choose an appropriate value for C that is in the range stated earlier. Since we require a fairly low value of p.r.f., we will choose a value for C of 1PF. This should help to ensure that the value of R is neither too small nor too large. A value of 1PF should also be easy to obtain. Making R the subject of

Fig.7.11. Circuit for a 5V 50Hz square wave genrator (see Example 4)

Teach-In 2011 large. A value of 100nF should be about right, and should also be easy to locate. Making R2 the subject of the formula and substituting for C = 100nF gives:

R2 = =

0.72 0.72 = = p.r.f.Ă&#x2014;C 50Ă&#x2014;100Ă&#x2014;10-9 0.72 5Ă&#x2014;10-6

Hence:

R2 =

0.72 Ă&#x2014; 106 5

= 0.144Ă&#x2014;106 = 144 kČ? Alternatively, the graph shown in Fig.7.10 can be used. The value of R2 is more than 100 times larger than the value that we are using for R1. As a consequence, the timer should produce a good square wave output. The complete circuit of our 5V 50Hz square wave generator is shown in Fig.7.11.

Check â&#x20AC;&#x201C; How do you think you are doing? 7.1. Explain the difference between monostable and astable timer operation.

7.5. Design a timer circuit that will produce a 67% duty cycle output at 250Hz.

7.2. Sketch the circuit of a monostable timer and identify the components that determine the time for which the output is high.

7.6. A 555 timer is rated for a maximum output current of 120mA. What is the minimum value of load resistance that can be used if the device is to be operated from a 6V DC supply?

7.3. Sketch the circuit of an astable pulse generator and identify the components that determine the time for which (a) the output is high, and (b) the output is low.

For more information, links and other resources please check out our Teach-In website at:

7.4. Design a timer circuit that will produce a 6V 20ms pulse when a 6V negative-going trigger pulse is applied to it.

www.tooley.co.uk/ teach-in

Build â&#x20AC;&#x201C; The Circuit Wizard way Kitchen timer

UR Ă&#x161;RST PRACTICAL CIRCUIT USES THE TIMER CONĂ&#x161;GURED AS A MONOSTABLE TO OPERATE AS A kitchen timer, as shown in Fig.7.12. When SW1 is closed the buzzer will sound until SW2 is pressed to start the timer. The two probes help us to see the charge building in C1 and the status of the output. A sample trace is shown in Fig.7.13. This is particularly useful for testing long delays where the circuit may seem to being inactive.

'JH ,JUDIFO UJNFS VTJOH B JO B NPOPTUBCMF DPOĂ&#x153;HVSBUJPO

Fig.7.13. Sample trace for the kitchen timer circuit

Fig.7.14. Charge building on C1 in â&#x20AC;&#x2DC;Voltage Levelsâ&#x20AC;&#x2122; view

Similarly, in â&#x20AC;&#x2DC;Voltage Levelsâ&#x20AC;&#x2122; or â&#x20AC;&#x2DC;Current Flowâ&#x20AC;&#x2122; we are able to visualise the charge building on the capacitor as a series of â&#x20AC;&#x2DC;+â&#x20AC;&#x2122; and â&#x20AC;&#x2DC;-â&#x20AC;&#x2122; appear on the plates (see Fig.7.14).

Everyday Practical Electronics, May 2011

Teach-In 2011

The amount of elapsed time before the buzzer activates can be altered by changing the value of pot VR1. Experiment with running the timer for various settings of VR1 to ascertain the minimum/maximum times, priate formulae that was introduced in â&#x20AC;&#x2DC;Learnâ&#x20AC;&#x2122; (you may have to be very patient for the maximum delay!). A soft boiled egg is cooked for four minutes (240 seconds) â&#x20AC;&#x201C; calculate the value required for VR1, then set this on your circuit and check out your theory in practice.

In our second circuit (see Fig.7.15), we utilise the 555 in an astable plications might include childrenâ&#x20AC;&#x2122;s toys, signs, alarm systems, and level crossings. Varying the value of VR1

$% & ' ##*

will alter the frequency Circuit Wizardâ&#x20AC;&#x2122;s â&#x20AC;&#x2DC;Current Viewâ&#x20AC;&#x2122; comes in to its own here for visualising the continuously changing state of the circuit, as shown in Fig.7.16. Apart from looking like a 70s disco, the colours clearly show how current is sinking and sourcing though the output (pin 3) as each of the LEDs is lit. You can also monitor how the capacitor charges until the threshold voltage

is reached, and is then discharged through pin 7.

and trace (Fig.7.16) also help us to understand the inputs and outputs. The blue probe/line showing the voltage to pin 2 and pin 6, and the red line showing the output (pin 3).

As well as using the 555 as a timer in monostable mode, it can also be used as a bistable. A neat application of this is a simple â&#x20AC;&#x2DC;on-offâ&#x20AC;&#x2122; circuit, where SW1 is pressed to turn on or â&#x20AC;&#x2DC;setâ&#x20AC;&#x2122; the output and SW2 is pressed to â&#x20AC;&#x2DC;resetâ&#x20AC;&#x2122; or turn off the output (see Fig.7.17). A further application of this might be a signalling circuit, where SW1 is pressed to â&#x20AC;&#x2DC;set greenâ&#x20AC;&#x2122; and SW2 is pressed to â&#x20AC;&#x2DC;set redâ&#x20AC;&#x2122;, as shown in Fig.7.18.

! " #

Everyday Practical Electronics, May 2011

In Part 6 ( ), we constructed a decade (ie, 0 to 9) 51

Teach-In 2011 The Circuit Wizard way Dual timers In some circuits we may want to use more than one timer. The 556 IC effectively contains two 555s in one physical package. Our last circuit uses two timers â&#x20AC;&#x2DC;daisy-chainedâ&#x20AC;&#x2122; together to create a sequence of four

Fig.7.18 A 555 red/green signal circuit

counter circuit using a 4-bit ripple counter followed by a seven-segment driver and display. We used Circuit Wizardâ&#x20AC;&#x2122;s built in clock to test the circuit. However, in real life we would need circuitry to create this clock.

One way of doing this would be to use a 555 configured in astable mode. Try out the circuit shown in Fig. 7.19 (if you have your 0-9 counter circuit saved from Part 6 you could amend it to include the additional components).

Fig.7.20. Tooltip showing pin description and number

Fig.7.19. A 0 to 9 counter circuit, with 555 an astable clock generator

Everyday Practical Electronics, May 2011

Teach-In 2011

To use both timers contained within the 556 in Circuit Wizard, you need to drag two separate instances of the 556 on to the circuit â&#x20AC;&#x2DC;aâ&#x20AC;&#x2122; and the second â&#x20AC;&#x2DC;bâ&#x20AC;&#x2122; (eg, IC1a and IC1b). As both are contained within

"#$ & ''' #

* ; ''< @ G JK

X Z [ \]^ Construct the circuit shown in Z [ \_ $ X`#_ ^ { ] 'J; output from this timer is then used X`#_ ^ { \J; During the period when the output of timer one is high, the # second timer is not powered and |}~

perhaps changing the sequence to { timer.

+ ! ;

G K X `#_ `#_ ^ #_ #\ ]Â&#x20AC;

_Â Â&#x201A; { the output of timer one (IC1a) and the X`#_ ^ the effect that on the initial sequence only |}~ rather than four! Can you design a

Teach-In to produce the same sequence, but without the same issues?

Circuit Wizard A Standard or Professional version of Circuit Wizard can be purchased from the editorial ofďŹ ce of EPE â&#x20AC;&#x201C; see CD-ROMs for Electronics page and the UK shop on our website (www. epemag.com). Further information can be found on the New Wave Concepts website; www.new-wave-concepts.com. The developer also offers an evaluation copy of the software that will operate for 30 days, although it does have some limitations applied, such as only being able to simulate the included sample circuits and no ability to save your creations.

++ ! ;

Everyday Practical Electronics, May 2011

Teach-In 2011

Investigate The complete circuit diagram of a variable pulse generator is shown in Fig.7.23. Look at this circuit carefully and then answer the following questions: 1. Identify the component or components that: (a) determine the pulse repetition frequency (b) provide variable adjustment of the pulse width (c) provide variable adjustment of the output amplitude (d) limit the range of variable adjustment of pulse width (e) protect IC2 against a shortcircuit connected at the output (f) remove any unwanted signals appearing on the supply rail (g) form the trigger pulse required by the monostable stage.

Fig.7.23. Practical circuit diagram for a variable pulse generator

2. Sketch waveforms to a common time scale showing the signals at (a) TPA and (b) TPB â&#x20AC;&#x2DC;test pointsâ&#x20AC;&#x2122;. 3. Determine the pulse repetition frequency of the output.

4. Determine the maximum and minimum pulse width of the output. 5. Determine the maximum and minimum amplitude of the output.

Amaze In last monthâ&#x20AC;&#x2122;s Amaze we de

speed at which digital logic can operate. This month, we will be looking at the way in which we accurately measure time:

Simple audible and visible signals were once used to inform people about the passing of time and as a means of setting their own clocks. For example, a canon could be K

Fig.7.24. FOCS-1, a continuous cold caesium fountain atomic clock in Switzerland. The clock started operating in 2004 and keeps time to an accuracy of one second in 30 million years

day. However, with the advent of telegraph, telephone and radio in the 20th century, time signals could be broadcast internationally and made accessible to anyone that needed them.

Fig.7.25. Atomic clocks are usually large and cumbersome devices, but much effort has been directed in making them small enough to be carried around. This is NISTâ&#x20AC;&#x2122;s recently developed chip-scale atomic clock

Everyday Practical Electronics, May 2011

Teach-In 2011 Since time is the reciprocal of frequency, a time standard can be easily derived from an accurate frequency standard or â&#x20AC;&#x2DC;clockâ&#x20AC;&#x2122;. All you need to do is count the number of cycles generated by the clock and, as long as the frequency is accurately known, the number of cycles will be an accurate measure of time. Todayâ&#x20AC;&#x2122;s off-air broadcast time signals use oscillators that are locked to atomic clocks.

Atomic clocks brations of ammonia molecules and was invented over sixty years ago. Atomic clocks use the vibrations of atoms or molecules, but because the frequency of these oscillations is so high, it is not possible to use them as a direct means of controlling a clock. Instead, the clock is controlled by a highly stable crystal oscillator whose output is automatically multiplied and compared with the frequency of the atomic system. If two atomic clocks are compared there is always the possibility of a difference in their readings. This â&#x20AC;&#x2DC;uncertaintyâ&#x20AC;&#x2122; is the difference in indicated time if both were started at the same instant and later compared. For the early atomic clocks, this lack of certainty was estimated to be around one second in three thousand years.

Modern atomic clocks are based on caesium and rubidium, and they offer uncertainties of better than one second in 20 million years. But, if thatâ&#x20AC;&#x2122;s not good enough for you to set your watch by, the latest generation of quantum logic clocks, developed in 2008 at the National Institute of Standards and Technology (NIST) in the USA, offer an uncertainty of better than one second in over a billion years!

Answers to Check questions 7.1. See pages 46 and 48 7.2. See Fig.7.4 and associated text 7.3. See Fig.7.8 and associated text 7.4. See Fig.7.4 with R = 182k: and C =100nF and operating from a 6V DC supply 7.5. See Fig.7.8 with R1 = 19.2k:, R2 = 19.2k: and C = 100nF 7.6. 50:.

Next month! In next monthâ&#x20AC;&#x2122;s Teach-In, we will be looking at some applications of

and attenuators.

CIRCUIT WIZARD â&#x20AC;&#x201C; featured in this Teach-In series Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard and Professional. By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ďŹ nish â&#x20AC;&#x201C; even including on-screen testing of the PCB prior to construction!

Circuit diagram design with component library * (500 components Standard, 1500 components Professional) instruments (4 Standard, 7 Professional) * Virtual On-screen animation *

Layout * PCB Interactive PCB layout simulation * Automatic PCB routing * Gerber export *

This is the software used in our Teach-In 2011 series. Standard ÂŁ61.25 inc. VAT Professional ÂŁ91.90 inc. VAT See Direct Book Service â&#x20AC;&#x201C; pages 75-77 in this issue

Everyday Practical Electronics, May 2011

Teach-In 2011

TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS Part 8: Analogue Circuit Applications By Mike and Richard Tooley

N LAST monthâ&#x20AC;&#x2122;s instalment of Teach-In 2011 WE INTRODUCED YOU TO THE HIGHLY VERSATILE INTEGRATED CIRCUIT TIMER 7E SHOWED you how you can quickly and easily DESIGN CIRCUITS THAT WILL PRODUCE time delays from a few hundred nanoseconds to several hundred SECONDS AND SQUARE WAVE PULSES OF GIVEN FREQUENCY PERIOD AND DUTY CYCLE )N THIS INSTALMENT WE INTRODUCE some practical applications of ANALOGUE CIRCUITS INCLUDING ACTIVE AND PASSIVE Ă&#x161;LTERS AND TONE CONTROL CIRCUITS )N Learn we will show YOU HOW CIRCUITS CAN BE DESIGNED SO THAT THEY ACCEPT OR REJECT SIGNALS WITHIN A SPECIĂ&#x161;ED BAND OF FREQUENCIES AND HOW THE SHAPE OF THE

frequency response can be altered in order to modify and enhance the SOUND PRODUCED BY AN AMPLIĂ&#x161;ER We also introduce decibels (dB) AS A MEANS OF DEĂ&#x161;NING GAIN AND LOSS IN AN ANALOGUE ELECTRONIC SYSTEM Build and Investigate extend this further with a detailed look at some PRACTICAL Ă&#x161;LTER CIRCUITS &INALLY IN Amaze WE LOOK AT THE RANGE OF SIGNALS FOUND IN RADIO AND TELEVISION

Learn Attenuators

Attenuators provide us with a means OF REDUCING THE LEVEL OF A SIGNAL PRESENT IN AN ANALOGUE CIRCUIT 4HEY PROVIDE THE OPPOSITE OF GAIN AND WE refer to it as attenuation )N ORDER TO

produce loss or attenuation we only need a network of passive compoNENTS AND IF SIGNALS AT ALL FREQUENcies are to be attenuated by the same AMOUNT WE ONLY NEED TO USE RESISTORS IN OUR NETWORK 3EVERAL DIFFERENT TYPES OF NETWORK ARE POSSIBLE INCLUDING THE BASIC 4 AND S-networks SHOWN IN &IG )N ORDER TO WORK CORRECTLY IE provide the required amount of attenuation) an attenuator needs to be matched to the system in which it is USED 4HIS SIMPLY MEANS ENSURING THAT THE IMPEDANCE OF THE SOURCE AS WELL AS THAT OF THE LOAD MATCHES THE characteristic impedance of the attenUATOR )N THIS CONDITION WE SAY THAT an attenuator is correctly terminated &IG ILLUSTRATES THIS CONCEPT

Everyday Practical Electronics, June 2011

Teach-In 2011

Fig.8.1. Basic T and S-network attenuators

Before we take a look at the operation of two simple forms of attenuator, it is worth pointing out that the impedances used in attenuators are always pure resistances. The reason for this is that an attenuator must provide the same attenuation at all frequencies and the inclusion of reactive components (inductors and/or capacitors) would produce a non-linear attenuation/frequency characteristic.

Balanced/unbalanced The simple T and S-networks that

weâ&#x20AC;&#x2122;ve just met can exist in two basic forms, balanced and unbalanced. In the former case, none of the networkâ&#x20AC;&#x2122;s input and output terminals are connected directly to common or ground. The unbalanced and balanced forms of the basic T and S-networks are shown for comparison in Fig.8.3. The networks shown in Fig.8.3 all have two ports. One port (ie, pair of terminals) is connected to the input, while the other is connected to the output. For convenience, many twoport networks are made symmetrical and they perform exactly the same function and have the same characteristics, regardless of which way round they are connected.

Please note!

It is conventional to express the values of the resistances present in an attenuator in terms of the effective series or parallel resistance. Thus, for example, the two series resistors in an unbalanced T-network Everyday Practical Electronics, June 2011

Fig.8.2. A matched network

attenuator are both labelled R1/2 where R1 is the effective series resistance. S i m i l a r l y, t h e two parallel resistors present in an unbalanced S-network are labelled 2R2 where R2 is the effective resistance of the two components when connected in parallel. We will be adopting a similar convention when we label the cirFig.8.3. Balanced and unbalanced forms of the T and CUITS USED FOR Ă&#x161;LTERS

S-networks

Filters

Filters provide us with a means of passing or rejecting signals within A SPECIĂ&#x161;ED FREQUENCY RANGE &ILTERS are used in a variety of applications, INCLUDING AMPLIĂ&#x161;ERS RADIO TRANSmitters and receivers. They also provide us with a means of reducing noise and unwanted signals that might otherwise be passed along power lines. Filters are usually described according to the range of frequencies that they will accept or reject. The following types are possible:

p Low-pass p High-pass p Band-pass p Band-stop. Filters can also be categorised as either passive or active, depending

on whether they are based on networks of passive components (ie, resistors, capacitors and inductors) or active components (ie, transistors AND OPERATIONAL AMPLIĂ&#x161;ERS WORKING together with resistors, capacitors and/or inductors. The symbols used to represent THESE FOUR TYPES OF Ă&#x161;LTER IN BLOCK SCHEmatic diagrams are shown in Fig.8.4.

,OW PASS Ă&#x161;LTERS ,OW PASS Ă&#x161;LTERS EXHIBIT VERY LOW attenuation of signals below their SPECIĂ&#x161;ED cut-off frequency. Beyond the cut-off frequency, they exhibit increasing amounts of attenuation, as shown in Fig.8.5. A simple C-R LOW PASS Ă&#x161;LTER IS shown in Fig.8.6. The cut-off freQUENCY FOR THE Ă&#x161;LTER OCCURS WHEN the output voltage has fallen to 47

Teach-In 2011 0.707 of the input value. This occurs when the reactance of the capacitor, XC, is equal to the value of resistance, R. Using this information we can determine the value of cut-off frequency, f, for given values of C and R: Since

R = XC or

1 2S fC

from which:

1 2S CR

where f is the cut-off frequency (in Hz), C is the capacitance (in F), and R is the resistance (in :).

'JH 4ZNCPMT VTFE UP SFQSFTFOU Ă&#x153;MUFST B MPX QBTT C IJHI QBTT D CBOE QBTT BOE E CBOE TUPQ

(IGH PASS Ă&#x161;LTERS

Please note!

(IGH PASS Ă&#x161;LTERS EXHIBIT VERY LOW attenuation of signals above their SPECIĂ&#x161;ED CUT OFF FREQUENCY "ELOW THE CUT OFF FREQUENCY THEY EXHIBIT increasing amounts of attenuation, as shown in Fig.8.7. A simple C-R HIGH PASS Ă&#x161;LTER IS shown in Fig.8.8. Once again, the CUT OFF FREQUENCY FOR THE Ă&#x161;LTER OCCURS when the output voltage has fallen to 0.707 of the input value. This occurs when the reactance of the capacitor, XC, is equal to the value of resistance, R. Using this information we can determine the value of cut-off frequency, f, for given values of C and R: Since

The term â&#x20AC;&#x2DC;cut-offâ&#x20AC;&#x2122; can be a bit misleading because it might imply that A Ă&#x161;LTER WILL PRODUCE NO OUTPUT AT ALL beyond a certain point. This is not the case. The response of a practical

Ă&#x161;LTER WILL SIMPLY lROLL OFFm BEYOND the cut-off frequency and one of the most important characteristics OF A Ă&#x161;LTER IS THE RATE AT WHICH THIS roll-off occurs.

'JH 'SFRVFODZ SFTQPOTF GPS B MPX QBTT Ă&#x153;MUFS

'JH " TJNQMF $ 3 MPX QBTT Ă&#x153;MUFS

R = XC or

1 2S fC

and once again:

1 2S CR

where f is the cut-off frequency (in Hz), C is the capacitance (in F), and R is the resistance (in :). 48

'JH 'SFRVFODZ SFTQPOTF GPS B IJHI QBTT Ă&#x153;MUFS

'JH " TJNQMF $ 3 IJHI QBTT Ă&#x153;MUFS

Everyday Practical Electronics, June 2011

Teach-In 2011 Example 1

A simple C-R LOW PASS ÚLTER HAS C = 100nF and R = 10k: $ETERMINE THE CUT OFF FREQUENCY OF THE ÚLTER 7E CAN ÚND THE CUT OFF FREQUENCY using:

1 2S CR

1 6.28 u100 u 10 9 u 10 u 104 100 15.9 Hz Hz 6.28

Example 2

A simple C-R LOW PASS ÚLTER IS TO HAVE A CUT OFF FREQUENCY OF K(Z )F THE VALUE OF CAPACITANCE USED IN THE ÚLTER IS TO BE N& DETERMINE THE VALUE OF RESISTANCE 2E ARRANGING THE EQUATION FOR CUT OFF FREQUENCY GIVES

1 2S fC

1 6.28 u1u 103 u 47 u10 9

EQUAL TO THE VALUE OF THE REACTANCE OF THE INDUCTOR XL 4HIS INFORMATION ALLOWS US TO DETERMINE THE VALUE OF FREQUENCY AT THE CENTRE OF THE PASS BAND f0:

XC = XL THUS

1 2S f 0C

2S f 0 L

FROM WHICH

f02

1 4S 2 LC

OF THE INDUCTOR RECALL THAT A PRACTICAL COIL HAS SOME RESISTANCE AS WELL AS INDUCTANCE 4HE BANDWIDTH IS GIVEN BY

Bandwidth

f 2 f1

f0 Q

2S f 0 L R WHERE f0 IS THE RESONANT FREQUENCY IN (Z L IS THE INDUCTANCE IN ( and R IS THE LOSS RESISTANCE OF THE INDUCTOR IN :

"AND STOP ÚLTERS

WHERE f0 IS THE RESONANT FREQUENCY IN (Z L IS THE INDUCTANCE IN ( and C IS THE CAPACITANCE IN & 4HE BANDWIDTH OF THE BAND PASS : ÚLTER IS DETERMINED BY ITS quality factor OR Q-factor 4HIS IN TURN IS LARGELY DETERMINED BY THE LOSS RESISTANCE R

"AND STOP ÚLTERS EXHIBIT VERY HIGH ATTENUATION OF SIGNALS WITHIN A SPECIÚED RANGE OF FREQUENCIES KNOWN AS THE stop-band AND NEGLIGIBLE ATTENUATION OUTSIDE THIS RANGE /NCE AGAIN THIS TYPE OF ÚLTER HAS TWO CUT OFF FREQUENCIES a lower cut-off frequency f1 AND an upper cut-off frequency f2 4HE DIFFERENCE BETWEEN THESE FREQUENCIES f2 – f1 IS KNOWN AS THE bandwidth OF THE ÚLTER 4HE RESPONSE OF A BAND STOP ÚLTER IS SHOWN IN &IG

Fig.8.9. Frequency response for a CBOE QBTT ÜMUFS

Fig.8.10. A simple L-C band-pass ÜMUFS PS BDDFQUPS

Fig.8.11. Frequency response for a CBOE TUPQ ÜMUFS

Fig.8.12. A simple L-C band-stop ÜMUFS PS SFKFDUPS

AND THUS

1 2S LC

106 3.39 k: k: 295.16 "AND PASS ÚLTERS "AND PASS ÚLTERS EXHIBIT VERY LOW ATTENUATION OF SIGNALS WITHIN A SPECIÚED RANGE OF FREQUENCIES KNOWN AS THE pass-band AND INCREASING ATTENUATION OUTSIDE THIS RANGE 4HIS TYPE OF ÚLTER HAS TWO CUT OFF FREQUENCIES a lower cut-off frequency f1 AND an upper cut-off frequency f2 4HE DIFFERENCE BETWEEN THESE FREQUENCIES f2 – f1 IS KNOWN AS THE bandwidth OF THE ÚLTER 4HE RESPONSE OF A BAND PASS ÚLTER IS SHOWN IN &IG A simple L-C BAND PASS ÚLTER IS SHOWN IN &IG 4HIS CIRCUIT USES an L-C RESONANT CIRCUIT AND IS OFTEN REFERRED TO AS AN acceptor circuit. 4HE FREQUENCY AT WHICH THE BAND PASS ÚLTER IN &IG EXHIBITS MINIMUM ATTENUATION OCCURS WHEN THE CIRCUIT IS resonant IE WHEN THE REACTANCE OF THE CAPACITOR XC IS Everyday Practical Electronics, June 2011

Teach-In 2011 A simple L-C band-stop filter is shown in Fig.8.12. This circuit uses an L-C resonant circuit and is referred to as a rejector circuit. The frequency at which the bandSTOP Ă&#x161;LTER IN &IG EXHIBITS MAXImum attenuation occurs when the circuit is resonant, ie, when the reactance of the capacitor, XC, is equal to the reactance of the inductor, XL. This information allows us to determine the value of frequency at the centre of the pass-band, f0:

XC = XL thus

1 2S f 0C

2S f 0 L

from which

1 4S 2 LC

f02 and thus

1 2S LC

Fig.8.13. The characteristic impedance (Z0) of a network is determined by the values of resistance (or impedance) within the network â&#x20AC;&#x201C; see text

where f0 is the resonant frequency (in Hz), L is the inductance (in H) and C is the capacitance (in F). !S WITH THE BAND PASS Ă&#x161;LTER THE BANDWIDTH OF THE BAND PASS Ă&#x161;LTER IS determined by its quality factor (or Q-factor). This, in turn, is largely determined by the loss resistance, R, of the inductor (recall that a practical coil has some resistance as well as inductance). Once again, the bandwidth is given by:

Bandwidth

f 2 f1

f0 Q

2S f 0 L R where f0 is the resonant frequency (in Hz), L is the inductance (in H), and R is the loss resistance of the inductor (in :).

Example 3

A simple acceptor circuit uses L = 2mH and C = 1nF. Determine the 50

frequency at which minimum attenuation will occur. The frequency of minimum attenuation will be given by:

Termination, matching and characteristic impedance

&OR THE PERFORMANCE OF A Ă&#x161;LTER OR an attenuator to be predictable we 1 need to take into account the input f0 (source) and output (load) imped2S LC ances. These impedances are said to 1 terminate THE Ă&#x161;LTER q WITHOUT TAKING 3 9 them into account the performance 2S 2 u10 u 1u 10 can be somewhat unpredictable! 106 When a filter or attenuator is 112.6 kHz kHz correctly terminated it is said to 8.88 be matched. Analogue systems are Example 4 often designed so that they have a A 15kHz rejector circuit has a Q-fac- particular input/source and output/ tor of 40. Determine the bandwidth load impedance. In many audio of the circuit. systems the impedance chosen is The bandwidth can be found from: 600: but in radio frequency (RF) applications impedances of 50:, f 0 15 u103 75: or 300: are common. Bandwidth 375 Hz It is often convenient to analyse 40 Q the behaviour of a signal transmis375 Hz Hz sion path in terms of a number Everyday Practical Electronics, June 2011

Teach-In 2011 of identical series connected networks. One important feature of any NETWORK IS THAT WHEN AN INĂ&#x161;NITE number of identical symmetrical networks are connected in series, the resistance (or impedance) seen looking into the network will have a DEĂ&#x161;NITE VALUE 4HIS VALUE IS KNOWN as the characteristic impedance of the network 4AKE A LOOK AT &IG )N &IG A AN INĂ&#x161;NITE NUMBER OF identical networks are connected in SERIES "Y DEĂ&#x161;NITION THE IMPEDANCE seen looking into this arrangement will be equal to the characteristic impedance, Z0. Now suppose that we remove the Ă&#x161;RST NETWORK IN THE CHAIN AS SHOWN IN &IG B 4O ALL INTENTS AND PURposes, we will still be looking into an INĂ&#x161;NITE NUMBER OF SERIES CONNECTED NETWORKS 4HUS ONCE AGAIN WE WILL see an impedance equal to Z0 when we look into the network. &INALLY SUPPOSE THAT WE PLACE AN impedance of Z0 across the output terminals of the single network that WE REMOVED EARLIER 4HIS TERMINATED NETWORK SEE &IG C WILL BEHAVE exactly the same way as the arrangeMENT IN &IG A )N OTHER WORDS

by correctly terminating the network in its characteristic impedance, we have made one single network section appear the same as a series of identical networks stretching to INĂ&#x161;NITY 4HE CHARACTERISTIC IMPEDANCE Z0) of a network is determined by the values of resistance (or impedance) within the network, as we shall see next.

-OREÂŞCOMPLEXÂŞlLTERS 4HE SIMPLE C-R and L-C Ă&#x161;LTERS THAT we have described in earlier sections have far from ideal characteristics. )N PRACTICE MORE COMPLEX CIRCUITS are used and a selection of these (based on matched T-section and S-section networks) are shown in &IG 4HE DESIGN EQUATIONS FOR these circuits are as follows:

)NDUCTANCE:

Z0 2S f C

L Capacitance:

1 2S f C Z 0

where Z0 is the characteristic impedance (in :), fC is the cut-off frequency (in Hz), L is the inductance (in H), and C IS THE CAPACITANCE IN &

Example 5

Determine the cut-off frequency and CHARACTERISTIC IMPEDANCE FOR THE Ă&#x161;LTER NETWORK SHOWN IN &IG

Characteristic impedance:

L C

Cut-off frequency:

1 2S LC

'JH 4FF &YBNQMF JO UFYU

Comparing the circuit shown in &IG WITH THAT SHOWN IN &IG SHOWS THAT THE Ă&#x161;LTER IS A HIGH PASS type with L M( AND C N& (note that the value of C is the effective series capacitance and is EQUIVALENT TO THE TWO N& CAPACItors connected in series). Now

1 2S LC

6.28 5 u10 3 u 20 u10 9 105 1.59kHz kHz 6.28 and

Z0 Fig.8.14. Improved T-section and S TFDUJPO Ă&#x153;MUFST

Everyday Practical Electronics, June 2011

L C

5 u 10 3 20 u10 9

0.5 u 103

5 u103 20

500 : 51

Teach-In 2011

'JH 'JSTU PSEFS BDUJWF MPX QBTT Ă&#x153;MUFS

'JH 'JSTU PSEFS BDUJWF IJHI QBTT Ă&#x153;MUFS

'JH 4FDPOE PSEFS 4BMMFO BOE ,FZ BDUJWF MPX QBTT Ă&#x153;MUFS

'JH 4FDPOE PSEFS 4BMMFO BOE ,FZ BDUJWF IJHI QBTT Ă&#x153;MUFS

!CTIVEÂŞlLTERS The simple R-C filters that we described earlier in Fig.8.6 and Fig.8.8 require a very low source impedance and a very high load impedance in order to behave in a predictable manner (ie, to satisfy the equation for cut-off frequency that we met earlier). One way of improving the performance of these Ă&#x161;LTERS IS TO TERMINATE THEM USING A UNITY GAIN OPERATIONAL AMPLIĂ&#x161;ER buffer, as shown in Fig.8.16 and Fig.8.17. These circuits maintain the predicted frequency response, but the rate at which the output voltage falls above cut-off may be INSUFĂ&#x161;CIENT FOR MANY APPLICATIONS Fortunately, we can easily solve this problem by exploiting the gain available from the operational amPLIĂ&#x161;ER &IG AND &IG SHOWS popular second-order Sallen and +EY LOW PASS AND HIGH PASS Ă&#x161;LTERS 4HESE Ă&#x161;LTERS ROLL OFF AT TWICE THE RATE that can be obtained with the simple Ă&#x153;STU PSEFS Ă&#x161;LTERS SHOWN IN &IG 52

and Fig.8.17. Later, in Build you will have the opportunity to build and test these circuits.

The cut-off frequency of the secondORDER Ă&#x161;LTERS SHOWN IN &IG AND &IG IS GIVEN BY

$ECIBELS One of the most important parameters of an analogue circuit is the amount of gain or loss that it provides. Gain can be expressed in various ways, but basically it is just the ratio of output to input expressed in terms of either voltage, current or power. Since gain and loss can sometimes be quite large we

often use a logarithmic scale to express our ratios. This measurement is based on decibels (dB), where one decibel is equivalent to one tenth of a Bel (the logarithm of the voltage, current or power ratio). In case this is beginning to sound a little complicated we have summarised all of this in Table 8.1.

Table 8.1. Gain or loss expressed in decibels of voltage, current and power Basis of measurement Voltage

Current Power

Gain or loss as a ratio

Vout Vin Iout Iin Pout Pin

Gain or loss expressed in decibels (dB) Â§ Vout Âˇ 20log10 Â¨ Â¸ ÂŠ Vin Âš Â§ Iout Âˇ 20log10 Â¨ Â¸ ÂŠ Iin Âš Â§ Pout Âˇ 10log10 Â¨ Â¸ ÂŠ Pin Âš

Everyday Practical Electronics, June 2011

Teach-In 2011 ยง AP ยท antilog10 ยจ ยธ ยฉ 10 ยน ยช ยง Pout ยท ยบ antilog10 ยซlog10 ยจ ยธยป ยฉ Pin ยน ยผ ยฌ

1 2S C1R1 u C 2 R 2

7HEN C1 = C2 = C AND R1 = R2 = R THIS EQUATION SIMPLIร ES TO

ยง 6 ยท antilog10 ยจ ยธ ยฉ 10 ยน antilog10 0.6

4HE ร RST ORDER ร LTERS THAT WE MET IN &IG AND &IG ROLL OFF THEIR RESPONSE AT THE RATE OF D" PER OC TAVE WHILE THE SECOND ORDER ร LTERS SHOWN IN &IG AND &IG HAVE A RESPONSE THAT ROLLS OFF AT D" PER OCTAVE .OTE THAT lPER OCTAVEm SIM PLY MEANS A DOUBLING OR HALVING OF FREQUENCY

Pout

Pout Pin

Pin u antilog10 0.6

1.6 u 0.25 0.4W W

Please out ยง outnote! ยท 10 ยจ ยธ 7HEN PLOTTING THE FREQUENCY RE SPONSE OF A ร LTER WE OFTEN USE A LOGARITHMIC SCALE FOR FREQUENCY BECAUSE THIS ALLOWS A MUCH WIDER RANGE OF VALUES TO BE ACCOMMODATED AND AVOIDS CRAMPING 4HE TERM lCUT OFFm CAN BE A BIT MIS LEADING BECAUSE IT MIGHT IMPLY THAT A ร LTER WILL PRODUCE NO OUTPUT AT ALL BEYOND A CERTAIN POINT 4HIS IS NOT THE CASE 4HE RESPONSE OF A PRACTICAL ร LTER WILL SIMPLY lROLL OFFm BEYOND THE CUT OFF FREQUENCY AND ONE OF THE MOST IMPORTANT CHARACTERISTICS OF A ร LTER IS THE RATE AT WHICH THIS ROLL OFF OCCURS

Check โ How do you think you are doing? 8.1. )DENTIFY EACH OF THE CIRCUITS SHOWN IN &IG

!N AMPLIร ER USED IN A MATCHED SYSTEM PRODUCES AN OUTPUT VOLTAGE OF 6 FOR AN INPUT OF M6 7HAT IS THE VOLTAGE GAIN OF THE AMPLIร ER WHEN EXPRESSED IN DECIBELS 4HE VOLTAGE GAIN A6 CAN BE CAL CULATED FROM

ยง Vout ยท 20log10 ยจ ยธ ยฉ Vin ยน

8.2. 3KETCH THE CIRCUIT OF A A SIMPLE L-C ACCEPTOR CIRCUIT AND B A SIMPLE L-C REJECTOR CIRCUIT

ยจ ยฉ

ยง 2 ยท 20log10 ยจ ยธ ยฉ 0.02 ยน 20 u 2

40 dB dB

Example 7 ! D" MATCHED ATTENUATOR IS USED TO REDUCE THE POWER LEVEL PRODUCED BY AN AMPLIร ER THAT PRODUCES AN OUTPUT OF 7 7HAT POWER WILL APPEAR AT THE OUTPUT OF THE ATTENUATOR 2EARRANGING THE EQUATION FOR POWER GAIN IN 4ABLE PRODUCES

Now AP

.OTE THAT WE HAVE INSERTED A MINUS SIGN IN ORDER TO INDICATE A loss OF D" 2EARRANGING THIS EXPRESSION GIVES

Example 6

20log10 100

Pout Pin

&ROM WHICH

1 2S CR

Please note!

ยง Pout ยท 10log10 ยจ ยธ ยฉ Pin ยน

2EARRANGING THIS EXPRESSION GIVES

ยง Pout ยท ยง AP ยท log10 ยจ ยธ ยฉ Pin ยน ยฉ 10 ยน

4AKING INVERSE LOGARITHMS IE ANTI LOGS OF BOTH SIDES WE ARRIVE AT Everyday Practical Electronics, June 2011

8.3. ! SIMPLE 2 # HIGH PASS ร LTER u $E HAS 10 AND C N& ยธ R K: ยน TERMINE THE CUT OFF FREQUENCY OF THE ร LTER

OF THE ATTENUATOR IS M6 FOR AN INPUT OF M6 WHAT LOSS DOES IT PRODUCE %XPRESS YOUR ANSWER IN D" 8.8. !N AMPLIFIER USED IN A MATCHED SYSTEM PROVIDES A POWER GAIN OF D" 7HAT INPUT POWER IS REQUIRED TO PRODUCE AN OUTPUT POWER OF 7

8.4. 4HE OUTPUT OF A LOW PASS ร LTER IS 6 AT (Z )F THE ร LTER HAS A CUT OFF FREQUENCY OF K(Z WHAT WILL THE APPROXIMATE OUTPUT VOLT AGE BE AT THIS FREQUENCY 8.5. !N L-C TUNED CIRCUIT IS TO BE USED TO REJECT SIGNALS AT K(Z )F THE VALUE OF CAPACITANCE IS N& DETERMINE THE REQUIRED VALUE OF INDUCTANCE 8.6. 3KETCH THE FREQUENCY RE SPONSE FOR A A SIMPLE L-C ACCEP TOR CIRCUIT AND B A SIMPLE L-C REJECTOR CIRCUIT 8.7. !N ATTENUATOR IS USED IN A MATCHED SYSTEM )F THE OUTPUT

Fig.8.20. See Question 1

Teach-In 2011

ÂŞÂŞ"UILDÂŞnÂŞ4HEÂŞ#IRCUITÂŞ7IZARDÂŞWAY

E ARE now going to try out SOME PRACTICAL Ă&#x161;LTER CIRCUITS and see how they behave when we apply different signals to them. One of the features that Circuit 7IZARD LACKS THAT WE OFTEN Ă&#x161;ND IN higher-end electronics packages is the ability to directly carry out AC ANALYSIS TO A GIVEN CIRCUIT 5SUALLY this would involve modelling the CIRCUIT ENTERING THE SIGNAL CHARACTERISTICS AND LIMITS THEN LETTING the software â&#x20AC;&#x2DC;sweepâ&#x20AC;&#x2122; through the frequency range and plot the output amplitude and phase. There are a number of useful appliCATIONS THAT CAN DO THIS FOR EXAMPLE 5Spice Analysis (www.5spice.com). "E WARNED THOUGH THESE SOFTWARE PACKAGES ARE OFTEN RATHER DIFĂ&#x161;CULT to use unless you are familiar with similar SPICE analysis programmes.

SIGNALS THAT CHANGE VERY RAPIDLY it just canâ&#x20AC;&#x2122;t keep up in real-time. 4HEREFORE WE NEED TO SLOW DOWN the simulation speed in order to give the software a chance to accurately simulate. )N THE AUTHORmS EXPERIENCE THE PROCESS OF Ă&#x161;NDING A SUITABLE SPEED FOR A CIRCUIT TO SIMULATE IS TO BE HONEST A BIT OF A Ă&#x161;DDLE 4HEREFORE YOU WILL NEED TO EXPERIMENT TO SOME DEgree to get your traces looking right.

Speed trap

Under certain circumstances Circuit Wizard will warn you about accurate high speed simulation (see Fig.8.21). (OWEVER IN PRACTICE IT WILL HAPPILY present you with bizarre results with no warning. Fig.8.22 shows an EXAMPLE TRACE OF A K(Z SINEWAVE simulated in real time!

Changing the simulation speed is achieved by clicking on â&#x20AC;&#x2DC;Time:â&#x20AC;&#x2122; FOUND ALONG THE BOTTOM GREY BAR AND selecting an appropriate timing (see Fig.8.23). Note that this only appears when the simulation is running.

,OW PASSÂŞlLTERÂŞTESTÂŞCIRCUIT ,ETmS BEGIN BY LOOKING AT A Ă&#x161;RST ORDER LOW PASS Ă&#x161;LTER CIRCUIT %NTER THE CIRCUIT shown in Fig. 8.24 below. This is an acTIVE Ă&#x161;LTER CIRCUIT USING AN OPERATIONAL AMPLIĂ&#x161;ER "E SURE TO USE TERMINALS FOR the output terminals and voltage rails for the supply to the operational amPLIĂ&#x161;ER GETTING THIS WRONG IS A COMMON mistake that students make. Please note that in order for our Circuit Wizard circuits to match the circuit diagrams you have seen in Learn you will need to â&#x20AC;&#x2DC;mirrorâ&#x20AC;&#x2122; the OPERATIONAL AMPLIĂ&#x161;ER SYMBOL SO THAT Fig.8.23 (below). Changing simulation speed

Fig.8.21. Simulation speed warning

Although Circuit Wizard canâ&#x20AC;&#x2122;t do THE ANALYSIS FOR US AUTOMATICALLY IT still does a great job of modelling Ă&#x161;LTER CIRCUITS AS WE WILL SEE LATER We can then bring our results together and plot our own frequency CURVES )N FACT THIS IS A GREAT WAY TO understand whatâ&#x20AC;&#x2122;s really going on and what happens to the signals as we vary the frequency of the input.

3IMULATIONS Circuit Wizard carries out literally thousands of mathematical calculations in the background in order to show you how the circuit operates OVER TIME (OWEVER WHEN WE ARE working with higher frequency

Fig.8.22. The bizarre result of simulating a high frequency circuit in real-time

Everyday Practical Electronics, June 2011

Teach-In 2011

'JH 'JSTU PSEFS MPX QBTT Ă&#x153;MUFS UFTU DJSDVJU

the inverting (â&#x20AC;&#x2DC;-â&#x20AC;&#x2122;) input is at the top (see Fig.8.25). Using your new knowledge from Learn you should be able to calculate the cut-off frequency to be around 159Hz. This means that we should expect it to happily pass low frequency signals below this frequency and reject high frequency signals. In order to test this out weâ&#x20AC;&#x2122;ll simulate the circuit with various frequencies and record the amplitude of the output. We can then plot this in Excel and see the characteristics OF THE Ă&#x161;LTER Start by simulating the circuit with a 1Hz input frequency (ie, set the frequency of the function generator to 1Hz â&#x20AC;&#x201C; Circuit Wizard will do this happily in real time.

'JH .JSSPSJOH UIF PQFSBUJPOBM BNQMJĂ&#x153;FS

You should alter the properties of the graph as follows; maximum: 6V, minimum: 6V, time: 200ms. Your trace should look similar to Fig.8.26. You should also notice that the output (blue) and input (red) are basically identical, meaning that the signal has passed directly through THE Ă&#x161;LTER UNCHANGED Now change the frequency of the signal generator to 100Hz. You will also need to decrease the simulation speed and graph properties. These were 5ms and 2ms in the authorâ&#x20AC;&#x2122;s case, but you should experiment to

'JH " )[ JOQVU USBDF r MPX QBTT Ă&#x153;MUFS

Everyday Practical Electronics, June 2011

get the best results. The resulting waveform is show in Fig.8.27. Notice that the amplitude has been reduced or attenuated to around 4.2V, and the output waveform has been delayed and is out of phase. Experiment with various frequencies between 1Hz and 200Hz, recording your results. When you have a number of results plot them on a graph with frequency along the x-axis and amplitude along the y-axis. If you are using Excel to plot the graph, make sure that you select the â&#x20AC;&#x2DC;scatterâ&#x20AC;&#x2122; graph type, as this will

'JH " )[ JOQVU USBDF r MPX QBTT Ă&#x153;MUFS

Teach-In 2011

ÂŞÂŞ"UILDÂŞnÂŞ4HEÂŞ#IRCUITÂŞ7IZARDÂŞWAY &Ĺ?Ć&#x152;Ć?Ć&#x161; KĆ&#x152;Ä&#x161;Ä&#x17E;Ć&#x152; >Ĺ˝Ç Í˛WÄ&#x201A;Ć?Ć? &Ĺ?ĹŻĆ&#x161;Ä&#x17E;Ć&#x152; Ďą

ĹľĆ&#x2030; Ć&#x2030;ĹŻĹ?Ć&#x161;ĆľÄ&#x161;Ä&#x17E;Í&#x2022; sĹ˝ĹŻĆ&#x161;Ć?

Ď°Í&#x2DC;Ďą

Ď°

ĎŻÍ&#x2DC;Ďą

ĎŻ Ď

ĎĎŹ

ĎĎŹĎŹ

&Ć&#x152;Ä&#x17E;Ć&#x2039;ĆľÄ&#x17E;ĹśÄ?Ç&#x2021;Í&#x2022; ,Ç&#x152;

Fig.8.28. Graph showing the response of the low-pass Ă&#x153;STU PSEFS Ă&#x153;MUFS

'JH 'JSTU PSEFS IJHI QBTT Ă&#x153;MUFS UFTU DJSDVJU

the phase difference. Our results are shown in Fig.8.30.

correctly plot the two values against each other. Fig.8.28 shows our results taking readings every 10Hz.

3ECOND ORDERÂŞlLTERS Now weâ&#x20AC;&#x2122;re going to ramp things up a little and look at second-order filters. Fig.8.31 and Fig.8.32 show a low-pass and highpass second-order Ă&#x161;LTER RESPECTIVELY Use your theory knowledge from Learn to calculate the cut-off frequency for each circuit and use this to help you select an appropriate

(IGH PASSÂŞlLTERÂŞTESTÂŞCIRCUIT %DIT THE LOW PASS Ă&#x161;LTER CIRCUIT BY essentially swapping the capacitor and resistor. You should now have THE Ă&#x161;RST ORDER HIGH PASS Ă&#x161;LTER SHOWN in Fig.8.29. Experiment to see how the output changes with different frequencies from 1Hz to 600Hz recoding your results and plotting them on A GRAPH 9OU SHOULD Ă&#x161;ND THAT IN CONTRAST TO THE LOW PASS Ă&#x161;LTER LOW frequencies are attenuated while higher frequencies are passed unaltered. You should also notice that the lower the frequency the higher

frequency range to test the circuit. Simulate the circuit and collect a series of results in order to help you produce graphs for each circuit showing how they respond.

'JH 4FDPOE PSEFS MPX QBTT Ă&#x153;MUFS UFTU DJSDVJU

&Ĺ?Ć&#x152;Ć?Ć&#x161; KĆ&#x152;Ä&#x161;Ä&#x17E;Ć&#x152; ,Ĺ?Ĺ?Ĺ&#x161;Í˛WÄ&#x201A;Ć?Ć? &Ĺ?ĹŻĆ&#x161;Ä&#x17E;Ć&#x152; Ďą

ĹľĆ&#x2030; Ć&#x2030;ĹŻĹ?Ć&#x161;ĆľÄ&#x161;Ä&#x17E;Í&#x2022; sĹ˝ĹŻĆ&#x161;Ć?

Ď°

ĎŻ

ĎŽ

ĎŹ Ď

ĎĎŹ

ĎĎŹĎŹ

&Ć&#x152;Ä&#x17E;Ć&#x2039;ĆľÄ&#x17E;ĹśÄ?Ç&#x2021;Í&#x2022; ,Ç&#x152;

Fig.8.30. Graph showing the response of the high-pass Ă&#x153;STU PSEFS Ă&#x153;MUFS

'JH 4FDPOE PSEFS IJHI QBTT Ă&#x153;MUFS UFTU DJSDVJU

Everyday Practical Electronics, June 2011

Teach-In 2011

"AND PASSÂŞlLTER

For more information, links and other resources please check out our Teach-In website at:

'JH #BOE QBTT Ă&#x153;MUFS UFTU DJSDVJU

Ä&#x201A;ĹśÄ&#x161; WÄ&#x201A;Ć?Ć? &Ĺ?ĹŻĆ&#x161;Ä&#x17E;Ć&#x152; &Ć&#x152;Ä&#x17E;Ć&#x2039;ĆľÄ&#x17E;ĹśÄ?Ç&#x2021; ZÄ&#x17E;Ć?Ć&#x2030;Ĺ˝ĹśĆ?Ä&#x17E; Ďą Ď°Í&#x2DC;Ďą Ď°

ĹľĆ&#x2030; Ć&#x2030;ĹŻĹ?Ć&#x161;ĆľÄ&#x161;Ä&#x17E;Í&#x2022; sĹ˝ĹŻĆ&#x161;Ć?

Last, we are going to produce a BAND PASS Ă&#x161;LTER USING THE TWO SECOND ORDER Ă&#x161;LTERS %NTER THE CIRCUIT SHOWN IN &IG 9OU MAY Ă&#x161;ND IT QUICKER TO COPY and paste your two second ORDER CIRCUITS ON TO ONE SHEET RATHER THAN DRAWING IT FROM SCRATCH &INALLY BY ALTERING THE INPUT FREQUENCY MONITOR HOW THE Ă&#x161;LTER RESPONDS 2ECORD YOUR RESULTS AND PRODUCE A FREQUENCY RESPONSE GRAPH OUR EXAMPLE IS SHOWN IN &IG 5SING EVERYTHING THAT YOUmVE LEARNT PRODUCE AND TEST A Ă&#x161;LTER CIRCUIT WITH A LOWER CUT OFF FREQUENCY OF (Z AND UPPER CUT OFF FREQUENCY OF K(Z 0ROVE YOUR Ă&#x161;NAL DESIGN BY CREATING A FREQUENCY RESPONSE CURVE

ĎŻÍ&#x2DC;Ďą ĎŻ ĎŽÍ&#x2DC;Ďą ĎŽ ĎÍ&#x2DC;Ďą Ď

www.tooley.co.uk/teach-in

ĎŹÍ&#x2DC;Ďą ĎŹ ĎąĎŹ

'JH SJHIU &YBNQMF CBOE QBTT Ă&#x153;MUFS GSFRVFODZ SFTQPOTF HSBQI

Circuit diagram design with component library * (500 components Standard, 1500 components Professional) Virtual instruments (4 Standard, 7 Professional) * On-screen animation *

Layout * PCB PCB layout simulation * Interactive Automatic PCB routing * Gerber export *

This is the software used in our Teach-In 2011 series. Standard ÂŁ61.25 inc. VAT Professional ÂŁ91.90 inc. VAT See Direct Book Service â&#x20AC;&#x201C; pages 75-77 in this issue

ĎąĎŹĎŹ

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&Ć&#x152;Ä&#x17E;Ć&#x2039;ĆľÄ&#x17E;ĹśÄ?Ç&#x2021;Í&#x2022; ,Ç&#x152;

!NSWERSÂŞTOÂŞ#HECKÂŞ QUESTIONS 8.1. A 3IMPLE C-R UNBALANCED LOW PASS Ă&#x161;LTER B BALANCED 4 NETWORK ATTENUATOR C UNBALANCED LOW PASS S NETWORK ATTENUATOR 8.2. 3EE PAGE 8.3. K(Z 8.4. 6 8.5. M( 8.6. 3EE PAGE 8.7 D" 8.8 M7

Everyday Practical Electronics, June 2011

Teach-In 2011

Investigate Table 8.2.

Frequency (Hz) Voltage gain (dB)

20k

100

200

700

10k

-3

+12.5 +15

+16

+15

+12.5 +5.5

40k

60k

-2

-7.5

The data shown in Table 8.2 was obtained during an experiment on an active tone control. Plot the frequency response curve using the logarithmic grid shown in Fig.8.35 and use it to determine: (a) the maximum value of voltage gain (in dB) (b) the maximum value of voltage gain (expressed as a ratio) (c) the approximate voltage gain at 50Hz and 30kHz (d) the two frequencies at which the voltage gain falls to zero (e) the range of frequencies over WHICH THE GRAPH IS lĂ&#x203A;ATm TO WITHIN -1dB of the maximum

(f) the two frequencies at which the gain has fallen by 6dB from its maximum value.

Fig.8.35. See Investigate

Amaze In most electronic circuits, the signal voltages that we have to deal with range from a few millivolts to a few volts. Similarly, the power levels present in these circuits tend also to be rather modest and usually range from a few milliwatts to a few WATTS )TmS WORTH CONSIDERING A FEW This 50-foot dish antenna at the North Kennedy Space Center is supplied with a power of 3kW from a C-band radar to produce an effective radiated power (ERP) of around 3MW!

examples where signal voltages and power are either very much smaller or very much larger than this. When you receive a signal on your radio or TV at home, the signal voltage present at the input of the radio or TV receiver is often only a few tens or hundreds of microvolts. Since the impedance of the aerial, coaxial cable and input of the receiver is invariably 75:, this suggests that, for a signal of 1 mV, the actual power present at the input of your radio or TV will be in the region of:

V2 Z

3 2

1 u 10

10 6 75

0.0133 Č?W Č?W At the other extreme, consider the power that is delivered to the aerial of a high power transmitting station. This is very much larger. For example, the Crystal Palace TV transmitter currently radiates a power of 1MW (analogue) and 20kW 58

(digital) to reach an estimated viewing population of 11 million people. !FTER lDIGITAL SWITCH OVERm $3/ THE digital power output will increase tenfold to 200kW. If it were possible to absorb all of the currently radiated 1MW of analogue power in a single 50 ohm resistor the voltage generated across the ends of the resistor would be given by:

PuR

1 u 106 u 50

7.07 kV If the 1MW of radiated power from #RYSTAL 0ALACE ISNmT QUITE ENOUGH FOR you, the Boshakova transmitter (used until recently by the Voice of Russia) produced a staggering 2.5MW of output, and its output was radiated by no less than eight guyed masts, each around 250 metres tall.

Next month! )N NEXT MONTHmS 4EACH )N WE WILL look at digital-to-analogue and analogue-to-digital conversion.

Everyday Practical Electronics, June 2011

Products Catalog 2011

50W Audio Power Amplifier HT-AV50W 50+ watts from a 12V battery power supply !! This integrated power output amplifier consists of little more than one integrated circuit. It is intended especially for use in motor vehicles and other battery operated applications. Although it appears simple and hardly worth looking at, the amplifier can produce an appreciable audio power output ! High power output through Class-H operation

80Wx2 Class-D Audio Power Amplifier HT-AU280 With efficiencies as high as 94% - compared to around 50% for Class-AB amplifiersâ&#x20AC;Ś The required installation space is very small thanks to the extremely compact construction. This is primarily made possible by the very high efficiency of the PWM output stage (up to 94%), which reduces the complexity of the circuit and minimises the cooling footprint.

â&#x20AC;Śfrom engineers to engineers

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Teach-In 2011

TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS Part 9: Digital-to-Analogue and Analogue-to-Digital Conversion By Mike and Richard Tooley

N THIS instalment of Teach-In 2011, we introduce some combined applications of analogue and digital circuits in the form of digital-to-analogue and analogueto-digital converters (DAC, ADC). In Learn we explore the circuits and techniques used in DAC and ADC. Investigate extends this further with a look at a popular DAC, which is available from several semiconductor manufacturers. Build looks at some further applications of digital circuits using both combinational and sequential logic techniques. Finally, in Amaze we look at the way that very large numbers are handled in digital systems.

Learn

Quantisation

Because signals in the real world exist in both digital (on/off) and analogue (continuously variable) forms, digital and computer systems need to be able to accept and generate both types of signal as inputs and outputs respectively. Because of this, there is a need for devices that can convert signals in analogue form to their equivalent in digital form, and vice versa. This chapter introduces digitalto-analogue and analogue-to-digital conversion. We shall begin by looking at the essential characteristics of analogue and digital signals and the principle of quantisation.

In order to represent an analogue signal using digital codes, it is necessary to approximate (or quantise) the signal into a set of discrete voltage levels, as shown in Fig.9.1 The sixteen quantisation levels for a simple analogue-to-digital converter using a four-bit binary code are shown in Fig.9.2. Note that, in order to accommodate analogue signals that have both positive and negative polarity we have used the twoâ&#x20AC;&#x2122;s complement representation to indicate negative voltage levels. Thus, any voltage represented by a digital code in which the MSB (most SIGNIĂ&#x161;CANT BIT IS LOGIC WILL BE NEGAtive. Fig.9.3 shows how a typical analogue signal would be quantised Everyday Practical Electronics, July 2011

Teach-In 2011 into voltage levels by sampling at regular intervals (t1, t2, t3, etc).

Digital-to-analogue conversion

Fig.9.1. The process of quantising an analogue signal into its digital equivalent

The basic digital-to-analogue converter (DAC) has a number of digital inputs (often 8, 10, 12, or 16) and a single analogue output, as shown in Fig.9.4. The simplest form of DAC shown in Fig.9.5(a) uses a set of binary-weighted resisTORS TO DEÚNE THE VOLTAGE GAIN OF AN OPERATIONAL SUMMING AMPLIÚER and a four-bit binary latch to store the binary input while it is being converted. .OTE THAT SINCE THE AMPLIÚER IS connected in inverting mode, the analogue output voltage will be negative rather than positive. HowEVER A FURTHER INVERTING AMPLIÚER stage can be added at the output to change the polarity if required. The voltage gain of the inputs to the operational amplifier (determined by the ratio of feedback to input resistance and taking into acCOUNT THE INVERTING CONÚGURATION is shown in Table 9.1. If we assume that the logic levels produced by the four-bit data latch are ‘ideal’ (such that logic 1 corresponds to +5V and logic 0 corresponds to 0V), we can

Fig.9.2. Quantisation levels for a simple ADC that uses a four-bit binary code

Everyday Practical Electronics, July 2011

Fig.9.4. Basic DAC representation

determine the output voltage corresponding to the eight possible input states by summing the voltages that will result from each of the four inputs taken independently. For example, when the output of the latch takes the binary value 1010 the output voltage can be calculated from:

Vout = (–1 × 5) + (–0.5 × 0) + (–0.25 × 5) + (–0.125 × 0) = –6.25V Similarly, when the output of the latch takes the binary value 1111 (the maximum possible) the output voltage can be determined from:

Vout = (–1 × 5) + (–0.5 × 5) + (–0.25 × 5) + (–0.125 × 5) = –9.375V Table 9.1. Table of voltage gains for the simple DAC shown in Fig.9.5(a) Bit 3 (MSB)

Voltage gain –R/R = –1

–R/2R = –0.5

–R/4R = –0.25

0 (LSB)

–R/8R = –0.125

Fig.9.3. An analogue signal quantised into voltage levels by sampling at regular intervals (t1, t2, t3, etc.)

Teach-In 2011 The complete set of voltages corresponding to all eight possible binary codes is given in Table 9.2.

Binary-weighted DAC

An improved binary-weighted DAC is shown in Fig.9.5(b). This circuit operates on a similar principle to that shown in Fig.9.5(a), but uses four analogue switches instead of a four-bit data latch. The analogue

switches are controlled by logic inputs so that a switchâ&#x20AC;&#x2122;s output is connected to the reference voltage (Vref) when its respective logic input is at logic 1, and to 0V when the corresponding logic input is at logic 0. When compared with the previous arrangement, this circuit offers the advantage that the reference voltage is considerably more accurate and stable than using the logic level to

DEĂ&#x161;NE THE ANALOGUE OUTPUT VOLTAGE A further advantage arises from the fact that the reference voltage can be made negative, in which case the analogue output voltage will become positive. Typical reference voltages are â&#x20AC;&#x201C;5V, â&#x20AC;&#x201C;10V, +5V and +10V. Unfortunately, by virtue of the range of resistance values required, the binary-weighted DAC becomes increasingly impractical for higher resolution applications. Taking a 10-bit circuit as an example, and assuming that the basic value of R is 1k:, the binary weighted values would become: Bit 0 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 Bit 8 Bit 9

1k: 2k: 4k: 8k: 16k: 32k: 64k: 128k: 256k:

Table 9.2. Output voltages produced by the simple DAC shown in Fig.9.5(a) Bit 3 Bit 2

Fig.9.5. Simple DAC arrangements

Bit 1

Bit 0

Output voltage

â&#x20AC;&#x201C;0.625V

â&#x20AC;&#x201C;1.250V

â&#x20AC;&#x201C;1.875V

â&#x20AC;&#x201C;2.500V

â&#x20AC;&#x201C;3.125V

â&#x20AC;&#x201C;3.750V

â&#x20AC;&#x201C;4.375V

â&#x20AC;&#x201C;5.000V

â&#x20AC;&#x201C;5.625V

â&#x20AC;&#x201C;6.250V

â&#x20AC;&#x201C;6.875V

â&#x20AC;&#x201C;7.500V

â&#x20AC;&#x201C;8.125V

â&#x20AC;&#x201C;8.750V

â&#x20AC;&#x201C;9.375V

Everyday Practical Electronics, July 2011

Teach-In 2011

Fig.9.6. Filtering the output of a DAC

)N ORDER TO ENSURE A SUFÚCIENTLY HIGH DEGREE OF ACCURACY ALL OF THESE RESISTORS WOULD NEED TO BE CLOSE TOLER ANCE TYPES TYPICALLY OR BETTER ! MORE PRACTICAL ARRANGEMENT USES AN OPERATIONAL AMPLIÚER IN WHICH THE INPUT VOLTAGE TO THE OPERATIONAL AM PLIÚER IS DETERMINED BY MEANS OF AN R-2R LADDER AS SHOWN IN &IG C .OTE THAT ONLY TWO RESISTANCE VALUES ARE REQUIRED AND THAT THEY CAN BE ANY CONVENIENT VALUE PROVIDED THAT ONE VALUE IS DOUBLE THE OTHER IT IS RELA TIVELY EASY TO MANUFACTURE MATCHED HIGH STABILITY RESISTANCES OF CLOSE TOL ERANCE ON AN INTEGRATED CIRCUIT CHIP

OUTPUT VOLTAGES BUT IN PRACTICE WE WOULD PROBABLY REQUIRE MANY MORE AND CORRESPONDINGLY SMALLER INCRE MENTS IN OUTPUT VOLTAGE 4HIS CAN BE ACHIEVED BY ADDING FURTHER BINARY INPUTS &OR EXAMPLE A $!# WITH EIGHT INPUTS IE AN BIT $!# WOULD BE CAPABLE OF PRODUCING IE OR TWO RAISED TO THE POWER EIGHT DIFFERENT OUTPUT VOLTAGE ! BIT DEVICE ON THE OTHER HAND WILL PRODUCE IE OR TWO RAISED TO THE POWER TEN DIFFERENT VOLTAGE LEVELS 4HE RESOLUTION OF A $!# IS GENERALLY STATED IN TERMS OF THE NUMBER OF BINARY DIGITS IE BITS USED IN THE CONVERSION

Accuracy and resolution

Please note!

4HE ACCURACY OF A $!# DEPENDS NOT ONLY ON THE VALUES OF THE RESISTANCE USED BUT ALSO ON THE REFERENCE VOLT AGE USED TO DEÚNE THE VOLTAGE LEVELS 3PECIAL BAND GAP REFERENCES SIMI LAR TO PRECISION :ENER DIODES ARE NORMALLY USED TO PROVIDE REFERENCE VOLTAGES THAT ARE CLOSELY MAINTAINED OVER A WIDE RANGE OF TEMPERATURE AND SUPPLY VOLTAGES 4YPICAL ACCURA CIES OF BETWEEN AND CAN BE ACHIEVED USING MOST MODERN LOW COST $!# DEVICES 4HE RESOLUTION OF A $!# IS AN INDICATION OF THE NUMBER OF INCRE MENTS IN OUTPUT VOLTAGE THAT IT CAN PRODUCE AND IT IS DIRECTLY RELATED TO THE NUMBER OF BINARY DIGITS USED IN THE CONVERSION 4HE TWO SIMPLE FOUR BIT $!#S THAT WE MET EARLIER CAN EACH PROVIDE SIXTEEN DIFFERENT Everyday Practical Electronics, July 2011

The resolution OF A $!# DEPENDS ON THE NUMBER OF BITS USED IN THE CON VERSION PROCESSrTHE MORE BITS THE GREATER THE RESOLUTION 4YPICAL $!#S HAVE RESOLUTIONS OF OR BITS

Please note!

The accuracy OF A $!# DEPENDS ON THE ACCURACY OF THE RESISTANCE VALUES USED AS WELL AS THE ACCURACY OF THE REFERENCE VOLTAGE 4YPICAL $!#S HAVE ACCURACIES OF OR

Filters !S WE HAVE SEEN THE OUTPUT OF A $!# CONSISTS OF A SERIES OF QUANTISED VOLTAGE LEVELS 4HE PRESENCE OF THESE LEVELS ON THE OUTPUT SIGNAL CAN BE UNDESIRABLE FOR SOME APPLICATIONS AND HENCE THEY ARE REMOVED IN ORDER TO lSMOOTHm THE OUTPUT VOLTAGE

Fig.9.7. Basic ADC representation

4HIS CAN BE EASILY ACCOMPLISHED BY PASSING THE OUTPUT SIGNAL THROUGH A LOW PASS ÚLTER AS SHOWN IN &IG 4HE ÚLTER IS DESIGNED SO THAT THE RESIDUAL SAMPLING FREQUENCY COM PONENTS IE THOSE THAT CAUSE THE lSTEPSm IN THE ANALOGUE SIGNAL ARE WELL BEYOND THE CUT OFF FREQUENCY OF THE ÚLTER AND ARE SUBJECT TO AN APPRECIABLE AMOUNT OF ATTENUATION

Analogue-to-digital conversion 4HE BASIC ANALOGUE TO DIGITAL CON VERTER !$# HAS A SINGLE ANALOGUE INPUT AND A NUMBER OF DIGITAL OUT PUTS OFTEN OR LINES AS SHOWN IN &IG 6ARIOUS FORMS OF ANALOGUE TO DIGITAL CONVERTER ARE AVAILABLE FOR USE IN DIFFERENT APPLICATIONS INCLUD ING MULTI CHANNEL !$#S WITH UP TO ANALOGUE INPUTS 4HE SIMPLEST FORM OF !$# IS THE ÛASH CONVERTER SHOWN IN &IG A )N THIS TYPE OF !$# THE INCOMING ANALOGUE VOLTAGE IS COMPARED WITH A SERIES OF ÚXED REFERENCE VOLTAGES USING A NUMBER OF OPERATIONAL AMPLIÚERS )# TO )# IN &IG 7HEN THE ANALOGUE INPUT VOLTAGE EXCEEDS THE REFERENCE 49

Teach-In 2011 voltage present at the inverting input OF A PARTICULAR OPERATIONAL AMPLIĂ&#x161;ER stage, the output of that stage will go to logic 1. So, assuming that the analogue input voltage is 2V, the outputs of IC1 and IC2 will go to logic 1 while the remaining outputs will be at logic 0. The priority encoder is a logic device that produces a binary output code that indicates the value of the MOST SIGNIĂ&#x161;CANT LOGIC RECEIVED ON one of its inputs. In this case, the output of IC2 will be the most sigNIĂ&#x161;CANT LOGIC AND HENCE THE BINARY output code generated will be 010 (as shown in Fig.9.8(b). Flash ADC are extremely fast in operation (hence the name), but they become rather impractical as the resolution increases. For example, AN BIT Ă&#x203A;ASH !$# WOULD REQUIRE OPERATIONAL AMPLIĂ&#x161;ER COMPARATORS while a 10-bit ADC would need a staggering 1024 comparator stages! Typical conversion times for a FLASH !$# LIE IN THE RANGE NS TO 1Ps, so this type of ADC is ideal for â&#x20AC;&#x2DC;fastâ&#x20AC;&#x2122; or rapidly changing analogue signals. Due to their complexity, flash ADC are relatively expensive.

Successive approximation

A successive approximation ADC is shown in Fig.9.9. This shows an 8-bit converter that uses a DAC (usually

'JH " TJNQMF Ă?BTI "%$

based on an R-2R ladder) together WITH A SINGLE OPERATIONAL AMPLIĂ&#x161;ER comparator (IC1) and a successive approximation register (SAR). The 8-bit output from the SAR is applied to the DAC and to an 8-bit output latch. A separate end of conversion (EOC) signal (not shown in Fig.9.9) is generated to indicate that the conversion process is complete and the data is ready for use. When a start conversion (SC) signal is received, successive bits

Fig.9.9. A successive approximation ADC

within the SAR are set and reset according to the output from the comparator. At the point at which the output from the comparator reaches zero, the analogue input voltage will be the same as the analogue output from the DAC and, at this point, the conversion is complete. The end of conversion signal is then generated and the 8-bit code from the SAR is read as a digital output code. Successive approximation ADCs ARE SIGNIĂ&#x161;CANTLY SLOWER THAN Ă&#x203A;ASH

Fig.9.10. A ramp-type ADC

Everyday Practical Electronics, July 2011

Teach-In 2011 types and typical conversion times (ie, the time between the SC and EOC signals) are in the range 10Ps to 100Ps. Despite this, conversion times are fast enough for most non-critical applications, and this type of ADC is relatively simple and available at low-cost.

Ramping it up

A ramp-type ADC is shown in Fig.9.10. This type of ADC USES A RAMP GENERATOR AND A SINGLE OPERATIONAL AMPLIÚER comparator, IC1. The output of the comparator is either a 1 or a 0 depending on whether the input voltage is greater or less than the instantaneous value of the ramp voltage. The output of the comparator is used to control a logic gate (IC2) which passes a clock signal (a square wave of accurate frequency) to the input of a pulse counter whenever the input voltage is greater than the output from the ramp generator.

Fig.9.11. Waveforms for a single-ramp ADC

The pulses are counted until the voltage from the ramp generator exceeds that of the input signal, at which point the output of the comparator goes low and no further pulses are passed into the counter. The number of clock pulses counted will depend on the input voltage and the ÚNAL BINARY COUNT THUS GIVES A DIGITAL representation of the analogue input. Typical waveforms for the ramp-type waveform are shown in Fig.9.11.

Dual-slope ADC &INALLY THE DUAL SLOPE !$# IS A REÚNEment of the ramp-type ADC, which

Fig.9.12. Waveforms for a dual-ramp ADC

Check – How do you think you are doing? 9.1. Explain with the aid of a sketch what is meant by quantisation. 9.2. A DAC can produce 256 different output voltages. What is the resolution of the DAC? 9.3. How many discrete voltage levels can be produced by a 10bit DAC? 9.4. Explain the advantage of an R-2R ladder DAC compared a binary-weighted DAC. 9.5. 3TATE THE ADVANTAGE OF A ÛASH ADC and suggest an application in which it can be used.

Everyday Practical Electronics, July 2011

9.6. The binary codes produced by a four-bit bipolar analogue-todigital converter (see Fig.9.2 and Fig.9.3) sampled at intervals of 1ms, have the following values: Time (ms) 0 1 2 3 4 5 6 7

Binary code 0101 0100 0011 0010 0001 0000 1111 1110

If the ADC uses two’s complement to represent negative values (ie, 1111 represents -1, 1110 represents -2, and so on) sketch and identify the waveform of the analogue voltage. For more information, links and other resources please check out our Teach-In website at:

www.tooley.co.uk/ teach-in

Teach-In 2011 involves a similar comparator arrangement, but uses an internal voltage REFERENCE AND AN ACCURATE Ă&#x161;XED SLOPE negative ramp which starts when the positive going ramp reaches the analogue input voltage. The important thing to note about this type of ADC is that, while the slope of the positive ramp depends on the input voltage, THE NEGATIVE RAMP FALLS AT A Ă&#x161;XED RATE Hence, this type of ADC can provide a very high degree of accuracy and can also be made so that it rejects noise and random variations present on the input signal. The main disadvantage, HOWEVER IS THAT THE PROCESS OF Ă&#x161;RST ramping up and then ramping down requires some considerable time, and hence this type of ADC is only suitable for â&#x20AC;&#x2DC;slowâ&#x20AC;&#x2122; signals (ie, those that are not rapidly changing). Typical conversion times lie in the range 500Ps to 20ms.

Fig.9.13. A simple four-bit binary-weighted DAC

Fig.9.14. Graph of results for the simple four-bit binary-weighted DAC

N this edition of Build we will try out some of the DAC circuits that we introduced in Learn (Fig.9.5). As we have seen, these can be conSTRUCTED USING OPERATIONAL AMPLIĂ&#x161;ERS with cleverly arranged arrays of input resistors.

Binary-weighted DAC

'JH 5IF NPEJĂ&#x153;FE GPVS CJU CJOBSZ XFJHIUFE %"$ ^Ĺ?ĹľĆ&#x2030;ĹŻÄ&#x17E; Ĺ?Ć&#x161;Í˛tÄ&#x17E;Ĺ?Ĺ?Ĺ&#x161;Ć&#x161;Ä&#x17E;Ä&#x161; tĹ?Ć&#x161;Ĺ&#x161; hĹśĹ?Ć&#x161;Ç&#x2021; /ĹśÇ&#x20AC;Ä&#x17E;Ć&#x152;Ć&#x161;Ä&#x17E;Ć&#x152; ĎĎŹ

Fig.9.16. Graph of results for UIF NPEJĂ&#x153;FE four-bit binaryweighted DAC shown in Fig. 9.15

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First enter the simple binary-weighted DAC circuit shown in Fig.9.13. This is a practical circuit based on the one shown in Learn Fig.9.5(a). We have used a series of logic input toggles to simulate standard logic level inputs, with the output voltage shown on a virtual voltmeter instrument. Set various input bit patterns and monitor the resulting output voltage. Using your theory from Learn to calculate the expected output voltage for two different input bit patterns and then test your answers using the simulation. Take readings of the output voltage for the binary coded decimal inputs from 0 (0000) to 15 (1111) and produce a graph of your results. Fig.9.14 shows our example results plotted using Microsoft Excel.

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Ď´

Ďľ

ĎĎŹ

ĎĎ

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Everyday Practical Electronics, July 2011

Teach-In 2011

Build â&#x20AC;&#x201C; The Circuit Wizard way One of the drawbacks to the simple DAC circuit is the fact that by USING AN OPERATIONAL AMPLIĂ&#x161;ER IN AN INVERTING CONĂ&#x161;GURATION THE OUTput is negative. A common way of dealing with this issue is to add an ADDITIONAL INVERTING AMPLIĂ&#x161;ER WITH a gain of -1. This is often referred to as a unity gain inverter. Modify your binary-weighted DAC circuit (Fig.9.13) to that shown in Fig.9.15 below, and experiment with changing the input bits. Notice that THE OUTPUT OF THE Ă&#x161;RST OPERATIONAL AMPLIĂ&#x161;ER 6 IS EQUAL IN MAGNItude to the output voltage (Vout) but opposite in polarity. Plotting Vout against BCD input for this new arrangement should now look as shown in Fig.9.16. ! FURTHER MODIĂ&#x161;CATION TO THE binary-weighted DAC is shown in Fig.9.17. Here the output voltage is taken across the outputs of THE TWO OPERATIONAL AMPLIĂ&#x161;ERS In this way the output voltage is effectively doubled. In fact, this method is commonly employed in many commercial DAC integrated circuit devices.

Fig.9.17. Improved binary weighted DAC with differential output

A switch in time

In Fig.9.5(b) we described an improved DAC circuit using analogue SWITCHES 7E CAN MODEL THIS QUITE simply for simulation purposes using single-pole double-throw (SPDT) switches, as shown in Fig.9.18. Note that in a real circuit these would be controlled by logic inputs. Simulate the circuit by changing the binary input patterns by toggling switches SW1 to SW4. Notice that by having a negative reference voltage we achieve a positive output voltage. Experiment by changing the

Fig.9.18. Binary-weighted DAC using analogue switches and a negative voltage reference

Everyday Practical Electronics, July 2011

reference voltage (Vref) and note how this affects the output voltage range.

On the ladder

Finally, we will try out a third type of DAC circuit that utilises a so called R-2R resistor ladder arrangement, like that shown earlier in Fig.9.5(c). As we discussed in Learn, there are practical advantages to this type of CIRCUIT FOR EXAMPLE ONLY REQUIRING one matched pair of resistor values. Construct the circuit shown in Fig.9.19 and experiment with the simulation.

Fig.9.19. Four-bit DAC using an R-2R ladder arrangement

Teach-In 2011

Investigate ADCs and DACs invariably take the form of integrated circuit devices. Obtain data sheets for a DAC0800 digital-to-analogue converter (these can be freely downloaded from the websites of semiconductor manufacturers like National Semiconductor and Motorola) and use them to answer each of the following questions: 1. How many data bits are used? 2. What range of supply voltages can be used with this device? 3. What package styles are used for

the device and how many connecting pins do the packages have? 4. What is the typical power consumption of the device when used with a Âą10V supply? 5. What is the absolute maximum power dissipation for the device? 6. Which pins are used for (a) the LSB input and (b) the MSB input? 7. On what principle does the DAC operate? 8. What is the typical time taken for the output voltage to settle in response to a change at the input?

Amaze As you have seen, the resolution of a DAC or ADC is determined by the number of data bits that it uses. The simple four-bit DAC that you met in Build was only capable of generating sixteen different voltage states. By increasing the number of bits we can gain a corresponding increase in THE RESOLUTION 3O A Ă&#x161;VE BIT $!# CAN produce 32 different output voltages, a six-bit DAC is able to produce 64 different output levels, and so on. In many applications, the digital output of an ADC is processed using a computer or some form of embedded processor (such as those used in the engine control and management systems of motor vehicles). The unit of data in a computer (ie, the number of bits that can be handled

by its processing unit as one single entity) is referred to as a word. So, ultimately, the digital output of an ADC must be converted into words that the computer or embedded systemâ&#x20AC;&#x2122;s processor can operate on. The number of bits in a word is an important characteristic of a particular processor family or computer architecture. This, in turn, has an impact on the size and range of the quantities that it can manipulate. Early computers, such as the IBM PC and Commodore Amiga, as well as early console systems, such as the Sega Genesis, Super Nintendo, Mattel Intellivision, used a word length of 16-bits. This allowed them to manipulate integer numbers having a total of 65,536 different values.

Layout * PCB Interactive PCB layout simulation * Automatic PCB routing * Gerber export * This is the software used in our Teach-In 2011 series. Standard ÂŁ61.25 inc. VAT Professional ÂŁ91.90

Circuit diagram design with component library * (500 components Standard, 1500 components Professional) Virtual instruments (4 Standard, 7 Professional) * On-screen animation *

inc. VAT. See Direct Book Service â&#x20AC;&#x201C; pages 75-77 in this issue

Answers to Check questions 9.1. See page 46 and Fig.9.1 9.2. 8-bit 9.3. 1024 9.4. Only two values are needed in the resistor chain of an R-2R ladder (the ratio of the two resistances is more important than their absolute values). The resistance values in a binary-weighted DAC can become very large when a large number of bits are used 9.5. High speed of operation. A typical application would be for use with high-quality audio and video signals (ie, analogue signals at relatively high frequencies) 9.6. Falling ramp (the analogue value falls linearly) More powerful 32-bit computers (such as the Apple Macintosh, Pentium-based PC and popular console systems, including the Sony PlayStation, Nintendo GameCube, Xbox, and Wii) have word lengths of 32-bits and this allows them to manipulate integer numbers that can represent 4,294,967,296 different values. However, if thatâ&#x20AC;&#x2122;s not quite enough in terms of resolution, the most recent 64-bit systems including some games consoles, such as Nintendo 64, PlayStation 2, PlayStation 3, Xbox 360, can cope with integer numbers having a staggering 18,446,744,073,709,551,616 different values!

Next month!

In next monthâ&#x20AC;&#x2122;s Teach-In we will look at practical aspects of test instruments, measurements and testing circuits (including an introduction to PCB layout using Circuit Wizard). Everyday Practical Electronics, July 2011

HandsOn Technology

http://www.handsontec.com

USB-RS232 Interface Card: HT-MP213 A compact solution for missing portsâ&#x20AC;Ś Thanks to a special integrated circuit from Silicon Laboratories, computer peripherals with an RS232 interface are easily connected to a USB port. This simple solution is ideal if a peripheral does not have a USB port, your notebook PC has no free RS232 port available, or none at all ! After a slow and faltering start, the USB port has become commonplace on PCs, to the extent that the latest GHz machines have just one RS232 port left, or none at all. The compact USB-RS232 interface described in this article allows your good old RS232 peripherals (printer, programmer system, etc.) to be hooked up to a USB port. The free driver programs for Win 2000/XP, Linux and Apple Macintosh make the interface virtually transparent, enabling the USB port to behave like a regular COM interface. The driver and the conversion chip from Silicon Laboratories allow a full serial data link to be set up on a 9-way RS232 connector, including all handshaking signals.

1. THE SILICON LABORATORIES CP2103 SYSTEMS OVERVIEW The CP2103 is a highly-integrated USB-to-UART Bridge Controller providing a simple solution for updating RS232/RS-485 designs to USB using a minimum of components and PCB space. The simplified block diagram of the CP2103 is shown in Figure 1 and the pin assignment, in Figure 2. Royalty-free Virtual COM Port (VCP) device drivers provided by Silicon Laboratories allow a CP2103-based product to appear as a COM port to PC applications. The CP2103 UART interface implements all RS-232/RS-485 signals, including control and handshaking signals, so existing system firmware does not need to be modified. The device also features up to (4) GPIO signals that can be user-defined for status and control information. Support for I/O interface voltages down to 1.8 V is provided via a VIO pin. In many existing RS-232 designs, all that is required to update the design from RS-232 to USB is to replace the RS-232 level-translator with the CP2103. Silicon Laboratories has taken care of the PC side of things by supplying royalty-free Virtual COM Port (VCP) device drivers. If you've ever used a PC RS-232-to-USB converter, you know that it looks like a standard COM port to the PC and its applications. The VCP device driver also pretends to be a standard COM port. That means that we can use our newly acquired microcontroller USB interface to communicate with a Tera Term Pro terminal window on a computer just as if we were using RS-232 hardware on the embedded side.

2. HT-MP213 USB-to-RS232 CONVERTER BOARD The HT-MP213 is designed to transition a piece of hardware from an RS-232/485 interface to a USB interface. We were attracted to the CP2103 because of its skinny schematic diagram. If we believe what the CP2103 datasheet schematic is telling us, it doesn't require any external resistors or crystals to bring a fully compliant USB 2.0 interface to life. The silicon encapsulates a level 2.0 full-speed function controller, transceiver, EEPROM, oscillator, and UART in a tiny QFN-28 package. The internal EEPROM is used for storing vendor-specific information in commercial applications. If we find that we need to access the EEPROM, there is easy access and programming via its USB interface.

Teach-In 2011

TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS Part 10: Electronic circuit construction and testing By Mike and Richard Tooley

Our Teach-In series aims to provide you with a broad-based introduction to electronics. We have attempted to provide coverage of three of the most important electronics units that are currently studied in many schools and colleges in the UK. These include Edexcel BTEC Level 2 awards as well as electronics units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced reader with ANÂŞOPPORTUNITYÂŞTOÂŞhBRUSHÂŞUPvÂŞONÂŞSPECIlCÂŞTOPICSÂŞWITHÂŞWHICHÂŞHEÂŞORÂŞSHEÂŞMAYÂŞBEÂŞLESSÂŞFAMILIAR ÂŞ %ACHÂŞPARTÂŞOFÂŞOURÂŞ4EACH )NÂŞSERIESÂŞISÂŞORGANISEDÂŞUNDERÂŞlVEÂŞMAINÂŞHEADINGS ÂŞ,EARN ÂŞ#HECK ÂŞ"UILD ÂŞ)NVESTIGATEÂŞANDÂŞ !MAZE ÂŞ,EARNÂŞWILLÂŞTEACHÂŞYOUÂŞTHEÂŞTHEORY ÂŞ#HECKÂŞWILLÂŞHELPÂŞYOUÂŞTOÂŞCHECKÂŞYOURÂŞUNDERSTANDING ÂŞANDÂŞ"UILDÂŞWILLÂŞGIVEÂŞ you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge WHICHÂŞWILLÂŞALLOWÂŞYOUÂŞTOÂŞFURTHERÂŞEXTENDÂŞYOURÂŞLEARNINGÂŞANDÂŞlNALLYÂŞ!MAZEÂŞWILLÂŞSHOWÂŞYOUÂŞTHEÂŞ@WOWÂŞFACTOR ÂŞÂŞ

HIS month, we look at the practical aspects

of electronic circuit construction and testing. In Learn we introduce you to two of the most common and versatile items of test equipment, the multimeter and oscilloscope. Build looks at techniques that can be used to design, construct and test printed circuit boards (PCB) within Circuit Wizard. Investigate involves taking measurements and FAULT Ă&#x161;NDING ON A SIMPLE VOLTAGE REGULATOR CIRCUIT Finally, Amaze looks at the reliability of electronic components.

p Displaying waveforms and making measurements of voltage (peak and peak-to-peak) and time using an oscilloscope.

Learn

At BTEC Level 1 and Level 2 you need to be able to make measurements on simple DC and AC circuits including:

p Measuring voltage, current and resistance using a multi-range meter (or multimeter)

Fig.10.1. Multimeters can be either analogue (left) or digital (right)

Everyday Practical Electronics, August 2011

Teach-In 2011 In all cases, you will need to ensure that you work safely and observe correct procedures (for example, switching off and disconnecting the power supply before connecting test leads). We begin this monthâ&#x20AC;&#x2122;s Learn by introducing the test instruments that you will be using.

Multimeters

One of the most common, versatile and easy-to-use instruments is the multi-range meter, or multimeter. This instrument combines the functions of a voltmeter, ammeter and ohmmeter into a single instrument. Many multimeters also have additional ranges, for example to check continuity, measure capacitance or to check diodes and transistors. Most multimeters operate from internal batteries, and are thus independent of the mains supply. This allows you to easily carry them around and make measurements on electronic equipment when you are away from the laboratory or workshop. There are two main types of multimeter: analogue and digital (see Fig.10.1). Analogue multimeters employ conventional moving coil MOVEMENTS THE DISPLAY TAKES THE form of a pointer moving across a calibrated scale. This arrangement is not so convenient to use as that employed in digital instruments because the position of the pointer is rarely exact and may require interpolation. Analogue instruments do, however, offer some advantages, not least, is that itâ&#x20AC;&#x2122;s very easy to make adjustments to a circuit, while observing THE RELATIVE DIRECTION OF THE POINTER a movement in one direction representing an increase and in the other a decrease. Despite this, the main disadvantage of analogue meters is the rather cramped and sometimes confusing scale calibration. To determine THE EXACT READING REQUIRES Ă&#x161;RST AN

Fig.10.2. A comparison of the displays provided on analogue and digital multimeters. Both meters indicate the same value.

estimation of the pointerâ&#x20AC;&#x2122;s position, and then the application of some mental arithmetic based on the range switch setting (see Fig.10.2) Unlike their analogue counterparts, digital multimeters are usually extremely easy to read and have displays that are clear, unambiguous, and capable of providing a very high resolution. It is also possible to distinguish between

readings that are very close. This is just not possible with an analogue instrument. Digital multimeters offer a number OF SIGNIĂ&#x161;CANT ADVANTAGES WHEN COMpared with their analogue counterPARTS 4HE DISPLAY Ă&#x161;TTED TO A DIGITAL multimeter usually consists of a 3Â˝-digit seven-segment displayâ&#x20AC;&#x201D; THE Â&#x2022; SIMPLY INDICATES THAT THE Ă&#x161;RST digit is either blank (zero) or 1.

Fig.10.3. The procedure for making current and voltage measurements using a digital multimeter

Everyday Practical Electronics, August 2011

Teach-In 2011 Consequently, the maximum indication on the 2V range will be 1.999V. This suggests that the instrument is capable of offering a resolution of 1mV on the 2V range (in other words, the smallest increment in voltage that can be measured is 1mV). Depending on the size and calibration markings on the instrumentâ&#x20AC;&#x2122;s scale, the resolution obtained from a comparable analogue meter would typically be about 50mV, and so the digital instrument provides us with a resolution that is many times greater than its analogue counterpart.

Multimeter measurements

The procedure for making current and voltage measurements using a digital multimeter, is shown in Fig.10.3. Weâ&#x20AC;&#x2122;ve chosen this type of instrument for our example because you will probably be using a modern digital instrument rather than an older analogue type. Note how it is necessary to break the circuit and insert the meter when making a current measurement. Notice also how the voltmeter is connected in parallel with the circuit at the point at which you are making a measurement. It is essential that you get these two connections right and that you select the correct ranges on the multimeter. Failure to observe these two simple precautions can result in damage to the meter and/or the circuit under test! In Fig. 10.3, one of the meters is used to measure the supply current (note that the circuit must be broken and the meter inserted into it), while the second instrument is being used to measure the potential difference (voltage drop) across diode D1. The initial range settings (200mA for the current measurement, and 20V for the voltage measurement) are chosen so that they are both greater than those that we would expect to Ă&#x161;ND IN THE CIRCUIT &OR EXAMPLE WE 44

WOULD CALCULATE THE CURRENT Ă&#x203A;OWING in the circuit to be (9 â&#x20AC;&#x201C; 5.6)/100 amps or 34mA. Similarly, we could assume that the voltage that we would measure should be 5.6V (the same as the Zener voltage), but in no event would we expect it to be greater than the supply voltage (9V). We have, therefore, left quite a margin for safety with the two ranges that weâ&#x20AC;&#x2122;ve selected!

Please note!

It is essential to switch off and disconnect the power supply before attempting to connect test leads. When the meter ranges have been set and the connections made, the supply can be reinstated and switched back on, so that measurements can be made.

Please note!

In your school/college course you will only be working with equipment that uses safe low voltage supplies. Even so, it is essential to observe Health and Safety precautions whenever you are working on live electrical and electronic circuits. When in doubt, you should always refer to your tutor!

Please note!

When the circuit on test uses large value capacitors it may be necessary to wait a few minutes in order to allow them to discharge safely before making connections to the circuit.

as these can cause short-circuits to adjacent connections!

Oscilloscopes

Oscilloscopes can be used in a variety of measuring applications, the most important of which is the display of time related voltage waveforms. Older oscilloscopes (Fig.10.4) used cathode ray tubes (CRT) for their displays. In order to make accurate measurements, the face of the CRT WAS Ă&#x161;TTED WITH A graticule that was either integral with the tube or took the form of a separate translucent sheet. Modern oscilloscopes use Ă&#x203A;AT ,#$ DISPLAYS EITHER COLOUR OR monochrome, which incorporate an electronically generated measuring scale. Accurate voltage and time measurements are made with reference to the scale or graticule, applying a scale factor derived from the appropriate range switch. The use of the graticule is illustrated by the following example. An oscilloscope screen is depicted in Fig.10.5. This diagram is reproduced at a reduced size. If shown full-size, the gratical markings would be spaced AT CM AND THE Ă&#x161;NE GRATICULE MARKINGS would be every 2mm along the central vertical and horizontal axes. The oscilloscope is operated with ALL RELEVANT CONTROLS IN THE l#!,m position. The timebase (horizontal DEĂ&#x203A;ECTION IS SWITCHED TO THE MS CM

Please note!

Make sure that you only use properly insulated test leads to make connections to a circuit on test. The leads SHOULD BE Ă&#x161;TTED WITH clips and probes to make connections to a circuit. Never use bare Fig.10.4. A typical two-channel general purpose oscilwires and test prods loscope that uses a CRT display Everyday Practical Electronics, August 2011

Teach-In 2011 RANGE AND THE VERTICAL ATTENUATOR VERTICAL DEÛECTION IS SWITCHED TO THE 6 CM RANGE 4HE OVERALL HEIGHT OF THE TRACE IS CM AND THUS THE PEAK TO PEAK VOLTAGE IS ¯ 6 6 3IMILARLY THE TIME FOR ONE COMPLETE CYCLE PERIOD IS ¯ MS MS /NE FURTHER IMPORTANT PIECE OF INFORMATION IS THE SHAPE OF THE WAVEFORM THAT IN THIS CASE IS SINUSOIDAL 4HE FUNCTION OF SOME OF THE MORE COMMON CONTROLS AND ADJUSTMENTS FOR A GENERAL PURPOSE OSCILLOSCOPE ARE LISTED IN 4ABLE

Fig.10.7. A typical display produced by a PC-based virtual oscilloscope

Fig.10.5. Using an oscilloscope scale

Please note! "EFORE TAKING MEANINGFUL MEASUREMENTS FROM A #24 SCREEN IT IS ABSOLUTELY ESSENTIAL TO ENSURE THAT THE FRONT PANEL VARIABLE CONTROLS ARE SET IN THE calibrate #!, POSITION 2ESULTS WILL ALMOST CERTAINLY BE INACCURATE IF THIS IS NOT THE CASEØ

BECOME AVAILABLE 2ATHER THAN USING CONVENTIONAL ANALOGUE DIGITAL OR #24 DISPLAYS THESE virtual instruments USE PLUG IN ADAPTERS OR 53" CONNECTED INTERFACES TOGETHER WITH A 0# EITHER DESKTOP OR LAPTOP 4HE INTERFACE CIRCUIT CAPTURES A DIGITAL SAMPLE OF THE ANALOGUE INPUT WHICH CAN THEN BE STORED IN MEMORY AND RECALLED FOR LATER DISPLAY 6IRTUAL INSTRUMENTS OFFER A NUMBER OF ADVANTAGES WHEN COMPARED WITH CONVENTIONAL TEST INSTRUMENTS INCLUDING THE ABILITY TO DISPLAY WAVEFORM PARAMETERS SUCH AS TIME VOLTAGE FREQUENCY AND PHASE AS WELL AS BEING ABLE TO STORE RECALL AND PRINT WAVEFORM DATA ! TYPICAL VIRTUAL SOUNDCARD OSCILLOSCOPE DISPLAY IS SHOWN IN &IG

Oscilloscope measurements ! TYPICAL OSCILLOSCOPE MEASUREMENT IS SHOWN IN &IG )N THIS APPLICATION THE OSCILLOSCOPE IS BEING USED TO DISPLAY THE WAVEFORMS IN A SIMPLE HALF WAVE RECTIÚER POWER SUPPLY !S WITH THE MULTIMETER MEASUREMENTS THAT WE MET EARLIER IT IS ESSENTIAL TO MAKE INITIAL ADJUSTMENTS TO THE OSCILLOSCOPE "%&/2% CONNECTING THE OSCILLOSCOPE TO THE CIRCUIT AND SWITCHING ON THE SUPPLY /NCE AGAIN WHEN IN DOUBT YOU SHOULD REFER TO YOUR TUTORØ

Virtual instruments )N RECENT YEARS A NEW TYPE OF ELECTRONIC MEASURING INSTRUMENT HAS

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Everyday Practical Electronics, August 2011

Teach-In 2011 Table 10.1. Oscilloscope controls and adjustments

Control Focus Intensity Astigmatism Trace rotation Scale illumination Horizontal deflection system Timebase (time/cm)

Stability Trigger level Trigger slope Trigger source

Horizontal position Vertical deflection system Vertical attenuator (V/cm)

Vertical position AC-DC-ground

Chopped-alternate

Adjustment Provides a correctly focused display on the screen Adjusts the brightness of the display Provides a uniformly defined display over the entire screen area and in both x and y directions. The control is normally used in conjunction with the focus and intensity controls Permits accurate alignment of the display with respect to the graticule (CRT displays only) Controls the brightness of the graticule or scale Adjusts the timebase range and sets the horizontal time scale. Usually this control takes the form of a multi-position rotary switch and an additional continuously variable control is often provided. The ‘CAL’ position is usually at one, or other, extreme setting of this control Adjusts the timebase so that a stable waveform display is obtained Selects the particular level on the triggering signal at which the timebase sweep commences This usually takes the form of a switch that determines whether triggering occurs on the positive or negative going edge of the triggering signal This switch allows selection of one of several waveforms for use as the timebase trigger. The options usually include an internal signal derived from the vertical amplifier, a 50Hz signal derived from the supply mains, and a signal which may be applied to an External Trigger input Positions the display along the horizontal axis (CRT displays only) Adjusts the magnitude of the signal attenuator (V/cm) and sets the vertical voltage scale. This control is invariably a multi-position rotary switch; however, an additional variable gain control is sometimes also provided. Often this control is concentric with the main control and the ‘CAL’ position is usually at one, or other, extreme setting of the control Positions the display along the vertical axis of the display Normally an oscilloscope employs DC coupling throughout the vertical amplifier; hence a shift along the vertical axis will occur whenever a direct voltage is present at the input. When investigating waveforms in a circuit, one often encounters AC superimposed on DC levels; the latter may be removed by inserting a capacitor in series with the signal. With the ACAC position, a capacitor is inserted in the input DC-ground switch in the DC lead, whereas in the DC position the capacitor is shorted. If ground is selected, the vertical input is taken to common (0V) and the oscilloscope input is left floating. This last facility is useful in allowing the accurate positioning of the vertical position control along the central axis. The switch may then be set to DC and the magnitude of any DC level present at the input may be easily measured by examining the shift along the vertical axis. This control, which is only used in dual-beam CRT oscilloscopes, provides selection of the beam splitting mode. In the chopped position, the trace displays a small portion of one vertical channel waveform followed by an equally small portion of the other. The traces are, in effect, sampled at a relatively fast rate, the result being two apparently continuous displays. In the alternate position, a complete horizontal sweep is devoted to each channel alternately. Everyday Practical Electronics, August 2011

Teach-In 2011

Check – How do you think you are doing?

1 ms/cm

Fig.10.8. See Question 10.2

10.1. Briefly explain the difference between analogue and digital multimeters. Which type of instrument offers the greatest resolution? Why is this? 10.2. What indications are displayed on the analogue and digital multimeters shown in Fig.10.8? 10.3. What information (eg, amplitude, period) can be obtained from the oscilloscope displays shown in Fig.10.9? 10.4. Explain the function of each of the following oscilloscope controls: (a) Brightness

(b) Focus (c) Stability (d) Trigger source (e) Vertical attenuator. 10.5. Explain why it is important to ensure that the variable controls of an oscilloscope are placed in the ‘CAL’ position before attempting to make an accurate measurement. 10.6. What adjustment should be made to an oscilloscope when it is to be used to display a small AC voltage superimposed on a much large DC voltage? Explain why this adjustment is necessary.

Fig.10.9. See Question 10.3

For more information, links and other resources please check out our Teach-In website at:

www.tooley.co.uk/ teach-in

CIRCUIT WIZARD

Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard and Professional. By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ﬁnish – even including on-screen testing of the PCB prior to construction!

Circuit diagram design with component library (500 components * Standard, 1500 components Professional) instruments (4 Standard, 7 Professional) * Virtual * On-screen animation

Layout * PCB Interactive PCB layout simulation * Automatic PCB routing * Gerber export *

This is the software used in our Teach-In 2011 series. Standard £61.25 inc. VAT Professional £91.90 inc. VAT. See Direct Book Service – pages 75-77 in this issue

Everyday Practical Electronics, August 2011

Teach-In 2011

Build â&#x20AC;&#x201C; The Circuit Wizard way A soft touch

get all of the component values and connections correct. Once youâ&#x20AC;&#x2122;ve entered the circuit, run a quick simulation to make sure that it functions correctly. Press the â&#x20AC;&#x2DC;Runâ&#x20AC;&#x2122; button on the toolbar and raise/lower the light level on the LDR (R2) to ensure that the LED (D1) lights under low light conditions). Now weâ&#x20AC;&#x2122;re ready to begin the conversion process. Click on the â&#x20AC;&#x2DC;Convert to PCB Layoutâ&#x20AC;&#x2122; button on the toolbar (Fig.10.12), or alternatively use the menu to navigate through â&#x20AC;&#x2DC;Projectâ&#x20AC;&#x2122;, â&#x20AC;&#x2DC;Circuit Symbolsâ&#x20AC;&#x2122; then â&#x20AC;&#x2DC;Convert to PCB Layoutâ&#x20AC;Śâ&#x20AC;&#x2122;. This will start a short wizard to guide you through the conversion process. Click â&#x20AC;&#x2DC;Nextâ&#x20AC;&#x2122; to continue to the next screen, where you will be asked to select a board type (single or double-sided) and a track size. For most home/school low voltage DC projects, with a relatively low component count and where space and component density is not a premium, we would suggest normal tracks on a single-sided board.

N previous instalments of Build, weâ&#x20AC;&#x2122;ve been using Circuit Wizard to simulate and test various circuits in order to demonstrate electronic theory. However, in this edition, we are going to look at the process of taking an electronic circuit and converting it to a printed circuit board (PCB) design that can be produced for real. This is one of the real gems of the Circuit Wizard software as youâ&#x20AC;&#x2122;ll see later on. We will try out some of the softwareâ&#x20AC;&#x2122;s automatic conversion tools, as well as investigating some of the more advanced functionality. Once youâ&#x20AC;&#x2122;ve completed this tutorial you should be ready to enter, test and convert your own circuits to a PCB design. The electronics industry is heavily reliant on software throughout the product design cycle. An example design cycle for an electronic circuit is shown in Fig.10.10. A designer might use various tools and calculators to design the initial circuit. The circuit would then be drawn in an electronic format in a process known as schematic capture. The circuit may then be simulated and analysed using a Simulation Program with Integrated Circuit Emphasis (SPICE). SPICE software runs thousands of calculations on each junction point or node of a circuit, taking into account all of the components. There are various types of analysis that can be carried out: information can be displayed in real time (as in Circuit Wizard) to show a virtual simulation, or gathered and presented in reports or graphs/ charts to show how a circuit functions over time and/or with varying characteristics. In this way a designer can be pretty sure that a circuit will operate

'JH " UZQJDBM EFTJHO Ă?PX for an electronic circuit

correctly before spending time and money producing the physical board. Once the OPERATION IS CONĂ&#x161;RMED THE information from the circuit is then used to generate a PCB design ready for production and testing of the circuit.

On the board

So, letâ&#x20AC;&#x2122;s get to work and see Circuit Wizard in action generating a PCB! Start off by entering the circuit shown in Fig.10.11; a basic potential divider-based automatic 'JH " TJNQMF MJHIU PQFSBUFE TXJUDI light circuit. Ensure that you circuit ready for conversion to a PCB layout Everyday Practical Electronics, August 2011

Teach-In 2011

Therefore, select â&#x20AC;&#x2DC;Single-Sided; Normal Tracksâ&#x20AC;&#x2122; and then click on â&#x20AC;&#x2DC;Nextâ&#x20AC;&#x2122;. The next screen allows us to change the size and shape of the board. In this case, weâ&#x20AC;&#x2122;ll leave these as the default and click on â&#x20AC;&#x2DC;Nextâ&#x20AC;&#x2122;. ,AST ON THE Ă&#x161;NAL PAGE SELECT l#ONVERTm AND KEEP YOUR Ă&#x161;NGERS crossed! As Circuit Wizard carries out the conversion of your circuit to a PCB, it will animate the placing of the components, followed by the calculation of the optimum track layout. If all goes well, after

from yours. It should be noted that the automatic routing functionality of Circuit Wizard is a little limited, and it does struggle to route much more than the simplest circuits without a little help. However, weâ&#x20AC;&#x2122;ll be looking at tactics for creating more complex PCBs later in this article. Now that we have created our PCB layout, there are a number of exciting things that we can do with it. A superb feature of Circuit Wizard is that as well as simulating the circuit Fig.10.15. Off-board Components in the Component Gallery

'JH "VUPNBUJD SPVUJOH DPOĂ&#x153;SNBUJPO Fig.10.12 (above left). The â&#x20AC;&#x2DC;Convert to PCB layoutâ&#x20AC;&#x2122; toolbar button

a short period of time you should receive a completion message detailing the success of your conversion (Fig.10.13). Closing this should reveal your new PCB layout! Fig.10.14 shows our example PCB layout; this may vary slightly

schematic, you can also simulate a virtual copy of your PCB design. !S WITH A REAL CIRCUIT WE MUST Ă&#x161;RST attach a suitable power supply. Drag and drop across a PP3 9V battery from the Off-board Components in the Component Gallery (Fig.10.15).

Fig.10.14. Example PCB layout for the simple light-operated switch circuit in Fig.10.11, and wiring the PP3 9V battery to the PCB

Everyday Practical Electronics, August 2011

Make sure that you select the Offboard Component variant, not a PCB Component. Wire the PP3 batteryâ&#x20AC;&#x2122;s positive and negative connections to the two-pin screw terminal block by dragging from the ends of the battery connector wires (Fig.10.14).

Virtual test

You are now ready to virtually test your PCB; start the simulation using the â&#x20AC;&#x2DC;Runâ&#x20AC;&#x2122; button on the toolbar, as you would for a standard circuit, and try out the function of the circuit by changing the light level on the LDR. On the left-hand side of the screen you may select various different views of the PCB. The default is â&#x20AC;&#x2DC;Real Worldâ&#x20AC;&#x2122;, which shows a full colour representation of what the board will actually look like when constructed. â&#x20AC;&#x2DC;Normalâ&#x20AC;&#x2122; is a more traditional PCB design view. As with schematic simulation, the PCB may also be simulated in a â&#x20AC;&#x2DC;Current Flowâ&#x20AC;&#x2122; and â&#x20AC;&#x2DC;Logic Levelâ&#x20AC;&#x2122; view. In â&#x20AC;&#x2DC;Current Flowâ&#x20AC;&#x2122; view, the tracks are colour coded depending on the instantaneous voltage and â&#x20AC;&#x2DC;marching ANTSm DEMONSTRATE THE RATE OF Ă&#x203A;OW of current (Fig. 10.16). This is particularly useful for understanding the operation of the circuit, as well 49

Teach-In 2011

Build – The Circuit Wizard way as providing a comparison for fault ÚNDING TESTING OF THE COMPLETED CIRCUIT 4RY SIMULATING THE CIRCUIT IN THIS MODE 4HE l,OGIC ,EVELm VIEW IS EXCELLENT WHEN DEALING WITH DIGITAL CIRCUITS AS IT HIGHLIGHTS THE LOGIC STATE OF PINS AND TRACKS l!RTWORKm SHOWS THE OUTPUT 0#" MASK AND l5NPOPULATEDm SHOWS THE PHYSICAL BOARD ALONG WITH THE SILK SCREEN LAYER WHICH CAN BE VERY USEFUL AS A CONSTRUCTIONAL AID

Design output (OW YOU NOW OUTPUT YOUR DESIGN READY FOR PRODUCTION WILL DEPEND ON YOUR CHOSEN CIRCUIT BOARD PRODUCTION METHOD 4HE PRINT MENU &IG ALLOWS YOU TO PRINT VARIOUS ARTWORK INCLUDING TOP AND BOTTOM COPPER LAYERS SILK SCREEN AS WELL AS MIRRORED AND INVERTED DESIGNS &OR THOSE USING STANDARD 56 PHOTO RESIST BOARD AND A TRADITIONAL ETCHING TECHNIQUE l3OLDER 3IDE "OTTOM !RTWORKm WOULD BE PRINTED USING A LASER PRINTER ON TO ACETATE READY FOR 56 EXPOSURE )F YOU USE ISOLATION GAP ROUTING OR SENDING

Fig.10.16. Current Flow view of the PCB

YOUR DATA AWAY TO A THIRD PARTY FOR PRODUCTION THEN THE #!$ #!- MENU &IG PERMITS YOU TO OUTPUT THE 0#" DATA IN $8& .# AND 'ERBER FORMATS 3CHOOLS WITH 4ECHSOFT #!- EQUIPMENT MAY COPY THE 0#" DATA AND PASTE IT INTO 4ECHSOFT $ 0#" READY FOR #.# ROUTING AND drilling.

More complex circuits !S YOUmVE SEEN #IRCUIT 7IZARD DOES A NICE JOB OF AUTOMATICALLY CONVERTING A

SIMPLE CIRCUIT INTO 0#" WITH NO HELP FROM THE USER (OWEVER WITH A MORE COMPLEX CIRCUIT YOU MAY NEED TO MAKE A FEW TWEAKS AND GET A BIT MORE INVOLVED IN THE GENERATION PROCESS 4O DEMONSTRATE THIS WE WILL CONVERT A SLIGHTLY MORE COMPLEX CIRCUIT THIS TIME A ASTABLE MODE ,%$ ÛASHER CIRCUIT %NTER THE CIRCUIT SHOWN IN &IG AND VERIFY ITS OPERATION THROUGH SIMULATION &OLLOW THROUGH THE 0#" CONVERSION PROCESS AS YOU DID FOR THE ÚRST

Fig.10.17. The Circuit Wizard PCB print menu

Fig.10.18. Circuit Wizard’s CAD/CAM menu

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Everyday Practical Electronics, August 2011

Teach-In 2011

CIRCUIT /NCE COMPLETE YOU MAY Ă&#x161;ND that you receive a routing message similar to that shown in Fig.10.20, explaining that the software was unable to completely convert your circuit automatically. In our example, you can see that ONLY OF THE CONNECTIONS COULD BE MADE )T IS IMPORTANT TO NOTE THAT you may be more or less successful THAN OUR EXAMPLE CIRCUIT DEPENDING ON HOW YOU HAVE DRAWN YOUR CIRCUIT AND YOUR SOFTWARE SETUP 4HE DESCRIPTION HERE IS INDICATIVE OF HOW TO DEAL WITH A 0#" THAT FAILS to completely route using the automatic routing feature. Inspecting the GENERATED DESIGN &IG YOU CAN SEE THAT THE SOFTWARE INSERTED A JUMPER AND ONE CONNECTION COULD NOT BE MADE AT ALL SHOWN BY A THIN GREEN LINE .OTE THIS DOES NOT MEAN TO SAY THAT it is impossible to wire the circuit, just that the software was unable to DO SO AUTOMATICALLY AND OR USING THE CURRENT CONĂ&#x161;GURATION &ORTUNATELY we can step in here to make the job of the software a little easier.

Fig.10.20. Automatic routing message for the circuit of Fig.10.19

However, this time select â&#x20AC;&#x2DC;Rats Nest; .O 0LACEMENT OR 2OUTINGm ON THE SECOND SCREEN OF THE WIZARD 9OU SHOULD THEN BE PRESENTED WITH A BLANK 0#" BOARD AND A SET OF THE REQUIRED COMPONENTS AS SHOWN IN Fig.10.22. The pins of the components are LINKED BY GREEN LINES SHOWING WHERE THE CONNECTIONS ARE REQUIRED 4HIS mass of criss-crossing wires is often REFERRED TO AS A lRATS NESTm We now have to place the comPONENTS ON TO THE 0#" 2ATHER THAN simply placing components at ranDOM WHAT WE ARE LOOKING TO DO HERE

is to place the components so that THEY CAN BE ROUTED WITH TRACKS IN THE EASIEST AND MOST EFĂ&#x161;CIENT MANNER We might also require components IN SPECIĂ&#x161;C LOCATIONS FOR EXAMPLE AN OFF BOARD CONNECTOR AT THE SIDE OF THE 0#" OR THE Ă&#x161;XED LOCATION OF AN ,%$ so that it locates in the right place ON A Ă&#x161;NISHED PRODUCT To achieve the former, it is essentially a case of placing the components so that there are as few cross-overs of green lines as possible. Hence, this will make the job of routING THE TRACKS AS EASY AS POSSIBLE AND AVOID THE REQUIREMENT OF JUMPERS

Rats nest 2ETURN TO YOUR CIRCUIT DIAGRAM AND REPEAT THE CONVERSION PROCESS

Fig.10.21. The generated PCB layout showing incomplete routing

Everyday Practical Electronics, August 2011

Fig.10.22. Starting point for the â&#x20AC;&#x2DC;rats nestâ&#x20AC;&#x2122; PCB layout

Teach-In 2011

Build â&#x20AC;&#x201C; The Circuit Wizard way

Fig.10.24. Selecting automatic routing from the PCB Layout Tools menu Fig.10.23. Improved layout using â&#x20AC;&#x2DC;rats nestâ&#x20AC;&#x2122; technique

links. As well as component position, their orientation may be altered by rotation (keyboard shortcut CTRL+R). Notice that as you move components to a new location, the green lines will update to the nearest common point for that net. This allows YOU TO SIGNIĂ&#x161;CANTLY SIMPLIFY THE rats nest prior to routing the tracks. Fig.10.23 shows an example layout which places the battery connector at the edge of the board and attempts to leave the rats nest as clean as possible.

Fig.10.25. The completed auto-routed layout

Previous users of PCB drafting SOFTWARE WILL Ă&#x161;ND THE TRACK DRAWING PROCESS FAMILIAR WHEREAS Ă&#x161;RST TIME USERS MAY Ă&#x161;ND IT TAKES A LITTLE PRACtice for it to become intuitive. You MAY Ă&#x161;ND IT EASIER TO USE l.ORMALm view for manual track drawing. Fig.10.27 shows a track manually added to the 555 circuit.

Fig.10.26. The track button

#ONlGURATIONÂŞOPTIONS

On track

At this point we can either start to draw our tracks manually in-line with the green nets, or instruct Circuit Wizard to attempt to automatically route the board now that we have prepared the component LAYOUT MORE EFĂ&#x161;CIENTLY 4HE AUTHORmS personal preference is to have the software route the tracks automatically, then go in and modify the results as required to achieve a NICE NEAT JOB (OWEVER ITmS UP TO the individual user to experiment and decide upon their favoured approach. To initiate automatic routing, click ON THE l0#" ,AYOUT 4OOLSm ICON FROM THE TOOLBAR AND SELECT l!UTO 2OUTEcm (Fig.10.24). Our completed auto 52

Fig.10.27. A manually added PCB track

routed layout looks as shown in Fig. 10.25. The layout is now complete and ready for virtual simulation and output for production. If you prefer to draw the tracks manually (or indeed if Circuit Wizard fails to route your circuit automatically) select the track button from the toolbar (Fig.10.26). Tracks are started by left-clicking with additional segments added by further LEFT CLICKING AND ARE Ă&#x161;NISHED BY right-clicking.

A number of additional PCB conVERSION CONĂ&#x161;GURATION OPTIONS ARE available through the PCB wizard. On the second screen, tick â&#x20AC;&#x2DC;Allow me to customise the PCB layout conVERSIONm 9OU WILL THEN BE PROVIDED with many additional options as you proceed through the conversion process. One of these additional conĂ&#x161;GURATIONS IS THE ABILITY TO ALTER the physical component mappings. When converting to a PCB, Circuit Wizard selects the most appropriate PCB component footprint based on the component variant and values selected. However, there may be times when you wish to specify a different model from that chosen by default. The screen shown in Fig.10.28 will be included in the wizard when the tick box is checked as described earlier, allowing you to alter the package

Everyday Practical Electronics, August 2011

Teach-In 2011

used for each component (in this case showing the package selection window for the battery, B1). On the subsequent wizard screen you are given a number of component placement options. An interesting option is â&#x20AC;&#x2DC;Take into account component positionsâ&#x20AC;&#x2122;. When Circuit Wizard converts to a PCB it tries to order the components as you have set them out on your schematic. This may be convenient for keeping component numbering sequential. However, in practice this is not always the best way to place comPONENTS FOR EFĂ&#x161;CIENT ROUTING )F YOU Ă&#x161;ND YOUR CIRCUITS ARE NOT automatically routing and/or the components are being placed in a

Fig.10.28. Specifying different component models

poor manner, try unticking this option. This can have a dramatic effect on the results. Finally, one really useful tool is Quality Check. This may be accessed from the PCB Layout Tools icon on the toolbar, or by selecting â&#x20AC;&#x2DC;Projectâ&#x20AC;&#x2122;, â&#x20AC;&#x2DC;PCB Componentsâ&#x20AC;&#x2122; then â&#x20AC;&#x2DC;Quality Checkâ&#x20AC;&#x2122; from the menu. This will analyse the PCB layout in comparison to your circuit diagram, to ensure that all of the connections have been made correctly, as well as various other checks. This is particularly useful when routing manually to check the connectivity of your design. Fig.10.29 shows an example Quality Check Report. Weâ&#x20AC;&#x2122;ve really only scratched the surface of the PCB conversion and drafting tools within Circuit Wizard. As with any Fig.10.29. An example of a Quality Check Report

Everyday Practical Electronics, August 2011

software tool, the best way to learn more is to get â&#x20AC;&#x2DC;hands onâ&#x20AC;&#x2122; and use the software. In the next edition of Build weâ&#x20AC;&#x2122;ll be giving you the opportunity to do just that with a range of project circuits for you to enter, test, convert and build using all of the skills youâ&#x20AC;&#x2122;ve learnt throughout the series.

Answers to Check questions 10.1 See page 43 and page 44 10.2 (a) 83.0mA AC (b) 180: 10.3 (a) Sine wave; 5ms period (frequency = 200Hz); amplitude 6V pk-pk (b) Pulse wave; 8ms period (p.r.f. = 125Hz; high time = 2ms, low time 6ms; 25% duty cycle (mark-to-space ratio = 1:3; (amplitude 2.5V pk-to-pk 10.4 See page 46 and Table 10.1 10.5 See page 45 and Table 10.1 10.6 See page 46 and Table 10.1

Teach-In 2011

Investigate Fig. 10.30 shows a simple regulated power supply and three common items of test equipment. 1. Photocopy the diagram and add connecting wires to the diagram in order to show: (a) How the collector current of transistor TR1 is measured (b) How the base-emitter voltage of TR1 is measured. 2. For (a) and (b) above, list the initial adjustments that should be made to the test equipment. 3. If the output voltage of the circuit is measured at 0V and the input voltage as 15.1V, what measurements would you make, and in what order, to locate the fault? Explain your answer.

Fig.10.30. See Investigate

Amaze In our everyday lives we are increasingly reliant on highly complex electronic systems that involve large numbers of individual component parts. However, because each individual part can be prone to failure, we need to ensure that each component has a very high reliability in order to ensure that the equipment as a whole remains free from failure. Reliability (ie, the ability to operate without failure) is thus a paramount consideration for those involved with the design of electronic equipment. To put this into context: suppose that we know that one out of every 100000 of a particular component type is likely to break down every hour. This implies that an item of equipment that makes use of 100 of these components would break down at an average interval of 1000 hours or less than 42 days operation. In many cases this would be woefully inadequate! 54

The requirement for a very high degree of reliability is crucial in many applications. In satellite communications, the electronics is often expected to operate for at least 20 years without failure, simply because it would be impossible to recover and repair the satellite without spending far more than the satellite was actually worth. Added to this, there would be considerable loss of revenue while the satellite was out of service: in many cases this might amount to millions of pounds or dollars. The failure rate of individual components depends on the situation and environment in which they are used. A satellite experiences extreme forces and temperatures during launch and MANOEUVRE INTO Ă&#x161;NAL ORBIT In consequence, the environment in which a satellite operates is considered severe when compared with that in which most consumer elecTRONIC EQUIPMENT Ă&#x161;NDS ITSELF &OR THIS

reason, we need to ensure that only the most reliable types of electronic component are used in satellites. But just how reliable are the electronic components used in the circuits that you construct? A single low-cost metal oxide resistor operated within its rating and in a benign environment can be expected to a have working life of more than 1000 years. The same ITEM Ă&#x161;TTED INTO A SATELLITE WOULD NEED to have a reliability that is at least ten times and preferably more than 100 times greater than this!

Next month!

In next monthâ&#x20AC;&#x2122;s Teach-In 2011 we round up the series with a brief look back at previous parts. We shall also be including some fun revision activities as well as essential reference information. Our series concludes with a selection of electronic projects that you can build and test using Circuit Wizard.

Everyday Practical Electronics, August 2011

HandsOn Technology

http://www.handsontec.com

ISP to ICP Programming Bridge: HT-ICP200 In-Circuit-Programming (ICP) for P89LPC900 Series of 8051 Flash μController… …ICP uses a serial shift protocol that requires 5 pins to program: PCL, PDA, Reset, VDD and VSS. ICP is different from ISP (In System Programming) because it is done completely by the microcontroller’s hardware and does not require a bootloader… That the 80C51-based controllers are extremely popular is nothing new, certainly when considering the large number of designs that can be found on the web. The reason may well be the fact that the tools (both hardware and software) that are available for this controller are very affordable and there is an enormous amount of information readily available. In addition, a very active forum provides answers to many questions. One of the most significant features of the P89LPC900 Family is that the core now requires only 2-clock Cycles Per Instruction (CPI). 8051 experts will already know that this used to be 12 or 6 cycles until now. In practice, this means that the crystal frequency can be drastically lowered to achieve the same processing speed as their classic counter parts.

1. INTRODUCTION P89LPC9xx parts (affectionately know as the LPC900 series of micro-controllers) can be programmed 4 ways... 1. 2. 3. 4.

ISP (In-System-Programmed) using the UART of the LPC900. IAP (In-Application-Programmed) .. or "self programmed" by reprogramming the flash under code execution. ICP (In-Circuit-Programming)... using "Synchronous Serial".... Similar to SPI signaling - each data bit is clocked in/out under clock signal control. Parallel Programmer, available in expensive industry grade tools.

ISP Programming is only available for 20, 28 and 44pin parts. IAP is only available once your IAP program has been loaded in to the LPC900 part. ICP -can be used to program all the LPC900 parts. The LPC90x devices can only be programmed using a ICP programming method. In contrast to some of the larger LPC900 family members, the LPC90x devices do not offer other programming methods like Parallel Programming, InSystem Programming (ISP) or complete In-Application Programming (IAP). HOWEVER - ICP requires hardware control/ signaling of the LPC900 to be programmed. In some high-end applications, there may be a need to replace the code in the microcontroller without replacing the IC itself. This article described in detail the operation of the In-Circuit-Programming (ICP) capability which allows these microcontrollers to be programmed while mounted in the end product. To communicate between a PC (running Flash Magic) and the LPC900 Micro-Controller to be programmed an "ICP Bridge" circuit is required as shown in Figure 1.

HT-ICP200

P89LPC900 Target Application Board

Figure 1: Hooking up ICP to the P89LPC900 Application Board

Teach-In 2011

TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS Part 11: Summing it all up By Mike and Richard Tooley

N THIS instalment of Teach-In 2011, we bring our series to a conclusion with a quick review of the previous ten parts, and include a comprehensive index that will help you to locate the key topics that weâ&#x20AC;&#x2122;ve introduced as the series has progressed. Thereâ&#x20AC;&#x2122;s also a selection of questions and fun activities, including a crossword, that will help you to check your understanding. For good measure, weâ&#x20AC;&#x2122;ve also included eight additional circuits for you to investigate using the Circuit Wizard software.

Learn ,OOKINGÂŞBACK We began our Teach-In series by looking at the signals that are used to convey information in electronic circuits. We discussed the units and quantities that we use when making measurements in electronic circuits, and how waveforms are used to show how the voltage and current in an electronic circuit vary with time. We also introduced batteries and power supplies that we use to provide power to electronic circuits.

Part 2 dealt with resistors, capacitors, timing circuits and Ohmâ&#x20AC;&#x2122;s Law. We also found out what happens when a capacitor is charged or discharged. Part 3 provided you with an introduction to diodes and power supplies. We investigated the voltage/ current characteristics for two different types of diode, and showed how they could be used together with a transformer to produce a power supply. We also looked at light emitting diodes (LEDs) and Zener diodes.

Everyday Practical Electronics, September 2011

Teach-In 2011 Transistors were the subject of Part 4. We described the operation of NPN and PNP transistors, and explained how they are used to amplify current and operate as saturated switches. An introduction to operational AMPLIĂ&#x161;ERS OP AMPS WAS THE SUBJECT of Part 5. We showed how operaTIONAL AMPLIĂ&#x161;ERS CAN BE CONNECTED in inverting, non-inverting and differential arrangements, as well as

showing how they could be used as comparators, where one voltage is compared with another. Logic circuits were explained in Part 6. Here we met the symbols, truth tables and Boolean logic for each of the most common types of logic gate. We also introduced bistable devices, and showed how they could be used in binary counters. The highly versatile electronic timer (555/6) was introduced in Part 7.

These versatile circuits can be used to produce accurate time delays and repetitive pulse waveforms. Analogue circuit applications, in THE FORM OF ATTENUATORS AND Ă&#x161;LTERS were described in Part 8. We explained the characteristics of lowPASS HIGH PASS AND BAND PASS Ă&#x161;LTERS and showed how these could be built using simple arrangements of resistors, capacitors and inductors. We also introduced some simple active

Crossword Check â&#x20AC;&#x201C; How do you think you are doing? The monthâ&#x20AC;&#x2122;s Check panels provides you with an opportunity to test your understanding of the previous ten parts of our Teach-In 2011 series. 5IF Ă&#x153;STU RVFTUJPO UFTUT ZPVS LOPXMFEHF PG TPNF PG UIF UFSNT UIBU BSF DPNNPOMZ VTFE JO FMFDUSPOJDT

11.1. Solve the crossword shown in Fig.11.1. Clues across 5 Amplitude (4) 7 Instrument for measuring current (7) 8 Polarised capacitor (12) 10 Commonly used for logarithmic ratios (7) 15 Most positive connection of an NPN transistor (9) 18 Very common type of waveform (4) 19 Stores electric charge (9) 20 Unit of potential difference (4) 21 Instrument used to display waveforms (12) 22 P in PRF (5) 26 Most positive connection on a conducting diode (5) 27 Ă&#x2014;0.000001 (5) 29 Peak or maximum value (9) 30 Unit of frequency (5) Clues down 1 Used to produce delays (5) 2 Diode voltage reference (5) 3 Present on the plates of a capacitor (6) 4 Time for one cycle (6) 6 Circuit that has no stable state (form of oscillator) (7) 9 !LLOWS CURRENT TO Ă&#x203A;OW IN ONE direction only (5) 11 C in CRT (7) 12 )NPUT OF A COMMON EMITTER AMPLIĂ&#x161;ER 13 Fast analogue-to-digital converter (5)

Everyday Practical Electronics, September 2011

'JH $PNNPO UFSNT VTFE JO FMFDUSPOJDT

14 16 17 19 23 24 25 28

Ă&#x2014;1,000,000 (4) Steps alternating voltage up or down (11) Most positive connection of a PNP transistor (7) Smallest indivisible part of a battery (4) L in LED (5) Unit of capacitance (5) Ă&#x2014;0.001 (5) Unit of resistance (3) Crossword solution â&#x20AC;&#x201C; page 53

Teach-In 2011 Ă&#x161;LTERS BASED ON OP AMPS &OR GOOD measure, we explained how decibels are used to express gain or loss in electronic circuits. In Part 9, we showed how an analogue signal can be converted to digital data, and vice versa. We described the process of quantisation and explained how the number of data bits affects the accuracy and resolution of a DAC and ADC. Part 10 dealt with the practical aspects of constructing and testing electronic circuits. We introduced some basic items of test equipment in the form of multimeters and oscilloscopes, and showed how these could be used to measure voltage, current, frequency, time and waveform in an electronic circuit.

Check â&#x20AC;&#x201C; How do you think you are doing?

The next question tests your ability to recognise the symbols used in circuit diagrams:

Fig.11.2 See Question 11.2

11.2. Identify each of the symbols shown in Fig.11.2. Question11.3 and Question 11.4 test your ability to extract information from a waveform: 11.3. For the waveform shown in Fig.11.3(a): (a) What type of waveform is shown? (b) What is the frequency of the waveform? (c) What is the periodic time of the waveform? (d) What is the amplitude (peak value) of the waveform? 11.4. For the waveform shown in Fig.11.3(b): (a) What type of waveform is shown? (b) What is the pulse repetition frequency of the waveform? (c) What is the periodic time of the waveform? (d) What is the duty cycle of the waveform (e) What is the peak-peak value of the waveform? Fig.11.3 (right). See Question 11.3 and Question 11.4

Everyday Practical Electronics, September 2011

Teach-In 2011 The next two questions test your knowledge of some of the units and quantities used in electronics: Quantity

Unit

Electric potential

volt Volt Ampere ampere

Abbreviation

Electric power

Capacitance

ohm Ohm

Resistance Frequency

Bit rate

Bps

11.5. Complete the table of electrical quantities and units of measurement Definition

Unit

The potential that appears between two points points when when aa current ampereflows ďŹ&#x201A;owsininaacircuit circuithaving havingaa current of of one 1 Ampere resistance ohm resistance of of one 1 Ohm

The next question tests your ability to recognise some common electronic components: 11.8. &IG SHOWS A KIT OF PARTS needed to build a simple astable LED Ă&#x203A;ASHER )DENTIFY THE PARTS MARKED ! TO ) Question 11.9 checks a basic understanding of basic digital logic: 11.9. 3KETCH LOGIC CIRCUITS SHOWING HOW (a) a four-input AND gate can be built USING THREE TWO INPUT !.$ GATES (b) a four-input OR gate can be built USING THREE TWO INPUT /2 GATES C A TWO INPUT !.$ GATE CAN BE BUILT FROM TWO TWO INPUT .!.$ GATES D A TWO INPUT /2 GATE CAN BE BUILT FROM TWO TWO INPUT ./2 GATES Finally, Question 11.10 tests your ability to read and understand a simple electronic circuit diagram:

The current current that that flows ďŹ&#x201A;ows ininan anelectrical electricalconductor conductorwhen when The electric charge charge is is being being transported transported atatthe therate rateofof1 one electric coulomb per Coulomb persecond second

11Watt watt The resistance ampere resistance of of aacircuit circuitwhen whenaacurrent currentofofone 1 Ampere ďŹ&#x201A;owing in volt flowing in itit produces producesaapotential potentialdifference differenceofofone 1 Volt

11 Hertz hertz

11.6. #OMPLETE THE TABLE OF DEĂ&#x161;NITIONS SHOWN ABOVE Question 11.7 tests your ability to convert multiples and sub-multiples to fundamental units: 11.7. Express: (f) 885Hz in kHz (c) 68000: in k: (a) 250mV in V (d) 0.235W in mW (g) 1500pF in nF (h) 1.2kbps in bps (b) 0.15mA in PA (e) 0.22M: in k:

11.10 &IG SHOWS THE CIRCUIT OF A SIMPLE HEADPHONE AMPLIĂ&#x161;ER IN WHICH ALL OF THE Ă&#x161;XED RESISTORS HAVE A TOLERance of Âą5%. A 7HAT TYPE OF COMPONENT IS # B 7HAT TYPE OF COMPONENT IS 42 C 7HICH TWO COMPONENTS ARE CONNECTED TO THE BASE OF 42 D 7HAT COLOUR CODE WOULD BE MARKED ON 2 E 7HICH COMPONENT IS ADJUSTABLE F 7HAT VOLTAGE WILL APPEAR ACROSS # WHEN 3 IS CLOSED G )F A CURRENT OF M! Ă&#x203A;OWS IN 2 WHAT VOLTAGE WILL APPEAR AT THE BASE OF 42 H 7HICH COMPONENT PROVIDES NEGATIVE FEEDBACK

Fig.11.5. See question 11.10

Fig.11.4. See question 11.8

Everyday Practical Electronics, September 2011

The answers to these questions are shown on page 54

Teach-In 2011

Build – The Circuit Wizard way

VER the Teach-In series, our Build section has put theory into practice using Circuit Wizard to simulate a whole range of electronic circuits. We’ve shown how using simulation software is great for allowing you to really get to the bottom of how a circuit actually

operates, as well as being a crucial tool for electronic designers. In this, the last edition we are giving you the opportunity to try out your ‘wizard’ skills with a selection of practical circuits that you can enter and investigate. For each circuit, we’ve included a brief description,

along with some suggestions for experimentation and a few questions to help test and extend your understanding of the underpinning theory. These circuits are a great starting point for your own projects and circuit designs.

COIN TOSS Description The circuit shown in Fig.11.6 uses a J-K ÛIP ÛOP THAT IS CLOCKED AT A VERY HIGH speed. When switch SW1 is pressed, THE ÛIP ÛOP IS CLOCKED AND ALTERNATES at 1kHz (that’s one thousand times a second). During this time, the LEDs will apPEAR TO ÛICKER RAPIDLY OR MAY SEEM dimly lit. When the button is released, THE ÛIP ÛOP WILL REMAIN IN ONE STATE and hence one LED will remain lit to signify either ‘heads’ or ‘tails’. The circuit is not truly random, but because the output is changing so quickly it would be hard to get a consistent output by timing the button press.

Fig.11.6. Coin toss circuit diagram

Investigate: 1. We’ve used the in-built clock device – try to create your own clock generator (perhaps using a 555 astable or a Schmitt oscillator circuit). 2. The coin toss circuit is not truly

random – how could we generate a real random selection? 3. How could we extend the circuit to give six outputs – ie, to create an electronic dice?

EGG TIMER Description The egg timer circuit shown in Fig.11.7 is a classic 555 bistable circuit. Switch SW1 selects between a soft-boiled (~3 min) and hard-boiled (~5 min) egg by changing the resistor through which capacitor C1 is charged. When the circuit is powered, the buzzer (BZ1) will sound until switch SW2 is pressed to start the timer. For this reason a practical version of this circuit should include a further toggle switch to connect/disconnect the power supply. Investigate: 1. Monitor the charge on capacitor C1 by placing a probe on pin-6/7. 2. Use the theory that you learnt in Part 2 to calculate the time period for the circuit when timing both soft- and hard-boiled eggs (note that resistor R3 is in series with either R1 or R2 when you calculate the total resistance through which C1 is charged). 3. How would you alter the circuit to give a four-minute egg? 50

Fig.11.7. Egg timer circuit diagram

Everyday Practical Electronics, September 2011

Teach-In 2011

KNIGHT RIDER LIGHTS Description In Fig.11.8, a 4017 decade counter is used to produce a â&#x20AC;&#x2DC;running lightsâ&#x20AC;&#x2122; sequence illuminating each LED in turn. Each LED is connected to two outputs, so that Fig.11.8. Knight Rider â&#x20AC;&#x2DC;chaserâ&#x20AC;&#x2122; lights as the 4017 counts up further, the LEDs are lit again in reverse order. 2. The 4017 is clocked by a simple This gives the effect of the LEDs run- Schmitt oscillator circuit (IC1a). Use ning alternately forward/backwards. the Internet and/or other resources to HELP YOU Ă&#x161;ND OUT MORE ABOUT 3CHMITT Investigate: devices and how they may be used to 1. The speed of the lights can be make a simple clock signal. varied by â&#x20AC;&#x2DC;adjustingâ&#x20AC;&#x2122; potentiometer VR1. Check that this works.

3. What is the purpose of diodes D1 to D8?

4. Why is only one series resistor (R10) required?

INTRUDER ALARM Description The circuit shown in Fig.11.9 uses a thyristor (or silicon controlled RECTIĂ&#x161;ER $ 7EmVE NOT MET THIS particular device before, but it acts as a latch to hold the circuit in the â&#x20AC;&#x2DC;onâ&#x20AC;&#x2122; state once pushswitch (push-tobreak) SW1 is pressed. The alarm will remain on until the circuit is disconnected from the battery (for example with keyswitch SW2), even if SW1 is released. Switch SW1 could be replaced with a normally closed (NC) pressure pad, a trip wire or a door contact in a real circuit. Investigate: 1. Extend the circuit to include more than one trigger. 2. Use the Internet and/or other reSOURCES TO Ă&#x161;ND OUT HOW A THYRISTOR works.

Fig.11.9. Circuit diagram for a simple intruder alarm

3. What would happen if (a) resistor R1 became open-circuit or (b) if

transistor Q1 became short-circuit between collector and emitter?

Everyday Practical Electronics, September 2011

For more information, links and other resources please check out our Teach-In website at:

www.tooley.co.uk/ teach-in 51

Teach-In 2011

Build â&#x20AC;&#x201C; The Circuit Wizard way PUSH-ON/PUSH-OFF CONTROL SWITCH Description In Fig.11.10, a J-K flip-flop is clocked on/off when pushswitch (push-to-make) SW1 is pressed. The Schmitt trigger inverter (IC2a) and capacitor C1 are used to deBOUNCE THE CLOCK INPUT OF THE Ă&#x203A;IP Ă&#x203A;OP 4HE OUTPUT TRIGGERS TRANSISTOR Q1, which in turn allows current TO Ă&#x203A;OW THOUGH THE COIL OF THE RELAY (RL1), and hence completes the mains voltage circuit and powers THE LAMP )N THIS WAY THE SAME PUSHBUTTON MAY BE USED TO TURN the light on and off.

Fig.11.10. Circuit for a push-on/push-off control switch

Investigate: 7HAT IS SWITCH lBOUNCEm AND WHY do we need to reduce it? 2. What would happen if SW1 was NOT DEBOUNCED PROPERLY 3. What is the purpose of diode D1?

9V BATTERY TESTER

Fig.11.11. An LED 9V battery tester circuit

Description 4HE BATTERY TESTER CIRCUIT &IG USES THREE CONSECUTIVELY HIGHER breakdown voltage Zener diodes to control red, amber and green LEDs TO INDICATE THE BATTERY VOLTAGE 7E HAVE USED A VARIABLE POWER SUPPLY TO SIMULATE THE VOLTAGE OF THE BATTERY on test. Investigate: 7HY DO RESISTORS 2 TO 2 NEED TO be different values? 2. What would the effect be of changing the breakdown voltage of the Zener diodes? (OW WOULD YOU ALTER THIS CIRCUIT TO TEST OTHER BATTERY VOLTAGES q EG 5V, 12V etc.?

Layout * PCB Interactive PCB layout simulation * Automatic PCB routing * Gerber export * This is the software used in our Teach-In 2011 series. Standard ÂŁ61.25 inc. VAT Professional ÂŁ91.90

Circuit diagram design with component library * (500 components Standard, 1500 components Professional) Virtual instruments (4 Standard, 7 Professional) * On-screen animation *

inc. VAT. See Direct Book Service â&#x20AC;&#x201C; pages 75-77 in this issue

Everyday Practical Electronics, September 2011

Teach-In 2011

METRONOME Description A 555 timer is used in Fig.11.12 in an ASTABLE CONÚGURATION 4HE FREQUENCY OF THE OUTPUT IS CONTROLLED BY ADJUSTING VARIABLE lRESISTORm 62 WHICH VARIES THE SPEED AT WHICH CAPACITOR # IS CHARGED DISCHARGED !S THE OUTPUT PIN CHANGES FROM 6 TO 6 ,%$S $ AND $ ARE LIT ALTERNATELY .OTE THAT #IRCUIT 7IZARD WILL NOT SIMULATE THE lTICKm THAT YOU WOULD HEAR FROM THE SPEAKER AS THE OUTPUT CHANGES IN THE REAL CIRCUIT Fig.11.12. Metronome circuit using a 555 timer IC

Investigate: 7HAT IS THE PURPOSE OF CAPACITOR # (OW COULD YOU ADD AN ADDITIONAL RANGE OF TEMPO THAT WOULD BE A TEN TIMES SLOWER OR B TEN TIMES FASTER THAN THE ORIGINAL RATE 7HAT SINGLE COMPONENT WOULD NEED TO BE CHANGED

TEMPERATURECONTROLLED FAN Description ! SIMPLE POTENTIAL DIVIDER DRIVEN SENSOR CIRCUIT IS SHOWN IN &IG !S THE TEMPERATURE CHANGES THE RESISTANCE OF THE THERMISTOR 2 CHANGES ACCORDINGLY 4HIS AFFECTS THE VOLTAGE AT THE BASE OF THE TRANSISTOR /NCE THIS VOLTAGE IS SUFÚCIENT THE TRANSISTOR WILL ALLOW CURRENT TO ÛOW TROUGH THE COIL OF THE RELAY DOWN TO GROUND 6 THUS COMPLETING THE FAN CIRCUIT 6ARYING 62 WILL ADJUST THE POINT AT WHICH THE FAN IS ACTIVATED Investigate: (OW COULD YOU IMPROVE THIS CIRCUIT BY USING AN OPERATIONAL AMPLIÚER

Fig.11.13 (above). Temperature-controlled fan circuit

Fig.11.14 (right). Answer to Question 11.1

7HAT WOULD HAPPEN IF THE THERMISTOR WENT OPEN CIRCUIT 7HAT DOES DIODE $ DO 5SE THE )NTERNET AND OR OTHER RESOURCES TO ÚND OUT Everyday Practical Electronics, September 2011

Teach-In 2011

Answers to Check questions 11.5. 6 ELECTRIC CURRENT WATT FARAD : HERTZ BITS PER SECOND

11.1. See Fig.11.14 11.2. (a) switch (SPST) B RESISTOR ÚXED

C TRANSFORMER IRON CORED D LIGHT EMITTING DIODE ,%$ E CAPACITOR ÚXED NON ELEC TROLYTIC

11.6. ONE VOLT ONE AMP A POWER OF ONE WATT IS EQUIVALENT TO ONE JOULE OF ENERGY BEING USED EVERY SECOND ONE OHM A SIGNAL HAS A FREQUENCY OF ONE HERTZ IF ONE COMPLETE CYCLE OCCURS EVERY SECOND (b) 150PA

G ELECTROLYTIC CAPACITOR

J CELL OR BATTERY

(f) 0.885kHz

(k) preset potentiometer

O BRIDGE RECTIÚER 11.3. (a) sinewave (b) 40Hz (c) 25ms D 6 11.4. A PULSE REPETITIVE

(h) R2.

C SLIDE SWITCH $0$4

D LIGHT EMITTING DIODES (e) transistors (2)

F ELECTROLYTIC CAPACITORS

G PRINTED CIRCUIT BOARD

H BATTERY 6 00 TYPE

I BATTERY CONNECTOR

11.10. A ELECTROLYTIC CAPACITOR

G 6

(b) preset potentiometers (2)

/VER THE LAST TEN PARTS OF OUR TeachIn 2011 SERIES WEmVE ATTEMPTED TO COVER THE CORE ELECTRONICS SYLLABUS TAUGHT IN MANY SCHOOLS AND COLLEGES IN THE 5+ 7EmVE INTRODUCED EACH OF THE MAIN TOPICS STUDIED AT ,EVEL EQUIVALENT TO '#3% AS WELL AS A FEW THAT BRIDGE THE GAP INTO FURTHER STUDIES AT ,EVEL EQUIVALENT TO ! LEVEL l"UILDm PROVIDES YOU WITH EIGHT ADDITIONAL CIRCUITS TO BUILD AND IN VESTIGATE USING THE #IRCUIT 7IZARD

(h) 1200bps.

11.9. See Fig. 11.15

Round-up

F 6

11.8. (a) resistors (4)

(b) 5ms

E 6

E 26

(g) 1.5nF

L VARIABLE CAPACITOR

N 2 3 BISTABLE OR ÛIP ÛOP

D M7

I OPERATIONAL AMPLIÚER

M .0. BIPOLAR JUNCTION TRAN sistor (BJT)

D BROWN RED YELLOW GOLD

11.7. A 6

F VARIABLE POTENTIOMETER H !.$ GATE

(b) PNP transistor

Fig.11.15. Answer to Question 11.9

C 2 AND 2

SOFTWARE !LL OF THESE CIRCUITS CAN BE MODIÚED AND EXTENDED AND WEmVE SUGGESTED HOW THIS CAN BE DONE AND THINGS THAT YOU MIGHT WANT TO TRY !S MENTIONED PREVIOUSLY IN OUR SERIES YOU CAN LEARN A GREAT DEAL BY EXPERIMENTATION &INALLY WE TRIED TO KEEP THE MATHEMATICS TO A LEVEL THAT IS SUF ÚCIENT TO UNDERSTAND AND APPLY THE UNDERPINNING THEORY FOR EXAMPLE TO CALCULATE THE VALUES REQUIRED TO ACHIEVE A PARTICULAR TIME CONSTANT in a C-R CIRCUIT )F YOU ARE INTENDING

tO PROGRESS TO HIGHER LEVEL COURSES IN ELECTRONICS YOU WILL REQUIRE FURTHER STUDY OF MATHEMATICS AT ,EVEL BUT PLEASE DONmT LET THIS PUT YOU OFF q THE MOST IMPORTANT THING IS TO DEVELOP A lFEELm FOR HOW ELECTRONIC CIRCUITS BEHAVE AND THE BEST WAY TO DO THIS IS TO DO IT THE lPRACTICAL WAYm 'OOD LUCK WITH YOUR STUDIES OF ELECTRONICS AND DONmT FORGET THAT lSUMS CIRCUITS UNDERSTANDINGmØ Mike and Richard Tooley

Everyday Practical Electronics, September 2011

TEACH-IN 2011 – Topic Index 555 timer 556 timer 741 operational ampliﬁer ADC AND logic Acceptor circuit Accuracy Active ﬁlter Ampere Amplitude Analogue meter Analogue signal Analogue-to-digital conversion Anode Astable oscillator Astable pulse generator Attenuators Automatic light switch Automatic routing BJT

4-53, 7-44, 7-45 7-46, 7-53 5-48 1-51, 9-49, 9-51 6-45, 6-47 8-49 9-49 8-50 1-51, 2-51 1-53 10-43 1-51, 9-47 1-51, 9-46, 9-49 3-48 4-55 7-48 8-46 5-56 10-49 4-46, 4-47, 4-48, 4-49 Balanced attenuator 8-47 Band-gap reference 9-49 Band-pass filter 8-47, 8-48, 8-57 Band-stop filter 8-47, 8-48 Bandwidth 5-51, 8-50 Base 4-46 Batteries 1-54 Bias 3-48, 4-50 Binary 6-49, 9-46 Binary-weighted DAC 9-48, 9-52 Bipolar junction transistor 4-46, 4-47 Bistable 6-48 Bits per second 1-51 Block schematic 1-55 Boolean logic 6-46 Bridge rectifier 3-50 Buffer 6-46 C-R circuits 2-54 C-R high-pass filter 8-48 C-R low-pass filter 8-48 CLEAR input 6-48, 6-49 CMOS 6-50 CRT 10-44 Capacitors 2-53, 2-57, 2-58 Cathode 3-48 Cathode ray tube 10-44 Cells 1-54 Characteristic impedance 8-50 Charge 2-54 Circuit Wizard 1-56, 10-48 Collector 4-46 Collector load 4-50 Colour code 2-52 Combinational logic 6-47 Common base 4-48 Common collector 4-48 Common emitter 4-48 Common-emitter amplifier 4-49, 4-51 Comparator 5-53, 5-55 Complex waveform 1-52 Counter 7-52 Current 1-51 Current gain 4-49, 4-53, 5-50, 8-50 Current measurement 10-43, 10-44 Everyday Practical Electronics, September 2011

Teach-In 2011

Cut-off frequency D-type bistable DAC DIL package Darlington transistor Decade counter Decay Decibels Depletion mode MOSFET Dielectric Differential amplifier Digital logic Digital meter Digital signal Digital-to-analogue conversion Digital-to-analogue converter Diode characteristics Diodes Discharge Dual timer Dual-in-line Dual-slope ADC Duty cycle Electric charge Electrolytic capacitor Emitter Energy storage Enhancement-mode MOSFET Equivalent circuit Exclusive-NOR logic Exclusive-OR logic Exponential decay Exponential growth FET Feedback Field effect transistor Filters Fixed resistor Flash ADC Follower Forward bias Frequency Frequency response Full-wave rectifier Gain Gain-bandwidth product Gates Germanium Giga Graticule Growth Half-wave rectifier Hertz High-frequency cut-off High-frequency roll-off High-pass filter Input resistance Integrated circuits Intruder alarm Inversion Inverter Inverting amplifier Inverting input J-K bistable JFET

5-52, 8-51, 8-49 6-48, 6-50 1-51, 9-47, 9-49 6-50 4-48 6-54 2-55 8-50 4-48 2-53 5-52 6-44 10-43 9-47 9-47 1-51 3-49, 3-51 3-48, 3-52 2-54 7-52 6-50 9-51 1-54 2-54 2-53 4-46 2-54 4-48 5-50 6-46, 6-47 6-46, 6-47 2-55 2-55 4-46, 4-47 4-51 4-46, 4-47 8-47, 8-51 2-51 9-50 5-52, 5-53 3-48 1-53 5-51, 5-52 3-50 4-53, 5-50, 5-51 5-51 6-45 3-49 1-52 10-44 2-55 3-50 1-51 5-52 5-52 8-47, 8-48, 8-51, 8-50, 8-56 5-50 5-48 6-53 6-46 6-46, 6-47 5-52, 5-54 5-49 6-48, 6-49 4-48

Teach-In 2011 Kilo

1-52 Kitchen timer 7-50 L-C band-pass filter 8-49 L-C band-stop filter 8-49 LDR 2-51 LED 3-50, 3-51, 3-55 LED flasher 7-51 Light-dependent resistor 2-51 Light-emitting diode 3-50 Light-emitting diodes 3-51 Load 4-48, 4-50 Logic 6-44, 6-47 Logic 0 6-44 Logic 1 6-44 Logic gates 6-45, 6-46, 6-52 Low-frequency cut-off 5-52 Low-frequency roll-off 5-52 Low-pass filter 8-47, 8-48, 8-51, 8-50, 8-55 MOSFET 4-48 MSB 9-46 Matching 8-50 Mega 1-52 Micro 1-52 Mid-band 5-52 Milli 1-52 Monostable pulse generator 7-46 Most significant bit 9-46 Motor control circuit 4-53 Multimeters 10-42, 10-43 Multiples 1-52 Music 1-52 N-type material 3-48, 4-46 NAND logic 6-46, 6-47 NOT logic 6-46 NPN transistor 4-46, 4-47 Nano 1-52 Negative feedback 4-51, 5-51 Non-inverting amplifier 5-52 Non-inverting input 5-49 OR logic 6-45, 6-46, 6-47 Off state 6-44 Off time 1-53 Ohm 1-51, 2-51 Ohm’s Law 2-50, 2-56 On state 6-44 On time 1-53, 7-46 Operating point 4-50 Operational amplifier 5-48, 5-49 Oscillator 4-55, 5-56 Oscilloscope 10-44, 10-45 Output resistance 5-50 P-type material 3-48, 4-46 PCB 10-48 PNP transistor 4-46, 4-47 PRESET input 6-48, 6-49 Parallel plate capacitor 2-53 Periodic time 1-53 Phase shift 5-49 Photodiode 3-50 Pi-network 8-47 Polarising voltage 2-53 Potentiometer 2-51 Power gain 5-50, 8-50 Power supplies 1-54 Pre-set resistor 2-51 Printed circuit board 10-48 Pulse generator 7-46, 7-48 Pulse period 1-53

Pulse repetition frequency Pulse waveform Q-factor Quantisation R-2R ladder DAC RESET input Ramp waveform Ramp-type ADC Rats nest Rectifier Rectifier diode Rejector circuit Resistor colour code Resistors Resolution Resonance Reverse bias Ripple counter Roll-off SET input Sallen and Key filter Saturated switch Sawtooth waveform Schematic diagram Second-order filter Semiconductor Signal diode Signal diodes Signals Silicon Simulation Sinking Sourcing Speech Square wave generator Sub-multiples Successive approx. ADC T-network TTL Temp.-sensitive resistor Termination Thermistor Time constant Timer circuit Timing diagram Tolerance Transfer characteristic Transformers Transistor amplifier Transistor switch Transistors Triangle waveform Trigger input Unbalanced attenuator Valves Variable capacitor Variable resistor Virtual instrument Virtual test Volt Voltage follower Voltage gain Voltage measurement Watt Waveform measurement Waveforms

1-53, 7-48 1-52, 1-53 8-50 9-46, 9-47 9-48 6-48 1-52 9-50, 9-51 10-51 3-50 3-49, 3-50 8-49 2-52 2-51 9-49 8-49 3-48 6-53 5-52 6-48 8-50 4-52 1-52 1-55 8-56 3-48 3-50 3-49 1-51, 1-50 3-49 1-56 7-45 7-45 1-52 7-49 1-52 9-50 8-47 6-50 2-51 8-50 2-51 2-55 7-47 6-48, 6-49 2-51 4-49 3-50 4-54 4-51 4-46 1-52 7-48 8-47 5-57 2-53 2-51 10-45 10-49 1-51, 2-51 5-52, 5-53 5-50, 5-51, 8-50 10-43, 10-44 1-51 10-45 1-52, 1-58

Zener diode 3-50, 3-51, 3-54 Everyday Practical Electronics, September 2011

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LCD+Keyboard Shield

10-Segments LED Bar Display

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MicroSD Breakout Board

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