Course: Practical
Electronics
Electronics
Level: National 4
May 2013
This advice and guidance has been produced for teachers and other staff who
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These previously published materials, which teachers have found to be
helpful, have been updated in line with the new qualifications. They are neither
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learning which are appropriate to the needs of learners within their own
context.
Staff should also refer to the course and unit specifications and support notes
which have been issued by the Scottish Qualifications Authority.
http://www.sqa.org.uk
Acknowledgements
© Crown copyright 2013. You may re-use this information (excluding logos) free of
charge in any format or medium, under the terms of the Open Government Licence.
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ELECTRONICS (NATIONAL 4, PRACTICAL ELECTRONICS)
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Contents
Section 1: Input and output devices
4
Section 2: Logic gates
13
Section 3: Summary notes: input, process and output
24
Section 4: Electronics: problems
36
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SECTION 1: INPUT AND OUTPUT DEVICES
Section 1: Input and output devices
The thermistor
This activity studies the function of a thermistor.
Apparatus
Thermistor, multimeter and prototype circuit board.
Circuit diagram
Layout diagram
Instructions




Place the thermistor into a prototype circuit board.
Set the multimeter to ohms (Ω).
Connect the multimeter as shown in the layout diagram.
Copy the following table.
Temperature
Resistance (Ω)
Cold
Hot
 Record the resistance of the thermistor; this is when it is cold (adjust the
range if necessary).
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SECTION 1: INPUT AND OUTPUT DEVICES
 Warm the thermistor by holding it between your fingers. Hold until the
reading on the meter stops changing.
 Compare the resistance of the thermistor when it is hot and when it is cold,
ie what happens to the resistance when the thermistor heats up?
 State whether the thermistor is an input device or an output device.
Thermistor
Multimeter
Block diagram
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SECTION 1: INPUT AND OUTPUT DEVICES
The light dependent resistor (LDR)
This activity studies the function of an LDR.
Apparatus
LDR, multimeter and prototype circuit board.
Circuit diagram
Layout diagram
Instructions



•





Place the LDR into a prototype circuit board.
Set the multimeter to ohms (Ω).
Connect the multimeter as shown in the layout diagram.
Construct a table to record your results using the following headings:
- light level
- resistance (ohms).
Record the resistance of the LDR; this is in the light (adjust the range if
necessary).
Cover the LDR.
Record the resistance of the LDR; this is in the dark.
Compare the resistance of the LDR in the light and in the dark, ie what
happens to the resistance when the LDR is covered?
State whether the LDR is an input device or an output device.
LDR
Multimeter
Block diagram
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SECTION 1: INPUT AND OUTPUT DEVICES
Switches
This activity studies the function of switches.
Apparatus
Variety of switches labelled A, B and C, and multimeter.
Circuit diagram
Switch
Multimeter
Block diagram
Instructions
 Set the multimeter to ohms (Ω).
 Connect the multimeter leads to both ends of switch A.
 Copy the following table.
Temperature
Resistance (ohms)
Open (off)
Resistance (ohms)
Closed (on)
A
B
C





Record the resistance of the switch; this is the switch open (off).
Operate the switch – this will depend on the type of switch used.
Record the resistance of the switch; this is the switch closed (on).
Repeat for switches B and C.
Compare the resistance of the switches when open and closed, ie what
happens to the resistance when a switch is open then closed?
 Is the switch an input device or an output device?
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SECTION 1: INPUT AND OUTPUT DEVICES
The loudspeaker
This activity studies the function of a loudspeaker.
Apparatus
Loudspeaker and signal generator.
Circuit diagram
Signal generator
Loudspeaker
Block diagram
Instructions
 Connect the loudspeaker to the signal generator.
 Set the output to 5 Hz; this is low frequency. Gradually increase the
frequency control of the signal generator until you hear a tone.
 Describe the movement of the speaker cone and the sound that is
produced.
 Set the output to 8 kHz; this is high frequency.
 Describe the movement of the speaker cone and the sound that is
produced.
 Copy and use the table below to compare the sound produced and
movement of the cone at low and high frequencies.
Frequency
Sound
Cone movement
Low
High
 What is the energy change in the loudspeaker?
 Is the loudspeaker an input device or an output device?
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SECTION 1: INPUT AND OUTPUT DEVICES
The buzzer
This activity studies the function of a buzzer.
Apparatus
Buzzer, battery (min. 4.5V) or power supply.
Circuit diagram
Power supply
Buzzer
Block diagram
Instructions
 Connect the buzzer, ensuring that the positive terminal of the battery is
connected to the positive terminal of the buzzer.
 Describe the sound produced.
 Describe which way the buzzer has to be connected in the circuit to allow it
to work.
 What is the energy change in the buzzer?
 Is the buzzer an input device or an output device?
Layout diagram
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SECTION 1: INPUT AND OUTPUT DEVICES
The lamp
This activity studies the function of a lamp.
Apparatus
Lamp, lamp-holder and power supply.
Circuit diagram
Power supply
Lamp
Block diagram
Instructions




Connect the lamp to the battery or power supply.
Describe the brightness of the lamp.
What is the energy change in the loudspeaker?
Is the loudspeaker an input device or an output device?
Layout diagram
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SECTION 1: INPUT AND OUTPUT DEVICES
The light emitting diode (LED)
This activity studies the function of an LED.
Apparatus
LED, 390Ω protective resistor, prototype circuit board and 6 volt power supply.
Circuit diagram
Power supply
LED
Block diagram
Instructions
 Place the LED and resistor into
a prototype circuit board.
 Ensure that the negative lead of
the LED (short lead at the side
with the flat) is connected to the
0 volt rail or – ve terminal of the
battery.
 Connect up the power leads.
 Describe the brightness of the
LED.
 What energy change takes
place in the LED?
 Is the LED an input or an output
device?
Layout diagram
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SECTION 1: INPUT AND OUTPUT DEVICES
The motor
This activity studies the function of a motor.
Apparatus
Low voltage motor, toggle switch, battery or power supply (about 5 volts).
Circuit diagram
Power supply
Motor
Block diagram
Instructions




Connect the switch and motor to form an end-to-end circuit with the battery.
Put the switch to the on position.
Describe the motion of the motor.
Reverse the connections to the battery and describe what happens to the
motion of the motor.
 What energy change takes place in the motor?
 Is the motor an input or an output device?
Layout diagram
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SECTION 2: LOGIC GATES
Section 2: Logic gates
The NOT gate or inverter
This activity studies the function of a NOT gate.
Apparatus
Modular circuit boards.
Power
connection
Switch unit
Inverter
Transducer
driver
Bulb unit
Block diagram
Instructions





Construct the system shown in the block diagram.
Note the bulb state (on or off) with the switch off.
Press the switch and note the state of the bulb.
Copy the symbol and truth table on the next page.
Complete the truth table.
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SECTION 2: LOGIC GATES
Truth table
The results can be represented in a table called a truth table. This shows the
inputs and outputs as 1 for on and 0 for off. This can be seen on the switches
of electrical and electronic devices. This is known as logic 1 and logic 0.
A
0
1
Symbol for NOT gate
14
B
1
0
Truth table
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SECTION 2: LOGIC GATES
The AND gate
This activity studies the function of an AND gate.
Apparatus
Modular circuit boards.
B
Switch unit
Power
connection
A
AND gate
Switch unit
Transducer
driver
Bulb unit
Block diagram
Instructions







Construct the system shown in the block diagram.
Note the bulb state (on or off) with both switches off.
Press switch B only and note the state of the bulb.
Press switch A only and note the state of the bulb.
Press both switches and note the state of the bulb.
Copy the symbol and truth table.
Complete the truth table.
Truth table
It can be worked out that there are four input combinations.
A
0
0
1
1
Symbol for NOT gate
B
0
1
0
1
Z
Truth table
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SECTION 2: LOGIC GATES
The OR gate
This activity studies the function of an OR gate.
Apparatus
Modular circuit boards.
B
Switch unit
Power
connection
A
OR gate
Switch unit
Transducer
driver
Bulb unit
Block diagram
Instructions







Construct the system shown in the block diagram.
Note the bulb state (on or off) with both switches off.
Press switch B only and note the state of the bulb.
Press switch A only and note the state of the bulb.
Press both switches and note the state of the bulb.
Copy the symbol and truth table.
Complete the truth table.
Truth table
It can be worked out that there are four input combinations.
A
0
0
1
1
Symbol for NOT gate
16
B
0
1
0
1
Truth table
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SECTION 2: LOGIC GATES
Temperature control
The problem
People in an office find that it gets too hot in the summer. An electronic system
is required to turn on the motor of a fan when it is too hot.
Boards/sub-systems available
Light
sensor
The output is high
(logic 1) when it
is light.
Switch
Inverter
Motor
Driver
Temperature
sensor
The output is high
(logic 1) when it
is hot.
A power supply and other boards are also available.
Instructions




Select appropriate boards or sub-systems.
Draw a block diagram.
Assemble the boards/sub-systems.
At room temperature, turn the dial on the sensor board so that the output is
just off (logic 0).
 Test the system.
 Get your system checked.
 Complete the report page.
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SECTION 2: LOGIC GATES
Alarm
The problem
At certain times of the year a farmer would like an alarm to wake him/her up
when it gets light.
He/she would like the alarm to sound only when it gets light and it has been
switched it on.
Boards/sub-systems available
Light
sensor
The output is
high (logic 1)
when it is
light.
Temperature
sensor
The output is
high (logic 1)
when it is
hot.
AND gate
Inverter
Buzzer
Driver
Switch
The output is
high (logic 1)
when the
switch is on.
A power supply and other boards are also available.
Instructions




Select appropriate boards or sub-systems.
Draw a block diagram.
Assemble the boards/sub-systems.
Press the switch to the on position. In daylight turn the dial on the sensor so
that the output is just on (logic 1).
 Test the system.
 Get your system checked.
 Complete the report page.
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SECTION 2: LOGIC GATES
Security lights
The problem
A shop has had a number of break-ins at night. An electronic system is
required to make a light come on when it gets dark.
Boards/sub-systems available
AND gate
Light
sensor
The output is
high (logic 1)
when it is
light.
Inverter
Temperature
sensor
The output is
high (logic 1)
when it is
hot.
Bulb
(lamp)
Motor
(fan)
Driver
A power supply and other boards are also available.
Instructions







Select appropriate boards or sub-systems.
Draw a block diagram.
Assemble the boards/sub-systems.
In daylight turn the dial on the sensor so that the output is just off.
Test the system.
Get your system checked.
Complete the report page.
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SECTION 2: LOGIC GATES
Keeping watch
The problem
Many outdoor lamps are also security devices. An electronic system is
required that lights a lamp when heat is detected.
Boards/sub-systems available
Light
sensor
The output is
high (logic 1)
when it is light.
OR gate
Inverter
AND gate
Bulb
(lamp)
Buzzer
Driver
Temperature
sensor
The output is
high (logic 1)
when it is hot.
A power supply and other boards are also available.
Instructions




Select appropriate boards or sub-systems.
Draw a block diagram.
Assemble the boards/sub-systems.
At room temperature, cover the light sensor and turn the dial on the
temperature sensor so that the output is just off.
 Test the system.
 Get your system checked.
 Complete the report page.
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SECTION 2: LOGIC GATES
Camping out
The problem
Jimmy likes to play in his tent but his mum worries about him being cold. An
electronics system is required to sound a buzzer in the house if it gets too
cold. Include a switch to allow Jimmy to call his mum in an emergency.
Boards/sub-systems available
Light
sensor
The output is
high (logic 1)
when it is light.
Temperature
sensor
The output is
high (logic 1)
when it is hot.
Switch
The output is
high (logic 1)
when the
switch is on.
AND gate
Inverter
Buzzer
Driver
OR gate
A power supply and other boards are also available.
Instructions




Select appropriate boards or sub-systems.
Draw a block diagram.
Assemble the boards/sub-systems.
Press the switch to the on position. Warm the temperature sensor and turn
the dial so that the output is just off.
 Test the system.
 Get your system checked.
 Complete the report page.
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SECTION 2: LOGIC GATES
Design problems
1.
A city council is having problems with birds
perching on the ledges of buildings and messing
the pavements. Design a system that makes a
sound to scare away a bird if it lands on two trip
wires (connected to switches).
2.
A freezer food shop is worried about
people leaving the freezer doors open,
allowing the temperature of the food, to
increase. This could allow germs to
contaminate the food making it unfit to
eat.
Design a system that lights a lamp
above the freezer if someone leaves the
lid up or it gets too warm inside.
3.
Modern buildings have a double
alarm system to control fire. A
motor drives a pump that sprays
water whenever it gets too hot
or if there is smoke present.
Design a system that will drive the
pump motor when it gets too hot or if
there is too much smoke to let light
reach a sensor.
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SECTION 2: LOGIC GATES
4.
Some cars have sidelights that
come on automatically when it gets
dark.
Design a system that automatically
turns the sidelights on if it is dark.
Include a master switch to allow the
sidelights to be turned on for parking.
5.
Sam likes to sit up in bed at night
reading (usually horror stories). His
parents do not mind him reading but
they do not like him being awake
when they are asleep.
Design a system that will only allow
Sam’s bedroom light to be switched
on at night if his parents’ light is on.
Sam should be able to operate his
light during the day if he wants to.
6.
Some modern camcorders do not allow
operation of the record mode unless there is
a tape inserted and the lens cap is
removed.
Design a system that allows the motor to be
switched on only if there is a tape in the
camcorder and light is entering the lens.
7.
The pump motor in an automatic
heating system is designed to be on
all the time, day or night, unless it
gets too hot in the daytime.
Design a system which drives the
pump motor constantly except when
it is hot during the day.
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
Section 3: Summary notes: input, process and
output
Electronic systems
When something is made up of lots of parts that are put together to do a job, it
is called a system.
When the parts are electronic components the system is called an electronic
system. Electronic systems can do lots of jobs. The type of job will depend on
the components used to make the system. A calculator is an example of an
electronic system.
Every electronic system has three main sections, called sub-systems. These
are called the input, the process and the output.
Sub-system
What it does
Input
Detects some type of energy, for example light, heat or
sound, and changes it to electrical energy. This is then
passed to the process sub-system
Process
Changes the electrical energy from the input so that the
system can do its job. This is then passed to the output
sub-system.
Output
Converts the electrical energy from the process subsystem into another type of energy, for example heat,
light or movement.
Block diagrams
A block diagram is an easy way to draw a system. Instead of drawing a
complicated diagram showing all the components, we draw a box or block to
take the place of the input, process and output sub-systems. Each block is
labelled so that we know what it is.
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
Input
Process
Output
Keypad
Calculating
circuits
Display
The block diagram for a calculator is shown above. Any sub-system can be
further broken down into smaller and smaller sub-systems – down to actual
components if required.
Block diagram examples
Input
Public address
system
Process
Output
Microphone
Amplifier
Loudspeaker
Smoke
alarm
Smoke
sensor
Logic
circuits
Buzzer
Intruder
lamp
Heat sensor
Logic
circuits
Lamp
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
Input and output devices
Input sub-systems contain a device that changes some form of energy into
electrical energy. Output sub-systems contain a device that changes electrical
energy into some other form. These sub-systems are often called
transducers.
Input devices
Device
What it looks
like
Circuit symbol
Microphone
How it works
The inside of the
microphone vibrates
exactly the same
way as sound
waves.
This makes identical
electrical waves.
Thermistor
The resistance of
the thermistor
changes as the
temperature
changes.
Lightdependent
resistor
The resistance of
the LDR decreases
as the light level
gets brighter.
(LDR)
Switch
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Moving the switch
from one setting to
the other makes or
breaks the circuit.
SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
Output devices
Device
Loudspeaker
What it looks
like
Circuit symbol
How it works
Electrical energy →
sound energy
Electrical waves make
vibrations inside the
loudspeaker, producing
sound waves.
Buzzer
Electrical energy →
sound energy
A voltage across the
buzzer makes it sound.
The buzzer just
switches sound on and
off.
Lamp
Electrical energy →
light energy
A voltage across the
lamp makes it light.
The greater the
voltage, the brighter the
lamp gets.
Light-emitting
diode (LED)
Electrical energy →
light energy
A voltage across the
LED makes it light.
LEDs are used to
indicate when
something is on or off.
Electric motor
Electrical energy →
kinetic energy
A voltage across the
motor makes it turn.
The greater the
voltage, the faster the
motor turns.
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
Examples of input and output applications
Application
Device
Reason
Output of a radio
Loudspeaker
The output should be
sound waves
Input of an automatic
lamp
LDR
The LDR will change
resistance when the
brightness changes
Input of a heating
controller
Thermistor
The thermistor will
change resistance when
the temperature
changes
Output of a fan
Motor
The motor will turn the
blades of the fan
Digital logic gates
Digital signals





Digital signals are either on or off.
An ‘off’ signal has zero voltage (called ‘low’).
An ‘on’ signal has a non-zero voltage (called ‘high’).
The ‘off’ signal, low state is called ‘logic 0’ (or just ‘0’).
The ‘on’ signal, high state is called ‘logic 1’ (or just ‘1’).
A graph of a digital signal being switched on and off is shown below.
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
Logic gates
Digital logic gates are used to combine or change digital electronic signals.
There are three basic types of logic gate. These are called the NOT gate
(sometimes called an inverter), the AND gate and the OR gate.
1.
The NOT gate
This is the simplest gate. It has one input and one output. The output is
always the opposite to the input.
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
2.
The AND Gate
The AND gate has two inputs and one output. The output of the AND
gate is always at logic 0 unless both the inputs are at logic 1, when the
output becomes logic 1 as well.
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
3.
The OR gate
The OR gate has two inputs and one output. The output of the OR gate
is always at logic 1 unless both of the inputs are at logic 0. When this
happens the output becomes logic 0 as well.
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
Logical solutions
1.
Donnie’s dad wants to be wakened if Donnie gets up
at night. Design a system to sound a buzzer if
Donnie switches on his light or if he stands on a mat.
(A switch is under the mat.)
How it works
When the light is turned on, the light sensor output is
high. This causes the OR gate output to go high,
which sounds the buzzer.
When the switch under the mat is pressed, it closes –
making its output high. This causes the OR gate
output to go high, which sounds the buzzer.
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
2.
A tomato grower wants to protect the
delicate plants that are in her
greenhouse. Design a system to
sound a buzzer if it gets too cold in
the greenhouse during the night
(when it is dark).
How it works
The buzzer can only switch on when the output from
the NOT gate is high, therefore the output from the OR
gate must be low.
The OR gate output can only be low if both the inputs
are low. This means it must be both dark and cold.
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
3.
Grandad can’t use the stair light switch easily since he
got his walking stick. Design a system that will switch
on the stair light automatically when it gets dark.
There must be a manual switch as well.
How it works
When it is dark, the light sensor output is low which is
changed to high by the NOT gate. This causes the
OR gate output to become high, which lights the
lamp.
When the switch is closed, its output is high. This
causes the OR gate to become high, which lights the
lamp.
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SECTION 3: SUMMARY NOTES: INPUT, PROCESS AND OUTPUT
4.
Design a system for a bathroom to switch on a fan
motor when the bathroom gets steamy. The fan
must only come on when it is hot as well as
steamy.
How it works
When it is steamy, the light sensor output is low which
is changed to high by the NOT gate. When it gets too
hot the output from the temperature sensor is high.
Only when it is hot and steamy at the same time will
both inputs of the AND gate be high and make the
output high and therefore turn the motor.
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SECTION 4: ELECTRONICS: PROBLEMS
Section 4: Electronics: problems
1.
Describe what is meant by an electronic system. Give two examples.
2.
The block diagram for a calculator is shown below. Copy the block
diagram and identify the input, process and output sub-systems.
Keypad
3.
Display
Draw a block diagram of the following systems. Identify the input,
process and output sub-systems in each case:
(a)
(b)
(c)
(d)
(e)
4.
Calculating
circuits
a public address system
a smoke alarm
an automatic porch light (lamp lights when it gets dark)
an automatic fan (fan operates when it gets too warm)
a radio.
What is sensed by each of the following input devices?
(a)
(b)
(c)
(d)
Microphone
Thermistor
Light-dependent resistor
Switch.
5.
What can change the resistance of a thermistor?
6.
State how the resistance of a light-dependent resistor changes with light
level.
7.
Describe an experiment you would perform to determine how the
resistance of a thermistor changes with temperature.
8.
Describe an experiment you would perform to determine how the
resistance of a light-dependent resistor changes with light level.
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ELECTRONICS (NATIONAL 4, PRACTICAL ELECTRONICS)
© Crown copyright 2013
SECTION 4: ELECTRONICS: PROBLEMS
9.
Describe the energy changes which take place in the following output
devices:
(a)
(b)
(c)
(d)
(e)
10.
loudspeaker
buzzer
lamp
light emitting diode
electric motor.
Study the circuit symbols below. In each case:
(a)
(b)
(c)
(d)
name the device
state whether it is an input or output device
state the energy changes in the device
give an example of where it could be used.
Device 1
Device 5
11.
Device 6
Device 3
Device 7
Device 4
Device 8
In the applications below identify which of the above devices would be
suitable. Give a reason for the choice of each device.
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
12.
Device 2
Output of a radio
Input of an automatic lamp
Input of a heating controller
Output of a fan
Output of an electronic timer
Input of cassette recorder – recording sub-system
Output of a cassette recorder – drive sub-system
Output of a cassette recorder – playback sub-system.
Describe what is meant by a ‘digital signal’.
ELECTRONICS (NATIONAL 4, PRACTICAL ELECTRONICS)
© Crown copyright 2013
37
SECTION 4: ELECTRONICS: PROBLEMS
13.
Draw the symbol for the following logic gates:
(a)
(b)
(c)
14.
The following is a truth table for a logic gate.
(a)
(b)
15.
NOT gate or inverter
AND gate
OR gate.
Name the logic gate.
Explain in terms of voltage levels what is meant by the ‘1’s and
‘0’s.
Draw the truth table for each of the logic gates below:
Gate 1
16.
Gate 3
The system below is designed to allow water to be sprayed onto plants if
the air becomes too hot or the gardener switches the sprayer on.
(a)
(b)
(c)
38
Gate 2
Identify the logic gate used in the system.
When the gardener switches the sprayer on, what is the logic level
at B?
What input device could be used in the heat sensor?
ELECTRONICS (NATIONAL 4, PRACTICAL ELECTRONICS)
© Crown copyright 2013