CfE Physics – SCN 4-09 b & c
Electronics

Input, Process and Output

Digital Logic Gates
SCN 4-09b: By contributing to investigations into the properties
of a range of electronic components, I can select and use them
as input and output devices in practical electronic circuits.
SCN 4-09c:Using my knowledge of electronic components and
switching devices, I can help to engineer an electronic system
to provide a practical solution to a real-life situation.
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CfE Physics SCN 4-09b
Electronics
Input, Process
and Output
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



Learning Intentions:
State that an electronic system consists of
three parts: input, process and output.
Identify from a block diagram the input, process
and output subsystems of an electronic system.
Draw a block diagram showing the input,
process and output subsystems of an
electronic system.
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Input, Process and Output
Electronic Systems
When something is made up of lots of parts which are put
together to do a job, it is called a ssystem.
_____.
When the parts are electronic components the system is
called an e _ _electronic
_ _ _ _ _ _ _ system.
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Electronic Systems
Electronic systems can do lots of jobs.
The type of job will depend on the components used to
make the ssystem.
_____.
A calculator is an example of an electronic system.
Every electronic system has tthree
_ _ _ _ main sections called sub-systems.
These are called the i _input,
_ _ _ , the p _process
_ _ _ _ _ and the
o_
_ _ _ _.
output.
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Subsystem - Input
What It Does
Detects some type of eenergy.
_____.
(for example: light, heat, sound) and changes it
to e _ _electrical
_ _ _ _ _ _ _ energy.
This is then passed to the pprocess
______
subsystem
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Subsystem - Process
What It Does
Changes the electrical energy from the iinput
____
so that the system can do its job. This is then
passed on to the o _output
_ _ _ _ subsystem.
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Subsystem - Output
What It Does
Converts the electrical e _energy
_ _ _ _ from the
process subsystem into another type of energy which
can be used. For example: hheat,
_ _ _ , light,
l____,
m
_______
movement.
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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 b _block
_ _ _ to take the place of
the iinput,
_ _ _ _ , process
p _ _ _ _ _ _ and ooutput
_____
subsystems.
Each block is labelled so that we kknow
___
what it is.
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Block Diagrams
Input
Process
Output
Keypad
Calculating
Circuits
Display
The block diagram for a calculator is shown
above. Any subsystem can be further broken
down to smaller and smaller subsystems - down
to the actual components if required.
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Block Diagram Examples
Public Address System
Input
mmicrophone
Process
aamplifier
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Output
lloudspeaker
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Block Diagram Examples
Smoke Alarm
IInput
Smoke
Sensor
P
Process
O Output
Logic
Circuits
b
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buzzer
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Block Diagram Examples
Intruder Lamp
Input
H Heat
Sensor
Sensor
Process
Output
Logic
Circuits
l
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lamp
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Learning Intentions




State that an input device changes some form of
energy into electrical energy.
State that the microphone, thermistor, LDR and
switch are all examples of input device.
State that the resistance of a thermistor changes
with temperature.
State that the resistance of an LDR decreases
when the light on it gets brighter.
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Input and Output Devices
Input subsystems contain a device which changes
some form of e _energy
_ _ _ _ into electrical energy.
Output subsystems contain a device which
changes e _ _electrical
_ _ _ _ _ _ _ energy
e _ _ _ _ _ into some
other form.
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Input Devices
Device: microphone
What it looks like:
Circuit Symbol:
How it Works: The inside of the microphone
v_ _vibrates
_ _ _ _ _ exactly the same way as the sound
waves. This makes identical electrical waves.
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Input Devices
Device: thermistor
What it looks like:
Circuit Symbol:
How it Works: The resistance of the thermistor
changes as the t_ _ _
_ _ _ _ _ _ _ _ changes.
temperature
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Input Devices
Device: Light Dependent Resistor
What it looks like:
Circuit Symbol:
How it Works: The resistance of the LDR
decreases as the light level gets b_
______.
brighter.
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Input Devices
Device: switch
What it looks like:
Circuit Symbol:
How it Works: Moving the switch from one setting
to the other makes or b_breaks
_ _ _ _ the circuit.
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Learning Intentions



State that an output device changes electrical
energy into another form of energy.
State that a loudspeaker, buzzer, lamp, LED and
electric motors are all forms of output devices.
State the energy conversions involved for a
given output device.
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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
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Output Devices
Device: buzzer
What it looks like:
Circuit Symbol:
+
How it Works: Electrical energy -> Sound energy
A voltage across the buzzer makes it sound. The
buzzer just switches sound on or off.
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Output Devices
Device: lamp
What it looks like:
Circuit Symbol:
How it Works: Electrical energy -> Light energy
A voltage across the lamp makes it light. The
greater the voltage, the brighter it gets.
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Output Devices
Device: Light emitting diode
What it looks like:
Circuit Symbol:
How it Works: Electrical energy -> Light energy
A voltage across the LED makes it light. LEDs are
used to indicate when something is on or off.
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Output Devices
Device: electric motor
What it looks like:
Circuit Symbol:
M
How it Works: Electrical energy -> Kinetic energy
A voltage across the motor makes it turn.
The greater the voltage, the faster it turns.
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Learning Intentions


Identify from a list an appropriate input device
for a given job.
Identify from a list an appropriate output device
for a given job.
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Examples of input and output applications
Application
Reason
Device
Output of radio
Loudspeaker The output should be
s _sound
_ _ _ _ waves
Input of an
automatic lamp
LLDR
_ _
Input of a heating Thermistor
controller
Output of fan
M
____
Motor
The LDR will change
resistance when the
brightness changes
The thermistor will
c_
_ _ _ _ resistance
change
when the temperature
changes
turn
The motor will t_
__
the blades of the fan.
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CfE Physics
Electronics
Digital
Logic Gates
Scn 4-09c:Using my knowledge of electronic components
and switching devices, I can help to engineer an electronic
system to provide a practical solution to a real-life situation.
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Physics
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Learning Intentions:






State that high voltage = logic 1.
State that low voltage = logic 0.
Draw and identify symbols for 2 input AND and OR gates
and a NOT gate.
State that for a NOT gate the output is the opposite of the
input.
State that for an AND gate both inputs must be high for
the output to be high.
State that for an OR gate either of the inputs must be high
for the output to be high.
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Digital Signals
Digital signals are either on or off
o__.
An ‘off’ signal has a zero voltage (called ‘l‘low’
_ _’ ).
An ‘on’ signal has a non-zero voltage(called ‘h‘high’
_ _ _’ ).
The ‘o‘off’
_ _’ signal; low state is given the name ‘logic
0’ (most often just ‘0’).
The ‘o‘on’
_’ signal; high state is given the name ‘logic 1’
(most often just ‘ 1’).
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Digital Signals
An oscilloscope can show logic states since it
measures the high and low voltages.
High voltage: Logic _1
Oscilloscope trace showing
a digital logic
signal which is changing
from 1 to 0
several times.
Low voltage: Logic _
0
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Logic Gates
Digital logic gates are used to combine or change
digital electronic signals. There are three basic
types of logic gate called the N
_ _ gate
NOT
(sometimes called an i _ inverter
_ _ _ _ _ _ ), the A _
_
AND
gate and the O
_ gate.
OR
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The NOT gate
This is the simplest gate. It has oone
_ _ input and
oone
_ _ output.
The output is always the opposite of the
i _ input.
___.
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Logic Gate
Symbol
NOT gate (Inverter)
i nput
How it behaves
The NOT gate
changes the input
signal to the
opposite state.
output
NOT Truth table
Input
Output
High
Low
(1)
(0)
Low
(0)
High
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(1)
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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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Logic Gate
AND gate
Input B
Output
Low
(0)
Low
(0)
Low
(0)
High
Low
(0)
High
Low
Input A
Symbol
i nput A
AND Truth table
output
i nput B
How it behaves
The AND gate combines
the input signals so that
the output is only 1
when both inputs are 1.
Low
(0)
(1)
(1)
(0)
High
High
(1)
(1)
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Low
(0)
High
(1)
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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 the inputs are at logic 0 when the output
becomes logic 0 as well.
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Logic Gate
OR gate
Input B
Output
Low
(0)
Low
(0)
Low
(0)
Low
(0)
High
High
(1)
High
Low
Input A
Symbol
i nput A
OR Truth table
output
i nput B
How it behaves
The OR gate combines
the input signals so that
the output is 1
when either input is 1.
(1)
(1)
(0)
High
High
(1)
(1)
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High
(1)
High
(1)
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Learning Intentions

Explain how to use logic gates for control in
simple situations.
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Logical solutions
1. Donnie's dad wants to be wakened if he 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.)
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Solution System Diagram
Light
sensor
Buzzer
switch
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How it Works
Light Sensor
Dark
Light
low
high
Switch
Open
Closed
low
high
When the light is turned on, the light
sensor output is hhigh.
___.
This causes the OR gate output to go high
which sounds the bbuzzer.
_____.
When the switch under the mat is
pressed, it c _ _
_ _ _ _ . This makes
closes.
its output hhigh.
___.
This causes the OR gate output to go
hhigh
_ _ _ which sounds the buzzer.
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2. A tomato grower wants to protect his
delicate plants which are in his greenhouse.
Design a warning system to sound a buzzer
if it gets too cold during the night (dark).
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Solution System Diagram
Light
sensor
Buzzer
Temperature
sensor
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How it Works
Light Sensor
Dark
Light
low
high
Temperature Sensor
Cold
Warm
low
high
The buzzer can only switch on when the
output from the NOT gate is hhigh.
___.
Therefore the output from the OR gate
must be llow.
__.
The OR gate output can only be low if
b
_ _ _ the inputs are low.
both
This means it must be both ddark
___
and c cold
_ _ _ as well.
.
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Grandad can't use the stair light switch
easily since he got his walking stick.
Design a system which will switch on the
stair light automatically when it gets
dark.
There must be a manual switch as well.
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Solution System Diagram
Light
sensor
Lamp
switch
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How it Works
Light Sensor
Dark
Light
low
high
Switch
Open
Closed
low
high
When it is dark, the light sensor output is
low which is changed to h high
_ _ _ by the
NOT gate. This causes the OR gate
output to go high which l _lights
_ _ _ _ the
lamp.
When the switch is closed, its output
is high. This causes the OR gate
output to go h high
_ _ _ which lights the
lamp.
.
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4. Design a system for a bathroom to switch on a fan
motor when the bathroom gets so steamy, the light
from the window is blocked. The fan must only come on
when it is hot as well as steamy.
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Solution System Diagram
Light
sensor
Motor
Temperature
sensor
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How it Works
Light Sensor
Dark
Light
low
high
Temperature sensor
Cold
Warm
low
high
When it is steamy, it gets darker, the
light sensor output is l low
_ _ which is
changed to high by the N
_ _ gate.
NOT
When it gets too hhot
_ _ the output from
the temperature sensor is hhigh.
___.
Only when it is hot and steamy at the
ssame
_ _ _ time will both inputs of the
AND gate be high to make the output
high to t turn
_ _ _ the motor.
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CfE Physics
Electronics
End of Unit
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