year program - centenary heights state high school · year program year 9 electronics duration: 4...

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YearProgram

ERTElectronics WorkbookYr9

2

Contents Page

Term Dates 3

Year Program 6

Notes 8

Projects 61

4

Semester 1

Term 1

TERM 2

WEEK #

BEGINNING DATE

AREA Details

11 – Flashing Rear Light Further develop practical skills by commencing

Flashing Rear Bikelight project in the workshop.

Draw & test in circuit wizard, do a mock‐up on bread

board, then make the actual project.

12 – Flashing Rear Light Soldering Project

13 – Flashing Rear Light Soldering Project

14 – Flashing Rear Light Sketching – Isometric & orthographic views

15 – Flashing Rear Light Commence designing case to contain electronics.

16 – Inventor Using Inventor to design the case for the bike light

17 – Flashing Rear Light Begin Case and continue soldering.

18 – Flashing Rear Light Folio Organization & Completion

19 – Flashing Rear Light Project Completion

20 ‐ Flashing Rear Light Project Completion

WEEK #

BEGINNING DATE

AREA Details

1 & 2 – Electronics Theory behind electronics including components & their

role

3 – Circuit Wizard Creating & Designing circuits using circuit wizard.

4 – Soldering Introduce soldering and practice skill

Commence construction of Single Flashing LED Project.

5 – Assembling

6 – Revision Complete Project and Test.

Revisit safety. (OnGuard)

Electronics revision & test

Begin Inventor an introduction.

7 – Inventor Drawing 3D with inventor

8 – Inventor Drawing 3D with inventor

9 – 3D Printer Introduction to 3D printer

10 ‐ 3D printer Produce a 3D printed Object

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Term 3

WEEK #

BEGINNING DATE

AREA Details

1 ‐ Lego Kits Check for missing parts in boxes and

assemble the robot in the kit booklet

2 – Basic Course In groups of two work through the Basic

Course Mind storms. 3 – Basic Course

4 – Basic Course

5 – Balloon Busting Challenge Students now design a robot to bust 3

balloons in the shortest time. Three lessons

to prepare.

6 – Balloon Busting 3 lessons to trial and complete

7 – Three Challenge Folio Students complete the three challenges and

then complete folio.

8 – Three Challenge Folio

9 – Three Challenge Folio

10 ‐ Three Challenge Folio Folio Completion

TERM 4

WEEK #

BEGINNING DATE

AREA Details

11 – Nascar Challenge Build a robot to follow a line of an oval

and race another

12 – Circuit Wizard Circuit diagram LED Dice

13 – Bread Board Circuit diagram LED Dice

14 – LED Dice manufacture Using vero & PC board assemble

electronic components need. Design a

case for the components and

manufacture.

Assemble project

15 – LED Dice

16 – LED Dice

17 – LED Dice

18 – Project Report Project Completion

19 –

20 ‐

7

Year Program

Year 9 Electronics Duration: 4 Terms

3 lessons per week

Theory Students will complete the following:

Electrical Safety

Tools required for Electronics

Electricity and the Electron

Power and Energy

Voltage and Current

Quantities and Units in Electronics

Ohms Law

Circuit Symbols

Practical

Soldering and De‐Soldering

The Breadboard

Multimeter

Project 1:

This project exposes the students to working with basic electronics circuitry and components. It also

exposes students to the following:


Circuit Construction

Component Identification and operation

Wiring and assembly

Project 2:

This project exposes the students to working with analogue electronics circuitry, integrated circuits

and basic components. It also exposes students to the following:


Circuit Construction

Component Identification and operation

Wiring and assembly

Project 2:

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Electrical Safety Rules 1. Do not renew a blown fuse until you are satisfied as to the cause and have rectified

the irregularity.

2. Do not close any switch unless you are familiar with the circuit which it controls and know the reason for its being open.

3. Do not work on the live circuit without the express orders of the supervisor. Make sure that all safety precautions have been taken and you are accompanied by a second person competent to render First Aid and Artificial Respiration.

4. Do not touch or tamper with any electrical gear or conductor unless you have made sure that it is DEAD and EARTHED.

5. Do not disconnect earth connections or render ineffective the safety gadgets installed on mains and apparatus.

6. Do not open or close switch or fuse slowly or hesitatingly. Do it quickly and positively.

7. Do not use wires with poor insulation.

8. Do not touch any electrical circuit when your hands are wet or bleeding from a cut or an abrasion

9. Do not work on energized circuit without taking extra precaution such as the use of rubber gloves.

10. Do not disconnect a plug by pulling a flexible cable when the switch is on.

11. Do not use fire extinguisher on electrical equipment unless it is clearly marked for that purpose. Use sand and blanket instead.

12. Do not throw water on live electrical equipment in cases of fire.

13. Do not attempt to disengage a person in contact with a live apparatus, which you cannot switch off immediately. Insulate yourself from earth by standing on rubber mat or dry board, before attempting to get him clear. Do not touch his body; push him clear with a piece of dry wood.

14. Do continue artificial respiration until recovery or death certified by doctor.

15. Do not allow visitors and unauthorized person to touch or handle electrical apparatus or come within the danger zone of HV apparatus.

16. Do not test circuit with bare fingers

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Electrical Safety This is presented as a public service. Please inform me if you find any errors...

CURRENT KILLS (not voltage)

Current effects on human body, current through chest

(A, amps)

<0.01 tingling or imperceptible

0.02 painful, cannot let go

0.03 breathing disturbed

0.07 breathing very difficult

0.10 death due to fibrillation

>0.20 no fibrillation, but severe burning, no breathing

Effects of different current levels through human body

Current passing through victim is determined by resistance. Dry skin resistance is typically ~500,000 ohms. Wet skin resistance falls to ~1000 ohms. Internal resistance of body is only 100 to 500 ohms. Most household electrical injuries occur in the bathroom as a consequence. Our skin, when dry, normally protects us from electrocution if we make

inadvertent contact with 115V household voltages. Not so when wet... GFCIs (Ground Fault Circuit Interrupters) are essential in the kitchen and

bathroom o How a GFCI works, from Fuses, Circuit Breakers, and GFCI page of Electrical

Safety Awareness web‐based training at Lawrence Livermore National Lab

Fibrillation and resuscitation

Fibrillation is the fine, rapid, erratic, movements that replace the normal contraction of the ventricular muscle of the heart

Fibrillation can be stopped by application of another controlled electrical shock, known as defibrillation, often seen in movies and on TV...

A stopped heart can often be resuscitated with CPR techniques (cardiopulmonary resuscitation), but seldom a fibrillating heart.

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Dielectric breakdown and sparking

Stay Out!

Air suffers dielectric breakdown at ~3,000,000 volt per meter. ‐‐ Demonstration of Tesla coil

115 V source (wall socket) will not "reach" for you with a spark, but a 50,000 V power line will spark over before you actually contact (touch) it.

Contacting voltages higher that ~230 V often results in current puncturing skin, compromising the protection offered by its dry resistance.

Sometime a person contacts a wire that has sufficient current to contract hand muscles onto wire. The resulting current through the body may not be lethal initially, but skin resistance may drop with time, under these conditions, until a lethal current level is achieved. Remove person as soon as possible without endangering self!

Electrical Safety ‐ Questions

Question 1

What is the current effect on the human body when a 0.07A current flows through the chest?

_______________________________________________________________________

Question 2

The current passing through a victim is determined by the _______________________

of the body.

Question 3

When the skin is wet, the resistance falls to approximately ______________________.

Question 4

What fibrillation?

_______________________________________________________________________

_______________________________________________________________________

_____________________________________________________________________________

Question 5

How can fibrillation be stopped?

_______________________________________________________________________

_____________________________________________________________________________

12

Tools required for electronics

Soldering iron

For electronics work the best type is one powered by mains electricity (230V in the UK), it should have a heatproof cable for safety. The iron's power rating should be 15 to 25W and it should be fitted with a small bit of 2 to 3mm diameter.

Other types of soldering iron Low

voltage soldering irons are available, but their extra safety is undermined if you have a mains lead to their power supply! Temperature controlled irons are excellent for frequent use, but not worth the extra expense if you are a beginner. Gas‐powered irons are designed for use where no mains supply is available and are not suitable for everyday use. Pistol shaped solder guns are far too powerful and cumbersome for normal electronics use.

Soldering iron stand

You must have a safe place to put the iron when you are not holding it. The stand should include a sponge which can be dampened for cleaning the tip of the iron.

De‐soldering pump (solder sucker)

A tool for removing solder when de‐soldering a joint to correct a mistake or replace a component.

Solder remover wick (copper braid)

This is an alternative to the de‐soldering pump shown above.

Reel of solder

The best size for electronics is 22swg (swg = standard wire gauge).

Side cutters

For trimming component leads close to the circuit board.

Wire strippers

Most designs include a cutter as well, but they are not suitable for trimming component leads.

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Small pliers

Usually called 'snipe nose' pliers, these are for bending component leads etc. If you put a strong rubber band across the handles the pliers make a convenient holder for parts such as switches while you solder the contacts.

Small flat‐blade screwdriver

For scraping away excess flux and dirt between tracks, as well as driving screws!

Heat sink

You can buy a special tool, but a standard crocodile clip works just as well and is cheaper.

The following tool is only required if you are using strip board:

Track cutter

A 3mm drill bit can be used instead, in fact the tool is usually just a 3mm drill bit with a proper handle fitted. The following tools are only required if you make your own PCBs:

PCB rubber

This is an abrasive rubber for cleaning PCBs. It can also be used to clean strip board where the copper tracks have become dull and tarnished.

Small electric drill

Ideally this should be mounted in a drill stand. You will need a range of small drill bits, but for most holes a 1mm bit is suitable. Larger holes can be drilled with a hand drill but 1mm bits are too fragile to use reliably in a hand drill.

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Tools required for electronics ‐ Questions

Question 1

What is the best type of soldering iron for electronics work?

_______________________________________________________________________

Question 2

What is the purpose of a de‐soldering pump?

_______________________________________________________________________

Question 3

Solder is an alloy of lead and_________.

Question 4

What is the function of a small pliers?

_______________________________________________________________

Question 5

What tool is used for trimming and cutting component leads?

_______________________________________________________________________

Question 6

What tool is used for trimming and cutting component leads?

_______________________________________________________________________

Question 7

What is a track cutter?

______________________________________________________________________________

Question 8

Give another name for solder remover wick.

______________________________________________________________________________

Question 9

What should be included in a soldering iron stand?

______________________________________________________________________________

15

Soldering and De‐Soldering Guide

How to Solder

Firstafewsafetyprecautions:

Never touch the element or tip of the soldering iron. They are very hot (about 400°C) and will give you a nasty burn.

Take great care to avoid touching the mains flex with the tip of the iron. The iron should have a heatproof flex for extra protection. An ordinary plastic flex will melt immediately if touched by a hot iron and there is a serious risk of burns and electric shock.

Always return the soldering iron to its stand when not in use. Never put it down on your workbench, even for a moment!

Work in a well‐ventilated area. The smoke formed as you melt solder is mostly from the flux and quite irritating. Avoid breathing it by keeping you head to the side of, not above, your work.

Wash your hands after using solder. Solder contains lead which is a poisonous metal.

If you are unlucky (or careless!) enough to burn yourself please read the First Aid section.

Preparingthesolderingiron:

Place the soldering iron in its stand and plug in. The iron will take a few minutes to reach its operating temperature of about 400°C.

Dampen the sponge in the stand. The best way to do this is to lift it out the stand and hold it under a cold tap for a moment, then squeeze to remove excess water. It should be damp, not dripping wet.

Wait a few minutes for the soldering iron to warm up. You can check if it is ready by trying to melt a little solder on the tip.

Wipe the tip of the iron on the damp sponge. This will clean the tip.

Melt a little solder on the tip of the iron. This is called 'tinning' and it will help the heat to flow from the iron's tip to the joint. It only needs to be done when you plug in the iron, and occasionally while soldering if you need to wipe the tip clean on the sponge.

Youarenowreadytostartsoldering:

Hold the soldering iron like a pen, near the base of the handle. Imagine you are going to write your name! Remember to never touch the hot element or tip.

Touch the soldering iron onto the joint to be made. Make sure it touches both the component lead and the track. Hold the tip there for a few seconds and...

Feed a little solder onto the joint. It should flow smoothly onto the lead and track to form a volcano shape as shown in the diagram. Apply the solder to the joint, not the iron.

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Remove the solder, then the iron, while keeping the joint still. Allow the joint a few seconds to cool before you move the circuit board.

Inspect the joint closely. It should look shiny and have a 'volcano' shape. If not, you will need to reheat it and feed in a little more solder. This time ensure that both the lead and track are heated fully before applying solder.

If you are unlucky (or careless!) enough to burn yourself please read the First

Aid section.

UsingaheatsinkSome components, such as transistors, can be damaged by heat when soldering

so if you are not an expert it is wise to use a heat sink clipped to the lead

between the joint and the component body. You can buy a special tool, but a

standard crocodile clip works just as well and is cheaper.

FurtherinformationFor a much more detailed guide to soldering, including troubleshooting, please see the Basic Soldering Guide

on the Everyday Practical Electronics Magazine website.

Soldering Advice for Components It is very tempting to start soldering components onto the circuit board straight away, but please take time to

identify all the parts first. You are much less likely to make a mistake if you do

this!

1. Stick all the components onto a sheet of paper using sticky tape. 2. Identify each component and write its name or value beside it. 3. Add the code (R1, R2, C1 etc.) if necessary.

Many projects from books and magazines label the components with codes (R1, R2, C1, D1 etc.) and you should use the project's parts list to find these codes if they are given.

4. Resistor values can be found using the resistor colour code which is explained on our Resistors page. You can print out and make your own Resistor Colour Code Calculator to help you.

5. Capacitor values can be difficult to find because there are many types with different labelling systems! The various systems are explained on our Capacitors page.

6.

Some components require special care when soldering. Many must be placed the correct way round and a few

are easily damaged by the heat from soldering. Appropriate warnings are given in the table below, together

with other advice which may be useful when soldering.

For more detail on specific components please see the Components page or click on the component name in the table.

For most projects it is best to put the components onto the board in the order given below:

Crocodile clip

Photograph © Rapid Electronics

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Components Pictures Reminders and Warnings

1 IC Holders

(DIL sockets)

Connect the correct way round by making

sure the notch is at the correct end.

Do NOT put the ICs (chips) in yet.

2 Resistors

No special precautions are needed with

resistors.

3 Small value capacitors

(usually less than 1µF)

These may be connected either way round.

Take care with polystyrene capacitors because

they are easily damaged by heat.

4 Electrolytic capacitors

(1µF and greater)

Connect the correct way round. They will

be marked with a + or ‐ near one lead.

5 Diodes

Connect the correct way round.

Take care with germanium diodes (e.g. OA91)

because they are easily damaged by heat.

6 LEDs


The diagram may be labelled a or + for

anode and k or ‐ for cathode; yes, it really

is k, not c, for cathode! The cathode is the

short lead and there may be a slight flat on

the body of round LEDs.

7 Transistors


Transistors have 3 'legs' (leads) so extra

care is needed to ensure the connections

are correct.

Easily damaged by heat.

8 Wire Links between points on

the circuit board.

single core wire

Use single core wire, this is one solid wire

which is plastic‐coated.

If there is no danger of touching other parts

you can use tinned copper wire, this has no

plastic coating and looks just like solder but it is

stiffer.

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Battery clips, buzzers and

other parts with their own

wires


10 Wires to parts off the circuit

board, including switches,

relays, variable resistors and

stranded wire

You should use stranded wire which is

flexible and plastic‐coated.

Do not use single core wire because this will

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loudspeakers. break when it is repeatedly flexed.

11 ICs (chips)


Many ICs are static sensitive.

Leave ICs in their antistatic packaging until

you need them, then earth your hands by

touching a metal water pipe or window

frame before touching the ICs.

Carefully insert ICs in their holders: make

sure all the pins are lined up with the

socket then push down firmly with your

thumb.

What is solder?

Solder is an alloy (mixture) of tin and lead, typically 60% tin and 40% lead. It melts at a temperature of about 200°C. Coating a surface with solder is called 'tinning' because of the tin content of solder. Lead is poisonous and you should always wash your hands after using solder.

Solder for electronics use contains tiny cores of flux, like the wires inside a mains flex. The flux is corrosive, like an acid, and it cleans the metal surfaces as the solder melts. This is why you must melt the solder actually on the joint, not on the iron tip. Without flux most joints would fail because metals quickly oxidise and the solder itself will not flow properly onto a dirty, oxidised, metal surface.

The best size of solder for electronics is 22swg (swg = standard wire gauge).

De‐Soldering

At some stage you will probably need to de‐solder a joint to remove or re‐position a wire or component. There are two ways to remove the solder: 1. With a de‐soldering pump (solder sucker)

Set the pump by pushing the spring‐loaded plunger down until it locks.

Apply both the pump nozzle and the tip of your soldering iron to the joint.

Wait a second or two for the solder to melt. Then press the button on the pump to

release the plunger and suck the molten solder into the tool.

Repeat if necessary to remove as much solder as possible.

The pump will need emptying occasionally by unscrewing the nozzle.

Reels of solder

Using a de‐soldering pump (solder sucker)

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2. With solder remover wick (copper braid)

Apply both the end of the wick and the tip of your soldering iron to the joint.

As the solder melts most of it will flow onto the wick, away from the joint.

Remove the wick first, then the soldering iron. Cut off and discard the end of the wick coated with solder.

After removing most of the solder from the joint(s) you may be able to remove the wire or component lead straight away (allow a few seconds for it to cool). If the joint will not come apart easily apply your soldering iron to melt the remaining traces of solder at the same time as pulling the joint apart, taking care to avoid burning yourself.

First Aid for Burns

Most burns from soldering are likely to be minor and treatment is simple:

Immediately cool the affected area under gently running cold water. Keep the burn in the cold water for at least 5 minutes (15 minutes is recommended). If ice is readily available this can be helpful too, but do not delay the initial cooling with cold water.

Do not apply any creams or ointments. The burn will heal better without them. A dry dressing, such as a clean handkerchief, may be applied if you wish to protect the area from dirt.

Seek medical attention if the burn covers an area bigger than your hand.

To reduce the risk of burns:

Always return your soldering iron to its stand immediately after use. Allow joints and components a minute or so to cool down before you touch them. Never touch the element or tip of a soldering iron unless you are certain it is cold.

Solder remover wick

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Soldering and De‐Soldering Guide ‐ Questions

Question 1

Give 3 safety precautions that must be taken when soldering.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

Question 2

Write down the 5 steps needed to prepare the soldering iron?

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

Question 3

What is the best advice for soldering components?

_______________________________________________________________________

_______________________________________________________________________

Question 4

Name the 2 ways to remove solder.

_______________________________________________________________

_______________________________________________________________

Question 5

How can you reduce the risk of burns?

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

21

Electricity and the Electron

What is electricity?

Electricity is the flow of charge around a circuit carrying energy from the battery (or power supply) to components such as lamps and motors.

Electricity can flow only if there is a complete circuit from the battery through wires to components and back to the battery again.

The diagram shows a simple circuit of a battery, wires, a switch and a lamp. The switch works by breaking the circuit.

With the switch open the circuit is broken ‐ so electricity cannot flow and the lamp is off.

With the switch closed the circuit is complete ‐ allowing electricity to flow and the lamp is on. The electricity is carrying energy from the battery to the lamp.

We can see, hear or feel the effects of electricity flowing such as a lamp lighting, a bell ringing, or a motor turning ‐ but we cannot see the electricity itself, so which way is it flowing?

Which way does electricity flow?

We say that electricity flows from the positive (+) terminal of a battery to the negative (‐) terminal of the battery. We can imagine particles with positive electric charge flowing in this direction around the circuit, like the red dots in the diagram.

This flow of electric charge is called conventional current.

This direction of flow is used throughout electronics and it is the one you should remember and use to understand the operation of circuits.

However this is not the whole answer because the particles that move in fact have negative charge! And they flow in the opposite direction! Please read on...

Imaginary positive particlesmoving in the direction of the conventional current

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The electron

When electricity was discovered scientists tried many experiments to find out which way the electricity was flowing around circuits, but in those early days they found it was impossible to find the direction of flow.

They knew there were two types of electric charge, positive (+) and negative (‐), and they decided to say that electricity was a flow of positive charge from + to ‐. They knew this was a guess, but a decision had to be made! Everything known at that time could also be explained if electricity was negative charge flowing the other way, from ‐ to +.

The electron was discovered in 1897 and it was found to have a negative charge. The guess made in the early days of electricity was wrong! Electricity in almost all conductors is really the flow of electrons (negative charge) from ‐ to +.

By the time the electron was discovered the idea of electricity flowing from + to ‐ (conventional current) was firmly established. Luckily it is not a problem to think of electricity in this way because positive charge flowing forwards is equivalent to negative charge flowing backwards.

To prevent confusion you should always use conventional current when trying to understand how circuits work, imagine positively charged particles flowing from + to ‐.

Electricity and the Electron ‐ Questions

Question 1

What is electricity?

_______________________________________________________________________

Question 2

Electricity flow from positive to negative is called ______________________________.

Question 3

Electricity is really the flow of _____________________________________________.

Question 4

When was the electron discovered?

_______________________________________________________________

Question 5

What direction does electricity really flow?

_______________________________________________________________________

23

Voltage and Current

Voltage and Current are vital to understanding electronics, but they are quite hard to grasp because we can't see them directly.

Voltage is the Cause, Current is the Effect

Voltage attempts to make a current flow, and current will flow if the circuit is complete. Voltage is sometimes described as the 'push' or 'force' of the electricity, it isn't really a force but this may help you to imagine what is happening. It is possible to have voltage without current, but current cannot flow without voltage.

Voltage and Current The switch is closed making a complete

circuit so current can flow.

Voltage but No Current The switch is open so the circuit is broken and current cannot flow.

No Voltage and No Current Without the cell there is no source of

voltage so current cannot flow.

Voltage, V

Voltage is a measure of the energy carried by the charge. Strictly: voltage is the "energy per unit charge".

The proper name for voltage is potential difference or p.d. for short, but this term is rarely used in electronics.

Voltage is supplied by the battery (or power supply). Voltage is used up in components, but not in wires. We say voltage across a component. Voltage is measured in volts, V. Voltage is measured with a voltmeter, connected in parallel. The symbol V is used for voltage in equations.

Voltage at a point and 0V (zero volts) Voltage is a difference between two points, but in electronics we often refer to voltage at a point meaning the voltage difference between that point and a reference point of 0V (zero volts).

Zero volts could be any point in the circuit, but to be consistent it is normally the negative terminal of the battery or power supply. You will often see circuit diagrams labelled with 0V as a reminder.

You may find it helpful to think of voltage like height in geography. The reference point of zero height is the mean (average) sea level and all heights are measured from that point. The zero volts in an electronic circuit is like the mean sea level in geography.

Connecting a voltmeter in parallel

24

Zero volts for circuits with a dual supply

Some circuits require a dual supply with three supply connections as shown in the diagram. For these circuits the zero volts reference point is the middle terminal between the two parts of the supply.

On complex circuit diagrams using a dual supply the earth symbol is often used to indicate a connection to 0V, this helps to reduce the number of wires drawn on the diagram.

The diagram shows a ±9V dual supply, the positive terminal is +9V, the negative terminal is ‐9V and the middle terminal is 0V.

Current, I

Current is the rate of flow of charge. Current is not used up, what flows into a component

must flow out. We say current through a component. Current is measured in amps (amperes), A. Current is measured with an ammeter, connected in

series. To connect in series you must break the circuit and put the ammeter acoss the gap, as shown in the diagram.

The symbol I is used for current in equations. Why is the letter I used for current? ... please see FAQ.

1A (1 amp) is quite a large current for electronics, so mA (milliamps) are often used. m (milli) means "thousandth": 1mA = 0.001A, or 1000mA = 1A

The need to break the circuit to connect in series means that ammeters are difficult to use on soldered circuits. Most testing in electronics is done with voltmeters which can be easily connected without disturbing circuits.

Voltage and Current for components in Series

Voltages add up for components connected in series. Currents are the same through all components connected in series. In this circuit the 4V across the resistor and the 2V across the LED add up to the battery voltage: 2V + 4V = 6V. The current through all parts (battery, resistor and LED) is 20mA.

Voltage and Current for components in Parallel

Voltages are the same across all components connected in parallel. Currents add up for components connected in parallel. In this circuit the battery, resistor and lamp all have 6V across them. The 30mA current through the resistor and the 60mA current through the lamp add up to the 90mA current through the battery.

Connecting an ammeter in series

25

Quantities and Units in Electronics

Quantities

The table shows electrical quantities which are used in electronics.

The relationship between quantities can be written using words or symbols (letters), but symbols are normally used because they are much shorter; for example V is used for voltage, I for current and R for resistance:

As a word equation:

voltage = current × resistance

The same equation using symbols: V = I × R

To prevent confusion we normally use the same symbol (letter) for each quantity and these symbols are shown in the second column of the table.

Units

The first table shows the unit (and unit symbol) which is used to measure each quantity. For example: Charge is measured in coulombs and the symbol for a coulomb is C.

Some of the units have a convenient size for electronics, but most are either too large or too small to be used directly so they are used with the prefixes shown in the second table. The prefixes make the unit larger or smaller by the value shown.

Some examples: 25 mA = 25 × 10‐3 A = 25 × 0.001 A = 0.025 A 47µF = 47 × 10‐6 F = 47 × 0.000 001 F = 0.000 047 F 270k = 270 × 103 = 270 × 1000 = 270 000

Why not change the units to be better sizes?

It might seem a good idea to make the farad (F) much smaller to avoid having to use µF, nF and pF, but if we did this most of the equations in electronics would have to have factors of 1000000 or more

QuantityUsual Symbol

Unit Unit

Symbol

Voltage V volt V

Current I amp* A

Charge Q coulomb C

Resistance R ohm

Capacitance C farad F

Inductance L henry H

Reactance X ohm

Impedance Z ohm

Power P watt W

Energy E joule J

Time T second s

Frequency F hertz Hz

* strictly the unit is ampere, but this is almost always shortened to amp.

PrefixPrefixSymbol

Value

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

kilo k 103 = 1000

mega M 106 = 1000 000

giga G 109 = 1000 000 000

tera T 1012 = 1000 000 000 000

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included as well as the quantities. Overall it is much better to have the units with their present sizes which are defined logically from the equations.

In fact if you use an equation frequently you can use special sets of prefixed units which are more convenient...

For example: Ohm's Law, V = I × R the standard units are volt (V), amp (A) and ohm ( ), but you could use volt (V), milliamp (mA) and kilo‐ohm (k ) if you prefer. Take care though, you must never mix sets of units: using V, A and k in Ohm's Law would give you wrong values.

Work Page

27

Quantities and Units in Electronics ‐ Questions

Question 1

Write down the prefix that the following prefix symbols represent.

m ________________________________

µ ________________________________

M ________________________________

Question 2

Write down the value that the following prefixes represent.

kilo ________________________________

nano ________________________________

giga ________________________________

Question 3

Convert the following unit of measurement

1. 1000 mA to A _______________________________

2. 0.25 kV to V _______________________________

3. 470nF to µF _______________________________

4. 0.05A to mA _______________________________

5. 4.7kΩ to Ω _______________________________

28

Ohm's Law

To make a current flow through a resistance there must be a voltage across that resistance. Ohm's Law shows the relationship between the voltage (V), current (I) and resistance (R). It can be written in three ways:

V = I × R or I = V

R

or R = V

I

where: V = voltage in volts (V) I = current in amps (A) R = resistance in ohms ( )

or: V = voltage in volts (V) I = current in milliamps (mA) R = resistance in kilohms (k )

For most electronic circuits the amp is too large and the ohm is too small, so we often measure current in milliamps (mA) and resistance in kilohms (k ). 1 mA = 0.001 A and 1 k = 1000 .

The Ohm's Law equations work if you use V, A and , or if you use V, mA and k . You must not mix these sets of units in the equations so you may need to convert between mA and A or k and .

The VIR triangle

You can use the VIR triangle to help you remember the three versions of Ohm's Law. Write down V, I and R in a triangle like the one in the yellow box on the right.

To calculate voltage, V: put your finger over V, this leaves you with I R, so the equation is V = I × R

To calculate current, I: put your finger over I, this leaves you with V over R, so the equation is I = V/R

To calculate resistance, R: put your finger over R, this leaves you with V over I, so the equation is R = V/I

Ohm's Law Calculations

Use this method to guide you through calculations: 1. Write down the Values, converting units if necessary. 2. Select the Equation you need (use the VIR triangle). 3. Put the Numbers into the equation and calculate the answer.

It should be Very Easy Now!

V

I R

Ohm's Lawtriangle

V

I R

29

Ohm’s Law ‐ Questions

Question 1

3 V is applied across a 6 resistor, what is the current?

o Values: V = 3 V, I = ?, R = 6 o Equation: I = V/R o Numbers: Current, I = 3/6 = 0.5 A

Question 2

3 V is applied across a 6 resistor, what is the current?

o Values: V = 3 V, I = ?, R = 6 o Equation: I = V/R o Numbers: Current, I = 3/6 = 0.5 A

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Question 3

A 1.2 k resistor passes a current of 0.2 A, what is the voltage across it?

o Values: V = ?, I = 0.2 A, R = 1.2 k = 1200 (1.2 k is converted to 1200 because A and k must not be used together)

o Equation: V = I × R o Numbers: V = 0.2 × 1200 = 240 V

31

Circuit Diagrams

Circuit diagrams show how electronic components are connected together. Each component is represented by a symbol and a few are shown here, for other symbols please see the Circuit Symbols page.

Circuit diagrams and component layouts

Circuit diagrams show the connections as clearly as possible with all wires drawn neatly as straight lines. The actual layout of the components is usually quite different from the circuit diagram and this can be confusing for the beginner. The secret is to concentrate on the connections, not the actual positions of components.

The circuit diagram and stripboard layout for the Adjustable Timer project are shown here so you can see the difference.

A circuit diagram is useful when testing a circuit and for understanding how it works. This is why the instructions for projects include a circuit diagram as well as the stripboard or printed circuit board layout which you need to build the circuit.

Drawing circuit diagrams

Drawing circuit diagrams is not difficult but it takes a little practice to draw neat, clear diagrams. This is a useful skill for science as well as for electronics. You will certainly need to draw circuit diagrams if you design your own circuits.

Follow these tips for best results:

Make sure you use the correct symbol for each component. Draw connecting wires as straight lines (use a ruler). Put a 'blob' ( ) at each junction between wires. Label components such as resistors and capacitors with their

values. The positive (+) supply should be at the top and the negative (‐)

supply at the bottom. The negative supply is usually labelled 0V, zero volts. If you are drawing the circuit diagram for science please see the section about drawing diagrams the 'electronics way'.

32

If the circuit is complex:

Try to arrange the diagram so that signals flow from left to right: inputs and controls should be on the left, outputs on the right.

You may omit the battery or power supply symbols, but you must include (and label) the supply lines at the top and bottom.

Drawing circuit diagrams the 'electronics way'

Circuit diagrams for electronics are drawn with the positive (+) supply at the top and the negative (‐) supply at the bottom. This can be helpful in understanding the operation of the circuit because the voltage decreases as you move down the circuit diagram.

Circuit diagrams for science are traditionally drawn with the battery or power supply at the top. This is not wrong, but there is usually no advantage in drawing them this way and I think it is less helpful for understanding the circuit.

I suggest that you always draw your circuit diagrams the 'electronics way', even for science!

[I hope your science teacher won't mind too much!]

Note that the negative supply is usually called 0V (zero volts).

Work Page

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Circuit Diagrams ‐ Questions

Question 1 What does circuit diagrams show?

___________________________________________________________________________

Question 2 When is a circuit diagram useful?

___________________________________________________________________________

Question 3 Write down 5 tips to follow when drawing circuit diagram.

___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

34

Circuit Symbols

Circuit symbols are used in circuit diagrams which show how a circuit is connected together. The

actual layout of the components is usually quite different from the circuit diagram. To build a circuit

you need a different diagram showing the layout of the parts on stripboard or printed circuit board.

Wires and connections

Component Circuit Symbol Function of Component

Wire To pass current very easily from one part of a circuit to another.

Wires joined

A 'blob' should be drawn where wires are connected (joined), but it

is sometimes omitted. Wires connected at 'crossroads' should be

staggered slightly to form two T‐junctions, as shown on the right.

Wires not joined

In complex diagrams it is often necessary to draw wires crossing

even though they are not connected. I prefer the 'bridge' symbol

shown on the right because the simple crossing on the left may be

misread as a join where you have forgotten to add a 'blob'!

Power Supplies


Cell

Supplies electrical energy.

The larger terminal (on the left) is positive (+).

A single cell is often called a battery, but strictly a battery is two or

more cells joined together.

Battery Supplies electrical energy. A battery is more than one cell.

The larger terminal (on the left) is positive (+).

DC supply Supplies electrical energy.

DC = Direct Current, always flowing in one direction.

AC supply Supplies electrical energy.

AC = Alternating Current, continually changing direction.

Fuse A safety device which will 'blow' (melt) if the current flowing through it

exceeds a specified value.

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Transformer

Two coils of wire linked by an iron core. Transformers are used to step

up (increase) and step down (decrease) AC voltages. Energy is

transferred between the coils by the magnetic field in the core. There is

no electrical connection between the coils.

Earth

(Ground)

A connection to earth. For many electronic circuits this is the 0V (zero

volts) of the power supply, but for mains electricity and some radio

circuits it really means the earth. It is also known as ground.

Output Devices: Lamps, Heater, Motor, etc.


Lamp (lighting)

A transducer which converts electrical energy to light. This symbol is

used for a lamp providing illumination, for example a car headlamp

or torch bulb.

Lamp (indicator)

A transducer which converts electrical energy to light. This symbol is

used for a lamp which is an indicator, for example a warning light on

a car dashboard.

Heater A transducer which converts electrical energy to heat.

Motor A transducer which converts electrical energy to kinetic energy

(motion).

Bell

A transducer which converts electrical energy to sound.

Buzzer


Inductor

(Coil, Solenoid)

A coil of wire which creates a magnetic field when current passes

through it. It may have an iron core inside the coil. It can be used as

a transducer converting electrical energy to mechanical energy by

pulling on something.

Switches


Push Switch

(push‐to‐

make)

A push switch allows current to flow only when the button is

pressed. This is the switch used to operate a doorbell.

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Push‐to‐Break

Switch This type of push switch is normally closed (on), it is open (off)

only when the button is pressed.

On‐Off Switch

(SPST)

SPST = Single Pole, Single Throw.

An on‐off switch allows current to flow only when it is in the

closed (on) position.

2‐way Switch

(SPDT)

SPDT = Single Pole, Double Throw.

A 2‐way changeover switch directs the flow of current to one of

two routes according to its position. Some SPDT switches have a

central off position and are described as 'on‐off‐on'.

Dual On‐Off

Switch

(DPST)

DPST = Double Pole, Single Throw.

A dual on‐off switch which is often used to switch mains

electricity because it can isolate both the live and neutral

connections.

Reversing

Switch

(DPDT)

DPDT = Double Pole, Double Throw.

This switch can be wired up as a reversing switch for a motor.

Some DPDT switches have a central off position.

Relay

An electrically operated switch, for example a 9V battery circuit

connected to the coil can switch a 230V AC mains circuit.

NO = Normally Open, COM = Common, NC = Normally Closed.

Resistors


Resistor

A resistor restricts the flow of current, for example to limit the

current passing through an LED. A resistor is used with a capacitor

in a timing circuit.

Some publications still use the old resistor symbol:

Variable Resistor

(Rheostat)

This type of variable resistor with 2 contacts (a rheostat) is usually

used to control current. Examples include: adjusting lamp

brightness, adjusting motor speed, and adjusting the rate of flow of

charge into a capacitor in a timing circuit.

Variable Resistor

(Potentiometer)

This type of variable resistor with 3 contacts (a potentiometer) is

usually used to control voltage. It can be used like this as a

transducer converting position (angle of the control spindle) to an

electrical signal.

37

Variable Resistor

(Preset)

This type of variable resistor (a preset) is operated with a small

screwdriver or similar tool. It is designed to be set when the circuit

is made and then left without further adjustment. Presets are

cheaper than normal variable resistors so they are often used in

projects to reduce the cost.

Capacitors


Capacitor

A capacitor stores electric charge. A capacitor is used with a

resistor in a timing circuit. It can also be used as a filter, to block

DC signals but pass AC signals.

Capacitor,

polarised

A capacitor stores electric charge. This type must be connected

the correct way round. A capacitor is used with a resistor in a

timing circuit. It can also be used as a filter, to block DC signals but

pass AC signals.

Variable Capacitor A variable capacitor is used in a radio tuner.

Trimmer Capacitor

This type of variable capacitor (a trimmer) is operated with a

small screwdriver or similar tool. It is designed to be set when the

circuit is made and then left without further adjustment.

Diodes


Diode A device which only allows current to flow in one direction.

LED

Light Emitting Diode A transducer which converts electrical energy to light.

Zener Diode A special diode which is used to maintain a fixed voltage across

its terminals.

Photodiode A light‐sensitive diode.

38

Transistors


Transistor NPN

A transistor amplifies current. It can be used with other components to make an

amplifier or switching circuit.

Transistor PNP

A transistor amplifies current. It can be used with other components to make an

amplifier or switching circuit.

Phototransistor

A light‐sensitive transistor.

Audio and Radio Devices


Microphone

A transducer which converts sound to electrical energy.

Earphone


Loudspeaker


Piezo Transducer


Amplifier

(general symbol)

An amplifier circuit with one input. Really it is a block diagram symbol

because it represents a circuit rather than just one component.

39

Aerial

(Antenna)

A device which is designed to receive or transmit radio signals. It is also

known as an antenna.

Meters and Oscilloscope


Voltmeter

A voltmeter is used to measure voltage.

The proper name for voltage is 'potential difference', but most people

prefer to say voltage!

Ammeter An ammeter is used to measure current.

Galvanometer A galvanometer is a very sensitive meter which is used to measure tiny

currents, usually 1mA or less.

Ohmmeter An ohmmeter is used to measure resistance. Most multimeters have

an ohmmeter setting.

Oscilloscope An oscilloscope is used to display the shape of electrical signals and it

can be used to measure their voltage and time period.

Sensors (input devices)


LDR

A transducer which converts brightness (light) to resistance (an

electrical property).

LDR = Light Dependent Resistor

Thermistor A transducer which converts temperature (heat) to resistance (an

electrical property).

Logic Gates

Logic gates process signals which represent true (1, high, +Vs, on) or false (0, low, 0V, off). There are two sets of symbols:

traditional and IEC (International Electrotechnical Commission).

Gate

Type Traditional Symbol IEC Symbol Function of Gate

40

NOT

A NOT gate can only have one input. The 'o' on the output

means 'not'. The output of a NOT gate is the inverse

(opposite) of its input, so the output is true when the input is

false. A NOT gate is also called an inverter.

AND

An AND gate can have two or more inputs. The output of an

AND gate is true when all its inputs are true.

NAND

A NAND gate can have two or more inputs. The 'o' on the

output means 'not' showing that it is a Not AND gate. The

output of a NAND gate is true unless all its inputs are true.

OR

An OR gate can have two or more inputs. The output of an

OR gate is true when at least one of its inputs is true.

NOR

A NOR gate can have two or more inputs. The 'o' on the

output means 'not' showing that it is a Not OR gate. The

output of a NOR gate is true when none of its inputs are

true.

EX‐OR

An EX‐OR gate can only have two inputs. The output of an

EX‐OR gate is true when its inputs are different (one true,

one false).

EX‐

NOR

An EX‐NOR gate can only have two inputs. The 'o' on the

output means 'not' showing that it is a Not EX‐OR gate. The

output of an EX‐NOR gate is true when its inputs are the

same (both true or both false).

Circuit Symbols ‐ Questions

Question 1 Draw the IEC symbols for the following components.

Resistor Variable Resistor (Preset)

Polarised Capacitor Light Emitting Diode (LED)

41

NPN Transistor Light Dependant Resistor (LDR)

Question 2

Name the components that the following circuit symbols represent.

Breadboard

Uses of Breadboard

A breadboard is used to make up temporary circuits for testing or to try out an idea. No soldering is required so it is easy to change connections and replace components. Parts will not be damaged so they will be available to re‐use afterwards.

Almost all the Electronics Club projects started life on a breadboard to check that the circuit worked as intended.

The photograph shows a typical small breadboard which is suitable for beginners building simple circuits with one or two ICs (chips). Larger sizes are available and you may wish to buy one of these to start with.

Connections on Breadboard

Breadboards have many tiny sockets (called 'holes') arranged on a 0.1" grid. The leads of most components can be pushed straight into the holes. ICs are inserted across the central gap with their notch or dot to the left.

Small Breadboard

42

Wire links can be made with single‐core plastic‐coated wire of 0.6mm diameter (the standard size). Stranded wire is not suitable because it will crumple when pushed into a hole and it may damage the board if strands break off.

The diagram shows how the breadboard holes are connected:

The top and bottom rows are linked horizontally all the way across as shown by the red and black lines on the diagram. The power supply is connected to these rows, + at the top and 0V (zero volts) at the bottom.

I suggest using the upper row of the bottom pair for 0V, then you can use the lower row for the negative supply with circuits requiring a dual supply (e.g. +9V, 0V, ‐9V).

The other holes are linked vertically in blocks of 5 with no link across the centre as shown by the blue lines on the diagram. Notice how there are separate blocks of connections to each pin of ICs.

Large Breadboards On larger breadboards there may be a break halfway along the top and bottom power supply rows. It is a good idea to link across the gap before you start to build a circuit, otherwise you may forget and part of your circuit will have no power!

Building a Circuit on Breadboard

Converting a circuit diagram to a breadboard layout is not straightforward because the arrangement of components on breadboard will look quite different from the circuit diagram.

When putting parts on breadboard you must concentrate on their connections, not their positions on the circuit diagram. The IC (chip) is a good starting point so place it in the centre of the breadboard and work round it pin by pin, putting in all the connections and components for each pin in turn.

The best way to explain this is by example, so the process of building this 555 timer circuit on breadboard is listed step‐by‐step below.

The circuit is a monostable which means it will turn on the LED for about 5 seconds when the 'trigger' button is pressed. The time period is determined by R1 and C1 and you may wish to try changing their values. R1 should be in the range 1k to 1M .

Time Period, T = 1.1 × R1 × C1

IC pin numbers

Monostable Circuit Diagram

43

IC pins are numbered anti‐clockwise around the IC starting near the notch or dot. The diagram shows the numbering for 8‐pin and 14‐pin ICs, but the principle is the same for all sizes.

Components without suitable leads

Some components such as switches and variable resistors do not have suitable leads of their own so you must solder some on yourself. Use single‐core plastic‐coated wire of 0.6mm diameter (the standard size). Stranded wire is not suitable because it will crumple when pushed into a hole and it may damage the board if strands break off.

45

Yr9 Electronics Project 1

Starting Date: _____________________

Due Date: ________________________

SINGLE FLASHING LED

INSTRUCTION SHEET

Check your kit

1 ‐ 330K 1 ‐ 1K 1 ‐ 22R 1 ‐ LED 1 ‐ BC548 Transistor 1 ‐ BC558 Transistor 1 ‐ 10uF Electrolytic Capacitor 1 ‐ 0.01uF (10nF) PolyesterCeramic Capacitor (103) 1 ‐ Battery snap Solder 1 ‐ Printed Circuit Board 2 ‐ PCB Pins

46

Schematic Diagram

PCB Layout

DRAW UP THE CIRCUIT IN CIRCUIT WIZARD

47

1. Turn the PCBoard over so that you are looking at the PLAIN side. From the drawing, find the locations of the components. You will need to turn the PCB around so that it coincides with the placement sheet. Remember that you are seeing the copper track through the PCB.

2. Identify the values of the three resistors by their colour bands and/or an ohm‐meter. Bend the legs of the resistors to a shape that will fit into their location holes. Push them through and firm the resistor down against the PCB.

3. The two transistors look the same but are really quite different. Look for the identifying codes on the body of the transistors. Offer the transistors into their positions with the flat on the body the way round that the drawing indicates. Bend the legs to fit into the holes. Push them in, but allow to stand high off the board.

4. Spread the legs of the LED carefully so they spring into its correct holes. Push the legs just through the PCB so the LED stands high off the board. You should check that the small flat on the flange at the base of the globe is the same way round as the drawing shows. The LED is polarised ‐ a semiconductor ‐ and will not work if placed the wrong way round. The flat is adjacent to the Negative (K) leg.

5. The electrolytic capacitor is polarised. An arrow is printed on the body pointing down the negative leg. Check the placement sheet for its polarity and location, push the legs through and solder.

6. The disc ceramic capacitor is not polarised so it can go in either way. Notice that the value of this capacitor is coded on its surface. This one reads 103. The first and second numbers are value digits and the third (3 in this case) is a multiplier, viz. indicates the number of zeros following. This shows a value of 10000 ‐(1 + 0 + 000). This value is always expressed in picafarads. Reference to a table will show that this converts to 10 nanofarads, or 0.01 uF.

7. These components may be soldered in place. 8. Insert and solder the PCB pins. 9. The battery snap is soldered with the red wire to the positive rail, black to the negative rail. 10. Connect a battery and the flasher will commence. The current draw is very small and the voltage is not

critical, so the light will flash for a very long time from the battery even when the battery is almost completely flat.

11. Trouble shooting will consist of checking locations, polarity, and soldering.

48

Material List

Supply

Resistors

Connectors Capacitors

Sockets Semiconductors

Switches Miscellaneous

49

Design and Technologies Standards

Student Name: _____________________________

A B C D E

The folio of student work has the following characteristics:

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Comprehensive explanation of: factors that influence the design of products, services & environments to meet present and future needs

the contribution of design and technology innovations and enterprise to society

Detailed explanation of: factors that influence the design of products, services and environments to meet present and future needs


Explanation of: factors that influence the design of products, services and environments to meet present and future needs


Description of: factors that influence the design of products, services and environments to meet present and future needs


Statements about: factors that influence the design of products, services and environments to meet present and future needs


Tec

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ts comprehensive explanation how the

features of technologies impact on designed solutions and influence design decisions for each of the prescribed technologies contexts

detailed explanation of how the features of technologies impact on designed solutions and influence design decisions for each of the prescribed technologies contexts

explanation of how the features of technologies impact on designed solutions and influence design decisions for each of the prescribed technologies contexts

partial explanation of how the features of technologies impact on designed solutions and influence design decisions for each of the prescribed technologies contexts

statements about how the features of technologies impact on designed solutions and influence design decisions for each of the prescribed technologies contexts

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Investigating comprehensive evaluation of needs or opportunities for each of the prescribed technologies contexts

detailed evaluation of needs or opportunities for each of the prescribed technologies contexts

evaluation of needs or opportunities for each of the prescribed technologies contexts

explanation of needs or opportunities for each of the prescribed technologies contexts

statement about needs or opportunities for each of the prescribed technologies contexts

Gen

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purposeful creation and adaptation of design ideas making well-considered decisions

effective creation and adaptation of design ideas making considered decisions

creation and adaptation of design ideas making considered decisions

partial creation and adaptation of design ideas making decisions

fragmented creation and adaptation of design ideas

comprehensive and effective communication to different audiences using appropriate technical terms and a range of technologies and graphical representation techniques

effective communication to different audiences using appropriate technical terms and a range of technologies and graphical representation techniques

communication to different audiences using appropriate technical terms and a range of technologies and graphical representation techniques

partial communication to audiences using technical terms and technologies and graphical representation techniques

fragmented communication to audiences using everyday language and graphical representation techniques

Producing

proficient and consistent production of effective designed solutions for the intended purpose independently and safely

consistent production of effective designed solutions for the intended purpose independently and safely

production of effective designed solutions for the intended purpose independently and safely

guided production of designed solutions for the intended purpose safely

guided production of designed solutions for a purpose safely

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development of comprehensive criteria for success, including sustainability considerations

development of detailed criteria for success, including sustainability considerations

development of criteria for success, including sustainability considerations

development of partial criteria for success, including sustainability considerations

statements of criteria for success

discerning use of criteria for success (including sustainability considerations) to judge the suitability of:

their ideas

designed solutions

processes

informed use of criteria for success (including sustainability considerations) to judge the suitability of:

their ideas

designed solutions

processes

use of criteria for success (including sustainability considerations) to judge the suitability of:

their ideas

designed solutions

processes

partial use of criteria for success (including sustainability considerations) to describe the suitability of:

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designed solutions

processes

fragmented use of criteria for success to make statements about:

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designed solutions

processes

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application of project management skills to include comprehensive documentation and discerning use of project plans to manage production processes.

application of project management skills to include detailed documentation and informed use of project plans to manage production processes.

application of project management skills to document and use project plans to manage production processes.

application of project management skills to partially document project plans and use of production processes.

use of project management skills to partially document aspects of project plans and use aspects of production processes.

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Yr9 Electronics Project 2

REAR FLASHING BIKE LIGHT

Schematic Diagram

PCB Layout

52

DRAW UP THE CIRCUIT IN CIRCUIT WIZARD

The flashing warning lights for the rear of your bicycle uses SUPER-BRIGHT Light Emitting Diodes (LED) to produce a very visible safety feature for cyclists. The circuit is a variation of the "FLIP FLOP" Binary counter circuit that formed the basis of early computing. This circuit uses the principle of charging capacitors through metering resistors. A time lapse occurs while the capacitors charge. Changing the value of the capacitor and also varying the resistor value will give longer or shorter time lapse or delay. In this case the capacitors and their resistors are of different values to give unequal times in the ON and OFF modes. The flashing lights will flash about four times per second with the selected capacitors and resistors. You could experiment with different values to vary the frequency of flashes / second. As the capacitors are charged and reach the required voltage, they turn the transistors on in turn, turning them off again as the capacitors discharge. This crossover system of charging using two capacitors and two transistors gives an automatic free-running flip-flop called an astable flip-flop. It will keep going until switched off at the power supply.

Construction Method

1. Check your P.C.Board carefully for damage to the tracks. An Electronic Circuit Tester or a Multimeter will help check that there are no broken tracks.

2. Identify the resistors by their colour bands or with a multimeter. Bend the legs with long-nose pliers to match their holes and push them into place against the surface of the board. Remember that the drawing is looking at the PLAIN side with the tracks away from you. Bend the legs sideways a bit to stop the resistors from falling out.

3. The Electrolytic Capacitors are polarised. Look at the body of the cylinders to find the values and check their locations from the drawing. On the cylindrical body there is also an arrow pointing down one leg of the capacitor. This is the K (Negative) leg. This leg must go to the hole marked K on the drawing. They won't work if they are in the wrong way round.

4. The two transistors have a flat on the body. Mount them with the flats as the drawing shows.

5. The LEDs are also polarised. There is a flat on the small flange at the base of the globe. This is above the K leg, which is also the shorter leg. Put the flats as the drawing shows.

6. Soldering can be done but don't cook the transistors. Apply heat on the track first beside the leg. When the solder takes then apply solder and heat to form a small cone up to the leg, finally touching the leg with the soldering bit to make sure it is bonded. Don't try soldering the leg before you heat the track because cooling solder will run to the track, sit on top of it , but may not bond to it giving a "dry joint" which will not give proper contact - very hard to troubleshoot!

7. Solder the two pins in the holes for the switch connections, and solder wires to the pins and to the switch. Strip the insulation and solder the wires to centre and one end terminals on ONE side of the switch.

8. The legs of the battery holder are pushed through the holes in the Board from the TRACK side. Before putting it into the holes, tin the legs with a blob of solder right up near the plastic, and also put a blob on the pads where the legs will go. Keep the holes clear so the legs will fit in. Push the holder down almost to the board and touch the blobs of solder with the soldering bit to fuse the blobs of solder together.

9. Push in a battery and switch on. If your project doesn't work simply check locations, polarity of capacitors, transistors and LEDs, and re-solder all joints with a hot bit. Next you will need to design a case.

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Project 2: Rear Flashing Bike Light

Starting Date: _____________________Due Date: ________________________

Material List Supply

Resistors




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Enclosure Design


Student Name: _____________________________

A B C D E


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Yr9 Electronics Project 2 Dice Project Press the push switch to 'throw' the dice: this makes the circuit rapidly cycle through the dice numbers so that an effectively random dice number is displayed by the LEDs when the push switch is released.

Drill seven 5mm holes in a dice pattern to mount the LEDs on a panel such as a plastic box lid or sheet of thin plywood. They should be a tight fit but a little glue can be applied from the underside if necessary.

The 555 astable circuit provides clock pulses at about 5kHz for the 4017 counter which has ten outputs (Q0 to Q9). Each output becomes high in turn as the clock pulses are received. Only six counts (Q0-Q5) are needed so Q6 is connected to reset. Appropriate outputs are combined with diodes to supply the LEDs: for example Q1, Q3 and Q5 are combined for LED A.

The dice sequence has been started at 2 so the ÷10 output can be used for LEDs B1 and B2, this saves diodes and simplifies the circuit. Pressing the push switch makes the disable input low so that counting occurs. This project uses a 555 astable circuit to provide the clock pulses for the 4017 counter.

Parts Required

resistors: 330 ×3, 470, 10k ×3 capacitors: 0.01µF, 0.1µF diodes: 1N4148 ×6 LEDs: red 5mm diameter ×7 555 timer IC, such as NE555

4017 counter IC DIL sockets for ICs: 8-pin, 16-pin on/off switch push switch battery clip for 9V PP3 stripboard: 20 rows × 22 holes

Stripboard Layout

Circuit

diagram

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Project 2: Rear Flashing Bike Light

Starting Date: _____________________Due Date: ________________________

Material List

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Enclosure Design


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year program - centenary heights state high school · year program year 9 electronics duration: 4...

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