school electronic supplies... · the solderless breadboard page 23 fault finding page 24 ... using...

School Electronic Supplies

INTRODUCTION

TO

ELECTRONICS

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School Electronic Supplies Introduction to Electronics

CONTENTS

The Basics of Electronics Page 4

OHMs law Page 7

The Components and symbols Page 10

Diodes Page 14

Light Emitting Diodes Page 15

Resistors Page 16

Variable Resistors Page 18

Light Dependent Resistors Page 19

Transistors Page 19

Capacitors 0

Integrated Circuits Page 21

Batteries Page 22

The Solderless Breadboard Page 23

Fault Finding Page 24

Simulation Software Page 25

Project 1 Light up an LED Page 26

Project 2 Using a Light Dependent Resistor Page 30

Project 3 Using a Potentiometer Page 31

Using Transistors Page 33

Project 4 Dark Activated Switch Page 36

Adding More LEDs Page 38

Project 5 Touch Sensitive Switch Page 41

Project 6 Flashing Two LEDs Page 43

Project 7 Dual Variable Flashing LEDs Page 45

Soldering Page 46

Project 8 Soldering the Dual Variable Flashing LEDs Project Page 48

Basic Electronics Knowledge Test Page 50

K1094 The Night Light Project Page 52

Resources Page 56

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The parts required to complete Projects 1 to 8 in this notebook are as follows: -

1 x K1000 Dual Variable Flashing LEDs Kit

1 x Solderless Breadboard

1 x 9 Volt Battery

1 x Light Dependent Resistor

Tinned Copper Jumper Wire

The parts for the Night Light Project are contained in the K1094 Night Light Kit except for the Solderless

Breadboard and a 9-volt Battery.

The aim of the introduction to electronics notebook.

This notebook has been designed to give students the opportunity to learn about what the components do

and also how they work in an electronic circuit.

It also teaches them essential skills, such as identifying components, reading schematic diagrams,

constructing a circuit, soldering and how to fault find.

Acknowledgment’s

Anza Properties Pty ltd

LAPTEK Pty ltd www.laptek.com.au

School electronic supplies www.schoolelectronicsupplies.com.au

Steven Penna Email: [email protected]

Aaron Penna Email: [email protected]

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The basics of electronics

Electronics gets its name from the electron, a tiny particle which forms part of all atoms

which make up everything in the world. Atoms contain protons, neutrons and electrons but it

is the electrons that are important to us in learning about electronics.

Electrons and protons have the property of charge. Protons have positive charge and electrons

have negative charge and they normally balance each other out. It is not known what charge

really is. It’s just a property like weight or colour, but it is this property which makes the

whole of electronics happen. It is also important to know that just like magnets, opposite

charges attract and similar charges repel.

When electrons move together in a unified way this is what is known as a current flowing.

Electrons are actually moving constantly in materials like metals but they are moving in a

random disordered way. A current is when they all flow together in one particular direction.

Have you ever walked across a synthetic carpet to press a lift button and felt a shock? This is

caused by a build-up of static electricity in your body and when you touch the button

electrons flow through you to the ground. That is what current is, a flow of electrons in a

certain direction. For future reference, static electricity can be very damaging to some

electronic components and precautions need to be taken when handling these devices. Anti-

static wrist straps should be worn when handling some components. An example of the

dangers of static electricity to your students is that in most of their homes they would have a

surge protector in line with their computer and other valuable electronic equipment to protect

against damage from lightning.

Electrons cannot flow through every type of material. Materials that allow current to flow

easily are called conductors. Conductors conduct electrical current very easily because of

their free electrons. Materials that do not allow a current to flow are called non-conductors or

insulators. Insulators oppose current and make poor conductors.

Some common conductors are copper, aluminium, gold, and silver.

Some common insulators are glass, air, plastic, rubber, and wood.

.

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Copper is a good conductor and is used for tracks on most printed circuit boards to connect the

components together. Solder is another good conductor and this is used to make the actual join between the

leg of the component and the copper track.

The plastic that printed circuit boards are made of is an insulator. Current can only flow through the copper

tracks on the printed circuit board and cannot jump from one track to another. For the same reason wires

are coated in plastic to stop them conducting to anything they may be touching.

There are certain materials that are somewhere between the two extremes of conductor and insulator and

these are called semi-conductors. A good example of a semi-conductor is silicon. Components, commonly

called “semi-conductors”, are a very important part of electronics.

We will use a 9-volt battery to power our circuits and this will provide the ‘force’ that makes the electrons

move. The force is called voltage. The bigger the voltage the more force that is generated. For this reason,

mains electricity which is 240 volts is much more powerful than a 9-volt battery.

Currents are measured in amps and Voltages are measured in volts.

They are named after the scientists André-Marie Ampère (1775–1836) French mathematician and

physicist, considered the father of electrodynamics and Alessandro Volta (1745 –1827) was an Italian

physicist, chemist, and a pioneer of electricity and power, who is credited as the inventor of the electrical

battery.

Voltages are sometimes referred to as potential differences or electromotive forces EMF.

Voltage V is the unit of electrical pressure. One volt is the potential difference needed to cause one amp of

current to flow through one ohm of resistance.

Many people are confused as to the difference between voltage and current. They talk about volts going

through something when they really mean amps. So, let’s think about it a different way.

Imagine water being pumped through a pipe to fill up a pond. The water represents the electrons flowing in

the circuit. The pipe represents the copper wire or conductor. The pump provides the pressure to force the

water through the pipe. The pump is the battery. The amount of water that flows out of the end of the pipe

each second is the current. The amount of force at which the water is being pumped is the voltage.

A narrow pipe will take a long time to fill the pond, whereas a wide pipe will do it faster using the same

pump. Clearly the rate of flow depends on the thickness of the pipe and it is also obvious that the same

pump pressure can produce different flow rates depending on the size of the pipe. So now if we equate that

in electronics terms we can have the same voltage producing different current flows depending on the

amount of resistance in the conductor.

An electric current needs a complete path called a circuit before it can flow, we use a battery to supply the

voltage. A chemical reaction in the battery releases electrons which flow around the circuit and then back

into the battery. It takes energy to keep the current flowing and so eventually the battery wears out.

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When current flows into a component, the same amount of current flows out of the component. It is not

‘used up’ in any way. As current passes through components in a circuit, things happen. For example, in

the circuit below, the current flows through the resistor into the led, causing the LED to light up.

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Ohm’s Law

Named form the German physicist Georg Ohm (1789-1854),

Ohm’s Law addresses the key quantities at work in circuits: the

relationship between voltage V , current I and resistance R.

which states that the current flow through a conductor is

directly proportional to the potential difference voltage) and

inversely proportional to the resistance.

When Ohm published his formula in 1827, his key finding was that the amount of electric current flowing

through a conductor is directly proportional to the voltage imposed on it. In other words, one volt of

pressure is required to push one amp of current through one ohm of resistance. There is always a constant

ratio between the voltage and current for a particular value of resistor. The value of the resistance is

measured in ohms Ω. If you know any two values of the Voltage, Current or Resistance quantities. We can

use Ohms Law to find the third missing value. Ohms Law is used extensively in electronics formulas and

calculations so it is “very important to understand and accurately remember these formulas”.

You need any two of these variables to work out the missing one using the formulas below.

To find the Voltage, V

[ V = I x R] V (volts) = I (amps) x R (Ω)

To find the Current, I

[ I = V ÷ R] I (amps) = V (volts) ÷ R (Ω)

To find the Resistance, R

[ R = V ÷ I] R (Ω) = V (volts) ÷ I (amps)

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In other words, if you know the resistance and the voltage you can work out the current. Or if you know

the resistance and the current you can work out the voltage and if you know the voltage and the current

then you can calculate the resistance.

Ohm’s Law is undoubtedly the most commonly used formula in electronics. For example, it can be used to

calculate the value of a resistor to protect an LED from too much current and an Electrician would use it to

work out how much current a heater element would draw.

Example Voltage

I = 0.02 amps

R = 470 Ω

V = I x R 0.02 x 470 = 9.4 V

Therefore, batteries come in increments of 1.5V. 6 x 1.5 = 9V

Example Current

V= 9V

R= 470 Ω

I = V ÷ R 9.0 ÷ 470 = 0.019 amps

Therefore, tolerances for components would allow a 20mA LED

Example Resistance

V= 9V

I= 0.02 amps

R = V ÷ I 9.0 ÷ 0.02 = 450 Ω

Therefore, we would use the next highest standard resistor value,

which is 470 Ω (470R).

You can double check your answers by using your answer for V, I or R and replacing a known value. To

see if you get the same result.

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The mathematical symbol for each quantity is meaningful as well. The “R” for resistance and the “V” for

voltage are both self-explanatory, whereas “I” for current doesn’t seem to relate to its use. The “I” is

thought to have been meant to represent “Intensity” (of electron flow) Ampere at that time thought of

electricity in terms of fluid dynamics and so he named it the intensité de courant and although the intensité

bit is now forgotten the initial letter ‘I’ stuck as it wasn’t being used for anything else at the time standards

were laid down. The other symbol for voltage, “E,” stands for Electromotive force, the symbols “E” and

“V” are interchangeable for the most part, although some texts reserve “E” to represent voltage across a

source (such as a battery or generator) and “V” to represent voltage across anything else.

Voltage measured in volts, symbolized by the letters “E” or “V”.

Current measured in amps, symbolized by the letter “I”.

Resistance measured in ohms, symbolized by the letter “R”.

Ohm’s Law: E = IxR I = E÷R R = E÷I

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COMON COMPONENTS AND SYMBOLS

WIRES

Wires Represents a conductor that conducts

electrical current.

Connected

Wires

Represents the connection of two

conductors. Dot shows the junction

point.

Unconnected

Wires

Represents two unconnected

wires/conductors. Any of the two

methods can be followed. Drawing two

lines perpendicularly is an older

method of representing unconnected

wires.

POWER SOURCES

DC Supply This represents the DC power supply.

It applies DC supply to the circuit.

Single Cell

Battery This provides supply to the circuit.

Multi Cell

Battery

Combination of multiple single cell

batteries or a single large cell battery.

The voltage is usually higher.

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RESISTOR SYMBOL

Fixed Resistor

A resistor opposes the flow of current

in a circuit. These two symbols are

used to represent fixed resistor.

VARIABLE RESISTOR

LDR

The resistance of LDR varies with the

intensity of the light incident on it.

They are generally used in light

sensing applications. They are also

called as Photo Resistors.

Potentiometer A potentiometer, informally a trim pot, is

a three-terminal resistor with a sliding or

rotating contact that forms an adjustable

voltage divider. If only two terminals are

used, one end and the wiper, it acts as a

variable resistor or rheostat.

DIODES

Pn Junction

Diode

A PN Junction Diode is one of the

simplest Semiconductor Devices

around, and which has the

characteristic of passing current in only

one direction only.

Led

Light emitting diode is similar to PN

junction diode but they emit energy in

the form of light instead of heat. These

are mostly used for indication

purposes.

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TRANSISTOR SYMBOLS

NPN

It is made of combination of P-type

semiconductor between two N-type

semiconductors. It is switched ON

when the base-emitter junction is

forward biased. They are commonly

used for amplifying and switching

applications.

PNP

It is made of combination of N-type

semiconductor between two P-type

semiconductors. It is switched ON

when the base-emitter junction is

reverse biased. These are used for

amplifying and switching applications.

CAPACITOR SYMBOLS

Non-Polarized

Capacitor

Capacitor stores the charge in the form

of electrical energy. These two

symbols are used for non-polarized

capacitor. Non-polarized capacitors are

big in size with small capacitance.

They can be used in both AC and DC

circuits.

Polarized

Capacitor

Polarized capacitors are small in size

but have high capacitance. They are

used in DC circuits. They can be used

as filters, for bypassing or passing low

frequency

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MISCELLANEOUS

Buzzer

This is sound producing device. This

produces buzz sound when the voltage

is applied.

Loud Speaker

This is also an audio device. The

electrical signal is converted into sound

signal here.

Motor This converts the electric energy to

mechanical energy.

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DIODES

Diodes are components that only allow current to flow in one direction. They have a positive side and a

negative side. When the voltage on the positive side is higher than the voltage on the negative side, then

current flows through the diode because the resistance is very low. Conversely, when the voltage on the

positive leg is lower than on the negative leg then the current does not flow because the resistance is very

high. Therefore, a diode is a device that is a conductor in one direction and an insulator in the other.

The negative leg is the one with the line closest to it and is called the cathode (k). Yes, it is k not c.

The positive end is called the anode (a).

Normally when a current is flowing through a diode, the voltage on the positive leg is approximately 0.7

volts higher than on the negative.

Diodes are commonly used as protection devices to prevent accidental damage to other components in a

circuit from reverse polarity. This can occur when the positive and negative of a battery or power supply

have been connected backwards.

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LIGHT EMITTING DIODES

Light Emitting diodes (LED), are diodes that are

made of a special semi-conductor material, which

emits light when current flows through it. Because

they are a diode, they are polarised which means

that they will only conduct one way. LEDs have a

positive (a) leg and a negative (k) leg just like a

regular diode. The positive leg is the longer one.

However, if you already trimmed the legs look for

the flat spot on the base of the LED. This is the

negative side.

Unlike light globes, LEDs never burn out. Unless

their current limit is passed.

LEDs must have a resistor in series with them to

limit the current to a safe value.

‘In series’ just means in line with each other.

The value of this resistor is determined by the supply voltage of the circuit, the operating voltage of the

LED and the current limit of the LED. These values can vary depending on the colour of LED and how

bright it is (mcd). The operating voltage can be between 2 volts and 4 volts. The current limit can be from

0.02 amps (20ma) to 0.04 amps. The resistor value can be calculated by using Ohms Law as shown below

Ohms Law

R = ( VS – VL )

I

Where: R = Resistor Value

VS = Supply Voltage

VL = LED Voltage

I = LED Current in Amperes

For Example: R = ( 9.0 – 2.0 ) = 7.0 = 350 Ohms

0.02 0.02

Therefore, the nearest standard resistor you would use is 390 Ohms (390R).

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RESISTORS

Electrons move more easily through some materials than others when a voltage is applied. We measure

how much opposition to the movement of electrons (current) as resistance.

Resistors are components that have a predetermined resistance. The resistance determines how much

current will flow through a component and resistors are used to control voltages and currents. Carbon film

resistors are a fixed form type resistor. They are constructed out of a ceramic carrier with a thin pure

carbon film around it, that functions as resistive material. The desired resistance value can be obtained by

choosing the right layer thickness, and by cutting a spiral shape in the carbon layer. The helical cut in the

film increases the length of the current path. By decreasing the pitch of the helix, the length of the resistive

path increases, and there with the resistance value increases. Furthermore, by fine tuning the cutting of the

spiral the resistor can have a higher accuracy of resistance value

A very high resistance allows very little current to flow. Air has very high resistance and that is why the

bare high voltage power lines you see everywhere do not short out. Current almost never flows through air.

Sparks and lightning are brief displays of current flow through the air. The light you see when this happens

is created by the current causing parts of the air to burn.

A low resistance allows a large amount of current to flow. Metals have a very low resistance. That is why

wires and tracks on PCBs are made of metal such as copper.

Resistance is measured in Ohms and is named after the man who invented the law relating to voltage and

current. Georg Simon Ohm. Ohms are represented by the Greek letter omega Ω. However, computer

keyboards do not have this symbol so we now substitute it with the letter ‘R’. The letter ‘k’ stands for kilo

which is 1,000 and this is used to shorten the description of some resistor values and it is also used to show

the position of the decimal point.

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Here are some examples:

10R = 10 ohms

10k = 10 kilohms = 10,000 ohms

4k7 = 4.7 kilohms = 4,700 ohms

Common resistor values range from 1 ohm to 1,000,000 ohms. It is very difficult to make a resistor to an

exact value and in most circuits, it is not that critical anyway. Resistance values are stated with a certain

accuracy called tolerance. This is expressed as a percentage such as + or – 5%. What it means is that a

100R resistor could have a real value anywhere between 95R and 105R. In general, the rule of thumb for

values of many types of components in most circuits can be treated as near enough is good enough.

Resistors are not polarity sensitive so they can be installed either way.

Resistor Colour Code

The electronic colour code is used to indicate the values or ratings of electronic components

The colour code shown is used to designate the value of a 4 band resistor.

Ten different colours represent the numbers 0 to 9.

The first two coloured bands on the body of the 4

band resistor denote the first two digits of the

resistance value and the third band is the

‘multiplier’. The multiplier is the number of zeroes

that are added to the first two digits.

For example, A resistor with Brown, Red, Red,

Gold

First band Brown = 1

Second band Red = 2

Third band (multiplier) Red = x100

12 x 100= 1200. Or 1.2k 1k2

The fourth band is the tolerance, which for most

carbon film resistors is gold and means +/-5%

accuracy.

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VARIABLE RESISTORS

Variable resistors are, as the name suggests, a resistor that has a dial or a knob that

allows you to alter the resistance. They are referred to by a number of names e.g.

potentiometer, pre-set and trimpot.

Variable resistors are used in circuits to vary things that need changing such as

volume controls. When you move the volume control you are changing the resistance

which changes the current. Making the resistance higher will let less current flow so the volume goes

down. Making the resistance lower will let more current flow so the volume goes up.

Trimpots have a moveable metal wiper resting on a circular track of carbon. The wiper moves along the

track as the trimpot is turned. When voltage is applied to the circuit, the current flows through the wiper

and then through part of the carbon track. The more track the current has to go through the greater the

resistance and the less track, the less resistance. There are three pins

or terminals on a trimpot and the middle one is the wiper.

Generally, only the wiper and one of the outside legs are used when

you are using a trimpot as a variable resistor. All three legs are used

when it is used as a potentiometer or voltage divider.

The maximum resistance a trimpot can provide is written on it. For

instance, larger potentiometers usually have a value such as 500K.

However, because trimpots are small they usually have a number on

them. The first two digits represent the first two numbers of its

value and the third number denotes how many zeroes are added.

The value of the trimpot shown here is 10 + 5 zeroes = 1,000,000 ohms = 1 Megaohms

(1M). So, this trimpot can be altered to have a value of anywhere between zero ohms

and one million ohms.

The wiper in the trimpot can be rotated in a clockwise or anticlockwise direction and we can use this

feature to decide whether the resistance increases or decreases depending which way it is turned. To do

this we can either use legs A and B or legs B and W. If we use legs A and B and rotate the wiper in a

clockwise direction then the resistance will increase from 0 to maximum.

When it is turned in an anticlockwise direction the resistance will decrease. If we use legs B and W and

rotate the wiper in an anticlockwise direction then the resistance will increase from 0 to maximum. When

it is turned in a clockwise direction the resistance will decrease.

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Light Dependent Resistors

A Light Dependent resistor (LDR) is a special type of resistor that varies

its resistance according to the amount of light falling on it. When it is

dark it will have a very high resistance and when it is in the presence of

very bright light the resistance is very low. This varies depending on the

type of LDR but typically it can be anywhere between 2K and 10M

ohms.

This makes it very useful to use in many applications when we want to switch things on when it is dark

such as street lights. Because the resistance of an LDR is directly proportional to amount of light shining

on them they are used in lux meters to measure light intensity. They are also used in cameras to turn on the

flash when the light level is low.

We can use an LDR to switch on a LED when it is dark. But we could quite easily change the circuit to

make the LED turn on when it is light.

A Light dependent resistor is not polarised so it can be installed either way.

TRANSISTORS

NPN PNP

Transistors are semiconductor devices that can be used as a switch or an amplifier. As a switch they are

used to turn currents on and off and as amplifiers to make currents larger. For example, the Night Light

circuit uses a BC548 NPN transistor as a switch to turn on the LED.

Transistors have three legs: collector, base and emitter. A small current flowing into the base – emitter

junction causes a much larger current to flow between the collector and emitter. This then switches on any

device connected to it.

Transistors can only be installed one way and must match up with the collector, emitter and base legs.

Transistors are considered to be the most important device in modern electronics. They can be found

everywhere. They used in watches, cameras, calculators, microwaves, computers and the list goes on.

Intel has developed 10 nanometres chips that have 100million transistors per square mm!

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CAPACITORS

Capacitors are components that are used to store an electrical charge.

When power is supplied to a circuit that includes a capacitor, the capacitor charges up. When the power is

turned off, the capacitor will discharge its electrical charge. Like a rechargeable battery.

A capacitor is basically composed of two metal conductor plates separated by an insulating material called

a dielectric. The dielectric can be paper, plastic film, ceramic, air or a vacuum. The size of the metal

conductor plates dictates the amount of charge the capacitor can store.

The amount of charge or energy a capacitor can hold is called capacitance. Capacitance values of

capacitors are usually specified in farads (F), microfarads (μF), nanofarads (nF) and picofarads (pF) Farads

are named after the English scientist Michael Faraday. (1791-1867)

1 Farad (1F) is quite a large unit and the ones we will be using are only a fraction of this size. For instance,

a 47 microfarad (47uF) capacitor is 47 millionths of a Farad. The symbol used for a millionth is the Greek

letter ‘Mu’ (µ) which is usually represented by the English letter ‘u’ because it is the closest thing available

to the Greek letter on a modern keyboard.

Capacitors can be polarised or non-polarised.

Polarised means that they have a positive (+) and negative (-) lead and need to be connected in a circuit the

correct way around. Electrolytic capacitors normally have a black line on the body to indicate the negative

leg.

Non-polarised capacitors can be connected in a circuit in any direction.

Electrolytic capacitors can store more charge than non-electrolytic capacitors. However, electrolytic

capacitors slowly leak their charge when not in use and they also have quite large tolerances. A 47uF

capacitor might actually be as high as 80uF or as low as 10uF. So, this means that two identical circuits

can produce quite different results.

Capacitor Markings.

Capacitors have a voltage range and you must ensure that the voltage rating of the capacitor is higher than

the voltage of the circuit. E.G. If you are using a 9-volt battery you would need to use a capacitor with a

rating of 16 volts or higher.

Electrolytic capacitors normally have the capacitance and voltage printed on the case and a tolerance of

approximately +/- 20%.

Non-electrolytic capacitors such as polyester, ceramic and monolithic types use a marking system called

EIA Coding. The EIA coding uses a two-digit number that refers to the value, a third digit that defines the

multiplier and fourth character that represents the tolerance.

Example Code: 103K

This expands to:

1 = 1

0 = 0

3 = K = +/-10% Tolerance ( J= +/-5%, K= +/-10%, M= +/-20%. )

Then we combine these numbers together:

10 x 1,000 = 1,000,000pF = 1,000nF = 1uF = 0.000001 Farad @ +/- 10% Tolerance

pF = Picofarad, nF = Nano farads, μF = microfarads.

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INTEGRATED CIRCUITS

Electronic components can be divided into two groups, these being Discrete electronic components and

Integrated Circuits (ICs).

Discrete Electronic Components are separate components that you can combine to make a circuit.

Examples are: resistors, transistors, capacitors, diodes and light emitting diodes (LED).

Integrated circuits are complex, highly miniaturised circuits incorporating large numbers of components

that are all etched on to a tiny piece of silicon called a chip. These chips are encapsulated in small

rectangular plastic packages and have pins that enable them to be connected to external circuits.

A huge range of ICs are available and are manufactured in vast quantities. They are designed to be used in

many different applications and are used in virtually every modern-day appliance and device such as:

televisions, computers, mobile phones, aeroplanes, motor cars, credit cards and traffic lights.

The iPhone 7’s A10 processor has a 3.3 billion transistor count. Just imagine how big an iPhone would be

if there were no ICs.

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BATTERIES

A lot happens to a battery when you connect them to an electronic circuit. When the circuit is completed

between the negative (anode) and positive (cathode) ends of the batteries. The battery produces electricity

through a series of electromagnetic reactions between the positive, negative and electrolyte. The anode

experiences an oxidation reaction in which two or more ions (electrically charged atoms or molecules)

from the electrolyte combine with the anode, producing a compound and releasing one or more electrons.

At the same time, the cathode goes through a reduction reaction in which the cathode substance, ions and

free electrons also combine to form compounds. While this action may sound complicated, it's actually

very simple: The net product is electricity. The battery will continue to produce electricity until one or both

of the electrodes run out of the substance necessary for the reactions to occur.

Electrons flow out of the negative terminal of the battery and through the wires and components of the

circuit and then back into the positive battery terminal. It takes energy to do this so eventually all the

energy in the battery is used up and it needs to be replaced.

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The Solderless Breadboard

Uses of a Breadboard

A breadboard is used to make up temporary circuits or

to try an idea. No soldering is required so it is easy to

change connections and replace components. Parts will

not be damaged so they can be used at a later time.

The picture shows a typical small breadboard which is

ideal to build reasonably simple circuits with one or two

integrated circuits (ICs) and common through hole

components.

Connections on a Breadboard

Breadboards have tiny sockets called holes that are arranged on a 2.54mm 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. The breadboard shown has three hundred

holes that are divided into sixty rows of five. The five holes in a row are joined together in a continuous

strip and are called buses. The outside rows that are highlighted by the red and blue lines are one

continuous strip of twenty five holes each and these are called distribution buses. The red distribution

buses are used for positive connections and the blue ones for negative connections. Wire links made from

0.6mm diameter single core plastic coated wire are used to connect between buses to make circuit

connections. Do not use stranded wire because it will crumble when pushed into a hole and may damage

the board if strands break off. Some components such as switches do not have suitable leads of their own

so you need to solder on single core wires prior to using on your breadboard.

This diagram shows how the breadboard holes and buses are

connected. Once you have built your first simple circuit, you

will be surprised how quickly you start to understand how the

breadboard connections work.

FAULT FINDING

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The beauty of a breadboard is that when you do make a mistake it is usually easy to fix. If you do have a

problem, there are simple rules you can follow that will make it easier to find the faults in your circuit. At

this stage we are assuming that you are using a circuit that is actually known to work. If you have designed

the circuit yourself then you need to be sure that is a sound workable design by using a design and

simulation program such as Crocodile Clips or Circuit Wizard.

So you have built your circuit and it does not work. It’s Disappointing, but it’s not the end of the earth. The

good thing about fault finding is that you usually learn a lot.

Here is a list of logical steps to follow to help you find your problem.

FAULT FINDING CHECKLIST.

Learn how to use a multimeter so you can test voltage, current, resistance and continuity. Many

multimeters even have a transistor and diode tester.

A multimeter will help you to eliminate possible faults very quickly.

1. The first thing to do is to check your power supply or batteries, especially the polarity. If these are

OK, check that your on/off switch is on.

2. If your circuit still does not work, switch it off,

Check the following

• all connections carefully. Make sure that that none of the wire links are broken. The wires are

quite small and are easy to damage when you are stripping them.

• you have all the connecting wires in place. Most initial faults are caused by incorrect wiring.

• all components are pushed into the holes and are connected securely.

• the components are installed the correct way around. EG. LEDs, Capacitors, Transistors and

ICs etc.

• that no leads are shorting out. (Unless they are connected to the same bus).

• that you have used the correct components.

• the components are actually working by testing them outside the circuit.

Hopefully by now you have found your problem or problems. If not don’t go around in circles and never

assume anything. Be patient and calm and go back to the beginning and start again. If you still cannot find

the fault, put it away and come back to it later. This usually works!

Page | 25


SIMULATION SOFTWARE

If you have access to Software such as Circuit Wizard or Crocodile clips (Yenka), you can use these tools

to simulate your circuits on the computer screen. You can draw your schematic diagram by choosing

components from the ‘library’ and connecting them up on the screen. Then you can test it to see if it

works. It also lets you change the values of the components so that you can observe the effects it has on the

circuit. You can even ‘blow up’ components without costing you a cent. Most types have virtual test

instruments so that you can learn how to use a multimeter to test voltage, current and resistance etc. Some

even let you use breadboards to design, build, simulate and test your circuits.

Simulation software is quite easy to use and usually have very useful tutorials and sample circuits.

Page | 26


Project 1 Light up an LED

We will start with a very simple circuit that has only three components. The circuit is shown in the

schematic diagram below. It consists of a 390 Ohm resistor in series with an LED and is powered by a 9

volt battery. The resistor reduces the voltage to a suitable level for the LED and limits the current to

prevent the LED from blowing up.

Parts List

Solderless Breadboard

9 volt battery

Battery Snap

390 Ohm Resistor ( colour code orange – white - brown )

10K Ohm Resistor ( colour code brown – black – orange )

5mm LED

1N4004 Diode

Tinned Copper Wire ( Jumper wire )

Any standard LED will work in this circuit and are available in red, green, yellow and orange.

Green, yellow and orange are much brighter than red, brighter is better.

The KS1000 kit contains two high brightness red LEDs with water clear lenses which is even better.

We will connect the components on the breadboard as shown in the schematic diagram.

Page | 27


The following instructions will lead you step by step on how to build the circuit. This will help you to

develop a good method of constructing circuits on a breadboard for later projects in this notebook.

Step 1: Connect the red and black leads of the battery snap to the positive (+) and negative (-) rails on the

breadboard as shown in the picture above. The positive rail is highlighted in red and the negative in blue.

There two positive and two negative rails on our breadboard and we have used one of each on opposite

sides of the board. This makes it easier to see that we are building a ‘series’ circuit and matches the way

the circuit diagram has been laid out. Do not connect the battery at this stage.

Step 2: Install a jumper wire between the positive rail and hole ‘a4’.

Step 3: Install the 390 Ohm resistor between holes d4 and g4.

The resistor is not polarised so it does not matter which way round it is installed.

Step 4: Install the LED between holes numbers i4 and i5.

The LED is polarised so it needs to be installed the correct way around.

The positive leg or anode (A) is the longer leg and the negative leg or cathode (K) is the shorter

leg. The negative leg is also indicated by the flat side on the base of the LED.

This is very handy to know if you have already shortened the legs of the LED.

Step 5: Install a jumper wire between j5 and the negative rail.

Step 6: Connect the battery snap to the 9 volt battery. The LED should light up.

Congratulations, you have just built your first electronic circuit.

Page | 28


If it does not work then you will need to fault find your circuit. Firstly, check that all your components are

connected to the correct holes on the breadboard. If they are and it still does not work check to see if the

LED and the battery are connected the correct way around. Sometimes just taking the components out one

by one and replacing them can eliminate any bad connections.

Now we will do some experiments that will etch in to your mind the difference between polarised and non-

polarised electronic components. We are going to alter some of the components in the circuit to see what

happens.

Before you make an alteration to any circuit you should always disconnect the battery first and only

reconnect it when the change is complete. You can do this by physically disconnecting the battery or

simply by pulling the red positive battery wire out of the breadboard. If you use the second method make

sure the bare end does not short out on anything. See below for details on short circuits.

Experiment 1: Turn the resistor the opposite way. Reconnect the battery and note what happens.

Experiment 2: Relace the 390R resistor with the 10K and note what happens to the LED.

Experiment 3: Reverse the connections of the LED. Reconnect the battery and note what

happens.

Experiment 4: Reverse the connections from the battery to the positive and negative rails.

Reconnect the battery and note what happens.

Experiment 5: Remove one of the jumper wires. Reconnect the battery and note what happens.

That’s right. Nothing happens. That is because we do not have a continuous circuit so the electrons cannot

flow. This is called an ‘open’ circuit. The opposite is called a ‘short’ circuit.

A short circuit occurs when there is little or no resistance between the positive and negative sides of the

power supply. For example, if we accidently put a jumper wire between the positive and negative rails of

the breadboard we would bypass the components in our circuit. Because the jumper wire has a very low

resistance this would allow a very large current to flow from the battery in a short space of time. The result

would be a very dead battery or it could even blow up. Either way it would get extremely hot due the

energy dissipated. We are only using a 9 volt battery but imagine how dangerous a short circuit could be if

we were working with 240 volt mains voltage.

No matter what voltage you are using, you should always treat electricity with respect and always

disconnect your circuit if you have a problem, or before you work on it.

Page | 29


Adding a Diode to the Circuit.

Diodes are components that only allow current to flow in one direction and are commonly used as

protection devices to prevent accidental damage to other components in the circuit from reverse polarity.

This can occur when the positive and negative of a battery or power supply have been connected

backwards.

Now we will install it into our LED circuit as shown below.

First, remove the jumper wire between the positive rail and hole b4.

Then replace it with the diode. Ensure that the anode is connected to the positive rail and the cathode is

connected to hole b4.

Now reconnect your battery supply and the LED should come on.

Now we will confirm that you understand what reverse polarity means.

• Turn the diode round the opposite way and note what happens.

• Return the diode to its correct polarity and note what happens.

• Swap the red and black leads from the battery and note what happens.

Ok, that’s reverse polarity. Let’s move on to another circuit.

Take care not to damage your components or you will not be able to complete all of the projects.

The positive end is called the anode (a). The

negative end is the one with the line closest to

it and is called the cathode (k).

Page | 30


Project 2, Using a Light Dependent Resistor

A light dependent resistor (LDR) is a special type of resistor that varies its resistance according to the

amount of light falling on it.

When it is dark it will have a very high resistance and when it is in the presence of very bright light the

resistance is very low. Typically this resistance can be anywhere between 2K and 10M ohms.

In this circuit we are going to use a light dependent resistor to control the brightness of a light emitting

diode (LED).

We are going to connect the LDR in series with the LED and a 9 volt battery as shown in the circuit

diagram below and the picture of the layout on the breadboard. The minimum resistance of the LDR is

approximately 2K ohms and this will limit the current in the circuit and prevent any damage to the LED.

But it also means that we will not get full brightness from the LED because the resistance is too high.

However you should be able to see the effect of the varying resistance has on the light output of the LED.

When you have built your circuit on the bread board and connected the battery, the LED should light up. If

it does not, check your connections and the orientation of the LED. The LDR is not polarised so it does not

matter which way round it goes. If everything seems ok, it might mean that there is not enough light falling

on the LDR to lower the resistance enough to allow the LED to switch on. Move your circuit to a place

with more light and then the LED should come on. Or you could shine a torch on the LDR to get the same

effect.

While you are in a place of bright light you can experiment by shading the LDR with your hand. The more

shade you cast over the LDR the less bright the LED should be. If you block the light to the LDR

completely the LED will go off. Because the resistance of the LDR increases as the light level decreases

this causes the voltage across the LED to drop to a very low level. Most standard LEDs, like the one we

are using, need a minimum of approximately 1.2 volts to operate and once the voltage drops below this

threshold the LED turns off. Maximum voltage across a standard LED should not exceed 2.6 volts.

Page | 31


Project 3 Using a Potentiometer

In this project we will experiment with a potentiometer to vary the brightness of two LEDs.

As you can see in the schematic diagram below, it is quite a simple circuit. You have already used a

resistor, a diode and an LED so the only new component we are introducing is the potentiometer.

If you are not sure how to connect up the potentiometer (VR1) go to the section on Variable Resistors on

Page 8. You also may need to refer to Project 1 regarding the polarity of the Diode and the LEDs.

Parts List


9-volt Battery

Battery Snap

2 x 390R Resistors

(Orange – White – Brown)

2 x Light Emitting Diodes

1N4004 Diode

Potentiometer 200K (204)

Tinned Copper Wire

Now you can connect up your circuit on

the solderless breadboard as shown below.

Page | 32


Installing Potentiometers

Some potentiometers can be difficult to install into a breadboard because the flat side of their legs does not

line up with the spring-loaded contacts inside the board. This problem can be solved easily by using long

nose pliers to gently and carefully turn the legs 90 degrees.

Before After

After you have done this modification the potentiometer should fit into the breadboard easily and be held

securely to give a good contact.

Testing the Circuit

When you are confident that you have built the circuit correctly you can connect the battery and test it.

Use a small flat screwdriver to adjust the potentiometer. You will need to hold the potentiometer down

with your finger while are doing this to prevent it from popping out of the breadboard.

When you turn the potentiometer clockwise one LED should light up fully. When you rotate the

potentiometer anti-clockwise the other LED should come on fully. If you adjust the potentiometer to the

centre position both LEDs should be off or only have a very low output.

If this sequence of events does not occur then you need to start fault finding your circuit.

When you get your circuit working correctly, pat yourself on the back and then answer the questions

below.

If you do not know the answers then you will need to go back through the notebook to find the information

required to answer the questions correctly.

1. Why can we only get one LED to light up to full brightness at any one time?

2. What happens when the potentiometer is adjusted to the centre position?

3. What is the difference between a potentiometer and a variable resistor?

4. Why do we have the two resistors in the circuit?

5. What function does the 1N4004 diode perform in the circuit?

6. Which component has the highest value of resistance in this circuit?

7. If we powered our circuit with 12 volts, what changes would we need to make?

8. What other symbol could we have used in the schematic diagram to represent the resistors?

9. Are the resistors R1 and R2 in series or parallel with the two LEDs?

10. Which components in the circuit are polarised?

Using Transistors

Transistors are semiconductor devices that can be used as switches or to amplify signals.

Page | 33


Transistors have three main uses:

• As an electronic switch within a circuit.

• To switch on another part of a circuit when a change in resistance of a sensor device is detected.

• As an interface device to receive signals from low current devices (such as ICs) and to use these to

turn on high current devices (such as motors).

•

Transistors have three legs:

1. Collector (C)

2. Base (B)

3. Emitter (E)

The base is used to control and activate the electronic switch. When it receives a voltage of over 0.7 volts a

small current is passed through the base emitter connection, this allows a much larger current to flow

between the collector and emitter. This will then switch on any device connected to it.

Electrically it is as if the transistor is composed of two diodes that have been sandwiched together with the

common middle part being the base. See the picture below.

There are two types of transistor these being NPN and PNP. The different order of the letters refers to the

order in which the Negative (N) and Positive (P) materials are ‘sandwiched’ to make the transistor.

We will give you an analogy for how to understand how a transistor works

by substituting water for electricity. In the picture on the left you can see

three openings which are labelled “C” for Collector, “B” for Base and “E” for

Emitter.

C is a reservoir of water which is contained by the plunger valve shown in

black so the water cannot get into the outlet E. If we pour a small amount of

water into the B opening, it flows along the base pipe and pushes the

plunger valve upwards which allows quite a bit of water to flow from C to E.

Some of the water from B also joins it and flows to E.

If we pour even more water into B the plunger valve moves up further and

allows a greater amount of water to flow from C to E. We can increase the

amount of water poured into B until the plunger valve is fully open. When

this occurs we reach the maximum amount of flow from C to E and

increasing the amount of flow from B will not achieve anything. If you want

more water flow then you need a bigger system.

Page | 34


What can we learn from the water analogy?

• We need a DC power supply to provide the voltage to get a transistor to work. In the projects we

are building we are using a 9 volt battery. Transistors can only switch Direct Current (DC)

circuits. They will not work on Alternating Current (AC) circuits.

• A tiny amount of electrical current flowing from the base of the transistor to the emitter allows a

large amount of current to flow from the collector to the emitter. This gives an “amplification

effect” which is called ‘gain’ or ‘HFE’. A BC548 transistor has a gain of approximately 100. This

means that 1mA flowing into the base of the BC548 would allow 100mA to flow from the

collector to the emitter.

• The amount of current that can flow from the collector to the emitter is limited to the current

rating of the transistor being used. So no matter how much current we push into the base we can

not go past this limit. For instance the maximum current a BC548 can handle is 100mA. This is

fine if you want to drive a few LEDs that only take 20mA each. But if you need to drive an output

component such as a small DC motor you would need to use a larger capacity transistor such as a

BC337 (800mA), BD139 (1A) or a BD681 (4A).

• Depending on the amount of current flowing from the base to the emitter, the transistor can be in

one of the following states: Fully switched on, partially on or fully switched off.

Any restriction to the current flow in a transistor causes heat to be produced. This happens with air or

water in other devices and machinery. For example, when you pump air through your bicycle pump it

gets hot near the valve at the end because this is the restriction point. A transistor must be kept cool or

it will melt. It runs coolest when it is fully on and fully off. When it is fully on there is very little

restriction and even though a lot of current is flowing, only a small amount of heat is produced. When

it is fully off and providing we can stop base current leakage then no heat is produced. If a transistor is

half on then quite a lot of current is flowing through a restricted space and heat is produced. To help

get rid of this heat the transistor can be clamped to a metal plate which draws the heat away and

Page | 35


radiates it out to the air. Such a plate is called a ‘heat sink’ and they often have fins to increase the

surface area which improves its efficiency.

To avoid any problems always use the correct transistor for the job it needs to do.

We now have to admit that some of what we have told you about transistors is not strictly scientifically

correct. However, we believe that most explanations on how transistors work are just too hard to

understand and we hope that we have made it a little bit easier for you.

Page | 36


Project 4 Dark Activated Switch

In this project we are going to use a Light Dependent Resistor (LDR) as a sensor to control the base of a

transistor to switch on a Light Emitting Diode (LED) when the light level is low.

This circuit is commonly used for switching on security and street lights at night time.

The circuit consists of four building blocks: power supply, input, control and output.

The power is supplied by the 9-volt battery.

The LDR is the input component for this project.

The 10,000ohm (10K) resistor controls the signal to the base of the transistor.

The LED and its series resistor are the output part of the circuit.

How the circuit works.

The 10K resistor and the LDR are connected in series between the positive and negative of the power

supply. The base of the transistor is connected to the junction of the 10K resistor and the LDR. This

configuration forms a voltage divider. A voltage divider, also known as a potential divider, is a linear

circuit that produces an output voltage that is a fraction of its input voltage. The output voltage is what we

use to control the transistor. As we have discussed previously, the resistance value of the LDR increases as

the light level reduces and the resistance value decreases when the light level increases. So, in our circuit,

when the light level drops to a certain level and the resistance value of the LDR increases sufficiently, our

voltage divider will increase the voltage on the base of the transistor. When this happens, the transistor will

turn on and allow current to flow from the collector to the emitter. This in turn switches on the LED. Of

course, when the light returns the LED will switch off.

Putting the Circuit Together

You should now be familiar with how the breadboard works and you should be able to use the schematic

diagram to build the circuit. We have however given you a picture of a suggested layout to help you along.

If you come up with a different layout and it works, that is even better.

You have already used a resistor, an LDR and an LED, so you know that the resistor and the LDR are not

polarised but the LED is polarised. You are using a transistor for the first time and you need to ensure that

you get the orientation correct or your circuit will not work.

There are more components in this circuit so make sure that you give yourself enough space between the

components so that you can see your connections clearly. Take your time and make yourself familiar with

the circuit and components before you start installing the components on the breadboard.

If it does not work the first time then you will need to check your connections and the orientation of the

components. If it still does not work then go to the fault-finding page for some ideas.

Page | 37


Parts List


9 Volt Battery

Battery Snap

BC548 NPN Transistor

Light Emitting Diode

Light Dependent Resistor

390R Resistor (Orange – White – Brown)

10K Resistor (Brown – Black – Orange)

Jumper Wire

Schematic Diagram

Notice that we have shortened the legs on the

components so that our layout becomes tidier.

When you do this, you need to remember that the

flat side of the LED is negative. Make sure you

do not cut

them too short or you will not be able to solder

them into your final

project.

Testing the Circuit.

Place the breadboard in bright light.

Connect the 9-volt battery.

Hold your hand over the LDR and the LED will come on.

Now take it to a darker place and see what happens.

If you wanted to make this circuit a light activated switch, all you have to do is swap the positions of the

10K resistor and the LDR.

Now that you have successfully completed your circuit and you can see what it does, we can move on and

make the circuit a little bit more complicated. See the next page for details.

What you can do next

We can extend the operation of the dark activated circuit by adding a couple more components to make it

just like a real-life product called a ‘Night Light’.

We will use a rectifier diode to protect the circuit from reverse polarity and add a variable resistor to our

voltage divider so that we have more control over the circuit.

The variable resistor (VR1) acts as a sensitivity control so that you can adjust the trigger point at which the

LED illuminates. In other words, what we are going to do is play with the balance of the voltage divider to

alter the voltage to the base of the transistor.

Page | 38


You may find this circuit a little bit harder to build because we are adding extra components and changing

the breadboard layout a little. Well do you want to get good at this or not? It’s not that hard.

The only component you have not used so far is the variable resistor (VR1). If you are not sure how to

connect it go to the components section of this notebook and read up on it. Also see Installing

Potentiometers on Page 19.

Parts List


9-volt Battery

Battery Snap

1N4004 Diode

10K Resistor Brown – Black - Orange

390R Resistor Orange – White - Brown

Light Emitting Diode

Light Dependent Resistor

BC548 Transistor

Variable Resistor (Trimpot) 200K (204)

Tinned copper jumper wire

Page | 39


Testing the Circuit

Place the LDR in a bright light.

Connect the battery.

Turn the Trimpot until the LED is on.

Now turn the Trimpot the opposite way until the LED just goes off.

Now hold your hand over the LDR and the LED should go on.

Test your circuit by taking it to darker place.

Test your circuit in a range of different light levels so that the LED comes on at the correct darkness.

If you want a brighter light, you can add another LED or two.

Adding More LEDs

It is possible to have several LEDs on at the same time in a circuit.

You can see in the diagram on the below that we have two LEDs in the same circuit with their own

individual series dropping resistors.

You would think, using this method, that you could have as many LEDs in the circuit as you liked.

However, in practice this is not the case. The more LEDs there are the more the current increases and our

9-volt battery would not be capable of delivering sufficient current. Also, the more LEDs you have in the

battery the quicker the battery goes flat. But the good news is that you can run a lot of LEDs off a 9 volt

for quite a long time. How many? Google it and find out.

Page | 40


Connecting LEDs in Series

This next method enables you to run multiple LEDs by connecting them in series with the dropping

resistor as shown in the middle diagram. This gives better battery life because when you use LEDs of the

same type in series they will have the same current passing through them. What this means is that you are

running several LEDs with the same current as one and so prolonging the battery life.

In our projects we are using a 9-volt battery and we need to calculate how many LEDs we can run in series

and the value of the resistor.

At this stage we will make some assumptions and use some approximate values. We will assume that we

are using standard LEDs. These can be all one colour or a mixture of colours.

We have a 9-volt battery as our voltage source (VS) and our LEDs have a typical voltage (VLED) of 2

volts and a current (ILED) of 20Ma (0.02A). We also need to allow a voltage drop of 2 volts across the

resistor (R). So, if we subtract the voltage of the resistor from our 9-volt power supply that leaves us with 7

volts. We need 2 volts for each LED and if we divide this into the remaining 7 volts this means that we

could run 3.5 LEDs. Of course, this means we can run 3 LEDs.

That means that VLED would be 3 x 2v = 6 volts.

Now we still have to calculate the value of the resistor (R).

To do this we will use Ohms Law which states:

R= (VS – VLED) = (9 – 6) = 3 = 150 Ohms

ILED 0.02 0.02

We can use a standard value 150R resistor or to be on the safe side we can use the next standard value up

of 220R.

More LEDs can be used in a circuit by ‘stringing’ the series units in parallel as shown in the bottom

diagram.

If you are using high brightness LEDs especially white or blue ones then you would need to know the

manufacturer’s specifications to enable you to use the same calculations. White and blue LEDs are usually

rated at between 3 and 4 volts so that means you would only be able to use 2 of them with a power supply

of 9 volts.

Page | 41


Project 5 Touch Sensitive Switch

In the Using Transistors section we discussed that transistors could be used as an amplifier or a switch.

We are going to use two transistors in this circuit, one as an amplifier and one as a switch. Usually when

transistors are arranged in a pair it is known as a Darlington Pair. A Darlington Pair is used to amplify

weak signals so that they can be clearly detected by another device in the circuit.

What our circuit does

We are going to use our finger as a switch to turn on an LED. Normally, we would use an ordinary on/off

switch to do this but we want to demonstrate how a transistor can be an amplifier and a switch.

The skin of your finger has a resistance in the range of a few hundred thousand Ohms to a few million

Ohms. If your skin is dry the resistance would be high and if it was sweaty then the resistance would be

lower. In any case the resistance of your skin would always be considerably higher than a proper switch

which has almost nil. So, if we use our finger as the switch in our circuit then it is going to act like a

resistor.

We have given you two schematic diagrams, one using a single transistor and the other with two

transistors. In both circuits we have used two pieces of tinned copper wire to form our touch switch and we

have named these switch points A and B.

In the one transistor circuit, when we put our finger across points A and B we complete the circuit and

hopefully the LED lights up. This is called a transistor switch circuit.

In the two-transistor circuit, when we put our finger across switch points A and B we are putting another

resistor in series with resistor R2 and this will result in a very low current (weak signal) at the base of the

first transistor. However, this is enough for the first transistor to feed this signal through its emitter to the

base of the second transistor. This switches on the second transistor and lights up the LED. This circuit is

called a Darlington pair driver.

Parts List


9-volt Battery

Battery Snap

1 x 390R Resistor Orange – White – Brown

1 x 10K Resistor Brown – Black – Orange

1 x Light Emitting Diode

2 x BC548 NPN Transistors

Tinned Copper Wire

Page | 42


First, we will prove to ourselves that a Darlington pair is much more sensitive than just using a single

transistor. Build this for the one transistor circuit on your bread board then test it and note the results.

This a suggested layout for the one transistor touch switch.

Below is the schematic diagram for the two transistor Darlington pair touch switch.

Build it on your breadboard, test it and describe any difference you can see from the first circuit.

Here is a suggested layout for the two-transistor touch switch.

Sometimes the LED will light up weakly when you only touch switch point B. This is because your body

is acting like an antenna, which ‘receives’ electric and magnetic fields in your immediate environment and

this ‘induces’ a very small voltage into the base of the first transistor.

Page | 43


Project 6 Flashing Two LEDs

The circuit we are going to use to flash two LEDs is called an ‘a stable multi-vibrator’ or an ‘oscillator’. It

uses 4 resistors, 2 capacitors and 2 transistors to do this. In the circuit diagram you will see that the

transistors are ‘cross coupled’, which means that the base of each transistor is connected to the other

transistor’s collector via a capacitor. This means that only one transistor can be switched on at any one

time which also means that only one LED will be on at any one time.

How it Works

The two 390 Ohm resistors R1 and R4 are in series with the two LEDs to limit the current flowing through

them and prevent them from being damaged. The two transistors are used to switch the LEDs on and off.

We have learned in the previous projects that when the voltage on the base of a transistor reaches a certain

level the transistor switches on. In this circuit that voltage is controlled by the two resistor-capacitor pairs

(10K-10uf). They form the timing component of the circuit and control the speed at which the LEDs flash.

As each capacitor charges up the voltage at the base of the opposite transistor changes and at some point, it

reaches a voltage that is sufficient to switch the transistor on.

The time taken to charge a capacitor through a resistor depends on the value of the capacitor and the value

of the resistor. A bigger capacitance will take longer to charge and a larger resistance value will slow down

the current flow to the capacitor which will also mean a slower charge. The smaller the capacitance and the

lower the resistance the quicker the LEDs will flash. Hence the flash rate of the LEDs will vary greatly

depending on the time taken to charge and discharge the capacitors.

Let’s put it all together. The complete circuit acts like a seesaw. It has two states and it oscillates between

them. First one transistor-LED pair are switched on while one capacitor charges up. When it is charged it

switches the other transistor on which lights up its LED. Then, the first transistor pair switch off, the first

capacitor discharges and the second capacitor starts charging. When this capacitor is charged it switches

the first transistor-LED pair back on and then discharges itself. Now the circuit is back where it started and

the whole sequence can start again. It cycles continually with the two LEDs flashing alternatively for as

long as the battery is connected or for the life of the battery.

You may notice that the flash rate of the LEDs gets faster as the battery dies. This is because the voltage of

the battery drops below 9 volts as it comes to the end of its life. When this happens, the capacitors are

charging up to a lower voltage and this takes less time, so the circuit oscillates faster.

Page | 44


Parts List


9 volt battery

Battery Snap

2 x 390R resistors (Orange – White – Brown)

2 x 10K Resistors (Brown – Black – Orange)

2 x Light Emitting Diodes (LEDs)

2 x BC548 NPN Transistors

2 x 10uf Electrolytic Capacitors

Jumper Wire

The Breadboard Layout

You will be using more components to build this circuit than you have used before.

So as usual take your time and make sure that you get the polarity of the LEDs, transistors and the

capacitors correct. Also take care with the jumper wires so you do not create any short circuits.

Especially the ones from the base of the transistors to the junction of the resistor – capacitor pairs.


If you have access to other capacitors you could try changing them to anything from 1uf to 470uf and note

what happens. When installing the capacitors, you may find it easier to cut the legs so that they are the

same length and use the black stripe as the polarity indicator.

You can also use Software Simulation to do these experiments and then you do not need any extra

components. Or even better still, try both methods.

Software Simulation can also convert your circuit into a printed circuit board (PCB) layout so you can see

what your project would look like if you were designing a real world commercial product.

Now you can proceed to the next page where we are going to add a few more components to make our

circuit even more interesting.

Project 7 Dual Variable Flashing LEDs

Page | 45


In this project we are going to add three extra components to the Flashing Two LEDs circuit that will

enable us to prototype the same circuit that we are going to solder together in project 8.

Firstly, we are going to install a 1N4004 rectifier diode in series with the positive from the battery which

gives us polarity protection for our circuit.

Secondly, we will add two 200K variable resistors in series with the 10K resistors (R2 and R4) which will

provide us with a variable resistance of 10K to 210K in our resistor-capacitor networks. This will enable us

to vary the flash rate of the two LEDs independently.

You may need to refer to the components section of this notebook to help you install the diode and the

variable resistors correctly.

You will notice in the picture of the suggested layout we have turned the breadboard around to make it

easier to install the extra components.

Ensure that you install the diode the right way around.

You will need to use the centre leg and one of the outside legs of the variable resistors when you install

them on the breadboard. Which outside leg you use will determine whether the resistance increases or

decreases when you adjust the Trimpot clockwise or anticlockwise.

Some Trimpot can be difficult to install into a breadboard because the flat side of their legs does not line

up with the spring-loaded contacts inside the board. This problem can be solved easily by using long nose

pliers to gently and carefully turn the legs of the Trimpot 90 degrees.

When you have installed the diode and the Trimpot and you are satisfied that they installed correctly,

you can connect the battery and test the circuit. If both LEDs are flashing, then well done.

Now you can adjust the Trimpot and observe the flash rates of the two LEDs.

Remember to hold the Trimpot down with your finger when you are adjusting them to prevent them from

popping out.

If your circuit does not work correctly there should not be too much wrong with it because you already had

most of it working in the last project. Use the fault-finding skills you have learned to fix the problem or

problems.

Of course, as in the last project you could also experiment with the value of the capacitors and see what

happens.

The suggested breadboard layout on the next page is provided as a guide to help you get the circuit

working. However, there is no right or wrong way to build this circuit on the breadboard as long as it

works. We have only done it this way because it closely resembles the layout of the schematic circuit

diagram. Using this method is usually easier for inexperienced electronic students to follow.

But if you think that you can build it in a better way, go for it.

When you have successfully completed this project, you should have learned enough to understand what

the individual components do in the circuit and how the whole circuit operates. We hope you realise that

this was the whole point of the exercise. It should also be obvious that you would not have reached this

level of understanding if you had not worked through the previous projects.

Page | 46


In the next project you will be soldering this circuit into the KS1000 printed circuit board.

But first you will need to learn how to solder. Make sure you read the next section on how to solder very

carefully. This will give you the best chance of making a product that not only works correctly but is also

pleasing to the eye.

As mentioned on the previous page we modified the legs of the trimpots so that they fit into the breadboard

more securely.

SOLDERING Soldering is the process that bonds the electronic components to the copper tracks of a printed circuit board

to produce a permanent and reliable circuit.

A soldering iron is the tool used to melt solder to make the bond. Solder is a good conductor and so it not

only holds the components in place it also allows current to flow around the circuit easily.

Soldering is a skill and as with any skill it takes practice to master. But you have to start somewhere and

now is a good time to try it while you still have the basics of electronics fresh in your mind.

Whether you want to dabble with electronics as hobby or want to get a job in the electrical industry,

soldering is a very useful skill.

We have included a how to solder sheet so ensure you read this carefully before you commence any

soldering. In the meantime, we will discuss some of the safety aspects of soldering and also some tips and

tricks to make your first soldering exercise easier.

Your teacher will inform you of the occupational health and safety regulations that apply to your school.

But here are some common-sense rules you should always observe. Like any tool a soldering iron needs to

be treated with respect. You should never use it to damage anything or harm anybody. If you do you

should not be allowed to solder. When you are soldering you should treat your environment as a workplace

situation. Always leave the soldering iron in good condition for the next person to use.

Page | 47


Tips and Tricks

You need good tools to do a good job. The most important things to

remember about soldering irons are that the tip needs to be the correct

type and size for the job and that it needs to be maintained properly. We

will assume that your school has soldering irons that are suitable for

soldering electronic components onto a printed circuit board.

As you can see in this picture, the tip should be clean and not too worn.

Before you use the soldering iron you should ‘tin’ the tip. To do this

you heat up the iron and then coat the tip with solder.

You will know when the soldering iron is hot enough when you touch

the solder to the tip and it melts immediately. Never

use your finger to test how hot it is because it will

burn and it will hurt!

Clean off the excess solder on a wet sponge. Never

use sand paper to clean the tip asthis will remove

the iron clad chrome plating. Once this is removed

the tip will be useless. There are special tip cleaners

available which can improve tip life.

You may notice that the copper leads on the components and the copper tracks on some PCBs have been

‘tinned’ with solder. This makes them much easier to solder together. That is why you tin the tip.

Try not to use too much solder on your joints or you will end up shorting out tracks on your board.

Do not use too much heat for too long because you will damage your components or you may lift the

copper track off the PCB. The old saying is one, two, three. That is enough time.

When you have worked out where your components are going to be placed on the pcb, start soldering in

the lowest components first. EG. Resistors, diodes and jumper wires. Then work up according to the height

of the component.

If you make a mistake and for instance you soldered a component in the wrong place, you can remove it by

using a solder sucker or desoldering braid. So never panic, most things can be fixed.

Clean the tip of the hot soldering iron from time to time on a damp sponge.

• If you make a mistake use a solder sucker or desoldering braid to remove the solder.

• Treat any burns IMMEDTIATELY with cold running water for ten minutes and notify

your teacher of the incident

Page | 48


Project 8 Soldering Your Project

The picture below shows a completed KS1000 Dual Variable Flashing LEDs Project.

We have also included a picture of the solder side of the project to show you how yours should look.

Remember to read the soldering section carefully before you start assembling the PCB.

Use the instruction sheet on the next page to determine the location of the components on the PCB.

Solder in the diode and the resistors first and then the taller components according to height.

You will also notice that there are two extra holes on the PCB. Use the larger one to provide strain relief

for the battery leads and the smaller one for mounting your board into another product.

You have already built this circuit on the breadboard so you know that it works.

When you have finished soldering your circuit and it does not work then you will have to use the fault

finding skills you have already learned to find the problem. If your layout checks out ok then it probably

means that you have a soldering problem. For example, bad joint, short or a flat battery etc.

TROUBLE SHOOTING

• Carefully check that the components are fitted in the correct place.

• Check the colour code of the resistors against the component sheet.

• Pay particular attention to the polarity of the electrolytic capacitors, LEDs and battery snap.

• Check that the transistors haven’t been soldered into the printed circuit board backwards.

• Check all your soldering. A good solder joint looks shiny and smooth and covers the hole

completely. Refer to the “How to solder” section if you have not already done so.

• Hold your board up to the light. If any light shows through a hole then more solder is needed.

• Check that large blobs of solder are not causing short circuits across component legs. If too much

solder has been used it is often better to remove it completely using a solder sucker or desoldering

braid and then re-solder the joint.

• Also check for streaks of solder that might be bridging across tracks on the PCB.

Page | 49


What You Can Do Next.

Now that you have successfully completed your project you can start thinking about how you could

integrate it into a useful product. For example, you could make a rear bike light.

You also may find it convenient to install an on/off switch in the red positive battery lead of the

battery snap so that you do not need to keep disconnecting the battery.

You can extend the LEDs from the PCB with hook up wire to highlight a feature in a drawing or a

picture. You can change the LEDs for another colour.

Check out the section on adding more LEDs and see if this gives you any more ideas.

You could gang two or more KS1000 kits together to create a really dazzling display.

Page | 50


Basic Electronics Knowledge Test

1. What does IC stand for?

• Individual circuit

• Integrated circuit

• Integrated chip

2. On a diode, what would be indicated by a silver band at one end?

• Anode

• Tolerance of 10%

• Cathode

3. What does LED stand for?

• Low energy diode

• Light energy diode

• Light emitting diode

4. What is the current required to power an LED?

• Approximately 20 mA

• Approximately 20 A

• Approximately 20 MA

5. How does a resistor prevent damage to components in a circuit?

• By dissipating heat

• By restricting the flow of current

• By preventing reverse polarity

6. What will happen to the resistance of a Light Dependent Resistor as the amount of light falling on

it increases?

• The resistance will decrease

• There will be no change in resistance

• The resistance will increase

7. What is the unit of resistance?

• Volt

• Ohm

• Farad

8. What is the function of a capacitor?

• To limit the current in a circuit

• To store charge

• To act as a switch

9. Compared to using a single transistor, what is the advantage of using a darlington pair?

• It increases sensitivity

• It decreases sensitivity

• It decreases the current flow

Page | 51


10. Which of these are the leads on a BC548 Transistor?

• cathode, anode and gate

• base, emitter and collector

• gate, drain and source

11. What does the symbol I represent in electronic calculations?

• Voltage

• Resistance

• Current

12. Which of the following is equal to 100 microfarads?

• 0.001 farads

• 0.0001 farads

• 0.00001 farads

13. Ohm’s law states that if you know the value of the current and the resistance you can work out

what?

• The temperature

• The voltage

• The time delay

14. The current passing through a resistor is 20 milliamps. The value of the resistor is 100 ohms.

Using Ohm’s Law, what is the voltage across the resistor?

• 2 volts

• 5 volts

• 20 volts

15. Resistors are used to protect LEDs from too much current. How are the resistor and LED

connected together in a circuit?

• In parallel

• In context

• In series

16. Materials that allow current to flow easily are called?

• Semi-conductors

• Insulators

• Conductors

17. Which of the following is a permanent construction method?

• Breadboard

• Printed circuit board

• Terminal strip

18. Electronic components can be polarised or non-polarised. Which of these is non-polarised?

• Diode

• Resistor

• Electrolytic capacitor

Page | 52


19. If a resistor is colour coded Orange - White – Brown, what is its value?

• 270 ohms

• 330 ohms

• 390 ohms

20. What would be the colour code for a resistor with a value of 4,700 ohms with a 5% Tolerance?

• Yellow – Violet – Orange – Gold

• Yellow – Violet – Brown – Silver

• Yellow – Violet – Red – Gold

Page | 53


SES NIGHT LIGHT K1094

This project uses a Light Dependent Resistor (LDR) to activate a Light Emitting Diode (LED) when it is

dark. This circuit is commonly used in homes for nursery lights and security lights and in street lights so

they automatically come on at night and turn off during the day.

How it works.

A Light Dependent Resistor is a special kind of resistor that reacts to changes in light level. The resistance

of the LDR changes in relation to the amount of light available. When it is dark the resistance increases, as

the light increases the resistance decreases, this allows the circuit to respond to varying degrees of light.

So, when it is dark the LED lights up and when the light increases the LED goes off. In this circuit when

the resistance of the LDR is high it allows a small amount of current to flow into the base (b) of the

transistor which causes the transistor to act as a switch allowing current to flow through from the collector

(c) to the emitter (e) causing the LED to light up.

What the other components do.

The 1N4148 diode only allows current to pass through it in one direction and in this circuit, it is used as a

protection diode in case the polarity of the battery supply is accidently reversed.

Resistors are used to limit the amount of current flowing in a circuit. The higher the resistance the less

current flows and vice versa. Resistor values are measured in ohms and are identified by the coloured

bands on their bodies. In this instance the 10K resistor protects the transistor from excessive base current,

which can destroy it, when the variable resistor (VRI) is reduced to zero. The 220R resistor is used to drop

the voltage supplied to the LED and to limit the current so that it does not blow up.

The 500K variable resistor is used to vary the sensitivity of the LDR so that the LED can be switched on

and off at different light levels. In this case we are using a Trimpot which is actually a small potentiometer

and has three legs. To turn it into a variable resistor we only use two of these, the middle one and one of

the outside legs.

The 9-volt battery provides the power source.

For a more detailed description of these components refer to “The Components” section of this notebook.

Designing the layout.

This project is designed to give you the freedom to build the circuit in your own individual way.

You will need to give some thought to how you are going to do it before you attempt the construction.

Study the schematic circuit diagram on the next page and try to understand how it works and then make

sure that you are familiar with all of the components you are going to use.

You can follow Project 4 Dark Activated Switch to help you get started. The only differences to the circuit

will be the values of the Trimpot and the resistor (R2) in series with the LED. In this project we will use a

500K Trimpot to increase the sensitivity of the LDR and a 220 Ohm resistor to limit the current to the high

brightness white LED.

If you have access to Software such as Crocodile Clips or Circuit Wizard you can use these tools to

simulate the Night Light circuit on the computer screen. You will be able to see what happens when you

adjust the Trimpot and the amount of light falling on the LDR. You can even find out how to blow up the

LED.

Page | 54


When you are satisfied that you understand the circuit you can assemble your circuit on a solderless

breadboard. Test it and get it working and then you can rearrange the placement of your components to

achieve the best layout.

There is no absolutely correct way to build your circuit but you will find that neatness and simplicity

usually achieves the best result.

N.B. Adjusting a Trimpot on a breadboard can be tricky. It will tend to pop out of the spring terminals

during adjustment, so you will need to hold your finger on top of it to keep it in place. See Page 19 of this

Notebook to learn the easiest way to use a Trimpot on a solderless breadboard.

Use the half of the solderless breadboard which is the closest match to your prototyping board. Your

prototyping board may be slightly different to the one shown on Page 40, so you will need to make

allowances for this in your design.

Putting it together.

If you have not soldered before ask your Teacher to give you a demonstration and do some practice.

It is very important that you read the “Soldering” section on Page 32 prior to any construction.

The components are going to be soldered onto a ‘prototyping board’ and are wired together by a

combination of the tracks on the board and tinned copper “jumper wires”. When you have decided on your

layout and have adjusted it to suit the prototype board, start placing your components in the board and then

install the necessary jumper wires to join the circuit together. Ensure that your layout fits and there are no

shorts or missing connections. Then take out the transistor, LED and Trimpot so that you can solder the

“low components” and jumper wires in first. The BC548 transistor, the 1N4148 diode and LED are

polarised, so ensure that you install them the correct way around.

PARTS LIST

R1 10K Ohm Resistor Brown – Black –

Orange

R2 220 Ohm Resistor Red – Red –

Brown

D1 1N4148 Silicon Diode

RV1 500k Ohm Trimpot 5mm (504)

Q1 BC548 Transistor NPN

LDR Light Dependent Resistor

LED Light Emitting Diode White High

Brightness

Battery Snap

Prototyping Board

Tinned Copper Wire

Page | 55


This picture shows a suggested layout of the Night Light circuit on the Prototyping board.

However, we believe that you will not learn anything by just copying. So, we can tell you now that if you

build the circuit exactly like this it will not work. We can also tell you that there are a number of faults in

this circuit.

Construction Tips

Before soldering the battery snap leads into the PCB feed the red and black wires through the hole in the

corner of the board. This will act as a cable strain relief and prevent the wires snapping off during use.

Paying particular attention to the “Polarised” components now will save you a lot of heart ache later.

Testing the Project

When you are satisfied that you have built your circuit correctly, recheck the orientation of the components

and the connections between them. Also check your soldering for shorts and bad connections. Now you

can connect your battery. If it works then you can continue on with the test procedure. If it does not work,

disconnect the battery and refer to the fault-finding section of this notebook. You may also need to refer

back to the dark activated light project.

Test Procedure

Place the LDR in a bright light and turn the Trimpot until the LED is on.

Now turn the Trimpot the opposite way until the LED just goes off.

Now hold your hand over the LDR and the LED should come on.

Test your Night Light in a range of different light levels by adjusting the Trimpot until the LED switches

on at the correct amount of darkness you require.


You can design and build a suitable enclosure that would make your project useful or marketable.

If you would like a brighter light, you could add another LED or two.

If your project does not need to operate continuously you can incorporate an on/off switch.

Adding a switch can also give you a dark activated torch.

Now that you have successfully built your Night Light you should be able to write a brief description for

your Teacher of the reasons why the suggested layout in the picture above will not work.

Page | 56


RESOURCES to Continue electronics.

LAPtek produce workbooks using some of our kits.

Visit their website for more information www.laptek.com.au.

SE13-17U 1/2 Systems Engineering 2013-2017 Units 1 & 2 (Third edition)

ISBN: 978 1 921838 446

SE13-17U3/4 Systems Engineering 2013-2017 Units 3 & 4 (Third edition)

ISBN: 978 1 921838 453

SETR13-17U1/2 Systems Engineering 2013-2017 Units 1 & 2 Teacher Resource (Third edition)

ISBN: 978 1 921838 460

SETR13-17U3/4 Systems Engineering 2013-2017 Units 3 & 4 Teacher Resource (Third edition)

ISBN: 978 1 921838 477

AM 9/10 Year 9/10 Automotive Technology Studies

ISBN: 978 1 920914 028

BS Assemble & dismantle 4 stroke single cyl. Briggs & Stratton

engine (ISBN: 978 1 920914 882)

EPOD1 Design and Technologies - Book 1 (Fourth edition)

ISBN: 978 1 921838 750

EPOD2 Design and Technologies - Book 2 (Fourth edition)

ISBN: 978 1 921838 676

MICRO2 SES - Introduction to Microcontrollers (PICAXE)

ISBN: 978 1 921838 774

SEE 8/9 Electronic Fundamentals

ISBN: 978 1 920914 769

ROBOT_P Make a robot using Picaxe

ISBN: 978 1 920914 820

RnR Rockets and rockets cars

ISBN: 978 1 921838 255

Rheads Systems Engineering - Rev Heads

ISBN: 978 1 921838 279

LAPtek also produces workbooks for:

• 22015VIC CERTIFICATE II IN AUTOMOTIVE TECHNOLOGY STUDIES (PRE-

VOCATIONAL)

• 22216VIC - CERTIFICATE II IN BUILDING & CONSTRUCTION (CARPENTRY)

LAPtek was established in 1998 to meet the needs of students and people interested in learning about

vehicle repairs/service and the automotive industry. Since then, LAPtek has expanded its portfolio to

include Building and Construction, Systems Engineering, Microelectronics and Design Creativity and

Technology.

SES kits used in the workbooks shaded include:

• K1084 14M2 Starter Module

• K1086 Student Experimenter

• Kit K1063 Light Controlled Motor Kit

http://www.laptek.com.au/

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