Electronic Tutorial 110.626

110.626 Electronic Tutorial Parts 1-3 Light Emitting Diode - Resistor - Diode - Transistor - Capacitor

Contents

- Notes on mounting the components - The Light Emitting Diode - The Resistor - The Diode - The Transistor - The Capacitor - Practical circuits - Parts list

Please Note The OPITEC range of projects is not intended as play toys for young children.They are tea- ching aids for young people learning the skills of Craft, Design and Technolo- gy.These projects should only be undertaken and tested with the guidance of a fully qualified adult. The finished projects are not suitable to give to children under 3 years old. Some parts can be swallowed. Dan- ger of suffocation!

E110626#1 1 !!!WARNING!!!

Do not push the drawing pins into the board with your thumb or finger. Use a small pin hammer to drive them in.

Notes on building the circuits Solder or clamp?

The circuits are designed to be constructed on the base board. The choice is yours whether the components are held in clamps or soldered into position permanently.

SOLDER: The parts can be soldered to drawing pins which are tapped in to the base. The heads should be lightly tinned before mounting any of the parts, so that a minimum of heat is necessary during further work.

CLAMP: To clamp the parts into position, the springs can easily be mounted onto the base with the drawing pins. Then the springs only have to be bent back (see diagram).

Base

USING THE SPRINGS AS SWITCHES AND CONTACTS

For a short contact bend For a long contact hook the springs together the springs together.

Contact Switch

2 E110626#1 The LIght Emitting Diode

The Light Emitting Diode (L.E.D.) is not a lamp or bulb. The light from a L.E.D. is from a small crystal electro- magnetic wave, which we can see. If you hold a L.E.D. up to a light source, you can see the crystal inside.

Crystal

The light from a L.E.D. is not as bright as that from a bulb. LEDs are used mainly as warning and control lights to display a particular function, e.g.in Hi-Fi units, cassette players, computers, digital watches and televisions etc. Nearly every place you see small lights in electrical items, they are normally LEDs. They are available in red, yellow, green and blue, plus many different shapes. The most common shape for a Light Emitting Diode (LED) is rounded.

The advantages of LEDs over bulbs are their: - small power consumption - long life - vibration resistance - strength - their ability to fit in small places

Like all electronic components the LED has an Electronic Symbol.

Symbol The two arrows symbolise the light being given out

NOTE:

When you are using a LED, you should be aware of the following points:

1. The LED will only light if it is connected the correct way round. The polarity of the legs can usually be iden- tified as shown in the diagram. A denotes the anode and C the cathode connection. The LED is too small to print on, so the Anode (+) leg is usually longer the than the Cathode (-).

Symbol A Anode (+) connetion (plus) A C C Cathode (-) connection (minus)

2. The LED should not be subjected to more than 1.6 volts otherwise it can burn out. However most circuits need a greater supply than 1.6 volts and therefore you must add a resistor connected in series to ensure that the current flowing to the LED is kept under control. The most important component here is the RESISTOR

Differing power sources need different values of resistor. Here is a list of the most common power sources and the necessary resistor values.

130 Ohm 4,5 Volt 180 Ohm 6 Volt 390 Ohm 9 Volt 510 Ohm 12 Volt 1,2 K Ohm 24 Volt E110626#1 3 The resistor

The resistor is an electronic component which restricts the current flow in a circuit.The most common resistors are made from carbon on a ceramic core. (carbon is a poor conductor). At either end of the resistor is a wire for connection to other components.

Coloured rings show the value of the resistor. Resistance is measured in OHMs. These coloured rings are a code to show the differing values of each resistor and whether it will let a lot or litt- le current flow through. So a resistor with a value of 1.8 K Ohm (1800 Ohms) will let less current pass as one of 130 Ohms.

The following table shows the different Ohm values of resistors.

Ringcolour 1st. ring 2nd. ring 3rd. ring/ 4th. ring/ multiplier tolerance

black 0 0 1 brown 1 1 10 1% red 2 2 100 2% orange 3 3 1000 - yellow 4 4 10000 - green 5 5 100000 - blue 6 6 1000000 - violet 7 7 - grey 8 8 - white 9 9 - gold 0,1 5% silver 0,01 10% no ring 20%

resisistor symbols sample: 130 Ω with 5% tolerance

fixed value adjustable resist (potentiometer) brown orange brown gold 1 3 0 5%

4 E110626#1 EXPERIMENTS USING A LIGHT EMITTING DIODE AND A RESISTOR

+ circuit diagram

C 130Ω 130Ω -

drawing pin Experiment 1: Tap the drawing pins into the base to make the pattern as shown. Use the chart to identify a resistor with 130 Ohm resistance. Connect the battery as shown in the diagram.

The LED lights BRIGHTLY !.

circuit diagram +

1,8kΩ C 1,8kΩ -

Experiment 2: Exchange the 130 Ohm resistor for a 1.8 K resistor The LED now lights...... Why? Because the resistor is ......

circuit diagram +

1,8kΩ A 1,8kΩ -

Experiment 3: Remove the LED and turn it around and place it back in the circuit. Does the LED light...... Why? You can find the answer by making further experiments using DIODES. E110626#1 5 The DIODE

The diode is also a widely used component in electronics. It is what is generally known as a semi-conductor device. Taking copper as a good conductor and plastic as a poor conductor, a diode is made from silicon, a material with properties in between these two. The silcon diode has a special character. The semi-conductor diode lets the current flow in one direction only and acts like the valve on a bicycle tyre which will let air in but not out. This means it has the flow direction and reverse closed direction.

Due to this property diodes are used to convert alternating current to direct current by removing half of the in- coming wave. The diode can also be used to control the direction of current around a circuit. The diode has also an electronic symbol. This helps us to see how it functions. Looking at the diagram you must pay attention to the connections marked A = Anode (+) and C= Cathode (-).

A C

As diodes are also too small to print on, so the Cathode (-) connection is shown as a band.

A diode will only work when the correct connections are made to the battery.

flow direction

Anode + Cathode -

If a diode is reversed the current cannot flow.

closed direction

Anode - Cathode +

EXPERIMENTS USING A DIODE

circuit diagram +

130Ω C 130Ω - A C

Experiment 1: Make up the circuit as shown in the diagram. Be careful to connect the diode with the cathode(-) ring towards the negative side of the battery.

The LED will light up! 6 E110626#1 circuit diagram

A 130Ω

C 130Ω - C A

Experiment 2: Unsolder the LED and change it around, reconnect.

The LED does...... Why? The diode is...... connected If the circuit is to work ...... must be the correct way around.

Even LEDS must be correctly connected, as they have a flow and a closed direction.! ! ! EXAMPLES OF USING A DIODE circuit diagram +

T1 T2 T1 T2 A A

C 130Ω C 130Ω -

Experiment 1: Make up the circuit as shown in diagram 1. Imagine that you are making a intercom system such as in a wai- ting room. By pressing switch 1 LED 1 will light and by pressing switch 2 LED 2 will light. Now we can change the circuit so that by using switch 1 one LED can be lit and by using switch 2 both LEDs will light.

T2 Fix a wire to the two T1 switches A A

Experiment 2: Now press switch 1 and then switch 2 ! What happens ? In both cases the two LEDs light. However we want the left hand LED to light by pressing switch 1. This means that current must NOT flow to the right hand LED. But by pressing switch 2 we want current to flow to both LEDs. How can we alter the circuit? Do you remember the characteristics of a diode? Use a diode to solve the problem. The following circuit diagram shows you how to build the correct circuit. If you are still stuck, look at the diagram on the front cover.

T1 T2

circuit diagram

130Ω

E110626#1 7 BUILDING SOME PRACTICAL DIODE CIRCUITS

The following circuit diagrams show you how to make some practical projects using diodes. Use a wooden base to mount the components and build the circuit into a box. If you wish you can use an old soap holder or plastic box as a container for your circuit.

Project 1: A POLARITY TESTER

circuit diagram +

130Ω C A 130Ω

A C

red black red black Function: if the red crocodile lead is connected to the plus pole and the black lead is touched on to the negative pole, the +LED will light. If you change the leads over, the - LED will light. Using this idea you can also see the correct flow of the current in a direct current circuit

PROJECT 2: A CONTINUITY TESTER

+ circuit diagram

Battery A 130Ω fixed to board 130Ω

Function: To prove the continuity of a circuit connect the two crocodile clips. The circuit on test must not be connected to a battery. If LED on the continuity tester lights it means that current can flow.

PROJECT 3: PROTECTION CIRCUIT FOR BATTERY CONNECTION

Battery Note: operated object The size of the resistor depends on the size of the battery.

Function: If the battery is connected to the circuit incorrectly the LED will light and give a warning for you to change it around. 8 E110626#1 The TRANSISTOR

The transistor is a very versatile electronic component and can be used in many more situations. The resistor controls the current flow and diodes, LEDs allow the current to flow in one direction only. The transistor, however, can act as a diode and also determine whether current will flow or not, and how much. The transistor can also be used to switch the current on and off or make it stronger. The transistor can therefore be used as a SWITCH or as AMPLIFIER. About 30 years ago, before the transistor was developed, glass valves were used to do the job of a transistor. (look at old radios etc) They were much larger, more expensive and used a lot of electrical energy because they became hot in use. The invention of the transistor made it possible to design smaller and less expensive radios. In 1956 the three Americans, who developed the transistor, received the Nobel prize. The transistor enabled the minaturisation of electronic products. All of the well known items, such as walkman, C.D.-player, computer etc., would not have been possible without this development. When you handle a transistor, you can see just how small it is and how many connections it has. You will no- tice that it has three legs and a marking on the flat side of the body or a tag if it is round. The legs are known as the BASE, EMITTER and COLLECTOR and each has a different function. Look at the electronic symbol to help you understand these connections. Symbol C E = Emitter (sends electrons out) B B = Base(controls the flow of electrons) E C = Collector (collects the electrons) B E C

It can be seen that the electrons (current) flow from the emitter through the transistor to the collector. This flow is controlled by the base current. The base also influences whether the transistor works or not. Try the following experiments:

Make up the circuit as showm

Does the LED light?

circuit diagram + A

C 130Ω 130Ω C B C B E - E

Note: Do not mix up the legs on the transistor, it must be connected correctly otherwise it may be damaged

You will see that the base of the transistor has not been connected, so the transistor is closed and the current cannot flow through the LED. To turn the transistor on it must receive about 0.7 volts from a positive supply. Our battery produces 4.5 volts. So what can we do? How can we cut the supply down. By connecting a resistor of 6.8 K Ohm on the base of the transistor we can bring the 4.5 volt supply down to 0.7volt. Draw in the resistor on the diagram. E110626#1 9 circuit diagram + 4,5 V + A

C 6,8 kΩ 130Ω 130Ω 6,8 kΩ

C C + 0,7 V B B - E E

The LED will now light, because current can flow through the base and emitter to turn the transistor on. This is called an emitter switch system and is one of the three basic switching systems of the transistor.

Why Emitter switching ?

If you follow with your finger the flow of electricity from the battery to the 6.8K Ohm resistor you will see that it must continue into the base of the transistor to get back to the minus pole of the battery and complete the circuit.

This is why !

The Base - Emitter -circuit is known as the CONTROL and the Collector - Emitter - Circuit is known as the WORKING circuit.

Making the Emitter-Control circuit into an ALARM CIRCUIT

circuit diagram

+ A

C 130Ω 6,8 kΩ

B - E

This security wire would be snapped during a break in and set off the alarm.

How is the alarm set off ? and why ?

On this system the LED serves as the alarm warning signal.

In this circuit the TRANSISTOR is used as a SWITCH.

In the next circuit we will use the transistor as an AMPLIFIER. 10 E110626#1 Moisture sensor

In this circuit you will see how a transistor can amplifiy a small current and switch on a L.E.D.

circuit diagram + A

C 130Ω 130Ω

make these wires long enough to immerse in water

After building the circuit, place the two long wires into a small bowl of water or on your tongue.

Does the LED light?

No, the LED does not light because the dampness causes too much resistance. The current is too weak and must therefore be amplified, so we must add a transistor as an amplifier to this circuit. A 1.8 kOhm resistor is added to protect the transistor, in case the two wires accidentally touch each other.

Construct the circuit as shown in the diagram.

circuit diagram + A

1,8 kΩ 130 Ω 1,8 kΩ 130 Ω C

B - E

This circuit can be used as a plant water tester by placing the wires into the flower pot (if there is water, the LED will light, if not, it will stay off). It can also be used as an alarm for the water level in your bath or simply as a damp tester.

Try to think of other practical uses for this circuit.

E110626#1 11 SENSOR SWITCH

Can the amplification of the transistor be increased?

In the last ʻmoisture sensorʼ project only a LED had to be lit. If you had to light a bright bulb or activate a relay, the load would be too great and the transistor would be destroyed. In this project a second transistor is added and the load is now divided. The current at the base of the first transistor can now be even lower than with the moisture detector.

You only have to touch the contacts 1 and 2 in order to light the LED.

circuit diagram +

1,8 kΩ

1 6,8 kΩ 130Ω 1,8 kΩ 6,8 kΩ 2 1 B 2 130Ω C C B - E E

This combination of transistors is known as a DARLINGTON PAIR. These kind of switches react to minimal current. Sensor switches are found on television sets etc, they have replaced the heavier mechanical type and are far easier to use.

MINI LIGHT ORGAN

As you have seen, a transistor can not only switch and amplify. But can it carry out this function at speed? The next challenge is to construct a circuit where the two transistors are activated by music or speech - to make a light organ. Music and speech are made up of sound waves which can affect the thin membrane of a loud speaker and produce a small electric current. We can use this to control the base of the transistors and in turn switch the LEDʼs in time with the music or speech.

The two long wires leading away from the circuit should be connected to a loud speaker. Polarity is not important. This circuit can also be built into a radio or a loudspeaker box to give an opitical signal with the music.

circuit diagram

+ A A red green C C 130Ω 130Ω 130Ω 130Ω

C C B B - E E

Connect these wires with the speaker This circuit can be hooked up to any loud speaker. If you connect it with a radio or a speaker box, you will have an optical control display. 12 E110626#1 GUESSING GAME

This is an electronic version of “heads and tails” and when built into a small box, should give plenty of fun.

When connected to the battery, one of the transistors switches its LED on. First, the players must guess, which particular LED will light.

This is how it works: Let us assume that when the battery is connected, LED 1 receives a positive current which flows to the base of transistor 2. The transistor switches on and LED 2 lights. Now there is a negative current (minus) at the collector of transistor 2 and at the base of transistor 1. Therefore, transistor 1 cannot turn on, which causes LED 1 to stay off.

A trimmer is added to the circuit so that it is possible to choose which LED will light first. It is also possible to adjust the circuit so that both LEDs alternate at random, or that one of them lights more often than the other.

Note: Be careful with the transistor connections. Use two LEDs of the same colour.

This type of circuit is built into game machines. Then the results appear to be at random.

circuit diagram Trimmer 1 kΩ

+ A A red red C C 18 kΩ 130Ω 130Ω 18 kΩ 130Ω 18 kΩ 130Ω C C

B B - E E T T1 2

FLIP FLOP SWITCHING

The next stage is the construction of an electronic memory. This circuit is what today computer technology is based on. It can save an impulse and release it later.

Of course, computers contain thousands of such circuits. Imagine a calculator, for example, when you multiply 16 by 8, 16 is entered first, then the symbol x and then 8. What happens is, that the 16 disappears and 8 is displayed. The calculator stores the number 16 invisibly for you. It can store and reproduce many other number combinations.

The circuit shown here can store the information “on - off” which means that it switches back and forth between 2 stages (LED on or off). It is therefore called “BISTABLE” or “FLIP FLOP”. This Flip-Flop is ideal fo the so called shakey hand game. This is the well known game where a ring is passed along a bent wire without touching it. As soon as the wire is touched, the event is recorded by a LED, which stays lit until a reset button is pressed. This makes it impossible to cheat. When the circuit has been built and is understood, we suggest that you build it into a container and design the game to your own specification.

E110626#1 13 Circuit costruction

circuit diagram + A A red green C C 18 kΩ 130Ω 130Ω 18 kΩ 18 kΩ 130Ω 130Ω C C B B - E E T1 T2

connect with a wire

How does the flip flop recognise the impulse ?

When the battery is connected a postive potential flows through the red LED onwards to the base of transistor 2. The transistor is turned on and the LED lights. If the spring is touched with a wire, transistor 2 receives a negative potential at its base and switches off. Now the green LED sends a positve base siganal to transistor 1 and the red LED stays permanently on. Only when the battery is dis-connected does it go off. When the battery is switched on again the green LED lights up again.

14 E110626#1 THE CAPACITOR

Batteries are well known as stores of electrical energy and work while chemicals are changed into electricity. There are occasions in electronics when electrical energy needs to be stored for a short time only. The component for this use is a CAPACITOR.

Its make up is rather like its diagram in that it is formed from two separated plates between which the energy can be stored. To save place in the circuit most of the larger capacitors have a cylindrical shape.

groov = + Ring = -

+ -

normal poled Symbol component

Some capacitors can be placed in a circuit in any direction while others are poled and will only work in one direction. The direction is shown on the circuit diagram and on the component itself. The storage of electrical charge is called capacitance and is measured in FARADS (F).

The following experiments explain the working of the capacitor.

LOADING AND DISCHARGING CAPACITORS

Construct the following circuit:

circuit diagram A

+ C 1000 µF - 1000 µF

When the battery is connected the current flows through the capacitor and it stores the charge. The capacitor can hold this charge and give it up later.

E110626#1 15 What happens when you remove the battery clip from the minus pole and clip it to the minus on the LED?

circuit diagram A

+ 1000 µF C

1000 µF -

remove clip here

The light emitting diode (L.E.D.) will light as the capacitor gives up its electrical charge.

NOTE: The electric current does not come from the battery but from the capacitor.

This is the principle of camera flash lights and warning lamps.

There are of course other cicuits where the capacitor needs to be discharged more slowly. The capacitor must empty slower. Can you remember which component slows down the flow of the current ?

We are now going to use a 130 Ohm resistor in the circuit to see what effect it will have.

TIME SWITCH

circuit diagram A

C + 1000 µF 130 Ω - 1000 µF 130 Ω

load the capasitor here

Charge this capacitor as before, then remove the battery clip and make contact with the lead of the resistor.

What happens?

The LED will light for a longer time as the capacitor discharges slower through the resistor. You have designed a simple time switch. As we have seen, the introduction of a resistor slows down the discharge of the capacitor. 16 E110626#1 The next stage is to construct a TIME SWITCH with a delay of approx. 20 seconds. The transistor receives a small base current via the 1.8 kOhm resistor, therefore the capacitor takes a long time to give up its charge and the LED stays on accordingly. To recharge the capacitor, the switch must be pressed down.

circuit diagram A switch C 1,8 KΩ 130 Ω

130 Ω C 1000 µF 1,8 kΩ B + E

- 1000 µF

When the 1.8 kOm base resistor is changed for a larger value, e.g. 6.8 kOhm, or 18 K Ohm the LED will light for an even longer time.

If this circuit is enclosed in a small box it can be used as a game timer, for example timing the moves in chess.

The next stage is to construct a circuit where the capacitors charge and discharge automatically, switching the LEDs on and off.

To achieve this, we need to add a second transistor. This transistor will recharge the capacitor even though it is itself activated by a discharging capacitor. Both of the capacitors are alternately changing their state of charge thus switching the LEDs on and off. This circuit is commonly known as a Multivibrator. You can of course run just one LED by removing it and connecting a 130 Ohm resistor in its places. This will then give a single blinking light.

If the rhythm needs to be slower, change the capacitors for larger to larger 1000uF types.

This circuit can be used in a model railway for level crossings, or in a model car as warning lights.

circuit diagram

130 Ω T 1 A A - 6,8 KΩ gr. red C1 + 22 µF C C

6 , 8 6,8 KΩ C2 130 Ω C2 22 µF + 130 Ω 6,8 KΩ - C1 C C

T2 B B 130 Ω E E

E110626#1 17 A fuller explanation of the multivibrator circuit is as follows.

When the battery is connected, the green LED lights first. Capacitor 1 charges and cuts off transistor 1, the green LED turns off. The red LED lights and capacitor 2 charges turning off transistor 2. During this time capacitor 1 has recharged and through transistor 1 the green LED turns on again. This process then repeats itself, causing the flashing effect.

Contents

2 LEDS, red 1 LED, green 2 Transistors BC 548 or BC 547 2 Resistors 130 Ohm 1 Resistor 1.8 K Ohm 2 Resistor 6.9 K Ohm 2 Resistor 18 K Ohm 1 Potentiometer 1 K Ohm 1 Capcitors 1000 µF 12 Drawing pins 12 springs 1 Cocodile clip wire 1 Insulated wire approx 0.5 metre 1 Base (plywood) 80 x 80 mm 1 Universal Diode 1N 4148

18 E110626#1