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ELECTRONICS SETELECTRONICS SETELECTRONICS SETELECTRONICS SETELECTRONICS SET

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Electronics

Battery Safety

• Batteries can be hazardous - especially rechargeablebatteries and alkaline batteries.

• Never use rechargeable batteries for the activities inthese instructions.

• Always take care that the battery leads do not touchtogether and short-circuit the battery. This can resultin the battery getting hot and even melting the batterybox.

• Always remove the battery from your kit when youhave finished using it.

• Always store batteries safely where they cannot touchany metal objects.

• Never dispose of batteries in a fire. Put them in aspecial battery collection unit or in the normalhousehold waste.

2

Contents

Introduction 3How to use the kit 3

Level 1

Getting started 4A few basics 4

Circuit 1 5Making mistakes! 8Finding faults 8Switches 9

Circuit 2 9Resistors 11Variable resistors 11Light Emitting Diodes (LEDs for short) 11

Circuit 3 12Circuit 4 12Circuit 5 13Circuit 6 13Circuit 7 - Battery tester 13Circuit 8 - Fuse tester 14Circuit 9 - Moisture meter 14Circuit 10 - Signals through the earth 14Circuit 11 - Traffic lights 15

Electric magnets and motors 15Circuit 12 - Motor control 16Circuit 13 - Electric brake 16Circuit 14 - Electric generator 17

Buzzers and sounders 17Circuit 15 17

Level 2

Transistors 18Circuit 16 - Dampness indicator 19Circuit 17 - Water level alarm 19Circuit 18 - Water level alarm with a buzzer 20

Circuits with sensors 20Circuit 19 - Light alarm 1 20Circuit 20 - Light alarm 2 21Circuit 21 - Temperature alarm 21

Capacitors 22Circuit 22 - Simple timer/alarm 22

Level 3

Thyristor 23Circuit 23 - Basic alarm 23Circuit 24 - Breaking wire alarm 24

Integrated circuits and their use 25Circuit 25 - Music chip 25

555 timer 25Circuit 26 - Timer 26Circuit 27 - Flasher 28Circuit 28 - Musical instrument 29

QTC 30Circuit 29 - QTC switch 30

What next? 31Battery Safety 32

31

What next?If you have made all the circuits, you have made a good start in electronics.Although the number of components you have is quite small, you can now startto add to them so that you can alter the circuits and even make up new ones.Maplin sells a number of books that will help you to go forward – plus a widerange of kits and modules that will also give you a head start

After the prototyping stage, circuits are normally made on a printed circuit board(PCB for short). This consists of a copper tracks to which the components aresoldered using a soldering iron. These are easy to use once a teacher or adulthas shown you how.

Finally, circuits are normally packaged in suitable boxes or containers. Sometimesyou can find used packaging such as old VHS video cases that will do the trick. Ifnot, Maplin will have a wide range of cases you can buy off the shelf.

Integrated circuits have actually made electronics easierthan it used to be because so many components areassembled inside. The IQ controller, forexample, is easy to programme and will letyou to control things such as robots.With modern components andnew materials like QTC, youcan start creating things thatnobody has yet done – andbecome part of a newgeneration of electronicsdesigners.

Input

Output

B

C

E

+

–

-+

HEAV

Y

DU

TY

9 volts

P

1

+-

2

3

+-

IQ controller

printed circuitboard (PCB )

3

ELECTRONICSYour kit contains a range of components used by professional circuit builders.Before you start building anything, transfer the components from the box intothe case provided.

IntroductionThe modern world is driven byelectronics from the chips in creditcards to the complex processors inlaptop computers. Progress inelectronics has been very rapid indeedand few people will realise, forexample, that the electronics in amobile phone would virtually havefilled a building the size of St Paul’scathedral just 50 years ago!

This electronics kit is designed to give you a knowledge of basic electronics sothat you can:

• understand how things work• enjoy making electronic circuits• design and make new circuits of your own

Many people are turned off electronics because they are thrown in at the deepend and never quite get to understand enough to give them confidence. This kituses just a few components, but if you really get familiar with them, you canmake real progress later with other more advanced Maplin kits and components.

How to use the kitIf you are a complete beginner to electronics – whatever your age – it is a goodidea to start from page 1. If you know some of the basics, then you can skip tolevel 2 or 3 circuits. At each level there are ideas for things to make. Don’t beafraid to experiment. If you have an idea, try it out. Although components mightsometimes get damaged, you can get spares from your local Maplin store at verylow cost.

4

1

7

*

5

2

8

0

6

3

9

#

POW

CLR

MEM

DEL

SEN

MOB - 1

30

QTCQTC stands for quantum tunnellingcomposite and is one of the strangestand most recent materials to comeon the market. As you investigate theQTC in your kit electronics designersall over the world are coming up withnew ideas for its use.

QTC is normally an insulator but ifyou squeeze it gently, it becomes analmost perfect conductor. It is soamazing, it actually ‘teleports’electrons across tiny gaps inside it.This is why designers are so excitedand have already made clothing withbuilt-in QTC switches for controllingiPods and other equipment.

Circuit 29 - QTC switchMake a circuit as shown and wrap the bared ends of the stranded wires tightlyaround a couple of teaspoons. When you touch the ends together, the motorwill run. Now place the QTC pill between the two spoons and try again. Whenyou apply gentle pressure, the motor willnot run. If you press harder, it will start torun – and more pressure will make it gofaster. When you are squeezing hard,the motor will run at full speed. Youhave made a simple speed controllerof the type that might one daybe used in power tools!

pressure onQTC pill

current flows

QTC pill

without pressure theQTC pill is an insulatorso no current will flow

when the QTC pill is pressed it becomes aconductor so current will flow through it

QTC pillspoons

the harder the spoons arepressed the faster themotor will turn

4

Level 1

Getting startedFirst of all, you have to be able to connect parts orcomponents together. There are several ways ofdoing this without using solder which makes akind of welded joint. The worst way is the birdsnest method where you try to twist wires aroundto make things join up. Usually you will get a dryjoint. This is one that looks OK but in fact does notconduct electricity.

Here are three better ways of connecting things:

Terminal blockswith screws

Matrix block withholes and pins

Breadboard

We will start by using the first two and then go on to the breadboard which isused by professional electronics engineers to try out ideas.

A few basicsYou will be using AA size batteries as a source of electricalenergy. These have a stated voltage of 1.5volts. Ifyou connect them in series (end to end), thevoltages of the batteries are added up. TwoAA batteries in the battery box willgive 3v. Four batteries in thealternative box will give 6v.Six batteries would give 9v –and so on.

✗

1.5v + 1.5v = 3v

29

Circuit 28 - Sound generatorIf you use a 47k variable resistor in the circuit and swap the capacitors as shownyou can make a simple sound generator. Adjusting the resistor creates differentfrequencies. As we get older we lose the capacity to hear higher pitched sounds.Try using this circuit to test the hearing of different people. You might be ableto hear higher frequencies than your parents.

ABCDE

FGHIJ

ABCDE

FGHIJ

1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

NE555

-

HEAV

Y

DU

TY

9 volts

ed

wire

47K

10µF capacitor

20

small capacitor

20

NE555

10

47K47k

variable

resistor

piezo sounder

5

If we compare electricity to water,current is the amount of waterflowing and voltage is the pressure. Ifyou increase voltage, more water willflow. Think of a hosepipe at lowpressure: the water dribbles out (lowpressure) if the tap is partly open.Open the tap (high pressure) andmore water comes out.

A circuit is a number of connected parts that control the flow of current. Thesimplest circuit you can make is with a battery and bulb.

Circuit 1Insert 2 AA batteries into the battery box and screw a bulb into the bulb holder.Join the bulb to the battery box by passing the wires under the bulb holderscrews and tightening them gently. When you switch on, the bulb should lightup.

In fact the comparison with water can be a bit misleading because electricity is adifferent sort of ‘stuff’. It is actually the incredibly rapid movement of electrons‘bumping’each other along in a conductor like a metal wire. Although theseactually move from –ve to +ve in a circuit, we usually talk about current (the‘stuff’) flowing from + to -. That’s how we will describe it here.

electrons movingin a conductor

low pressure

high pressure

28

Circuit 27 - FlasherConnected in a slightly different way, the 555 chip will switch the LED on and offautomatically. It will do this faster or slower – depending on the values of theresistor and capacitor. You can experiment with these values and put in avariable resistor in place of the fixed 68k resistor to change the speed of flashing.

If you connect a speakerto the output pin 3, youwill get a buzzing noiseinstead of a lightflashing. If the speed ofswitching is very high,this can become a highpitched whistle.

FGHIJ

FGHIJ

1 5 10 15 20YY

NE555

piezo sounder

ABCDE

FGHIJ

ABCDE

FGHIJ

1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

NE555

-+

HEAV

Y

DU

TY

9 volts

red wire

68k resistor(blue, grey, orange)

1k resistor(brown, black, red)

LED 470R resistor(yellow, violet, brown)

make sure the mark on the side

of the capacitor faces towards

the bottom of the board

15

6

+3v

0v

3v

0v

This is a good example to begin with because it is the simplest one you canmake. Like the other circuits that follow, this is drawn as a diagram with symbolsstanding for the components and straight lines for connections. Like the Londonunderground map, a circuit diagram isn’t so much a real picture as a map thatallows you to find your way around. The circuit diagram for the bulb circuit canbe drawn in two ways:

Most circuit diagrams use just the two lines or rails for + and – and don’t showthe battery each time.

Looking at the diagram, you will be able to follow the path that the current takesfrom +v through the switch to 0v

If you make the bulb circuit using aterminal block, it would look like:

If you made the bulb circuit using amatrix block, it would look like:

bulb

switch

terminalblock

matrix block

pins

27

If you want the LED to be ‘off’ duringthe timed interval and then turn ‘on’at the end, you simply change theposition of the LED.

To show how the 555 timer is working,we sometimes draw a timing diagram.This shows how it switches on and offover a period of time.

ABCDE

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ABCDE

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1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

NE555

1M

-+

HEAV

Y

DU

TY

9 volts

red wire

triggerwires

LED

time

outputvoltage

7

Both of these circuits mean that you have tocut some insulted wires and strip off the plasticfrom the ends. Special tools are available forwire stripping. If you do not have access toone, you may need an adult to help you withthis. To push down the pins in the matrixboard, use the top of an old pen.

To use the breadboard, you first need to know a bit about it. The small holes aresockets into which you can plug the legs of components or connecting wires.These holes are joined up under the board in rows – as shown by the lines in thediagram. If you plug something into row A, it connects with anything else in thatrow. The two long rows top and bottom are normally used for the battery. Thetop row is + and the bottom 0v.

If you want to make the bulb circuit then:

• plug the battery leads into the top and bottom rows• screw two 100mm lengths of non-insulated wire to the bulb holder as shown• plug the other ends of the wires anywhere along the + and 0 rails

plasticinsulation

metal wirestrands

ABCDE

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ABCDE

FGHIJ

1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

ABCDE

FGHIJ

ABCDE

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1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

blackwire

26

Circuit 26 - TimerTo make the 555 into a timer, it is connected as shown. When the flying lead (orpress switch if you want) connects pin 2 to –v, the timing starts. The LED comeson and stays on until the end of the timed interval. The values of the capacitorand the resistor determine how long the timed interval will be for. You canexperiment with these: the higher the values of each, the longer the timedinterval. If a variable resistor is used, as shown in the diagram, the timed intervalcan be changed by adjusting the resistor.

ABCDE

FGHIJ

ABCDE

FGHIJ

1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

NE555

1M

-+

HEAV

Y

DU

TY

9 volts

red wire

triggerwires

10NE555

151M10

NE555

10

mark on IC inlower lefthand corner

make sure the mark onthe side of the capacitorfaces towards the bottomof the board

15

LED

variableresistor

4.7k resistor(yellow, violet, red)

8

If you think about it, you can make up the same circuit in many different wayson the board. For example, plug the two bulb leads into two vertical rows andthen make two small ‘U’ shaped pieces of wire to connect these to + and –. Aslong as you can follow a continuous path for the current, the circuit will work.

Finding faultsIt is always annoying whensomething doesn’t work, but thereare ways of finding faults. If your bulbcircuit doesn’t work is it the bulb orbatteries? First of all check on thebatteries. You could put them intosomething else that does work – likea torch. Or, for example, you couldtry the acid test. Put a tiny drop ofvinegar onto a shiny surface and holdthe two wires in the drop. If it fizzes,the batteries have some life! If thebatteries are good, make sure thebulb is screwed down. If this stillsfails, it is probably a faulty bulb.

Making mistakes!If you connect a wire from onerail to the other without anythingin between, it is called a shortcircuit. A big current will flow andthe battery will get flat veryquickly.

If you make up the bulb circuitbut use the wrong rows, currentwill not flow.

ABCDE

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ABCDE

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1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

blackwire

ABCDE

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1 5 10

1 5 10

X

Y

✗

vinegar

25

Integrated circuits and their useIntegrated circuits (ICs for short) are often now referred to as chips. They arecomplete circuits, some containing several million transistors, made by a specialprocess. A chip can be small enough to just cover a full stop on a page, but mostare contained in a larger package with legs so that they can be handled andconnected. Like transistors before them, integrated circuits have revolutionisedelectronics and made personal computers, mobile phones and iPods possible.

Circuit 25 - Music chipA very simple chip comes in apackage that looks like atransistor. The one in you kit hasa short tune in its memory andwill play this if connected to a smallspeaker. If you make up the circuit asshown, the piezo speaker will play the tunewhen the battery is connected. This kind ofchip is used in musical greetings cards. Thesound will be louder if the speaker is glued to acard surface.

555 timerThe music chip is dedicated to playing backa stored tune and will not do anything else.However, the larger 555 timer chip can beput to all sorts of uses. Two of the legs orpins are for connection to +v and –v and theothers are connected according to what youwant to do. The 555 is used most often oneof two ways:

• as a timer• as a multi-vibrator – flashing an LED or

making a sound.555 timer IC

ABCDE

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1 5 10

1 5 10

X

Y

piezo sounder

9

The circuits that follow are for testing other circuits!

SwitchesYour battery box has an on/offswitch. This allows current to flow ina circuit or stops it. The symbol for asimple switch really explains how itworks. When in the ‘off’ position,the switch makes a gap in thecircuit. In the ‘on’ position, it letscurrent flow normally.

Circuit 2Switches come in many shapes and sizes, butyou can also make your own. A popular ‘steadyhand’ game (sometimes called ‘buzzwire’) isreally just a switch. The circuit shows a switchand buzzer. When the switch is ‘on’, the buzzersounds. Instead of using a switch in the circuit,you connect one end of the circuit to a bent wireand the other end to a loop of wire as shown.You can do this with the terminal blocks. Thegame can be made more difficult by making theloop smaller.

switch open -no current flows

switch closed -current flows

buzzer

+v

0v

switch

connectingblock

connecting block

shape formedfrom an oldmetal coathangerbuzzer

redwires

blackwire

blackwire

24

An alternative way ofturning the thyristor off isto bypass it. This happensif you connect a switch (orpiece of wire) from anodeto cathod as shown in thediagram. When thisconnection is made forjust a split second, thethyistor is ‘robbed’ ofcurrent and turns off.

Circuit 24 - Breaking wire alarmSometimes alarms are made to sound when you break a connection. This mightbe a length of fine wire or foil tape on a window. To enable this to happen, thethyristor is connected in a slightly different way as shown on the diagram. Whenthe wire or foil link is in place, current will flow via the resistor from +v to –v.When the link is broken, current will now flow to the thyristor gate and cause itto turn on.

ABCDE

FGHIJ

10 15 20

10 15 20

X

Y

triggerwires

resetwires

ABCDE

FGHIJ

ABCDE

FGHIJ

1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

10k resistor(brown, black orange)

the buzzer will soundwhen this wire is brokenor disconnected

10

Another type of switch you can make is called a membrane panel. These areused in real life in things like thin calculators and vending machines.

• Cut three pieces of card from an old cornflakes box – each about 80mmsquare. In the centre of one piece cut a hole about 10mm square.

• Cover the faces of the other two cards with kitchen foil - using stick glue.

• Strip off the insulation from two lengths of wire and stick the bare ends ontothe foil with tape. Then put all three cards together as shown and connect upto a battery and bulb.

foil stuckto top ofcard

foil stuckto bottomof card

windowcut incard

wire strandsstuck on top offoil using tape

Normally your homemade switch is ‘off’because the two foils cannot touch eachother. But if you press in the centre, thetwo foils come together through thehole and the switch is ‘on’ for as long asyou press it. You can decorate the topcard with stickers etc. to make it looklike a real membrane switch.

Mid

dle

laye

r

Top

laye

r

press

here

23

Level 3

ThyristorThe thyristor is a bit like a transistorbut once switched ‘on’ it stays ‘on’until the supply current is turned off.This makes it very useful for alarmswhen you want something to staysounding automatically. Like thetransistor, the thyristor has three legsbut these are called gate (instead ofbase), anode (instead of collector) andcathode (instead of emitter). Thethyristor in your kit is also able to passmuch higher currents than thetransistor – up to 3 amps.

Circuit 23 - Basic alarmThe thyristor is connected and works like the transistor. When no current flows tothe gate, the thyristor is turned off and no current flows anode to cathode tomake the buzzer sound. If you connect the gate of a thyristor to +v for just afraction of a second, the thyristor turns on and stays on. It stays on until youswitch off the battery. When you switch on again the thyristor is ‘off’ until‘triggered’ by connecting the gate to +v.

cathodeanode

gate thyristor

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ABCDE

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1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

10 trigger wires

11

ResistorsA resistor limits the flow of current and canprovide different voltages at different placesin a circuit. Resistance is measured in ohmsand the higher the number the greater theresistance. A 1,000,000 ohm resistor isalmost an insulator and 1ohm resistor agood conductor. Instead of writing resistancevalues with lots of 0s, we use symbols asfollows:

R stands for anything under 1000k stands for 1000M stands for one million

For example: 1k = 1000 ohms 3M = 3,000,000 ohms

We also use the letter in place of decimal points so:

1k2 = 1.2k or 1,200 ohms 4M7 = 4.7M or 4,700,000 ohms

Ordinary resistors look similar except for the colour bands which tell you thevalue. Look at the colour sheet in your kit so that you can pick out the resistorsthat you want.

Variable resistorsThe value of these resistors can bealtered. The ones in your pack go upto 47k and 1M.

Light Emitting Diodes (LEDs for short)LED stands for Light Emitting Diode. This is acomponent that gives out light when currentflows through it. However, you mustremember three things about LEDs:

1. an LED only works one way around. Look carefully at the plastic case and youwill see a small flat part. This is always next to the leg you connect to 0v;

2. an LED can burn out if you connect it directly to the battery. It should alwaysbe used with a resistor in series. The resistor limits the flow of current;

3. LEDs need at least 2.2 volts so you will need a 3v battery, not 1.5v.

horizontal

vertical

light emittingdiode (LED)

flat side

22

CapacitorsA capacitor is something that stores electricity – a bitlike a rechargeable battery. The amount it can store ismeasured in units called Farads. This is a very largeunit and many capacitors are marked in micro-farads(µF). These units are one millionth of a farad. Acapacitor can be charged up by connecting it thecorrect way around to a battery. It then dischargeswhen connected to something else.

capacitor

Circuit 22 - Simple timer/alarmAs a capacitor discharges, it can be used for timing. Make up the circuit shown.When you switch on, the LED will light up and at the same time the capacitorwill charge up. When you switch off, the capacitor will now work like a secondbattery and keep the transistor switched on. After a time, the capacitor will bedischarged or ‘flat’ and the LED goes off.

Usually, an alarm circuit needs to stay ‘on’for a time whatever happens to the switchthat triggered it. The capacitor circuit makesa good alarm because it keeps the LEDgoing (or a buzzer sounding) for a period oftime. Instead of the battery box switch, youcan substitute a switch connected to a dooror window. Even if this is ‘on’ for just asecond or so the capacitor charges up andkeeps the LED on for a much longer time.

ABCDE

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ABCDE

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1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

flat side

1k

make sure the mark on the sideof the capacitor faces towards thebottom of the board

15

ABCDE

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1 5 10

1 5 10

X

Y

1k

to switch

12

Circuit 3This shows the circuit diagram for an LEDindicator lamp. It uses a 470R resistor (yellow,violet, brown) and any one of the coloured LEDs.The following pictures show how the circuit canbe built using the terminal blocks and theprototype board. Note that the 6 volt battery boxis needed.

Try swapping different value resistors. You will find that the higher the value, thedimmer the LED gets.

470R

+6v

0v

ABCDE

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1 5 10 1

1 5 10 1

X

Y

LED - makesure the flatside facestowards tobottom of theboard

Redwire

Blackwire

flat on

case

Red

wire

Black

wire

to 6v battery

ABCDE

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1 5 10

1 5 10

X

Y

Blackwire

Redwire

Circuit 4You can connect two ormore LEDs in series butthey get dimmer themore that you use.

21

Circuit 20 - Light alarm 2In this circuit, the LDR is connected to a second resistor in a circuit called apotential divider. This ‘divides’ the voltage of the battery. When the top resistor(LDR) has a high resistance in the dark, very little current flows to the transistorbase and to –v. When it is lit up, enough current will flow to turn on thetransistor and the LED comes on. If you want, you can now use a buzzer insteadof an LED. This circuit can be used as a warning if, for example, a valuable vaseis lifted off a base containing the LDR.

Circuit 21 - Temperature alarmThe sensor for temperature is a special resistor called a thermistor. Its resistancefalls when it gets warmer. If it is used in a circuit like the previous one, the LED orbuzzer comes on when the thermistor gets warm. This circuit can be used, forexample, if the temperature of bath water goes above a safe level.

ABCDE

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ABCDE

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1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

flat side

10k resistor(brown, black, orange)

LDR

1k

ABCDE

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ABCDE

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1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

flat side

100k resistor(brown, black, yellow)

thermistor (may be attachedusing connecting block and wires)

1k

13

Circuit 5You can connect LEDs inparallel. This circuit showsthem sharing a resistor.

Circuit 6This circuit uses one of thehigh bright red LEDs. It looksclear to begin with, but givesa really bright light. TheseLEDs are now used in trafficlights, car rear lights andcycle lights.

Circuit 7 - Battery testerThe circuit shown here gives an indication of battery condition. The LED willlight up if the battery can source enough current. It is shown constructed on amatrix block.

ABCDE

FGHIJ

1 5

1 5

X

Y

Redwire

Blackwire

ABCDE

FGHIJ

1 5

1 5

X

Y

clear LEDRedwire

Blackwire

flat on

caseLED

red wire

black wire

470R resistor(yellow, violet, brown)

20

Circuit 18 - Water level alarm with a buzzerThis is the same as the LED water alarm circuit butuses a buzzer in place of the LED

Circuits with sensorsThe transistor circuits can be made to work usingsensors. The simplest sensors are special resistorswhich can detect changes in light or temperaturelevels. For light, we use a light dependent resistor(LDR for short ). This has a high resistance in thedark (about 100k) and a low resistance in brightlight (about 100R).

Circuit 19 - Light alarm 1We can use an LDR in a very simplecircuit with an LED to show lightlevel. When the LDR is dark, notmuch current passes and the LEDstays ‘off’. When the LDR is lit up,its resistance drops and enoughcurrent passes to light up the LED.This circuit is simple but is not verysensitive and may damage theLDR. It is better to use a transistor.

ABCDE

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ABCDE

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1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

red wire

light dependent resistor (LDR)

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1 5 10

1 5 10

X

Y

-+

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9 volts

flat sideof LED

14

Circuit 8 - Fuse testerThis circuit is used for testing fusesand for checking connections from‘A’ to ‘B’. If the fuse wire is brokenno current will flow in the circuit.

Circuit 9 - Moisture meterFor this circuit you need a 9v battery(PP3 type). It is a simple moisturedetector – e.g., for potted plants. Forconvenience, it is made using aterminal block.

Circuit 10 - Signals through the earthNot many people know that the earth is often used as for passing electricalcurrent. There is so much of it, it makes a near perfect conductor! If you want tosignal in morse code (dots and dashes) to someone else then you can make up asimple transmitter and receiver as shown. The earth in this circuit is acting as oneof the wires and so you only need one length of wire laid over the ground.

flat oncase

Short pieces ofstranded wire.

flat

side

-+

HEAV

Y

DU

TY

9 volts

metal rods pressedinto the earth

bent metal rod - when this ispressed it touches the screwhead and completes the circuit

smallscrew

flat

side

-+

HEAV

Y

DU

TY

9 volts

metal rods pressedinto the earth

19

Circuit 16 - Dampness indicatorWe need a circuit to show that something is moist – like the dampness in thewall of a house. In Circuit 9 we saw that you could detect water with an LED. Butthat circuit is not very sensitive and needs a 9v battery to work. In this circuitonly a tiny current has to pass to the base to turn the transistor on and light upthe LED.

Make the circuit up on the prototyping board as shown so that your finger canbridge across the wire to +v and the base resistor leg. If you touch across with adry finger, nothing happens. If you now try again after licking it, the LED comeson. The tiny current that flowed through your moist skin was enough to turn iton.

This kind of circuit is used in American lie detectors which sense moisture causedby perspiration if you lie.

Circuit 17 - Water level alarmThis is the same as circuit 16except that the wires areconnected to two probes. Theprobes can be made from someplain wire held in a terminalblock. When water getsbetween the probe wires, basecurrent flows and the transistorwill turn on.

ABCDE

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ABCDE

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1 5 10 15 20

1 5 10 15 20

X

Y

X

Y

the LED will light upwhen a wet fingerbridges these wires

flat sideof LED

1k resistor(brown, black, red)

probes

15

ABCDE

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1 5 10

1 5 10

X

Y

Redwire

Blackwire

Circuit 11 - Traffic lightsThis circuit enables you toshow the sequence oftraffic light signals using aflying lead to connectonto the LEDs. This isshown on the diagram asa switch.

Electric magnets and motorsWhen a current flows through a wire, it becomes slightly magnetic. If the wire iscoiled around steel, this also becomes magnetic. If you wrap several coils of theinsulated wire around a long screw you have an electromagnet – something thatis magnetic only when you pass current. Try it out. Take about 300mm of theinsulated wire and strip the insulation off both ends. Wrap it around a screw andconnect to a battery as shown. When the switch is ‘on’ the nail will be magneticand pick up things like paperclips.

OFF - ON

WARNING: do not leave theelectromagnet on for more than afew seconds. It takes a lot of currentand will leave the batteries flat.

flying lead

touch in this row for red

touch in this row for yellow

touch in this row for green

+6v

0v

18

Level 2

TransistorsTransistors are at the heart of allelectronic circuits. Computers,mobile phones and iPods usemillions of them. It is surprising,though, what you can do with justone or two.

We will be describing the transistoras an electronic switch. It has threelegs called emitter (e for short),collector (c for short) and base (bfor short). The transistor isconnected into a circuit with theemitter and collector legs in placeof a normal switch. The exampleshows a hi-bright LED that needs tobe turned on and off.

If you connect everything up,nothing happens! The transistor isswitched off. If you now connectthe base to positive using a piece ofwire, the LED comes on. When acurrent flows base to emitter, thetransistor switches on and a largecurrent flows collector to emitterturning on the LED.

So, why not just use a normalswitch in the first place? Theanswer is that in a circuit yousometimes only have a smallcurrent to switch on somethingthat needs more. The followingcircuit is an example:

collector (c)base (b)

emitter (e)

c

e

b

circuit symbol

BC548 transistor

c

e

b

+v

0v

c

e

b

+v

0v

when a small current flows into thebase the transistor ‘switches on’

16

ABCDE

FGHIJ

1 5 10 15

1 5 10 15

X

Y

use the redsleeves toconnect the wiresto the motor

A cheap electric motor contains twoordinary magnets and anelectromagnet called an armature.When current is supplied to the motorit passes to the copper wire in thearmature through contacts calledbrushes. The armature then turnsbetween the two magnets. The morecurrent supplied to the motor, thefaster it turns.

Circuit 12 - Motor controlConnect two leads withbared ends to the motor asshown. Connect these tothe battery box using theprototyping board. Whenyou switch on the motorwill run. If you swap overthe leads from + to 0, themotor will run in theopposite direction.

Circuit 13 - Electric brakeWhen you switch off, themotor takes a bit of time tostop. If you connect a pieceof wire across the motorterminal (a short circuit) themoment after you switch off,the motor will stop instantly.This is because the motor isacting as a generator andthe wire makes it do work.

magnets

armature

brushes

ABCDE

FGHIJ

1 5 10 15

1 5 10 15

X

Y

switch off the power beforetouching the wires together

17

use the red sleeves to connectthe wires to the motor

if the LED does not light upwhen the motor spins,connectthe LED the other way aroundin the connecting block.

Circuit 14 - Electric generatorThe motor will also work as a generator if you can turn the spindle fast enough.To try this out, fix a second motor to the first one using a small length of rubbertubing. Now connect a high bright LED to the second motor. Because it is adiode, you may have to swap its legs around to get it to work. The first motorpowers the second and this generates current for the LED.

Buzzers and soundersBuzzers or sounders come in many shapesand sizes. The one in your kit works fromas low as 1.5v and makes quite a noise!But it has to be connected the right wayround: red lead to +v and black lead to 0v.

Circuit 15When you turn on the buzzer in thiscircuit, it will sound at full volume. If youconnect the buzzer via long leads, you willhave a door buzzer circuit.

red wireto +v

black wireto 0v

press

here

membranepanel switch