DET Practical Electronics (Intermediate 1)

DET

Practical Electronics

(Intermediate 1)

August 2000

DET

Practical Electronics

(Intermediate 1)

Support Materials

HIGHER STILL

CONTENTS

Section 1 – Learning about Resistors Section 2 – Learning about Diodes Section 3 – Learning about Transistors Section 4 – Learning about Capacitors

Section 5 – Learning about Integrated Circuits (ICs) Section 6 – Learning about Soldering

SECTION 1 – LEARNING ABOUT RESISTORS

Simple light switch

This circuit diagram and the layout diagram on the next page show a simple way to turn a lamp on and off by using a switch.

Circuit diagram  YROWV  YROWV  9  $ / 6:  63'7 Parts list

CODE COMPONENT VALUE/TYPE CHECK

- Prototype board

L1 Filament lamp MES 6 V 0.06 A

- Lamp holder MES

SW1 Slide switch SPDT

- Wire PVC 1/0.6

Instructions

• read up on any notes regarding the components used in this circuit

• make sure that you know the symbols and physical appearance of all components

• collect all of the components and check them off

• you must have each completed circuit and any report checked by your teacher/lecturer.

Layout diagram

What to do

• connect the lamp and switch as shown in the layout diagram

• make a connection from the prototype board to the 0Volt line of the supply

• carry out a pre-power-up test procedure

• make a connection from the prototype board to the +Volt line of the supply

• if the circuit does not work as expected, disconnect the power and repeat the pre-power-up test.

Report

• copy the circuit diagram

• write what happens when the switch is moved from one position to the other and back again

• make a note of any problems and how you fixed them.

Let your teacher/lecturer see the finished circuit and your report.

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Adding a resistor

You will now add a resistor in series with the lamp and switch. In series means that the lamp, switch and the resistor are connected one after the other.

Circuit diagram  YROWV  YROWV  9  $ / 6:  63'7 5 5 Parts list

CODE COMPONENT VALUE/TYPE CHECK

R1 Resistor 82R (ohms)

R2 Resistor 150R

- Prototype board

L1 Filament lamp MES 6 V 0.06 A

- Lamp holder MES

SW1 Slide switch SPDT

- Wire PVC 1/0.6

• you should already have the shaded parts from the previous circuit

Layout diagram

What to do

• Add the resistor R1 in series with the switch and lamp as shown in the layout diagram. Do this by first removing the wire link and replacing it with the resistor R1.

• What difference do you see from the previous circuit when the switch is moved to the ‘on’ position?

• Take out resistor R1 and replace it with resistor R2.

• Switch on and off again. You should see a difference in the brightness of the lamp.

Report

• copy out the circuit diagram

• write down what difference using a resistor made to the brightness of the lamp

• describe what you saw when you used a resistor with a higher value

• draw diagrams to show the coloured bands on the two resistors which you used.

Let your teacher/lecturer see the finished circuit and your report.  YROWV

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Comparing resistors – 1

Using this circuit you can choose which of the two brightnesses the lamp will have.

Circuit diagram  YROWV  YROWV  9  $ / 6:  63'7 5 5 5 5 Layout diagram What to do

• using the same parts, build the circuit shown in the layout diagram

• move the switch back and forwards and watch the brightness of the lamp.

Note

• the switch has been wired in this circuit as a change-over switch, so that either R1 or R2 is connected to the lamp.

Report

• copy the circuit diagram and the Note above.

Let your teacher/lecturer see the finished circuit and your report.

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Comparing resistors – 2

It is often the case that you cannot find a resistor of the particular value which you want for a circuit. It is possible to combine two resistors in series or in parallel to give the value that you want.

Use a resistance meter, or do a calculation if you know how, to find out what resistances you get when R1 and R2 are connected in series and in parallel. If you can, you should check the resistances of R1 and R2 on their own. The resistance values marked on them are only approximate.

R1 and R2 connected in series

R1 and R2 connected in parallel

Report

• draw the circuit diagrams

• note the measured and/or calculated resistances

• compare these to the stated manufacturers values.

Let your teacher/lecturer see the finished circuit and your report.

M u ltim eter

Varying the resistance

Resistors can be used to change the brightness of the lamp only in fixed steps. To change the brightness smoothly you can use a potentiometer wired as a variable resistor. Circuit diagram  YROWV  YROWV  9  $ / 6:  63'7 95 5 Layout diagram What to do

• set up the circuit as shown in the layout diagram

• move the switch to the on position

• to change the resistance of the variable resistor turn the control anti-clockwise and then clockwise

• watch what happens to the brightness of the lamp as you do this.

Report

• copy the circuit diagram

• describe what happens to the brightness of the lamp as the resistance of the variable resistor changes.

Let your teacher/lecturer see the finished circuit and your report. Extra parts needed

CODE COMPONENT VALUE/TYPE CHECK

VR1 Variable resistor 500R  YROWV  YROWV 6:  /DPS / 95 

Using the colour code

• using a colour code chart, find the resistance values of the following resistors

• write your answers in your normal report notes/jotter

Blue – Violet – Brown – Silver

Orange – White – Brown – Gold

Brown – Black – Red – Gold

Brown – Black – Green – Orange

• draw the resistors below – use coloured pencils to show the correct colour bands

1.

100

Ω

±

10

%

2.

100 k

Ω

±

3

%

3.

3.9 k

Ω

±

5

%

4.

2.2 M

Ω

±

5

%

• write your answers in your normal report notes/jotter.

SECTION 2 – LEARNING ABOUT DIODES

One way current

Diodes allow electric current to flow through them in only one direction. This circuit diagram and the layout diagram on the next page show a diode in operation.

Circuit diagram

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CODE COMPONENT VALUE/TYPE CHECK

- Prototype board

L1 Filament lamp MES 6 V 0.06 A

- Lamp holder MES

SW1 Slide switch SPDT

- Wire PVC 1/0.6

D1 Diode 1N4001

Layout diagram

What to do

• build the circuit as shown in the layout diagram

• place the diode in the circuit as shown

• make a connection from the prototype board to the 0Volt line of the supply

• carry out a pre-power-up test procedure

• make a connection from the prototype board to the +Volt line of the supply

• if the circuit does not work as expected, disconnect the power and repeat the pre-power-up test

• replace the diode the other way round – observe the brightness of the lamp.

Report

• copy the circuit diagram

• make a drawing of the diode and its circuit symbol

• describe what happens to the brightness of the lamp when the diode is reversed.

Let your teacher/lecturer see the finished circuit and your report.  YROWV

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Light emitting diodes

A light emitting diode (or LED) is a special diode that is often used as an indicator. A resistor is connected in series with the LED to prevent too much current flowing though. If too much current flows through the LED, it will be damaged.

Circuit diagram

Layout diagram

What to do

• build the circuit as shown in the layout diagram

• place the LED in position (make sure that the flat side is connected to the 0V line)

• make the 0Volt connection and carry out a pre-power-up test procedure

• make the +6 Volt connection

• if the circuit does not work as expected, disconnect the power supply and repeat the pre-power-up test

• reverse the LED and observe what happens to the LED brightness.

Report

• copy the circuit diagram and make a drawing of an LED and its circuit symbol

• describe what happens to the LED when it is reversed.

Let your teacher/lecturer see the finished circuit and your report. Extra parts needed

CODE COMPONENT VALUE/ TYPE CHECK LD1 LED 5 mm red R1 Resistor 390R  YROWV  YROWV 5 /'   YROWV  YROWV 5  5 /' 

Measuring voltage

Voltage across a component is measured with a voltmeter (or Multimeter). You will measure the voltage across the resistor R1, and the diode LD1, in the previous circuit.

Warning

The Multimeter must not be connected to the mains supply.

Circuit diagram

Layout diagram

What to do

• connect the circuit as shown

• set the multimeters to volts and the correct range.

Report

• copy the circuit diagram

• record the readings on both meters

• explain why they do not add up to the 6volts supplied.

Let your teacher/lecturer see the finished circuit and your report.

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Fuse tester

This circuit uses an LED to indicate if a fuse is broken or not. (Sometimes it is difficult to check if a fuse is broken because you cannot see the fuse wire inside the tube).

Circuit diagram

Parts list

CODE COMPONENT VALUE/TYPE CHECK

R1 Resistor 270R R2 Resistor 100R - Fuse holder -- Set of 5 fuses -- Prototype board LD1 LED 5 mm red - Wire PVC 1/0.6

• you should already have the shaded parts from the previous circuit

• collect all of the components and check them off.

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Layout diagram

What to do

• build the circuit as shown in the layout diagram

• make a connection from the prototype board to the 0Volt line of the supply

• carry out a pre-power-up test procedure

• make a connection from the prototype board to the +Volt line of the supply and the LED should light

• if the circuit does not work as expected, disconnect the power and repeat the pre-power-up test

• insert the fuse to be tested into the fuse holder

• with the fuse in the fuse holder:

• the LED is ON if the fuse is broken (blown)

• the LED if OFF if the fuse is working (not blown).

Report

• copy the circuit diagram

• test each of your 5 fuses with this circuit – copy the table below and record the results of your tests.

FUSE NUMBER/RATING LED (ON/OFF) FUSE (BLOWN/NOT

BLOWN)

Let your teacher/lecturer see the finished circuit and your report.  YROWV  YROWV 5 5 /'  )XVH

Low voltage polarity tester

This circuit will let you find out which terminal of an unmarked supply is positive (+) and which is negative (-). This is known as the polarity of the supply.

Warning

This circuit must not be connected to the mains supply. You could be hurt or killed.

Circuit diagram

Parts list

CODE COMPONENT VALUE/TYPE CHECK

R1 Resistor 390R LD1 LED 5 mm yellow LD2 LED 5 mm green - Wire PVC 1/0.6 (yellow) - Wire PVC 1/0.6 (green) - Prototype board

-• you should already have the shaded parts from the previous circuit

• collect all of the components and check them off.

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(green)

Layout diagram

What to do

• build the circuit being careful how the LED’s are arranged

• use your tester to find out which terminal (A or B) of the unmarked supplies are positive and which is negative.

Note

This circuit is suitable for use only on voltages up to about 12 Volts.

Report

• copy the circuit diagram

• write a brief description of how you found out the polarity of the unmarked supply

• record you results in a table as shown below.

SUPPLY POSITIVE (A OR B) NEGATIVE (A OR B)

1 2 3

Let your teacher/lecturer see the finished circuit and your report.

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SECTION 3 – LEARNING ABOUT TRANSISTORS

Transistor switch – 1

A transistor can be used as an electronic switch. It is controlled electronically at the base (b) terminal and, when it switches on, the current passes from the collector (c) and the emitter (e) terminals.

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Parts list

CODE COMPONENT VALUE/TYPE CHECK

R1 Resistor 1K0

LP1 Lamp MES 6 V 0.06 A

TR1 Transistor BC 109

- Lamp Holder MES

- Prototype board

-- Wire PVC 1/0.6

Layout diagram

What to do

• build the circuit as shown in the layout diagram

• make a connection from the prototype board to the 0Volt line of the supply

• carry out a pre-power-up test procedure

• make a connection from the prototype board to the +Volt line of the supply

• using the flying lead, connect the base of the transistor through the 1 kilo-ohm resistor to the +6Volt line at A – the lamp should light

• if the circuit does not work as expected, disconnect the power and repeat the pre-power-up test

• now connect the flying lead to the 0Volt line at B – is the lamp lit this time?

Report

• copy the circuit diagram

• make a copy of the pinout for a BC109 transistor clearly showing which lead is the base, which is the emitter and which is the collector

• make a brief note of the operation of the circuit.

Let your teacher/lecturer see the finished circuit and your report.

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Transistor switch – 2

Repeat the previous task but instead of a BC 109 transistor use a BC 179 transistor. The BC 179 is a PNP type transistor while the BC 109 is an NPN type.

Circuit diagram

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CODE COMPONENT VALUE/TYPE CHECK

TR2 Transistor BC 179

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Layout diagram

What to do

• build the circuit as shown in the layout diagram

• make a connection from the prototype board to the 0Volt line of the supply

• carry out a pre-power-up test procedure

• make a connection from the prototype board to the +Volt line of the supply

• using the flying lead, connect the base of the transistor through the 1 kilo-ohm resistor to the 0Volt line at B – the lamp should light

• if the circuit does not work as expected, disconnect the power and repeat the pre-power-up test

• now connect the flying lead to the +6Volt line at A – is the lamp lit this time?

Report

• copy the circuit diagram

• make a copy of the pinout for a BC179 transistor clearly showing which lead is the base, which is the emitter and which is the collector

• make a brief note of the operation of the circuit

• describe the difference the type of transistor (PNP or NPN) makes to the way in which the base is connected to make the lamp light.

Let your teacher/lecturer see the finished circuit and your report.

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Transistor Amplifier – 1

The transistor can be used to amplify (make bigger) changes in current. Small changes in the base current can cause much larger changes in the collector current.

Circuit diagram

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CODE COMPONENT VALUE/TYPE CHECK

R1 Resistor

LP 1 6 V 0.06 A

TR1 Transistor BC 109

VR1 Potentiometer

- Lamp Holder MES

- Prototype board

-- Wire PVC 1/0.6

• complete missing entries in the parts list

Layout diagram

What to do

• build the circuit as shown in the layout diagram

• make a connection from the prototype board to the 0Volt line of the supply

• carry out a pre-power-up test procedure

• make a connection from the prototype board to the +Volt line of the supply

• turn the control on the potentiometer clockwise then anti-clockwise

• watch what happens to the brightness of the lamp as you do this

• if the circuit does not work as expected, disconnect the power and repeat the pre-power-up test.

Report

• copy the circuit diagram

• describe what happens to the brightness of the lamp as you increase and decrease the resistance of the variable resistor.

Let your teacher/lecturer see the finished circuit and your report.

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Transistor amplifier – 2

The current through a circuit is measured with an ammeter. In this circuit, you will use a Multimeter set to measure current.

Circuit diagram

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CODE COMPONENT VALUE/TYPE CHECK

R1

LP 1 6 V 0.06 A

TR1

VR1 Potentiometer

- Lamp Holder MES

- Prototype board

-- Wire PVC 1/0.6

A1,A2 Multimeter Non-auto-ranging

• complete the missing entries in the parts list

Layout diagram

What to do

• set-up the circuit as shown in the layout diagram – Set multimeter A1 to the 0-10 mA setting

• set multimeter A2 to the 0–100 mA range

• make a connection from the prototype board to the 0Volt line of the supply

• carry out a pre-power-up test procedure

• make a connection from the prototype board to the +Volt line of the supply

• if the circuit does not work as expected, disconnect the power and repeat the pre-power-up test.

Report

• copy the circuit diagram

• copy the table on the following page. F 95  $  $  /3  H E 5  YROWV  YROWV

Measuring current

• copy out the following table

• turn VR 1 fully anti-clockwise and note the readings on A1 and A2

• turn VR 1 until it is halfway between fully anti-clockwise and the mid-point

• repeat for the rest of the positions

• complete the table by adjusting the position of VR 1 as indicated and noting the readings on the multimeters.

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• what can you say about the sizes of the currents measured by A1 and A2?

• draw a line graph showing the change in the collector current (A2) against the change in the base current (A1).

SECTION 4 – LEARNING ABOUT CAPACITORS

Storing electric charge

When a capacitor is connected to a voltage supply a current flows from the supply, and the capacitor becomes charged with electricity. When the capacitor becomes charged it stores energy. This energy can be used some time later to make lamps etc. operate. Circuit diagram

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Parts list

CODE COMPONENT VALUE/TYPE CHECK

R1 R2

LD1 5 mm red

LD2 5 mm green

C1 Capacitor 2200uF electrolytic

SW1 SPDT

- Prototype board

-- Wire PVC 1/0.6

• complete the parts list

Layout diagram  YROWV   YROWV _5 5 & /'  /'  6: 





• build the circuit as shown in the layout diagram

• make a connection from the prototype board to the 0Volt line of the supply

• carry out a pre-power-up test procedure

• make a connection from the prototype board to the +Volt line of the supply

• move the slide switch to position 1 – LD1 should light for a few seconds

• if the circuit does not work as expected, disconnect the power and repeat the pre-power-up test

• move the switch to position 2.

Report

• copy the circuit diagram

• describe what happens to the light-emitting diodes LD 1 and LD 2 in the circuit when you move the switch to position 1

• move the switch to position 2 – again describe what happens to the LEDs.

SECTION 5 – LEARNING ABOUT INTEGRATED CIRCUITS (ICs)

Operational amplifier as a switch – 1

This circuit uses the operational amplifier (or op-amp), one kind of integrated circuit, to compare the voltage across a sensor with a known voltage. The sensor used in this circuit is a thermistor (a device in which the resistance changes as the temperature changes). Depending on the temperature, the LED may be on or off.

Circuit diagram

Parts list

CODE COMPONENT VALUE/TYPE CHECK

R1 R2 R3 IC1 Op-amp LM 741 VR 1 Potentiometer Th 1 Thermistor NTC LD 1 5 mm red - Prototype board -- Wire PVC 1/0.6

• complete the parts list

• collect all of the components and check them off.

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Layout diagram

What to do

• build the circuit as shown in the layout diagram

• make a connection from the prototype board to the 0Volt line of the supply

• carry out a pre-power-up test procedure

• make a connection from the prototype board to the +Volt line of the supply

• adjust VR 1 until the LED is just on

• touch the thermistor – the heat from your fingers should raise the temperature of the thermistor and the LED should go off

• if the circuit does not work as expected, disconnect the power and repeat the pre-power-up test.

Report

• copy the circuit diagram

• write down a possible use for a circuit that operates in a similar manner to the one above.

Let your teacher/lecturer see the finished circuit and your report.

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Operational amplifier as a switch – 1

You can easily change the circuit so that it detects light rather than heat.

Circuit diagram

Extra parts needed

CODE COMPONENT VALUE/TYPE CHECK

LDR 1 Light Dependent Resistor ORP 12

What to do

• collect the extra component

• replace the thermistor with the LDR

• make a connection from the prototype board to the 0Volt line of the supply

• carry out a pre-power-up test procedure

• make a connection from the prototype board to the +Volt line of the supply

• with the LDR in bright light, adjust VR 1 until the LED is just off

• shade the LDR with your hand – the LED should come on – if it comes on only if you completely cover the LDR, fine-tune the setting of VR 1 until the LED switches on correctly

• if the circuit does not work as expected, disconnect the power and repeat the pre-power-up test

• note that this circuit is easier to adjust and has a wider operating range than circuits using transistors.

Report

• copy the circuit diagram.

Let your teacher/lecturer see the finished circuit and your report.

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SECTION 6 – LEARNING ABOUT SOLDERING

Letter S

To give you some practice in soldering, solder wires to a piece of stripboard to make the shape of the letter ‘S’ as shown below.

Track cutting diagram (track & solder side of board)

Layout diagram (component side of board)

Parts needed

ITEM VALUE/TYPE

Stripboard 9 strips x 25 holes

Wire PVC 1/0.6 single core

Construction

• using a track cutting tool cut the copper track on the underside of the stripboard at the positions marked by the letter ‘X’ as shown on the layout diagram (see also the track cutting diagram above)

• measure and cut a piece of single core insulated wire for the first part of the letter ‘S’, remembering to leave and extra 20mm for the soldered joints on the

stripboard

• strip about 10mm of insulation from each end

• solder into place as demonstrated

Testing the soldered joints

• Solder the two 50mm test leads at the ends of the board as shown in the layout diagram.

• Carry out a pre-power-up test.

• Using a multimeter set to measure ohms, check that the resistance of the ‘S’ shape. The resistance should be less than 5Ω. This will mean that you have made all the joints correctly.

• If the circuit does not work as expected, disconnect the power supply and repeat the pre-power-up test.

Note: it is often good to use a heat sink clipped to the end of the LED and Transistor

leads to protect them from the heat of the soldering iron.

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Soldered polarity tester

You may already have already built a polarity tester on prototype board. This polariry tester is soldered to a piece of stripboard for a more durable circuit. If you soldered the letter ‘S’, you can use the same piece of stripboard.

Circuit diagram

Stripboard layout diagram

What to do

• de-solder the letter ‘S’ as instructed

• place the resistor into the correct holes

• making sure that the resistor is close to the surface of the board solder it into position

• repeat for the two LEDs taking care to position them as shown in the diagram

• tin the ends of the wires as instructed

• carry out a pre-power-up test procedure

• test your circuit with a low voltage power supply i.e. a battery.

Report

• write a set of instructions on how to use your polarity tester

• find out what a continuity tester does

• investigate and report on how your circuit could be used as a continuity tester.

Parts list

CODE COMPONENT VALUE/TYPE CHECK

R1 Resistor 390R LD 1 LED 5 mm yellow LD 2 LED 5 mm green - Wire PVC 1/0.6 (yellow) - Wire PVC 1/0.6 (green) - Stripboard -5 5 /'  <HOORZ /' *UHHQ *UHHQ /HDG <HOORZ /HDG *UHHQ OHDG <HOORZ OHDG 5  5 /'  \HOORZ /'  JUHHQ

Warning lights – stripboard circuit

There are many occasions when a warning light is required to attract attention. A flashing warning lamp is more likely to noticed than one which is steady.

Circuit diagram

Parts list

Complete the component list below and select the components from stock.

QUANTITY ITEM CODE VALUE/TYPE CHECK

1 Stripboard - 17 strips x 24 holes

1 Resistor R1 100Ω

1 Resistor R2 10kΩ

1 Resistor R3 10kΩ

1 Filament lamp LP1 6 V, 0.06 A

1 Lamp holder - For above

2 Capacitor C1,C2 100 uF (16 V) electrolytic

2 Transistors TR1,TR2 BFY51

Layout diagram

Circuit specification

• all components must be correctly selected, inserted and soldered

• when the circuit is powered up, the lamp must flash at a steady rate.

Circuit construction

• Using pliers, form the legs of resistor R1 so it fits in the correct position.

• Insert R1 from the component side of the board and solder it into place. The body of the resistor should fit close to the surface of the board.

• Snip off the extra lengths of component leads sticking out from the soldered side of the board.

• Repeat this process for R2, R3, C1, C2, TR1, and TR2.

• Make up a set of flying leads to connect the lampholder.

• Tin the ends of the flying leads.

• Insert, solder and trim the flying leads and connecting wires.

• Carry out a pre-power-up test.

• Connect to the power supply.

• Switch on and observe the lamps flashing at a steady rate.

• If your circuit does not work as expected, disconnect the power and repeat the pre-power-up test.

Report

• copy the circuit diagram.

SECTION 7 – LEARNING ABOUT PCBs

14 pin IC circuit – Printed Circuit Board (PCB)

This circuit uses a 7414 schmit trigger chip to generate flashing lights.

Circuit diagram  YROWV               5 5 & & 5 5 5 5 /'  /'  /'  /'  ,& +&  YROWV

Complete the parts list below and select the components from stock.

QUANTITY CODE COMPONENT VALUE/TYPE CHECK

1 - PCB

-1 IC1 Integrated Circuit 74HC14

1 - Socket 14-pin DIL

1 R1 Resistor 1M0

1 R2 Resistor 2M7

4 R3, R4, R5, R6 Resistor 1K0

2 C1, C2 Capacitor 100 nF

4 LD 1 - 4 LED 5 mm low current

14 pin IC circuit – Printed Circuit Board (PCB) PCB diagram

It must be remembered that although the mask for the solder side of board is the same orientation as the component side, the process of transferring the image to the board will reverse the circuit.

Circuit specification

• all components must be correctly selected and inserted

• when the circuit is powered up the LEDs should flash in pairs.

Circuit construction

• drill all holes required in the PCB

• solder in place the 14-pin DIL socket

• using pliers, form the legs of resistor R1 so it fits in the correct position

• insert R1 from the component side of the board and solder it into place – the body of the resistor should fit close to the surface of the board

• snip off the extra lengths of component leads sticking out from the soldered side of the board

• repeat this process for R2, R3, R4, R5, R6, C1, C2, and LD1 – 4

• tin the ends of the flying leads

• insert, solder and trim the flying leads and connecting wires

• carefully insert 7414 IC in place

• connect to the power supply

• when the circuit is powered up the LEDs should flash in pairs

• if your circuit does not work as expected, disconnect the power and repeat the pre-power-up test.