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SA Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
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SA Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
CAMBRIDGE NATIONAL LEVEL 1 / LEVEL 2
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Engineering Programmable Systems Revision Guide and Workbook
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David Hills-Taylor
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
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First published 2022
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Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Contents Preparing for the exam Your Revision Guide and Workbook
4
Planning your revision
5
Revision techniques
7
Getting ready for the exam
9
What to expect in the exam
10
Revision checklist
16
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Unit R047: Principles of electronic and programmable systems Revision Guide TA1:
Basic electronic circuit principles
18
TA2:
Electronic and programmable systems, components and devices
26
TA3:
Methods of prototyping and testing systems and circuits
50
TA4:
Commercial circuit production and construction methods
59
TA1:
Basic electronic circuit principles
67
TA2:
Electronic and programmable systems, components and devices
73
TA3:
Methods of prototyping and testing systems and circuits
90
TA4:
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Workbook
95
Commercial circuit production and construction methods
Glossary
100
Command words
105
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Key terms
Answers
Answers to ‘Practise it!’ activities 106 Answers to Workbook questions 109
Acknowledgements 119
3 Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Preparing for the exam Your Revision Guide and Workbook Your Revision Guide will support you in preparing for the exam for Unit R047 Principles of electronic and programmable systems. This is the externally assessed unit of your Engineering Programmable Systems course. The Revision Guide contains two types of pages as shown below: •
Content pages help you revise the content you need to know.
•
Workbook pages with practice exam-style questions to help you prepare for your exam.
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Use these page references to move easily between the linked Revision Guide and Workbook pages.
What you need to know summarises key things you need to know for the topic.
the key points you need to remember.
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Activities
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Revision summary
to help you revise topics, test your knowledge and practise questions.
Workbook pages match the Revision Guide pages.
Practice short- and longanswer questions to help you prepare for the exam.
4
Write your answers in the spaces provided. Some of these answers have been started for you. Preparing for the exam
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Planning your revision Countdown to the exam Revision checklists are a good way for you to plan and structure your revision. They also allow you to make sure you have covered everything you need to cover:
Revision planner checklist Time before Things to do the exam Draw up a revision timetable so that you know how much time you have to get through everything.
•
Use the revision checklist on pages 16–18 to work out which topics you need to cover.
•
Use the topic area headings and bullets to organise your notes and to make sure you’ve covered everything in the specification.
•
Don’t do too much in one day – a couple of hours of good-quality work in a day is better than trying to cram.
•
Work out which of the areas you still find difficult and plan when you’ll cover them.
•
You may be able to discuss tricky topics with your teacher or class colleagues.
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4−6 weeks
•
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6–8 weeks
As you feel you’ve got to grips with some of the knowledge, you can ‘tick off’ the parts that have been worrying you.
•
Make the most of the revision sessions you’re offered in class. Don’t skip them!
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•
1 week
•
Make a daily plan to revise those few topics you’re not happy with and look back at your revision cards (see below) if you’ve made some.
Day before
•
Try not to cram today – get some exercise and relax in the afternoon.
•
Make sure you know what time and where the exam is and put all your things out (pencils, pens, calculator, bus pass, water) ready for the next day.
•
Get a good night’s sleep!
Revise it! Using the example above, create your own revision checklist. Identify areas that you are not so confident about and think of ways to tackle these.
Preparing for the exam
5
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Revision tips
Plan your revision
Choose the methods Make a list of all the key that work for you dates from when you For example: • use highlighters for key words and phrases
start your revision up to the exam date.
Plan to space your revision out so that you don’t do everything at once!
Take breaks
• make note cards
Plan regular breaks in your revision. Go for a short walk or get some fresh air. It will make you more focused when you do revise!
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• use mnemonics (the first letter of words): for example, ‘COUP’ stands for: current out of positive.
Lear n ever ythi ng!
Identify your strengths and weaknesses
Questions can be asked about any area of the specification.
Identify areas that you feel less confident about. Allow additional time to revise these areas.
It is easier to answer a question if you have revised everything.
Practis e!
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Stay healthy!
Don’t cram!
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Exercise, fresh air, good food and staying hydrated all help your revision.
Att end revi sion clas ses !
Don’t skip revision classes – it can really help to revise with your friends as well as by yourself.
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Practising exam-style questions will help you get to grips with the question types, time pressure and format of the exam.
Use mind maps! Mind maps are great for connecting ideas and memorising information more easily and quickly.
Find a quiet space
Variety is the spice of life!
It can be difficult to revise in loud or busy spaces, so try to find somewhere calm to work. You could use headphones and music to block out distractions.
Mix up your revision methods. Watch videos and listen to podcasts as well as making notes and mind maps. Preparing for the exam
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Revision techniques Flash cards/revision cards These are useful for summarising content, key word definitions and important facts. Use colours to make certain things stand out – for example, you could use different colours for advantages and disadvantages or for key words. You can test yourself using the revision cards.
Mind maps
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These are a really useful visual summary of information and you can put them on the wall. They allow you to show links between ideas and concepts. You can start by adding the topic to the centre of the diagram and then add the sub-topics around that and a summary of the information.
Current out of positive – COUP
Measured in volts, V
The flow of electrons around a circuit Measured in amps, A
V
The difference in electric potential between two points in a circuit
Ohm’s law – V = IR
A
Current
Potential difference
Also known as voltage
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Can be AC or DC Watt’s law – P = IV
Power
ELECTRONIC CIRCUIT PARAMETERS
Measured in ohms, Ω Resistance The opposition to the flow of current around a circuit
Measured in watts, W
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The rate at which electrical energy is transferred by a circuit
Capacitance
Measured in farads, F
The amount of charge that a component or circuit can store
Frequency
Measured in hertz, Hz
The number of waves that pass a fixed point over a set time period
Revise it! Create a mind map for a topic of your choice.
Preparing for the exam
7
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Highlighting Making notes and highlighting key areas to go back to is a good way of working out what you know and don’t know. You can then use these notes as you come to your final revision. You can use different colours to highlight different factors or different types of information. For example, when revising different types of electronic components, you could colour code which are input, process or output devices.
Summaries
Mnemonics
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On the revision pages of this book, you’ll find summaries of key ideas and themes. Use these to help you summarise the key points you’ll need to remember to answer questions on those topics. For example, you need to know the characteristics of measurement and test equipment and how they are used. You can make a summary of these yourself – and if you think through these points in the exam, you are more likely to remember them.
A mnemonic is another useful way of remembering key facts by using the first letter of each of the parts to make up a memorable phrase. For example, ‘victory in racing’ can be used to remember the formula V = IR.
Quizzes
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Everyone enjoys quizzes, and creating and sharing quizzes with your friends and class is a great way to remember facts and concepts. You could suggest to your teacher that in pairs you create a quiz of 10 questions and each week go through them together – swapping answers. It’s also a good way for you to check your knowledge. Make a note of the areas where you really didn’t know the answer and add these to your revision list.
Practice questions
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Doing past papers and practice exam questions is an essential part of your revision. It prepares you for answering different types of exam questions and allows you to become familiar with the wording of the questions used by OCR. You should also use the mark scheme. This will help you understand how to get full marks for each question. It is helpful to highlight key words in exam questions so you’re clear what the question is asking before you answer it.
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Preparing for the exam
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Getting ready for the exam Use the revision checklist and all your revision material to make sure you are as prepared as possible. Do plenty of practice with exam questions and quick quizzes.
In the exam
Keep hydrated but don’t drink too much
Make sure you have all the things you need
Get plenty of sleep Make sure you get a good night’s sleep the night before the exam. Don’t stay up late cramming as you need time to switch off and relax before going to bed.
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It’s important that you stay hydrated but don’t overdo it or else you’ll be running to the toilet. Exams can make you a bit nervous too which means you might need to go to the toilet a bit more frequently. Water is best.
Give yourself time to complete the whole paper, and check through it for mistakes. Most importantly, try to stay calm and relaxed – remember, this is your time to show off what you know!
Eat a good, healthy meal
Get everything ready the night before – including all writing equipment, a calculator if you need one (and are allowed one), a water bottle, tissues if you have a sniff, and any identification you might need (candidate number if you have been given one).
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Getting ready for the exam
Have a good, healthy meal that you enjoy the night before the exam and a filling breakfast on the day of the exam to give you a boost ready for your exam.
Arrive in plenty of time
Know when and where the exam is. Get there at least 15 minutes before it starts. If your exam is in an unfamiliar part of the school and away from where you normally study, you might have to leave home a bit earlier. Don’t be distracted on the way!
Preparing for the exam
Don’t be tempted to do too much cramming Too much last-minute cramming can scramble your brain! You may find that being relaxed will help you recall the facts you need rather than attempting last-minute cramming, but you may also want to revise the key facts before setting off for the exam.
Set your alarm If your exam is in the morning, set an alarm or two so you have plenty of time to get to the exam. If you’re still worried about oversleeping, ask a friend or someone in your family to make sure you’re up.
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Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
What to expect in the exam As part of your qualification in Engineering Programmable Systems you will be taking an exam that is worth 40% of your marks. It is important that from the beginning you start to think about the exam and the skills you’ll need to get the best possible grade. Answering exam questions is a skill. Like any other skill, it can be learnt, practised and improved. Below is an outline of what to expect in the exam, the types of questions and what the paper looks like. You need to answer all the questions.
Types of questions to expect in the exam Exam questions can be asked about any area of the specification, which means that you have to learn everything!
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The exam paper will be made up of two sections, with different types of questions. Section A will contain multiple-choice questions, and Section B will contain both short and long-answer questions. Question type
Description
Multiple-choice question (MCQ)
• •
A question with four answer options. Worth 1 mark.
Short-answer question
• •
Usually requires a one-word answer, a simple sentence or a short paragraph. Worth 1–4 marks.
Long-answer question
• • •
Open-response question where you are expected to do a piece of extended writing. Worth 6 marks. These questions allow you to be assessed on the quality of your written communication.
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Understanding the language of the exam
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The command word is the key term that tells you how to answer the question. It is essential to know what the different command words mean and what they are asking you to do. It is easy to confuse the words and provide too much information, not enough information or the wrong information. The tables below will help you understand what each command word is asking you to do.
Command words that ask you to get creative Command word
OCR definition
How you should approach it
Create
•
Produce a visual solution to a problem (for example: a mind map, flow chart or visualisation).
Show your answer in a visual way. You might want to use a mind map, flow chart or a diagram. Think about what is the best way to show the required information.
Draw
•
Produce a picture or diagram.
Create a picture/diagram to show the relevant information.
Command words that ask you to do your maths Command word
OCR definition
How you should approach it
Calculate
•
Do your maths. Give the final answer but make sure you show how you got there.
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Get a numerical answer showing how it has been worked out.
Preparing for the exam
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Command words that ask you to choose the correct answer Command word
OCR definition
How you should approach it
Choose
•
Select an answer from options given.
Pick the option that you think is correct.
Circle
•
Select an answer from options given.
Draw a circle around the right answer.
Identify
• •
Select an answer from options given. Recognise, name or provide factors or features.
Either choose the correct answer from those given or write the name, factors or features that are asked for.
Command words that ask you to add to something OCR definition
How you should approach it
Annotate
•
Add information, for example to a table, diagram or graph, until it is final. Add all the needed or appropriate parts.
Add short notes to the table/diagram/graph to say what each part is.
•
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Command word
Complete
• •
Add all the needed or appropriate parts. Add information, for example to a table, diagram or graph, until it is final.
Add the information that is missing. Often you will need to give just one word as an answer but sometimes you may need to write more. You may need to finish drawing a diagram or graph.
Fill in
• •
Add all the needed or appropriate parts. Add information, for example to a table, diagram or graph, until it is final.
Add the information that is missing. Often you will need to give just one word as an answer but sometimes you may need to write more.
Label
•
Add information, for example to a table, diagram or graph, until it is final. Add all the needed or appropriate parts.
This often refers to a diagram or a picture. Add words or short phrases to say what each part is. You could add arrows next to your label that point to the right part of the diagram/graph.
•
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Command words that ask you to give the main points Command word
OCR definition
How you should approach it
Outline
•
Give a short account, summary or description.
Write about the main points. Don’t write lots of detailed information.
• •
Give factors or features. Give short, factual answers.
Give a short answer that names factors or features of something. Sometimes you will be asked to give a certain number of factors/ features.
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State
Command words that ask you to be factual Command word
OCR definition
How you should approach it
Describe
•
Give an account including all the relevant characteristics, qualities or events. Give a detailed account.
This is the ‘what’. Write about what something is.
Give reasons for and/or causes of. Use the words ‘because’ or ‘therefore’ in answers.
This is the ‘how’ and the ‘why’. Write about how something happens or works and why it does.
•
Explain
• •
Preparing for the exam
11
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Command words that ask you to give an opinion Command word
OCR definition
How you should approach it
Analyse
•
Separate or break down information into parts and identify its characteristics or elements. Explain the pros and cons of a topic or argument and make reasoned comments. Explain the impacts of actions using a logical chain of reasoning.
This term wants you to write about the details. Write about each part in turn, giving key information and saying what is good or bad about it.
• • •
Give an account of the similarities and differences between two or more items or situations.
‘Compare’ means to say what is the same about two (or more) things. ‘Contrast’ means to say what is different about two (or more) things.
Discuss
•
Present, analyse and evaluate relevant points (for example, for/against an argument).
Write about something in detail, including its strengths and weaknesses. Say what you think about each side of the argument. You don’t need to take a side.
Evaluate
•
Make a reasoned qualitative judgement considering different factors and using available knowledge/experience.
Write down the arguments for and against something. Then give your opinion about which is the strongest argument.
Justify
•
Give good reasons for offering an opinion Write what you think would be the best or reaching a conclusion. option and say why you think this. Give evidence to support your answer.
Practise it!
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Compare and contrast
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Now go to www.cambridge.org/go/ and complete the practice questions on understanding the exam command words.
Common exam mistakes
Why it matters!
Not attempting a question
You won’t get any marks for a blank answer. • •
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Common mistakes
Not answering the question that is asked
You won’t get any marks for writing about another topic.
Not providing enough points to achieve the marks
You won’t gain full marks.
Solutions
• • • • • •
•
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Answer every question. Write something – you may pick up a few marks, which can add up to make the difference between grades. Use your general knowledge. State the obvious. Know what the command words are looking for. RTQ – read the question. ATQ – answer the question. Look at the number of marks next to the question – one mark = one point; two marks = two points; three marks = three points, etc. Consider if the question requires further explanation or discussion.
Preparing for the exam
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Answering long-answer questions Planning your answer To help you organise your thoughts, it is helpful to plan your answer for long-answer questions. You don’t need to take too long. A spider diagram, for example, will help you get your answer in the right order and makes sure you don’t forget anything. For example:
Lack flexibility
Not ideal for complex programs
Highly visual
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Easy to produce
Block-based editors
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Drag and drop interface
Restricted to the ‘blocks’ available
Not always easy to follow
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Speed of writing
Revise it!
Create a spider diagram plan like the one above for the following question: ‘An engineer decides to produce a prototype of a system to check that it works.’ ‘Explain the advantages and disadvantages of using a breadboard to prototype the system.’
(6 marks)
Tip: You could refer to page 52 of the Revision Guide to help you.
Preparing for the exam
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Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
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Make sure you know how long you have got.
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The exam paper
Write your first name and surname clearly in the box.
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Ensure that you write clear structured answers so that you can get maximum marks.
Preparing for the exam
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
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The number of marks indicates the number of points you need to give. In this case, one point is needed.
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The question is asking for one answer.
Highlight or underline key words in the question. Here you need to think carefully about what a megaohm is. Preparing for the exam
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Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Revision checklist Topic Area
What you should know
Topic Area 1:
1.1 Electronic circuit parameters
Basic electronic circuit principles
•
The meaning and unit of measurement of different electronic circuit parameters: potential difference, current, resistance, capacitance, power and frequency
•
The multiples and submultiples used with electronic circuit parameters, and how to convert between them
1.2 Electronic circuit theory, laws and associated calculations
•
The differences between series and parallel circuits
•
How to calculate the total resistance of series and parallel circuits
•
The differences between analogue and digital signals, including their waveform characteristics
•
The differences between alternating current (AC) and direct current (DC)
•
How to interpret and calculate values using Ohm’s law
•
How to interpret and calculate values using Watt’s law
2.1 Methods of representing electronic circuits and systems and interpretation of them •
How to interpret system block diagrams
•
The differences between open and closed loop systems
•
How to interpret circuit schematics
•
How to interpret printed circuit board (PCB) layouts
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Electronic and programmable systems, components and devices
What is meant by electron flow
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Topic Area 2:
•
2.2 The purpose, function and typical applications of electronic circuit components and devices including the recognition and interpretation of circuit symbols The purpose, function and applications of different types of switches: SPST, push-to-make, push-to-break, tilt, reed and QTC switches
•
The purpose, function and applications of different types of sensors and touch screens: LDRs, photodiodes, NTC thermistors, and pressure, infrared and smart sensors
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•
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•
The purpose, function and applications of amplifiers
•
The purpose, function and applications of counters
•
The purpose, function and applications of timers
•
The purpose, function and applications of latches
•
The purpose, function and applications of pulse generators
•
The purpose, function and applications of analogue to digital converters (ADCs)
•
The purpose, function and applications of logic gates, including their truth tables: AND, OR, NOT and NAND
•
How to apply logic gates both singly and in combination
•
The purpose, function and applications of different output components and devices: lamps, LEDs, LCDs, buzzers, piezo sounders and motors
•
The purpose, function and applications of drivers and interface devices: NPN transistors, Darlington drivers and relays
Revision checklist
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
•
The purpose, function and applications of resistors
•
The purpose, function and applications of capacitors
•
How and why different power supplies are used for different applications: batteries, photovoltaic (solar) cells, supercapacitors and mains adaptors
•
The characteristics of different types of wiring, and how they are suited to different applications: single- and multi-strand wire
2.3 Programmable components and systems How and why programmable components are used in the design and manufacture of electronic systems: microcontrollers and programmable logic controllers (PLCs)
•
The main features of different programming languages and systems, and how they are suited to different applications: text-based, block-based and flowchart systems
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•
Topic Area 3:
3.1 The purpose and characteristics of methods of prototyping circuits and systems
Methods of prototyping and testing systems and circuits
•
The purpose, characteristics, advantages and disadvantages of producing CAD models of circuits and systems
•
The purpose, characteristics, advantages and disadvantages of producing models of circuits and systems using non-permanent methods: breadboard and modular systems kits
•
The purpose, characteristics, advantages and disadvantages of producing models of circuits and systems using permanent methods: stripboard and printed circuit boards (PCBs)
•
The characteristics, purpose and use of measurement and test equipment: multimeter, continuity tester and logic probe
•
The characteristics, purpose and use of measurement and test equipment: oscilloscope and signal generator
4.1 Printed circuit boards (PCBs)
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Topic Area 4:
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3.2 The main characteristics, purpose and use of physical and virtual measurement and test equipment
Commercial circuit production and construction methods
•
How and why printed circuit boards (PCBs) are produced using the photo etching method
•
How and why PCBs are produced using CAM milling/routing processes
•
The characteristics and typical uses of single-sided PCBs
•
The characteristics and typical uses of double-sided PCBs
•
The characteristics and typical uses of flexible PCBs
4.2 The characteristics and processes of commercial circuit assembly methods
Revision checklist
•
The characteristics, uses, advantages and disadvantages of surface mount technology (SMT)
•
The processes used to construct SMT circuits
•
The characteristics, uses, advantages and disadvantages of through-hole circuit construction
•
The characteristics, uses, advantages and disadvantages of manual soldering
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Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Electronic circuit parameters 1
see p. 67
What you need to know •
What is meant by the terms: potential difference, current and resistance
•
The units of measurement for potential difference, current and resistance.
Parameters are key values that can be measured within an electronic circuit. They help engineers to understand how circuits work.
Circuit parameters 1
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Potential difference (voltage) is the difference in electrical potential between two points in a circuit.
Circuit parameters
Current is created by the flow of electrons around a circuit. Electrons carry a negative charge.
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Resistance is the opposition to the flow of current.
Ohm’s law shows how potential difference (voltage), current and resistance are related to each other.
Units of measurement
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The table shows the units that are used to measure each parameter and how each is abbreviated. Parameter
Unit of measurement
Unit abbreviation
Potential difference
volt
V
Current
amp
A
Resistance
ohm
Ω
For example, a current of 2 amps could also be written as 2 A. A resistance of 330 ohms could be written as 330 Ω.
Practise it!
Remember it!
State the units of measurement for potential difference, current and resistance.
•
Potential difference (voltage) ‘pushes’ current around a circuit.
•
Current is a flow of electrons.
•
Resistance opposes current flow.
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(3 marks)
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Electronic circuit parameters 2
see p. 67
What you need to know •
What is meant by the terms: capacitance, power and frequency
•
The units of measurement for capacitance, power and frequency.
Circuit parameters 2
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Capacitance is the ability of a component or circuit to store electrical charge.
Frequency is the number of signal wave cycles that pass a fixed point over a set amount of time.
More circuit parameters
Power is the rate at which energy is transferred by a circuit.
Watt’s law shows how power, current and potential difference (voltage) are related to each other.
Units of measurement
The table shows the units that are used to measure each parameter and how each is abbreviated. Parameter
Power Frequency
Unit abbreviation
farad
F
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Capacitance
Unit of measurement
watt
W
hertz
Hz
Frequency in waveforms
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Frequency is important when understanding electronic signal waveforms. For example, when analysing sine waves.
1 cycle period
low frequency
One hertz is equal to one wave cycle per second: frequency = f=
1 time period
high frequency
1 T
period
Revise it!
Remember it!
•
Make a list of all six main electrical parameters.
•
Capacitance shows how well a component stores charge.
•
Write down the meaning and unit of measurement for each parameter.
•
Power is the rate of energy transferred.
•
Frequency gives the number of wave cycles per second.
Revision Guide
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Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Multiples and submultiples
see p. 68
What you need to know •
The purpose of multiples and submultiples
•
How to simplify and convert units using multiples and submultiples.
Multiples and submultiples allow large or small measured values to be written in a clearer and easier to understand format.
Multiples and submultiples
PL E
The table shows the multiples and submultiples that are used to simplify measured electronic circuit parameters.
The multiple or submultiple, or its abbreviation, replaces the factor or decimal number. Multiple or submultiple
Abbreviation
Factor
Decimal
mega
M
106
1 000 000
kilo
k
103
1000
milli
m
10−3
0.001
micro
μ
10−6
0.000 001
nano
n
10−9
0.000 000 001
pico
p
10−12
0.000 000 000 001
M
Worked examples
1000 volts = 1 kilovolt = 1 kV
•
0.03 A = 30 milliamps = 30 mA
•
0.000 047 F = 47 microfarads = 47 μF
•
33 MΩ = 33 megaohms = 33 × 106 Ω
SA
•
•
1 pHz = 1 picohertz = 1 × 10−12 Hz
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5 nF = 5 nanofarads = 5 × 10−9 F
Measured values can give a very large or a very small number.
Practise it!
Remember it!
1
Explain the purpose of multiples (2 marks) and submultiples.
•
Multiples and submultiples are used to simplify large or small measurements.
2
Circle the correct simplification for 1200 V.
•
They can be abbreviated to save space.
20
(1 mark)
(a) 12 nV
(c) 1.2 kV
(b) 1.2 mV
(d) 12 kV
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Series and parallel circuits
see p. 69
What you need to know •
The differences between series and parallel circuits in terms of electron flow
•
The typical uses of series and parallel circuits.
Electronic circuit components can be arranged in different formats. The two main ways of doing this are in series and in parallel.
Types of circuits
Series circuits
PL E
A flow of electrons creates an electrical current. The type of circuit affects how the current flows around it.
•
Components are connected in one ‘chain’ one after another.
•
There is only one path for the current to flow through.
•
B1
The current is the same through any component.
9V
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The sum of the voltages across all components is equal to the voltage of the power supply (e.g. 9 V).
Parallel circuits
Components are connected via different ‘loops’, called branches.
•
There is more than one path for the current to flow through.
B1
M
•
•
The total current in the circuit is equal to the sum of the current through each component.
•
The voltage is the same across each component.
+
BL1
BL2
BL3
BL2
BL3
+
9V
BL1
Parallel circuits
Series circuits might be used:
Parallel circuits might be used:
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when switching several outputs on and off together – for example, lamps
•
when switching several outputs on and off independently
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when creating a simple AND function
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when creating a simple OR function
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to increase the overall resistance of a circuit
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to reduce the overall resistance of a circuit
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to reduce the overall capacitance of a circuit.
•
to increase the overall capacitance of a circuit.
SA
Series circuits
Practise it!
Remember it!
1
•
Series circuits are arranged using a single chain of components.
•
Parallel circuits are arranged using loops of components.
2
Explain what an electric current is. Explain, using examples, the differences between series and parallel circuits.
Revision Guide
(2 marks)
(4 marks)
21
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Resistors in series and parallel
see p. 69
What you need to know •
How to calculate the total resistance of resistors arranged in series
•
How to calculate the total resistance of resistors arranged in parallel.
Sometimes a circuit requires a resistance that is not possible from a single resistor. To solve this, resistors can be connected in series or in parallel.
Total resistance For resistors in series: Rtot = R1 + R2 + R3
PL E
The total resistance of series and parallel circuits can be calculated.
The total resistance is always higher than the highest resistor value. For resistors in parallel: 1 = 1 + 1 + 1 Rtot R1 R2 R3
The total resistance is always lower than the lowest resistor value.
Resistors in series 330 Ω
R2
R1
R3
M
R1
Resistors in parallel
220 Ω
1 kΩ
330 Ω
Rtot = R1 + R2 + R3
R2
Rtot = 330 + 220 + 1000
220 Ω
SA
Rtot = 1550 Ω = 1.55 kΩ
1 = 1 + 1 Rtot R1 R2 1 1 1 = + Rtot 330 220 Rtot = 132 Ω
Practise it!
Remember it!
1
•
2
22
Calculate the total resistance of a 1 kΩ and a 470 Ω resistor (1 mark) connected in series. Calculate the total resistance of two 330 Ω resistors connected (1 mark) in parallel.
Resistors in series formula: Rtot = R1 + R2 + R3
•
Resistors in parallel formula: 1 = 1 + 1 + 1 Rtot R1 R2 R3
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Analogue and digital signals
see p. 70
What you need to know •
The differences between analogue and digital signals
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The advantages and disadvantages of analogue and digital signals
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The differences between alternating current (AC) and direct current (DC).
Electronic information can be transmitted and received using different types of signals. The main two used are analogue and digital.
Digital signals
Analogue signals send information as a set of continuous values. They are shown as sinusoidal waveforms. For example, light and temperature levels.
Digital signals send information as a series of discrete values, such as ones and zeros. They are shown as square waveforms. For example, logic signals and digital audio signals.
They have advantages and disadvantages.
They have advantages and disadvantages.
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They are more accurate than digital signals.
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There is less noise and distortion.
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They give a truer representation of the signal.
•
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They often suffer from noise and distortion.
They are more flexible and secure than analogue.
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They are lower-quality signals than digital.
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They only use a finite number of values.
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They only represent a sample of the original signal.
PL E
Analogue signals
M
Waveforms
Waveforms have certain characteristics. AC
amplitude
1s time
SA
period (1 cycle)
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The amplitude of the wave is the distance from the centre line to the top of the wave.
•
The frequency is the number of wave cycles per unit time.
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The periodic time is the time taken for one complete wave cycle.
frequency = 2 Hz
AC and DC
Alternating current (AC) changes direction periodically. It is used for long-distance power transmission, as there is very little heat loss. Direct current (DC) only flows in a single direction. It is much easier to store than AC.
Remember it!
Practise it! 1 2
State one difference between analogue and digital signals. Describe the difference between AC and DC.
Revision Guide
(1 mark)
• •
Analogue signals are continuous. Digital signals are discrete.
(2 marks)
23
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Ohm’s law
see p. 71
What you need to know •
The meaning of Ohm’s law
•
How to calculate values using Ohm’s law.
Potential difference (voltage), current and resistance are related to each other. Understanding how is vital to being able to design circuits that work effectively.
V
Interpreting Ohm’s law
PL E
Ohm’s law shows the relationship between potential difference (voltage), current and resistance:
I
voltage (V) = current (I) × resistance (R)
Ohm’s law can be placed in a triangle to help with its rearrangement: •
Cover the value you need to find on the triangle to give the formula.
•
Then use it to work out the value that you need.
Worked example 1
Solution V=I×R V = 0.02 × 220
SA
V = 4.4 V
Worked example 2
A circuit has a power supply of 9 V and a current of 3 A flowing through it. What is the resistance of the circuit?
M
A 220 Ω resistor has a current of 0.02 A flowing through it. What is the voltage across the resistor?
R
Solution V=I×R So, R =
R=
V I
9 3
R=3Ω
Practise it!
Remember it!
1
•
Ohm’s law gives the relationship between potential difference (voltage), current and resistance.
•
The formula for Ohm’s law is:
2
24
A wire has a current of 3 A flowing through it and a resistance of 2.5 Ω. What is the voltage across (2 marks) the wire? A 910 Ω resistor has a voltage of 9 V across it. What is the current (3 marks) flowing through the resistor?
V=I×R
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Watt’s law
see p. 72
What you need to know •
The meaning of Watt’s law
•
How to calculate values using Watt’s law.
Power, current and potential difference (voltage) are related to each other. Understanding how is vital to being able to design circuits that work effectively.
P
Interpreting Watt’s law
PL E
Watt’s law shows the relationship between power, current and potential difference (voltage):
I
power (P) = current (I) × voltage (V)
Watt’s law can be placed in a triangle to help with its rearrangement: •
Cover the value you need to find on the triangle to give the formula.
•
Then use it to work out the value that you need.
Worked example 1
Solution P=I×V P = 0.4 × 9
SA
P = 3.6 W
Worked example 2
A component has a current rating of 5 A and a power rating of 30 W. What is the voltage rating of the component?
M
A 9 V battery can produce a current of 400 mA. What is the power of the battery?
V
Solution P=I×V So, V = V=
P I
30 5
V=6V
Practise it!
Remember it!
1
•
Watt’s law gives the relationship between power, current and voltage.
•
The formula for Watt’s law is:
2
A component has a voltage rating of 12 V and a current rating of 3 A. What is the power rating of (2 marks) the component? A 1.5 V light bulb has a current of 0.025 A flowing through it. What is the power usage of (2 marks) the bulb?
Revision Guide
P=I×V
25
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
