FT A R D Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
FT A R D 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
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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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A catalogue record for this publication is available from the British Library ISBN 978-1-009-12189-7 Paperback with Digital Access (2 Years) ISBN 978-1-009-11388-5 Digital Revision Guide and Workbook (2 Years) ISBN 978-1-009-11389-2 Site License (1 Year)
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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 Unit R047: Principles of electronic and programmable systems Revision Guide Basic electronic circuit principles
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TA2:
Electronic and programmable systems, components and devices
27
TA3:
Methods of prototyping and testing systems and circuits
51
TA4:
Commercial circuit production and construction methods
60
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TA1:
Workbook
Basic electronic circuit principles
68
TA2:
Electronic and programmable systems, components and devices
74
TA3:
Methods of prototyping and testing systems and circuits
91
TA4:
Commercial circuit production and construction methods
96
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Glossary
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TA1:
Key terms
101
Command words
105
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Answers
Answers to ‘Practise it!’ activities 107 Answers to Workbook questions 110
Acknowledgements 120
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 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
Revision summary The key points you need to remember.
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Summarises key things you need to know for the topic.
Activities
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Activities 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.
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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
•
Use the revision checklist on pages 16–17 alongside any previous past papers or assessments 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 spend too much time each day revising; quality, spaced revision is better than studying all day every day.
•
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.
•
As you feel you’ve got to grips with some of the knowledge, you can ‘tick off’ the parts that have been worrying you.
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Draw up a revision timetable so that you know how much time you have to get through everything.
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4−6 weeks
•
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6–8 weeks
Make the most of the revision sessions you’re offered in class. Don’t skip them!
1 week
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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!
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•
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
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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 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.
Don’t cram! Plan to space your revision out so that you don’t do everything at once!
Take breaks
• make note cards
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• use mnemonics (the first letter of words): for example, ‘COUP’ stands for: current out of positive.
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!
Identify your strengths and weaknesses
Questions can be asked about any area of the specification.
It is easier to answer a question if you have revised everything.
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Identify areas that you feel less confident about. Allow additional time to revise these areas.
Lear n ever ythi ng!
Stay healthy!
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Exercise, fresh air, good food and staying hydrated all help your revision.
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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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Practis e! 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
Current
Potential difference
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Also known as voltage
Can be AC or DC Watt’s law – P = IV
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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
Measured in farads, F
Capacitance
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
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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 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.
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Mnemonics
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.
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Practice questions
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.
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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
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.
Make sure you have all the things you need
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.
Eat a good, healthy meal
Getting ready for the exam
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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).
Get plenty of sleep
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Keep hydrated but don’t drink too much
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!
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
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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. Description
Multiple-choice question (MCQ)
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A question with four answer options. Worth 1 mark.
Short-answer question
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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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Question type
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.
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Command words that ask you to get creative Command word
OCR definition
How you should approach it
Create
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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
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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
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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
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Select an answer from options given.
Pick the option that you think is correct.
Circle
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Select an answer from options given.
Draw a circle around the right answer.
Identify
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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 Command word
OCR definition
How you should approach it
Annotate
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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.
• • •
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
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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
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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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Complete
Command words that ask you to give the main points OCR definition
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Command word
How you should approach it
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Give a short account, summary or description.
Write about the main points. Don’t write lots of detailed information.
State
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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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Outline
Command words that ask you to be factual Command word
OCR definition
How you should approach it
Describe
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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
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Command words that ask you to give an opinion Command word
OCR definition
How you should approach it
Analyse
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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
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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
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Make a reasoned qualitative judgement considering different factors and using available knowledge/experience.
Write down the argument for and against something. Then give your opinion about which is the strongest argument.
Justify
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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.
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Compare and contrast
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Practise it!
Now go to www.cambridge.org/go/ and complete the practice questions on understanding the exam command words.
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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
Block-based editors
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Highly visual
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Easy to produce
Drag and drop interface
Restricted to the ‘blocks’ available
Not always easy to follow
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Speed of writing
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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.
The exam paper
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Make sure you know how long you have got.
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.
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 What is meant by electron flow
•
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)
•
Electronic and programmable systems, components and devices
•
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 • • •
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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How to interpret system block diagrams
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Topic Area 2:
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•
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
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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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The purpose, function and applications of amplifiers
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The purpose, function and applications of counters
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The purpose, function and applications of timers
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The purpose, function and applications of latches
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The purpose, function and applications of pulse generators
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The purpose, function and applications of analogue to digital converters (ADCs)
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 logic gates, including their truth tables: AND, OR, NOT and NAND
•
How to apply logic gates both singly and in combination
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The purpose, function and applications of different output components and devices: lamps, LEDs, LCDs, buzzers, piezo sounders and motors
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The purpose, function and applications of drivers and interface devices: NPN transistors, Darlington drivers and relays
•
The purpose, function and applications of resistors
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The purpose, function and applications of capacitors
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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
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•
2.3 Programmable components and systems
•
The main features of different programming languages and systems, and how they are suited to different applications: textbased, block-based and flowchart systems
3.1 The purpose and characteristics of methods of prototyping circuits and systems
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Topic Area 3:
How and why programmable components are used in the design and manufacture of electronic systems: microcontrollers and programmable logic controllers (PLCs)
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•
•
The purpose, characteristics, advantages and disadvantages of producing CAD models of circuits and systems
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The purpose, characteristics, advantages and disadvantages of producing models of circuits and systems using non-permanent methods: breadboard and modular systems kits
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Methods of prototyping and testing systems and circuits
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The purpose, characteristics, advantages and disadvantages of producing models of circuits and systems using permanent methods: stripboard and printed circuit boards (PCBs)
3.2 The main characteristics, purpose and use of physical and virtual measurement and test equipment
Revision checklist
•
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
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Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Topic Area 4:
4.1 Printed circuit boards (PCBs)
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 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
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The characteristics, uses, advantages and disadvantages of manual soldering
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•
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Revision checklist
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
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Resistance is the opposition to the flow of current.
Current is created by the flow of electrons around a circuit. Electrons carry a negative charge.
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Ohm’s law shows how potential difference (voltage), current and resistance 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. Unit of measurement
Unit abbreviation
Potential difference
volt
V
Current
amp
A
Resistance
ohm
Ω
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Parameter
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!
1
•
2
State the units of measurement for potential difference, current and resistance. (3 marks) Explain, using an example, what is meant by frequency when analysing signal waveforms. (2 marks)
Revision Guide
• •
Potential difference (voltage) ‘pushes’ current around a circuit. Current is a flow of electrons. Resistance opposes current flow.
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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 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 Capacitance is the ability of a component or circuit to store electrical charge.
Power is the rate at which energy is transferred by a circuit.
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Frequency is the number of signal wave cycles that pass a fixed point over a set amount of time.
More circuit parameters
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. Unit of measurement
Unit abbreviation
farad
F
watt
W
hertz
Hz
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Parameter Capacitance Power
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Frequency
Frequency in waveforms
Frequency is important when understanding electronic signal waveforms. For example, when analysing sine waves.
1 cycle period
low frequency
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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.
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Revision Guide
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 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. 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
A
FT
Multiple or submultiple
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
•
1 pHz = 1 picohertz = 1 × 10−12 Hz
•
5 nF = 5 nanofarads = 5 × 10−9 F
Measured values can give a very large or a very small number.
D
R
•
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.
(1 mark)
(a) 12 nV
(c) 1.2 kV
(b) 1.2 mV
(d) 12 kV
Revision Guide
21
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 A flow of electrons creates an electrical current. The type of circuit affects how the current flows around it. Series circuits Components are connected in one ‘chain’.
•
There is only one path for the current to flow through.
•
B1
The current is the same through any component.
9V
•
The sum of the voltages across all components is equal to the voltage of the power supply (e.g. 9 V).
FT
•
Parallel circuits
Components are connected via different ‘loops’.
•
There is more than one path for the current to flow through.
A
•
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.
R
•
B1
+
BL1
BL2
BL3
BL2
BL3
+
9V
BL1
Parallel circuits
Series circuits might be used:
Parallel circuits might be used:
•
when switching several outputs on and off together – for example, lamps
•
when switching several outputs on and off independently
•
when creating a simple AND function
•
when creating a simple OR function
•
to increase the overall resistance of a circuit
•
to reduce the overall resistance of a circuit
•
to reduce the overall capacitance of a circuit.
•
to increase the overall capacitance of a circuit.
D
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
22
Explain what an electric current is. Explain, using examples, the differences between series and parallel circuits.
(2 marks)
(4 marks)
Revision Guide
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 The total resistance of series and parallel circuits can be calculated. For resistors in series: Rtot = R1 + R2 + R3 For resistors in parallel: 1 = 1 + 1 + 1 Rtot R1 R2 R3
FT
The total resistance is always higher than the highest resistor value.
The total resistance is always lower than the lowest resistor value.
Resistors in series 330 Ω
220 Ω
R1
R3
1 KΩ
R
Rtot = R1 + R2 + R3
R2
A
R1
Resistors in parallel
Rtot = 330 + 220 + 1000
R2 220 Ω
Rtot = 1550 Ω = 1.55 kΩ
D
330 Ω
1 = 1 + 1 Rtot R1 R2 1 1 1 = + Rtot 330 220 Rtot = 132 Ω
Practise it!
Remember it!
1
•
2
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.
Revision Guide
Resistors in series formula: Rtot = R1 + R2 + R3
•
Resistors in parallel formula: 1 = 1 + 1 + 1 Rtot R1 R2 R3
23
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
•
The advantages and disadvantages of analogue and digital signals
•
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.
•
They are more accurate than digital signals.
•
There is less noise and distortion.
•
They give a truer representation of the signal.
•
•
They often suffer from noise and distortion.
They are more flexible and secure than analogue.
•
They are lower-quality signals than digital.
•
They only use a finite number of values.
•
They only represent a sample of the original signal.
•
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.
•
The periodic time is the time taken for one complete wave cycle.
A
FT
Analogue signals
Waveforms AC
R
Waveforms have certain characteristics. amplitude
1s time
period (1 cycle)
D
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.
Practise it!
Remember it!
1
• •
2
24
State one advantage and one disadvantage of digital signals. (2 marks) Describe the difference between AC and DC. (2 marks)
Analogue signals are continuous. Digital signals are discrete.
Revision Guide
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 Ohm’s law shows the relationship between potential difference (voltage), current and resistance:
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.
A 220 Ω resistor has a current of 0.02 A flowing through it. What is the voltage across the resistor?
R
Solution
Worked example 2
A
Worked example 1
R
FT
I
voltage (V) = current (I) × resistance (R)
V=I×R
V = 0.02 × 220
D
V = 4.4 V
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?
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
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?
Revision Guide
V=I×R
25
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 Watt’s law shows the relationship between power, current and potential difference (voltage):
I
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.
A 9 V battery can produce a current of 400 mA. What is the power of the battery?
R
Solution P=I×V
Worked example 2
A
Worked example 1
V
FT
power (P) = current (I) × voltage (V)
P = 0.4 × 9
D
P = 3.6 W
A component has a current rating of 5 A and a power rating of 30 W. What is the voltage rating of the component?
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
26
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?
P=I×V
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
System block diagrams
see p.73
What you need to know •
The purpose of system block diagrams
•
How to interpret system block diagrams.
The systems approach allows electronic systems to be communicated clearly and effectively. It involves the use of block diagrams to show the different inputs, processes and outputs that will be used.
The systems approach A block diagram gives a top-down overview of a system. The blocks represent groups of components, or subsystems.
•
The arrows show the signals that flow between them.
FT
•
Input
Block diagrams
Process
Output
An input device takes an environmental signal and turns it into an electronic signal. For example, a light sensor.
•
A process device changes the electronic signal in some way. For example, by turning it on for a set amount of time.
•
An output device turns the electronic signal back into an environmental signal. For example, a buzzer produces sound.
R
A
•
Process
Output
Light sensor
Timer
Buzzer
D
Light level
Input
Electronic signal
Sound Electronic signal
Practise it!
Remember it!
1
A block diagram shows a top-down overview of a system in terms of its inputs, processes and outputs.
2
State what is represented by each of the following in a block diagram: (a) the blocks
(1 mark)
(b) the arrows.
(1 mark)
Name the three types of blocks used in a systems diagram. (3 marks)
Revision Guide
27
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Open and closed loop systems
see p.73
What you need to know •
The difference between open and closed loop systems
•
How feedback loops are used in electronic and programmable systems.
The main two types of systems are open loop and closed loop. Understanding the differences between them is an essential part of system design.
Open and closed loop systems A feedback loop is created when the output signal of a system becomes an input signal to the same system. Feedback allows systems to ‘self-correct’. Systems without a feedback loop are called open loop systems. For example, temperature control and robotic arm systems.
•
Systems with at least one feedback loop are called closed loop systems. For example, simple lighting systems, simple timers and counters.
A closed loop system
FT
•
A heating system is a good example of a closed loop system.
The heater is turned on by the microcontroller when the sensor detects that the temperature has dropped below the set level.
•
The new temperature information is then ‘fed back’ to the input of the system.
•
The microcontroller therefore knows when it is warm enough to turn the heater off again.
A
•
Process
R
Input
D
Temperature sensor
Output Heater
Microcontroller
Feedback
Practise it!
Remember it!
1
•
Closed loop systems use feedback, whereas open loop systems do not.
•
Feedback is when the output signal becomes an input signal to the system.
2
28
Describe what is meant by a closed loop system.
(2 marks)
Give two examples of closed loop systems.
(2 marks)
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Circuit schematics
see p.74
What you need to know •
The purpose of circuit schematics
•
How to interpret circuit schematics.
Circuit schematics show how all the individual components in a circuit are joined together. This is very useful for allowing engineers to clearly see the technical detail of each circuit that they are designing.
Interpreting circuit schematics This is a circuit schematic for a transistor switching circuit. Abbreviations are used to label the components
Circuit schematics are usually drawn from left to right, starting with the power supply
FT
Standard symbols are used to represent the components
BL1
VR1 42k
B1 9V
A
R1 525 lux
Q1
R2 1k
The value of a component is shown, if it is known
R
Wires are drawn with straight lines
Why circuit schematics are used
They use standard symbols. Therefore, it is clear which components are being shown in each circuit.
•
They show how all the individual components relate to each other.
•
They take up less space than pictorial diagrams.
•
If drawn in computer aided design (CAD) software, they can often be exported to automatically produce printed circuit board (PCB) layouts.
D
•
Practise it!
Remember it!
1
•
Schematics show how all the individual components in each circuit relate to each other.
•
Standard symbols and abbreviations are used to represent the components.
2
Describe the purpose of circuit schematics.
(2 marks)
State the abbreviation that should be used for each of the following: (a) the first battery in a circuit
(1 mark)
(b) the third resistor in a circuit
(1 mark)
(c) the second transistor in a circuit.
(1 mark)
Revision Guide
29
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Printed circuit board (PCB) layouts
see p.75
What you need to know •
The purpose of PCB layouts
•
How to interpret PCB layouts.
Once a circuit has been designed, a printed circuit board layout needs to be produced ready for manufacture and assembly.
The purpose of PCB layouts Printed circuit board (PCB) layouts show the physical layout of the circuit board that is to be manufactured, including: the layout of the copper tracks that join the components together
•
the pads where components will be soldered.
A PCB layout can be used:
FT
•
•
to produce a mask or a CAD file, to use for manufacturing the circuit board
•
to aid with assembling the components on a circuit board after the board has been manufactured.
Interpreting PCB layouts
A
PCB layouts are usually produced using CAD software. •
•
The ‘real world’ view shows what the PCB will look like with all the components soldered in place.
D
R
The ‘artwork’ view shows the mask that is used during manufacture.
Practise it!
Remember it!
1
•
PCB layouts show how the copper pads and tracks are to be arranged on the physical circuit board.
•
They can be used to produce a mask or exported to computer aided manufacturing (CAM) equipment for manufacture.
2
Describe the purpose of PCB layouts.
(2 marks)
State the purpose of each of the following PCB layout views: (a) artwork (1 mark) (b) real world.
30
(1 mark)
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Input components and devices 1
see p.76
What you need to know •
The purpose and function of different types of switches
•
The typical uses and applications of different types of switches.
Input devices respond to changes in the environment around them. They change environmental information into an electronic signal. Switches are a common type of input device.
Push switch
A single pole single throw (SPST) switch allows current to flow when closed and stops current flow when open.
There are two types of push switch: •
SPST switches can be used for turning power supplies on and off, and for latching output devices on and off. For example, light switches.
Push-to-make switches allow current to flow when pressed.
•
Push-to-break switches prevent current flow when pressed.
FT
SPST switch
Push switches can be used for games and score counting systems, and electronic doorbells.
Tilt switch
A
A tilt switch allows current to flow when tilted to one side.
Quantum tunnelling composite (QTC) switches vary their resistance with applied pressure. They can be used as more complex push switches, or touch sensors.
Reed switch A reed switch allows current to flow when close to an applied magnetic field. Reed switches can be used for door or window sensors in home security systems, and automatic door locks.
D
R
Tilt switches can be used for sensing movement and tip-over warnings. For example, for silos or items on conveyor belts.
Revise it!
Remember it!
•
Create a table showing different types of input devices (switches and sensors).
•
Switches allow or prevent current flow, depending on certain conditions.
•
Add columns for their function, purpose and typical applications.
•
Different types include SPST, push, tilt and reed switches.
•
Draw the circuit symbols for each input device.
Revision Guide
31
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Input components and devices 2
see p.76
What you need to know •
The purpose and function of different types of sensors
•
The typical uses and applications of different types of sensors.
Input devices respond to changes in the environment around them. They change environmental information into an electronic signal. Sensors are another common type of input device.
Light sensors
NTC thermistor
There are two types of light sensors:
A negative temperature coefficient (NTC) thermistor has a resistance that decreases as the temperature level increases, and vice versa.
Photodiodes use light energy to produce a flow of current.
•
LDRs and photodiodes can be used for night and street lighting, light meters and infrared receivers.
Pressure sensor
Infrared sensor
An infrared sensor measures the presence of infrared light within its field of view. Infrared sensors can be used for motion detectors in alarm systems, and proximity sensors for robots.
A
A pressure sensor allows current to flow according to the pressure level.
Pressure sensors can be used for monitoring pressure (for example, within a gas boiler), and fluid flow measurement.
R
Touch screen
NTC thermistors can be used for sensing temperature and climate control systems.
FT
Light-dependent resistors (LDRs) have a resistance that decreases as the light level increases, and vice versa.
•
A touch screen reacts when touched by another conductive medium, such as a finger. This changes the capacitive charge at the point of contact.
Smart sensor A smart sensor is any type of sensor that can send and receive wireless signals to or from a main processing device. Smart sensors can be used for home automation systems, such as automatic curtain openers and lighting systems.
D
Touch screens can be used for car infotainment systems, tablet computers and mobile phones.
Practise it!
Remember it!
Suggest a suitable input device for each of the following applications.
•
Sensors detect changes in the environment around them.
(a) Movement sensor for a home alarm. (1 mark)
•
Different types include light, temperature and infrared sensors.
(b) Climate control system for a food growing facility.
(1 mark)
(c) User interface for a smart home control system.
(1 mark)
32
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Amplifiers
see p.77
What you need to know •
The purpose and function of amplifiers
•
The typical uses and applications of amplifier circuits.
Amplifiers are process devices. Amplifiers are used in a huge range of electronic products, from audio systems to complex communications devices.
Purpose and function of amplifiers +
The amount of amplification is called the amplifier gain. It is calculated by dividing the output signal by the input signal:
–
gain (Av) =
FT
Amplifiers increase the size of the signal that is flowing into them. The signal is usually either a voltage or a current.
Vout I or gain (AI) = out Vin Iin
Op-amp
An operational amplifier (op-amp) is a type of amplifier integrated circuit (IC) that produces an extremely high gain.
•
Op-amps have two inputs (inverting and non-inverting) and one output.
•
Op-amps are often used when comparing an input signal to a reference.
R
Applications
A
•
Communications systems
Audio amplifiers and speaker systems
D
Uses
Temperature control
Comparator circuits
Practise it!
Remember it!
1
•
Amplifiers are used to increase the size of signals, such as voltage or current.
•
Operational amplifiers (op-amps) are often used in comparator circuits.
2
Describe what is meant by amplifier gain. State two applications of amplifier circuits.
Revision Guide
(2 marks) (2 marks)
33
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Counters
see p.77
What you need to know •
The purpose and function of counters
•
The typical uses and applications of counter circuits.
Counters are process devices. Counters are used in a huge range of electronic products and applications, from digital clocks to score counters for games.
Purpose and function of counters Counters add up the number of input signals or pulses received. This is usually in relation to a ‘clock’ input.
FT
Once the counted signals have exceeded the maximum value for the particular IC, the counter will reset back to zero.
Decade counter
A decade counter is a type of counter IC that can count ten decimal digits (0–9).
•
Results of counting can be outputted using a series of light emitting diodes (LEDs) or a digital display.
•
A push-to-make switch or a pulse generator can provide the input signals for each ‘count’.
R
Applications
A
•
D
Digital clocks
Practise it!
2
34
State two applications of counter circuits.
C B
Uses
Waveform generators
Describe the function of a decade counter IC.
UP DN LD CL
Q1 Q2 Q4 Q8
Measurement devices
Score counters
1
L1 L2 L4 L8
Remember it! •
Counters add up the number of input signals received.
•
Decade counters are decimal counters that can count from 0 to 9.
(2 marks) (2 marks)
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Timers
see p.77
What you need to know •
The purpose and function of timers
•
The typical uses and applications of timer circuits.
Timers are process devices. Timers are used in a huge range of electronic products, from security systems to electronic kitchen equipment.
Purpose and function of timers Timers produce an output signal, pulse or time delay that lasts for a certain period of time. For example, turning on a buzzer for five seconds when a doorbell is pressed.
FT
A simple timer can be created using a resistor–capacitor (RC) network, but this can lack accuracy.
555 timer IC •
The 555 timer IC is a type of timer IC that can be used in either astable (pulse generator) or monostable (timer) mode.
•
In monostable mode, the length of each timed pulse is set using resistor and capacitor values.
4
6 2
8 3
1
5
A
Applications
7
R
Alarms and security systems
D
Sports timers
Electronic doorbells Uses
Kitchen timers
Automated lighting systems
Practise it!
Remember it!
1
State two methods of achieving (2 marks) an electronic timer.
•
Timers produce an output signal that remains high or low for a set period of time.
2
State two applications of timer circuits.
•
A 555 timer IC can be used in monostable mode to achieve this.
Revision Guide
(2 marks)
35
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Latches
see p.77
What you need to know •
The purpose and function of latches
•
The typical uses and applications of latching circuits.
Latches are process devices. Latches are used in a huge range of electronic products, from security systems to electronic kitchen equipment.
Purpose and function of latches Latches produce an output signal that stays the same until it is reset. They effectively ‘lock’ it in place.
S (set)
Q set–reset latch
FT
Latches are triggered by a momentary high (on) or low (off) input signal, depending on the type used.
Q’
R (reset)
The output signal can also be high or low.
A bistable multivibrator is a type of latch that can be used to store logic state information.
Thyristor
A thyristor is a component that can be used to provide a simple latching function.
•
A push-to-make switch is typically used as the reset.
R
Applications
A
•
Computer memory
D
Data storage
Uses
Alarms and security systems
Power switching
Practise it!
Remember it!
1
•
Latches, once triggered, ‘lock’ the output signal into either a high or a low state.
•
Thyristors can be used to achieve a simple latching function.
2
36
Describe the function of a latching circuit. State two applications of latching circuits.
(2 marks) (2 marks)
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Pulse generators
see p.77
What you need to know •
The purpose and function of pulse generators
•
The typical uses and applications of pulse generator circuits.
Pulse generators are process devices. Pulse generators are used in a huge range of electronic products, from flashing lighting systems to electronic circuit test equipment.
Purpose and function of pulse generators Pulse generators produce a continuous series of digital pulses.
FT
The output signal cycles between high and low states until stopped. For example, when producing a series of flashing LEDs for a cycle safety light system.
555 astable •
The 555 timer IC acts as a pulse generator when in astable mode.
7
•
The time that the output signal is high (time high) or low (time low) depends on the resistor and capacitor values used.
6 2
A
Applications
R
Flashing lights
4
1
8 3 5
Signal waveform generators
Uses
Providing input signals to counters/digital clocks
D
Pulsing alarm sounders
Practise it!
Remember it!
1
State two components that control the ‘time high’ and ‘time low’ of (2 marks) an astable circuit.
•
Pulse generators produce a sequence of ‘high’ and ‘low’ pulses.
•
2
State two applications of pulse generator circuits.
A 555 timer IC can be used in astable mode to achieve this.
Revision Guide
(2 marks)
37
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Analogue to digital converters
see p.77
What you need to know •
The purpose and function of analogue to digital converters (ADCs)
•
The typical uses and applications of analogue to digital converter circuits.
ADCs are process devices. Digital integrated circuits cannot understand analogue signals. For example, from an analogue sensor. This means they need to be converted before they can be processed.
Purpose and function of ADCs
FT
Analogue to digital converters (ADCs) change analogue signals into digital signals. For example, converting the continuous signal from a temperature or light sensor into a discrete signal that a microcontroller can process. Many modern microcontrollers have ADCs built into them.
ADC analogue signal
digital signal
A
Applications
R
Temperature control systems
Signal processing
Uses
Computer and microcontroller systems
D
Light sensing systems
Practise it!
Remember it!
1
Describe the purpose of analogue (2 marks) to digital converters (ADCs).
•
ADCs take analogue signals and change them into digital signals.
2
State two applications of ADC circuits.
•
This is useful in microcontroller systems that need to interact with analogue sensors.
38
(2 marks)
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Logic gates 1
see p.78
What you need to know •
The purpose and function of different logic gates
•
The truth tables for AND, OR, NOT and NAND logic gates.
Logic gates are process devices. Logic gates respond to, and output digital signals. They produce an output based on the input signals that they receive. The output signal for each combination of input signals is shown using a truth table.
OR gate
An AND gate produces a high (1) output when both inputs are high. The output is low (0) when either or both inputs are low.
An OR gate produces a high (1) output when either or both inputs are high. The output is low (0) when both inputs are low.
Input A
Input B
Output
0
0
0
0
1
0
1
0
0
1
1
1
Input A
Input B
Output
0
0
0
0
1
1
1
0
1
1
1
1
Truth table
A
Truth table
FT
AND gate
NOT gate
NAND gate
R
A NOT gate produces a high (1) output when the input is low, and a low (0) output when the input is high.
A NAND gate produces a low (0) output when both inputs are high. The output is high (1) when either or both inputs are low.
Input
Output
Input A
Input B
Output
0
1
0
0
1
0
0
1
1
1
0
1
1
1
0
1
D
Truth table
Truth table
Revise it!
Remember it!
•
Produce a mind map of everything that you know about logic gates.
•
Logic gates are digital devices that respond to, and output, signals of 1 or 0.
•
Draw the logic gate symbols and truth tables for AND, OR, NOT and NAND gates.
•
•
Add typical uses and applications of logic gates to your mind map.
The truth table for each gate shows what the output state is depending on the inputs.
Revision Guide
39
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Logic gates 2
see p.78
What you need to know •
How logic gates are used both singly and in combination.
Logic gates can be used either on their own or in combination with other gates.
Combining logic gates Sometimes single logic gates cannot perform the functions required by the system designer. AND
FT
Combining them allows the system to perform more complex functions. These can be logic gates of the same or different types.
For example, this diagram shows a lift system with two AND gates. The lift only moves upwards when a person has entered, the floor button has been pressed and the doors have fully closed.
Applications
AND
A
Lift systems
R
Simple computer memory
Alarm systems
D
Uses
Latching circuits
Traffic control systems
Practise it!
Remember it!
1
Identify four types of logic gates. (4 marks)
•
2
State two applications of logic circuits.
Logic gates can be used on their own or in combination with other gates.
•
Combining logic gates allows more complex functions to be achieved.
40
(2 marks)
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Output components and devices 1
see p.79
What you need to know •
The purpose and function of different light output components and devices
•
The typical uses and applications of different light outputs.
Output devices change an electronic signal into an environmental signal that we can understand. For example, light outputs produce visible light, which can be used to light rooms or show information.
Light emitting diode
A lamp produces light when current flows through and heats up a filament.
A light emitting diode (LED) produces light when current flows from the anode (+) to the cathode (−).
Lamps can be used for decorative lighting, task lighting and indicator bulbs.
LEDs can be used for on/off indicators, garden solar lighting, car indicators, room lighting and coloured/ambient lighting.
R
A
FT
Lamp
D
Liquid crystal display
LED display
A liquid crystal display (LCD) uses liquid crystals and a fluorescent backlight to produce visible text and images.
An LED display works like an LCD, but the backlight is provided by LEDs, rather than fluorescent lighting.
LCDs can be used for instrumentation and information panels, TV/monitor screens and digital watches/clocks.
LED displays can be used for instrumentation panels, TV/monitor screens, digital watches/clocks and information screens.
Revise it!
Remember it!
•
Make a list of all the different light output devices you can see around your home or in school/college.
•
Light outputs change an electronic signal into visible light.
•
•
State what each one is used for.
This can then be adapted in the form of electronic displays to show information.
Revision Guide
41
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Output components and devices 2
see p.79
What you need to know •
The purpose and function of different sound and movement output devices
•
The typical uses and applications of different sound and movement outputs.
Output devices change an electronic signal into an environmental signal that we can understand. For example, sound outputs produce audible sounds, whereas motors produce rotary movement.
Buzzer
Piezo sounder
A buzzer uses an internal oscillator to produce a buzzing or bleeping sound when current flows through it.
A piezo sounder uses the piezoelectric effect to produce sound when current flows through it.
A
FT
Buzzers can be used for door buzzers, kitchen timers, quiz buzzers and collision warnings.
Piezo sounders can be used for door and window alarms, musical birthday/gift cards and smoke alarms.
Motor
Generator
R
A motor produces rotary movement when current flows through it. Reversing the direction of the current also reverses the direction of movement.
Generators can be used for producing electrical energy when they are rotated. For example, through wind turbines and hydroelectric dams.
D
Motors can be used for portable fans, robot arms and electric vehicles.
A generator is a motor in reverse.
Practise it!
Remember it!
1
•
Sound outputs change an electronic signal into audible sound.
•
Motors change an electronic signal into rotary movement.
2
42
Identify two output devices that could be used to produce indicator lighting (2 marks) for a car. Identify two output devices that could be used in a door alarm system to produce a (2 marks) warning sound.
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Drivers and interface devices
see p.80
What you need to know •
The purpose and function of transistors, Darlington drivers and relays
•
The typical uses and applications of drivers and interface devices.
Sometimes the process device in a system cannot supply enough current for the output to work effectively. In these instances, a driver (interface device) is needed.
Darlington driver
An NPN transistor allows current to flow from the collector to the emitter when the base voltage is 0.6 V or higher.
A Darlington driver is a pair of transistors connected together to create a much higher current gain.
An NPN transistor can be used as an electronic switch or as a current amplifier.
A Darlington driver can be used when an output device requires a high amount of current to function. For example, when using a microcontroller to control a motor.
Collector
A
Base
FT
NPN transistor
Emitter
Relay
R
A relay is an electrically operated switch. It uses a magnetic field to operate internal switch contacts.
D
A relay can be used as an interface between two separate circuits. For example, switching on a high voltage circuit from a low voltage supply.
Practise it! 1 2
Remember it!
Explain the function of a transistor.
(3 marks)
Describe one application of a relay.
(2 marks)
Revision Guide
•
Drivers increase the signal from the process device to the output of a system so that it can function correctly.
•
Transistors can operate as an amplifier or as an electronic switch.
43
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Resistors
see p.81
What you need to know •
The purpose and function of resistors
•
The typical uses and applications of resistors in circuits.
Sometimes it is necessary to control the flow of current around a circuit. This is where resistors are useful.
Purpose and function Resistors reduce the flow of current through a circuit. There are two types of resistors: Fixed resistors have a set resistance value.
•
In variable resistors, the resistance value can be adjusted.
FT
•
Resistors are passive components. This means they do not introduce any new energy into a circuit or require their own power supply. Fixed resistors are non-polarised. Therefore, they can be connected any way round in a circuit.
A
Uses in circuits
Fixed resistor symbol
Variable resistor symbol
To limit the current to protect other components from too much current.
•
To set the length of time periods or time delays. For example, in an RC network or monostable circuit. This diagram shows an RC timing network.
•
To create potential divider circuits. For example, to allow sensors to interact with process devices.
D
R
•
+
R1
B1
C1
Practise it!
Remember it!
1
Explain the difference between (2 marks) fixed and variable resistors.
•
Resistors reduce the flow of current.
•
They can be fixed or variable.
State two applications of resistors in circuits.
•
They are passive components.
2
44
(2 marks)
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Diodes
see p.82
What you need to know •
The purpose and function of diodes
•
The typical uses and applications of diodes in circuits.
Sometimes it is necessary to control the direction in which current can flow in a circuit. This is where diodes are useful.
Purpose and function Diodes allow current to flow in one direction only, from the anode to the cathode. Most diodes are passive components. However, some diodes are active components, because they can add energy into a circuit. For example, an LED is an active component.
FT
An LED is a special type of diode that emits light.
Diodes are polarised. Therefore, they must be connected the right way round in a circuit. Anode +
A
Applications in circuits
Cathode –
To convert AC to DC. For example, as shown in the diagram, in bridge rectifier circuits.
•
For signal processing.
•
For protecting components (for example motors) from back emf, which opposes the driving voltage and can cause overheating.
•
Clipping diodes are used in audio applications.
R
•
+
D
DC output –
AC input
Practise it!
Remember it!
1
Describe the purpose of diodes. (2 marks)
•
2
State two applications of capacitors in circuits.
Diodes allow current to flow in one direction only.
•
They are polarised components.
•
LEDs are special types of diodes that emit light.
Revision Guide
(2 marks)
45
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Capacitors
see p.83
What you need to know •
The purpose and function of capacitors
•
The typical uses and applications of capacitors in circuits.
Energy storage plays an important role in all our lives. Capacitors are becoming increasingly useful in this area of electronic engineering.
Purpose and function Capacitors store electrical charge. They are passive components. There are two types of capacitors: Polarised capacitors have a positive and a negative terminal. For example, electrolytic capacitors.
•
Non-polarised capacitors can be connected any way round in a circuit. For example, when used as a feedback capacitor in an op-amp circuit.
•
Most capacitors have a capacitance measured in microfarads. However, newer ‘supercapacitors’ can have capacitances measured in farads or tens of farads.
A
FT
•
Non-polarised capacitor symbol
+
Polarised capacitor symbol
R
Applications in circuits •
To set the length of time periods or time delays. For example, in an RC network or monostable circuit. The diagram shows an RC timing network.
To filter signals. For example, in an AC–DC converter circuit.
•
To store electrical energy. For example, capacitors can be used in place of batteries in electric vehicles.
R1
B1
C1
D
•
+
Practise it!
Remember it!
1
Explain the difference between polarised and non-polarised capacitors. (2 marks)
•
Capacitors store charge.
•
They can be polarised or non-polarised.
State two applications of capacitors in circuits.
•
They are passive components.
2
46
(2 marks)
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Power supplies
see p.84
What you need to know •
How different power supplies work
•
The suitability of different power supplies for different uses and applications.
Electronic and programmable systems need a source of power to be able to function. Engineers must be able to select the correct type for the application needed.
Batteries
Photovoltaic cells
Batteries store chemical energy and convert it into electrical energy.
Photovoltaic cells convert energy from the Sun into electrical current.
They come in a range of different voltages and packages, including 9 V PP3, AA, AAA and C types.
They are a clean and renewable source of energy. They cannot create electricity when there is no sunlight. However, the energy they do create can be stored.
FT
+
They are used when a portable, low voltage power supply is needed. For example, to power mobile phones, tablet computers, digital watches and clocks.
A
They are not suitable when an AC supply is required.
Mains adaptors
Supercapacitors
R
Supercapacitors are a special type of capacitor. They can store much more charge than normal capacitors.
+
D
They can be used instead of batteries for some low voltage applications, but need recharging regularly.
They are used in some countries to power electric transport systems.
In the UK, mains power is set at 230 V AC. Mains adaptors are used to reduce the voltage and/or convert the AC power supply to a DC supply. This is necessary because most programmable and electronic devices use a low voltage DC supply. Some adaptors can also be used as battery chargers. Mains electricity is extremely dangerous if dealt with incorrectly.
Practise it!
Remember it!
1
Identify two power supplies that would be suitable for powering an electric vehicle. (2 marks)
•
Power supplies ensure electronic and programmable devices have the correct voltage and/or current to work correctly.
2
Explain one problem with using mains adaptors to power products. (2 marks)
•
Most electronic and programmable systems require a low voltage DC supply.
Revision Guide
47
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
Wiring types
see p.85
What you need to know •
The characteristics of different types of wires
•
The typical uses and applications of different wiring types in circuits.
Wires create electrical connections between different components, thus allowing current to flow. It is important to choose the right wiring type for the application needed.
Single-strand wire Single-strand wire is made up of a single solid core of conducting material surrounded by insulation.
FT
Single-strand wire is more suitable for some applications than others:
It is easier to solder than multi-strand wire as it does not fray.
•
It is better suited to use with breadboards than multi-strand wire.
•
If the single core within it breaks when the wire is flexed, then conductivity is lost.
Multi-strand wire
A
•
Multi-strand wire is made up of several flexible strands of wire surrounded by insulation.
R
Multi-strand wire is more suitable for some applications than others: •
D
It is well-suited to applications where it might be moved, flexed or placed under mechanical stress. For example, when connecting a battery or a switch to a PCB.
•
If one strand breaks, the others will still conduct.
•
It is difficult to place through holes due to fraying. For example, in a breadboard, stripboard or a PCB.
Practise it!
Remember it!
1
•
Single-strand wire has a single core surrounded by insulation.
•
Multi-strand wire consists of several wired strands surrounded by insulation.
2
48
Explain one application of single-strand wire. Explain one application of multi-strand wire.
(2 marks) (2 marks)
Revision Guide
Original material © Cambridge University Press 2022. This material is not final and is subject to further changes prior to publication.
