Topic 1.2 – Electronic Sub-Systems.
Learning Objectives:
At the end of this topic you will be able to;
 Use the following sub-systems as part of a block diagram;
o Input units: light, temperature, rotation, magnetic, moisture,
sound, pressure pad/switch, and pulse generator.
o Output devices: lamp, buzzer, motor, solenoid, and LED.
o Signal processing: inverter, AND gate, OR gate, latch, time delay
and comparator.
 State the function of a transducer driver.
The following objectives have been reproduced from Topic 1.1, as they
are more appropriate for assessment in this unit.
 describe possible applications of an electronic system from a block
diagram;
 produce a block diagram for a system to solve a given problem;
 design and test electronic systems.
1
GCSE Electronics.
Unit E1 : Discovering Electronics
Electronic Sub-Systems
In this section we will investigate a range of electronic sub-systems, that can
be linked together to make much bigger systems to solve problems. You
should remember from topic 1.1 that there are three sections to an electronic
system:
i. Input Sensors.
ii. Signal Processing.
iii. Drivers.
iv. Output Devices.
You might be working on Alpha, E&L, or you might use a simulation like Control
Studio. All of these systems have a range of input, process, driver and
outputs. These notes are intended to be non-system specific and it should be
possible to adapt all of the activities to any system.
We will look at Input Sensors and output devices first as these provide the
interface with the real world. We will look at the signal processing units later.
Input Sensing Units
The processing section of an electronic system can only process electrical
signals. The Input Sensing Units convert non-electrical signals, e.g. light, into
an electrical form.
Input Signal
e.g. Light
Input Sensor
e.g. Light Sensor
Electrical
Signal
The Input Sensing Units can be subdivided into two types. They are
described on the following page:
2
Topic 1.2 – Electronic Sub-Systems.
(i)
Digital Type:
The signal coming out of such boards can only
have one of two values i.e. 0V or +5V.
We represent the changes in voltage that
occur in a digital system by the symbols on the
right.
(ii)
Voltage at output
falls instantly
Voltage at output
rises instantly
Analogue Type:
The signal coming out of these boards can
vary anywhere between 0V and +5V,
depending on the input signal level. The level
of the electrical signal from these boards is a
representation (an analogue) of the input
signal.
Voltage at output
falls gradually
Voltage at output
rises gradually
We represent the changes in voltage that occur in an analogue system
by the symbols on the right.
Voltages are measured with respect to the negative (-) line. This is often
referred to as the zero volt line (0V).
If a voltage is near the 0V line, say less than 2 volt, the point is said to be
LOW. If it is near the positive line, say greater than 3 volt, it is said to be
HIGH.
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GCSE Electronics.
Unit E1 : Discovering Electronics
Output Devices
The signal coming out of the processing section of a system is usually HIGH
or LOW. Output units receive this signal and can change the electrical signal
into some other form e.g. the bulb unit will convert the electrical signal into
heat and light energy.
Electrical
Output Device
Output Signal
Signal
e.g. Bulb Unit
e.g. Heat/Light
Most of the Input Sensing Units cannot supply sufficient current to directly
drive the Output Units. Later on you will be using output switching devices
(drivers). These units can take a voltage signal from the Input Sensing Units
or other processing blocks and boost it so that the signal can drive any of the
Output Units.
The function of the input sensing units and the output devices will be
investigated in the assignments.
COMPLETE ASSIGNMENTS 1.2A, 1.2B & 1.2C
4
Topic 1.2 – Electronic Sub-Systems.
Practical Work 1.2A : Investigating Input Sensors.
It has been assumed that you will have been shown how to make the basic
setup of whichever system you are using.
Activity 1a : (For use with Alpha Kit)
a.
Set up the following arrangement with the voltmeter on suitable range
(20V). Use yellow alpha links unless told otherwise.
+
+
+
9 - 12V
AC/DC
Power Supply Regulator
_
+
_
_
Switch Unit _
b.
Switch on the Power Supply.
c.
Record the voltage reading on the voltmeter. .........................................
d.
Using your finger, press the switch and record below the reading on the
voltmeter.
..........................................................
e.
Did the change occur quickly or slowly ? .......................................
f.
Try to alter the speed at which the output changes, by pressing the
switch at different speeds. Did you succeed?
......................................................................................................................................
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GCSE Electronics.
Unit E1 : Discovering Electronics
g.
Which type of Input Sensor do you think this unit is, Analogue or
Digital?
..........................................................................
Activity 1b. (For Control Studio Users)
a.
Set up the following arrangement with the digital voltmeter. (Note: the
default voltage for control studio is 9V.)
If the voltmeter shows
this symbol (µV) then
the voltage is
effectively 0V.
b.
Switch on the simulator, using the
c.
Record the voltage reading on the voltmeter. .........................................
d.
Using your mouse, click on the switch and record below the reading on
the voltmeter.
..........................................................
6
button.
Topic 1.2 – Electronic Sub-Systems.
e.
Did the change occur quickly or slowly ? .......................................
f.
Try to alter the speed at which the output changes, by clicking on the
switch at different speeds. Did you succeed?
......................................................................................................................................
g.
Which type of Input Sensor do you think this unit is, Analogue or
Digital?
..........................................................................
Save your circuit as “E1-Systems-Circuit1”
Summary of Activity 1.
The function of the unit is summarised in the following table.
Unit
Type
Action
H
Switch Unit
(13)
Input
(Digital)
Signal level from unit rises
instantly when switch is pressed
L
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GCSE Electronics.
Unit E1 : Discovering Electronics
Activity 2a: (For use with Alpha Kit)
a.
Set up the following arrangement with the voltmeter on suitable range
(20V). Use yellow alpha links unless told otherwise.
+
+
+
9 - 12V
AC/DC
Power Supply Regulator
_
+
_
_ Light Sensor _
b.
Set the variable resistor on the Light Sensing Unit to near mid-position.
Switch on the power supply.
c.
Record the voltage reading on the voltmeter.
d.
Using your finger, cover the window on the light dependent resistor
[LDR] and record below the reading on the voltmeter.
......................................
............................................................................
e.
Did the change occur quickly or slowly ?
.....................................
f.
Try to alter the speed at which the output changes, by changing the
speed at which your finger covers the window. Did you succeed ?
......................................................................................................................................
......................................................................................................................................
g.
8
Which type of Input Sensor do you think this unit is, Analogue or
Digital?
..................................................................
Topic 1.2 – Electronic Sub-Systems.
Activity 2b: (For use with Control Studio)
a.
Now try to make the following circuit using an analogue sensor.
b.
You will have to insert a <Sensor Unit>, and <Light Sensor> from the
<Insert> menu and link them in the same way as linking the multimeter.
c.
Switch on the simulator, using the
d.
Set the variable resistor on the Light Sensing Unit to near mid-position
(Arrow pointing upwards). Adjust the setting of the slider alongside the
light sensor, set this to Light
e.
Record the voltage reading on the voltmeter.
f.
Now change the light level setting to Dark and record below the reading
on the voltmeter.
............................................................................
button.
......................................
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GCSE Electronics.
Unit E1 : Discovering Electronics
g.
Did the change occur quickly or slowly ?
.....................................
h.
Try to alter the speed at which the output changes, by moving the slider
from Dark – Light at various speeds. Did you succeed ?
......................................................................................................................................
i.
Which type of Input Sensor do you think this unit is, Analogue or
Digital?
..................................................................
Save your circuit as “E1-Systems-Circuit2”
Summary of Activity 2.
The function of the unit is summarised in the following table.
Unit
Type
Action
H
Light
Sensing
Unit
(11)
Input
(Analogue)
Signal level from unit falls
gradually when window is
covered
L
Activity 3:
Use whichever system you have to investigate the other Input Sensing Units
listed in the table on the following page. The signal coming from each can be
investigated using a voltmeter, as we have done in the previous examples.
In each case complete the table to show if the unit is an analogue or digital
input sensing device and write a sentence which describes its action. Start by
copying in the two results you already know.
10
Topic 1.2 – Electronic Sub-Systems.
Unit
Type
Action
Switch Unit
(13)
Light Sensing Unit
(11)
Input Voltage Unit
(10)
Moisture / Rain
Sensor
(16)
Temperature
Sensor
(17)
Reed / Magnetic
Switch
(19)
Note : Control Studio has additional input units to these listed in the table
which you might want to investigate, e.g. rotation sensor, although these will
not be required for the examination.
There are sometimes alternative names used for a number of these input
units, these are listed below. Ask your tutor to explain if you do not
understand where the name comes from.
Input Voltage Unit
Magnetic Switch Unit
Switch Unit
Rain Sensor
-
Position Sensor.
Proximity Sensor.
Pressure Sensor.
Moisture Sensor.
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GCSE Electronics.
Unit E1 : Discovering Electronics
Activity 4a: (For Alpha Kit Users):
The Pulse Generator (15) can also be considered as an input device. It can
provide square pulses whose period can be controlled using the variable
resistor.
a.
Connect up the following arrangement with the 4 mm socket in the
470nF line.
+
+
+
9 - 12V
AC/DC
Power Supply Regulator
_
_
Pulse
Generator
_
Transistor
Switch/Indicator
b.
Switch on the power supply and observe the light emitting diode [LED]
on the transistor switch/indicator unit. The LED comes on when the
Pulse Generator is sending out a high signal.
c.
Adjust the setting of the control knob on the Pulse Generator and note
the effect.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
12
Topic 1.2 – Electronic Sub-Systems.
Activity 4b: (For Control Studio Users:)
The Pulse unit can also be considered as an input device. It can provide square
pulses whose period can be controlled using the variable resistor.
a.
Insert the Pulse unit.
b.
Switch on the simulator, using the
button. The LED comes on when
the Pulse Unit is sending out a high signal.
c.
Adjust the setting of the control knob on the Pulse Unit and note the
effect.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
Save your circuit as “E1-Systems-Circuit3”
13
GCSE Electronics.
Unit E1 : Discovering Electronics
Summary of Activity 4:
Unit
Type
Pulse Generator
Unit
(13)
Action
Number of pulses per second
increases as rotary control is
turned clockwise
Digital
continuous pulses
Practical Work 1.2B: Investigating Output Drivers.
Activity 1a (For Alpha Kit Users):
a.
Set up the following arrangement. Switch on the supply voltage.
+
+
+
9 - 12V
AC/DC
Power Supply Regulator
_
_
Bulb Unit
_
b.
Connect a 4 mm test lead to the Signal In socket of the bulb unit. This
is the middle socket on the Alpha link.
c.
Connect the other end of the test lead to the positive (+) line of the
board (as shown by the solid line) and then to the negative (-) line (as
shown by the dotted line).
14
Topic 1.2 – Electronic Sub-Systems.
Activity 1b (For Control Studio Users):
a.
Set up the following arrangement. Switch on the simulator, using the
button.
b.
Adjust the variable control on the input voltage unit, to investigate what
voltage is required at the input to the bulb unit to make the bulb light
up.
Save your circuit as “E1-Systems-Circuit4”
Summary of Activity 1.
You should find that the function can be represented by the following
table.
Unit
Lamp Unit [30]
Type
Output
Action
Bulb lights up when signal into
board is LOW.
15
GCSE Electronics.
Unit E1 : Discovering Electronics
Activity 2:
Use whichever system you have to investigate the other output devices and
complete the table provided.
Unit
Type
Action
Bulb lights up when signal into
Lamp Unit [30]
Buzzer Unit [31]
Motor Unit [33]
Solenoid Unit [34]
Output
board is LOW.
Buzzer sounds when signal
into board is ………………
Motor turns up when signal
into board is ………………
Solenoid activated when
signal into board is ……………
We have now looked at a number of input and output units which are used to
change input conditions into an electrical form, or change an electrical form
into an output signal more suitable than an electrical voltage.
We are now in a position to change physical properties like light into
electrical signals for processing, and electrical signals into physical outputs
e.g. sound.
Later on in this topic we will look at the sub-systems needed to process the
electrical signals to make the system do what we need it to do. First however
we will look at a couple of basic system examples.
16
Topic 1.2 – Electronic Sub-Systems.
Practical Work 1.2C: Setting up simple sensing systems.
Note: The power supply and the power supply regulator will not be
shown on future block diagrams. They must however be included in
any real system. All simulated systems will automatically insert the
power supply but will not display it on screen. All exercises from
here on will only show the Control Studio Solutions however it is
possible to make all systems using Alpha / E&L etc.
Activity 1:
PROBLEM 1:
1a.
A system is required which activates a
buzzer when light falls on a sensor.
Select, from your list of equipment, the units that you require to make
up the system. Start with the Input Sensing Unit then the Output
Driver and finally the Processing Unit.
Fill in their titles in the boxes provided below. Show clearly which are
INPUT, PROCESSING and OUTPUT units.
A
B
17
GCSE Electronics.
Unit E1 : Discovering Electronics
1b.
Set up the system in the control studio simulator with the rotary
control knob on the light sensing unit about mid position. It should look
like this:
Move the slider from dark to light and back again.
Describe what you observe and comment upon the effect that adjusting
the control knob, on the sensing unit, has upon the performance of the
system.
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
Save your circuit as “E1-Systems-Circuit5”.
18
Topic 1.2 – Electronic Sub-Systems.
1c.
Now add two voltmeters to your circuit to measure the voltages at the
output of the light sensor and of the transducer driver board to enable
you to complete the following table. The circuit should look like this:
Voltage
Out of
Sensor Board
Out of
Transducer Driver
LDR setting = Dark
LDR setting = Light
Save your circuit as “E1-Systems-Circuit6”.
19
GCSE Electronics.
Unit E1 : Discovering Electronics
Activity 2:
PROBLEM 2:
A system is required which lights up a
bulb when it gets dark.
If you simply replace the buzzer with a bulb unit you will find that the system
does not meet the specification. Try this out.
2a.
An INVERTER is required at some point within the system. Complete
the following diagram showing a suitable system.
N.B. The Inverter cannot drive the Bulb Unit.
Show clearly the input, processing and output sections.
A
2b.
B
C
Set up the system and describe its action.
...................................................................................................................
...................................................................................................................
20
Topic 1.2 – Electronic Sub-Systems.
Complete the following table:
A
Voltage
B
C
LDR Covered
LDR Uncovered
Save your circuit as “E1-Systems-Circuit7”.
2c.
It is possible to make the system work in this way without using an
Inverting Unit. A careful study of the <Insert> - <Input> option will
probably give the game away.
If you are certain of what to do try it out and explain what you did.
If you are not sure, consult your tutor.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
Another application for this type of circuit would be to control entry
into a dark room. The bulb could be a warning light outside the door.
When the lights are off in the room the bulb would serve as a warning
for people not to enter.
21
GCSE Electronics.
Unit E1 : Discovering Electronics
Now it’s your turn - Try to design a control system to satisfy the following
problem situations.
PROBLEM 3:
A system is required which switches on a motor on a heater
fan when the temperature falls below body temperature.
PROBLEM 4:
A system is required which sounds a buzzer when a magnet
passes a point.
PROBLEM 5:
A system is required which switches on a lamp when it rains.
In each case you should:
(a) decide upon which Input Units are required.
(b) decide which Processing Units are required.
(c) decide upon which Output Units are required.
(d) draw a block diagram of the system.
(e) set up the system and try it out.
(f) make changes, if required, and draw a block diagram for your final
design.
22
Topic 1.2 – Electronic Sub-Systems.
PROBLEM 3 - Solution.
(a)
Input Sensing Unit
-
...........................................................................
(b)
Processing Units
-
...........................................................................
(c)
Output Unit
-
...........................................................................
(d)
Block diagram.
(e)
Test report.
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
(f)
Modifications. [Describe the modifications needed - if required]
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
Save your final circuit as “E1-Systems-Circuit8”.
23
GCSE Electronics.
Unit E1 : Discovering Electronics
PROBLEM 4 - Solution.
(a)
Input Sensing Unit
-
...........................................................................
(b)
Processing Units
-
...........................................................................
(c)
Output Unit
-
...........................................................................
(d)
Block diagram.
(e)
Test report.
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
(f)
Modifications. [Describe the modifications needed - if required]
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
Save your final circuit as “E1-Systems-Circuit9”.
24
Topic 1.2 – Electronic Sub-Systems.
PROBLEM 5 - Solution.
(a)
Input Sensing Unit
-
...........................................................................
(b)
Processing Units
-
...........................................................................
(c)
Output Unit
-
...........................................................................
(d)
Block diagram.
(e)
Test report.
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
(f)
Modifications. [Describe the modifications needed - if required]
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
Save your final circuit as “E1-Systems-Circuit10”.
25
GCSE Electronics.
Unit E1 : Discovering Electronics
Homework Questions 1.
1.
Describe what you understand by the term ‘Analogue Sensor’.
........................................................................................................................................
2.
........................................................................................................................................
[1]
Describe what you understand by the term ‘Digital Sensor’.
........................................................................................................................................
3.
........................................................................................................................................
[1]
The following is a list of input sensors you have investigated in your
practical work.
Light Sensing Unit, Switch Unit, Temperature Sensing Unit, Input
Voltage Unit, Magnetic Switch Unit, Rain Sensor.
a)
b)
26
From the list select two that are digital type input units.
i)
.............................................................................
ii)
.............................................................................
From the list select two that are analogue type input units.
i)
.............................................................................
ii)
.............................................................................
[2]
[2]
Topic 1.2 – Electronic Sub-Systems.
c)
Name an output unit that could be used to convert electrical
energy into sound.
.............................................................................
4.
[1]
Give a brief description of the function of the following input and
output units.
a)
Light Sensing Unit.
....................................................................................
..............................................................................................................................
..............................................................................................................................
[2]
b)
Lamp Unit. .........................................................................................................
..............................................................................................................................
..............................................................................................................................
[2]
c)
Temperature Sensing Unit. ..........................................................................
..............................................................................................................................
d)
..............................................................................................................................
[2]
Magnetic Switch / Reed Unit.
...............................................................
..............................................................................................................................
..............................................................................................................................
[2]
27
GCSE Electronics.
Unit E1 : Discovering Electronics
Signal Processing Units
Once the input signals have been converted into an electrical form, by the
Input Sensing Units, it is possible to use electronic subsystems to process
the signals. The processed signal is then used to control Output devices.
The Processing Units available in each system can be divided up into three
groups.



Drivers (Transducer Drivers/ Transistor Switch.)
Logic Units.
Comparator Units.
A brief description of the function of the signal processing units is provided
with these notes. You will learn a lot more about them as you complete the
next five assignments.
Drivers
The voltage signal coming out of most of the boards is incapable of providing
enough current to drive output devices such as the motor unit.
The Transducer Driver and Transistor Switch units act as a switching
buffer between the processing boards and the output units. The transistor
switch unit can only switch on an output device which requires a small current.
e.g, buzzer, lamp, or motor. The solenoid requires a much larger current and
therefore a transducer driver must be used as this is capable of supplying
several amps to the output device if required.
You will discover that both the output driving units have an inverting action
i.e. if the voltage signal going into the board is HIGH, the signal coming out of
the board is LOW.
28
Topic 1.2 – Electronic Sub-Systems.
A driver must be connected between the signal coming out of
the processing section and the output unit.
Input
Signal
Input
Sensor
Signal
Processing
Output
Driver
Output
Device
Output
Signal
In most cases the Transistor Switch Unit provides a cheaper alternative for
the Transducer Driver Unit.
Logic Units
These units can be regarded as decision making units within electronic
systems. They are digital processing units.
Digital devices are designed to operate on two voltage levels only. These are
referred to as LOW and HIGH.
Signal Level
High
Low
If the voltage level is near to 0V (sometimes referred to as the 0V
rail) it is called logic level 0.
If the voltage level is near to the maximum positive supply (sometimes
referred to the positive rail) it is called logic level 1.
29
GCSE Electronics.
Unit E1 : Discovering Electronics
The integrated circuit (IC) packages
used in these systems are
Complementary Metal Oxide
Semiconductor (CMOS) types. They
will operate on any voltage between +3
volt and +18 volts. Logic level 0 is any
voltage less than 0.3 of the supply
voltage while logic level 1 is a voltage
greater than 0.7 of the supply
voltage. CMOS IC’s are available in
the 4000 series. The first number will
be a '4' e.g. 4011.
Logic Level 1
V
s
0.7Vs
0.3Vs
Logic Level 0
0V
CMOS Logic Levels
Voltages between the logic level bands should be avoided if possible. They
cannot be identified by the IC’s.
Many types of logic gate are available but we concentrate on the following
three types of logic gates. They are:
AND, OR, NOT gate (inverter)
The voltage signal out of a gate depends upon the logic level of signals into
the gate. It will be near 0V or very near the positive supply voltage. The
gates provided in your kit have two points where signals can enter the gates.
These are usually referred to as A and B. The function of each gate is
described in the following table.
30
Topic 1.2 – Electronic Sub-Systems.
Unit
Function
AND gate
Signal out of a gate of
logic level 1 if signals at
A AND B are 1's.
OR gate
Signal out of a gate of
logic level 1 if signal at
A OR B is 1.
NOT gate
(Inverter)
Signal out is NOT a 1
(i.e. 0) if the signal in is
a 1, and vice versa.
Symbol
A
Q
B
A
B
A
Q
Q
In the following assignments you will be asked several design problems which
can be carried out either on Alpha / E&L or Control Studio which will enhance
your understanding of the units and how they can be used to form simple
systems.
If you are using a simulator and you have time you might want to try and build
them using the real boards.
COMPLETE ASSIGNMENTS:
1.2D, 1.2E, & 1.2F
31
GCSE Electronics.
Unit E1 : Discovering Electronics
Practical Work 1.2D: Investigating the use of logic gates in systems.
INFORMATION:
Logic gates are used when decisions have to be made by the system. The
output device becomes operative when certain input signal conditions
are met e.g. a motor only comes on when two input switches are pressed.
Activity 1:
1a.
Set up the following system.
The signal from the switch units change from 0 V (low) to + 5 V (high) when the
A
B
1b.
Use your system to enable you to complete the following table.
Is Switch B
Pressed ?
No
No
Yes
Yes
32
Is Switch A
Pressed ?
No
Yes
No
Yes
Is the Output
Indicator On ?
Topic 1.2 – Electronic Sub-Systems.
Complete the following sentence:
The indicator is ON if switch A .........................................
are pressed.
For convenience we can use the following convention to indicate the state of
the signals.
SIGNAL IN
If a switch is not pressed, the signal coming out is at 0V and
its logic state is represented by a 0.
If a switch is pressed, the signal coming out is at +5V and
its logic state is represented by a 1.
SIGNAL OUT
If the indicator is OFF the signal coming out of the gate is
at 0V and its logic state is represented by 0.
If the indicator is ON the signal coming out of the gate is
at +5V and its logic state is represented by 1.
1c.
Complete the following table for the AND gate, using the convention
above. The table will show the state of the signal coming out of the gate
for all possible setting of the input switches.
Switch B
0
0
1
1
Switch A
0
1
0
1
Signal Out (Q)
33
GCSE Electronics.
Unit E1 : Discovering Electronics
Such a table is called a truth table for the gate
The signal coming out of the gate is a 1 if A AND B are 1s.
The symbol for an AND gate is shown below.
A
Q
B
Save your final circuit as “E1-Systems-Circuit 11”.
Activity 2.
2a.
Replace the AND gate with an OR gate and complete the truth
table for an OR gate.
Switch B
0
0
1
1
Switch A
0
1
0
1
Signal Out (Q)
Complete the following for an OR gate:
The signal out of the gate is a 1 if ____________________________
are 1.
The symbol used for an OR gate is shown below.
A
B
Q
Save your final circuit as “E1-Systems-Circuit12”
34
Topic 1.2 – Electronic Sub-Systems.
2b.
Replace the OR gate by a NOT gate and complete the following table.
(Note : only one switch is required)
Switch A
0
1
Signal Out (Q)
Complete the following:
The signal out of the gate is NOT 1 if .......................................................
The symbol for a NOT gate is shown below.
A
Q
Save your final circuit as “E1-Systems-Circuit13”.
35
GCSE Electronics.
Unit E1 : Discovering Electronics
Design Problem 1.
A family, living out in the country, require a system that brings on an
outside light when it gets dark. In order to test the lamp they would
like a press switch fitted into the system which can also be used to
switch on the lamp.
Which units are required as input sensors to the system ?
[a]
...............................................................................................
[b]
...............................................................................................
Which unit is required for the output unit ? ................................
The processing section has to light up the lamp when it gets dark OR if
the switch is pressed.
Which units are required for the processing section ?
[a]
...............................................................................................
[b]
...............................................................................................
The following block diagram suggests a possible layout for the system.
Label the blocks.
36
Topic 1.2 – Electronic Sub-Systems.
Set up the system and try it out. Report on your findings.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
Save your final circuit as “E1-Systems-Circuit14”.
Design Problem 2
A system is required to switch on a warning light that can be placed on a
rubbish skip to warn passing cars so that there isn’t an accident. The
lamp should flash when it gets dark.
Follow the design procedure suggested in previous Assignment.
Units required : .......................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
Block diagram.
37
GCSE Electronics.
Unit E1 : Discovering Electronics
Set up the system and try it out. Report on your findings.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
Save your final circuit as “E1-Systems-Circuit15”.
Design Problem 3
Modify the previous design problem, so that the system includes a switch
which enables workmen to check the flashing system before they go home.
HINT: You will need two different types logic gates.
Follow the design procedure suggested in previous Assignment.
Units required : .......................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
Block diagram.
38
Topic 1.2 – Electronic Sub-Systems.
Set up the system and try it out. Report on your findings.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
Save your final circuit as “E1-Systems-Circuit16”.
Other useful units
Two other very useful units that are often used in electronic circuits are the
Latch unit and the Delay Unit.
The Latch Unit.
The latch unit is used when you want to keep a signal on indefinitely until a
reset button or signal is applied. For example you may have a temperature
monitor on a freezer in a holiday caravan. If the power fails and the contents
of the freezer defrost before the power is restored, a light could be
triggered to indicate that the food has defrosted and should be thrown out.
The system can then be reset when the freezer has been restocked.
Unit
Type
Action
Output stays on indefinitely in
response to a trigger pulse.
Latch Unit
Digital
Input
Output
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GCSE Electronics.
Unit E1 : Discovering Electronics
The Delay Unit.
The Delay unit, as its name suggests introduces a delay into the signal, which
is of a predetermined duration. At the end of the set time the signal returns
to its original state automatically. e.g. an external security light, triggered by
the movement of an object, stays on for a couple of minutes before being
switched off.
Unit
Type
Action
Output is delayed by a fixed
period before going high in
response to a trigger pulse.
Delay Unit
Digital
Input
Delay
40
Output
Topic 1.2 – Electronic Sub-Systems.
Practical Work 1.2E : Investigating the Latch Unit and Delay Unit
Activity 1:
1a.
Set up the following system which is to serve as a burglar alarm. The
buzzer sounds if the burglar cuts a light beam.
1b.
Check that the system works. Note the effect of adjusting the rotary
control on the Light Sensing Unit.
...................................................................................................................................
Save your final circuit as “E1-Systems-Circuit17”.
The system has two weak points.
(i)
The burglar would see the light beam and avoid it. This could be
overcome by using an infrared source and detector.
41
GCSE Electronics.
Unit E1 : Discovering Electronics
What is the second weak point ?
(ii)
.........................................................................................................
........................................................................................................
Activity 2:
2a.
Set up the following system which should improve the previous
arrangement.
2b.
Press the RESET button (red button) on the Latch Unit then try cutting
the light beam. Describe what happens now.
.......................................................................................................................................
.......................................................................................................................................
.......................................................................................................................................
42
Topic 1.2 – Electronic Sub-Systems.
2c.
Add a switch unit to the system and link its output to the reset pin on
the Latch. Try resetting the system by using the extra switch.
Which logic level is required to reset the system ?
......................................................................................................................................
Remember this, it will prove useful later on in this assignment.
Save your final circuit as “E1-Systems-Circuit18”.
Design Problem 4
A system is required to sound an alarm if your cat has gone out and
switches it off when it returns. The cat enters and leaves the house through
a cat flap.
N.B. It must only work for your cat.
HINT: Your cat could carry something.
Units required : .......................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
Block diagram.
43
GCSE Electronics.
Unit E1 : Discovering Electronics
Set up the system and try it out. Report on your findings.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
Activity 3:
Save your final circuit as “E1-Systems-Circuit19”.
3a.
Set up the following system.
3b.
Set the control knob on the Delay Unit so that points vertically upwards.
3c.
Momentarily press the Debounced Switch and note what happens.
You should find that the lamp comes on for a short period of time.
Estimate this time period. ....................................
44
Topic 1.2 – Electronic Sub-Systems.
3d.
Set the control knob on the Delay Unit fully clockwise and estimate the
time for which the lamp remains on.
..................................................................
Save your final circuit as “E1-Systems-Circuit20”.
Activity 4 :
In Activity 2 you improved the burglar alarm from Activity 1 by using a latch.
It is possible to use a delay instead of the latch, to provide an alternative
solution to the alarm problem.
45
GCSE Electronics.
Unit E1 : Discovering Electronics
What is the disadvantage of using a delay unit in the alarm ? ...............................
..................................................................................................................................................
What is the advantage of using a delay unit in the alarm ? .....................................
..................................................................................................................................................
Save your final circuit as “E1-Systems-Circuit21”.
Design Problem 5.
A system is required which brings on a light when someone starts
walking down a corridor and switches off after about 6 seconds.
Units required : .......................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
Block diagram.
Set up the system and try it out. Report on your findings.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
Save your final circuit as “E1-Systems-Circuit22”.
46
Topic 1.2 – Electronic Sub-Systems.
Practical Work 1.2F : Investigating the use of a comparator in systems.
INFORMATION:
In this assignment we shall use a comparator to increase the sensitivity
of a system.
Activity 1:
1a.
Set up the following system.
1b.
Adjust the controls so that they are in a similar position to those shown
above. When set correctly the motor should be off.
Increase the sound input slightly - Describe what happens.
.......................................................................................................................................
.......................................................................................................................................
47
GCSE Electronics.
Unit E1 : Discovering Electronics
Decrease the sound input slightly - Describe what happens.
......................................................................................................................................
......................................................................................................................................
What is being compared ?
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
This system is very sensitive, only slight changes in noise will affect the
output. The comparator is used in situations where input voltages
change very little, and it is necessary to actually catch those changes.
Save your final circuit as “E1-Systems-Circuit23”.
48
Topic 1.2 – Electronic Sub-Systems.
Homework Questions 2.
Answer all questions in the spaces provided, continue on a separate piece of
paper if required.
1.
Describe the role of the Transducer Driver, or Transistor Switch as an
output unit ?
........................................................................................................................................
........................................................................................................................................
2.
........................................................................................................................................
[1]
Complete the following truth tables for the logic gates given that the
input signals are ‘A’ and ‘B’ and that the output is ‘Q’.
a)
b)
OR Gate.
A
B
0
0
1
1
0
1
0
1
Q
[2]
AND Gate.
A
B
0
0
1
1
0
1
0
1
Q
[2]
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GCSE Electronics.
Unit E1 : Discovering Electronics
3.
Describe the function of the NOT gate.
........................................................................................................................................
........................................................................................................................................
4.
........................................................................................................................................
[1]
Describe the function of a Voltage Comparator.
........................................................................................................................................
........................................................................................................................................
5.
........................................................................................................................................
[1]
Describe the function of the Pulse Generator.
........................................................................................................................................
........................................................................................................................................
6.
........................................................................................................................................
[1]
Describe the function of the Latch unit.
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
[1]
50
Topic 1.2 – Electronic Sub-Systems.
7.
Describe the function of the Delay unit.
........................................................................................................................................
........................................................................................................................................
8.
........................................................................................................................................
[1]
The following diagram shows a system that sounds a buzzer if it rains
during daylight.
A
C
Transducer
Driver
Buzzer
Unit
B
a)
b)
c)
Clearly indicate on the diagram the input, processing and output
sections of the system.
Name the units you would use for A, B and C.
i)
A
=
...............................................................
ii)
B
=
...............................................................
iii)
C
=
...............................................................
Give a practical application for this system.
[3]
[3]
..............................................................................................................................
[1]
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GCSE Electronics.
Unit E1 : Discovering Electronics
9.
You are provided with the following functional blocks.
Light Sensing Unit, Debounced Switch Unit, Temperature Sensing Unit,
OR gate, AND gate, Pulse Generator Unit, Rain Sensor, Buzzer Unit,
Lamp Unit, Transducer Driver.
a)
b)
Draw a block diagram showing how you would make a system that
produces bleeps of sound if a door is opened.
[3]
Draw another block diagram showing how you would modify this
system so that the bleeps were produced if a door was opened or a
light beam was broken.
[2]
52
Topic 1.2 – Electronic Sub-Systems.
c)
i)
This system could be used for a burglar alarm, what extra
unit would you need to ensure that the alarm stayed on once
activated even if the burglar shut the doors after him ?
.............................................................................
ii)
[1]
Where would you connect this extra unit ?
.........................................................................................................................
.........................................................................................................................
[1]
iii)
Redraw the modified circuit with this extra unit in place.
[1]
53
GCSE Electronics.
Unit E1 : Discovering Electronics
10.
A market gardener wishes to install a system in her greenhouse that will
open the ventilation grills automatically when the temperature of the air
reaches a predetermined value. There must also be a manual override to
the system.
a)
Select electronic subsystems from the list below and design a
solution to the market gardeners problem. Draw your solution as a
block diagram in the space below. (You do not have to use all of the
subsystems in the list)
Light Sensing Unit, Debounced Switch Unit, Temperature Sensing Unit,
OR gate, AND gate, Pulse Generator Unit, Rain Sensor, Buzzer Unit,
Lamp Unit, Transducer Driver, Inverter, Motor, Solenoid, Latch.
b)
[3]
Redesign the system so that the ventilation grill will only operate
in daylight.
[3]
54
Topic 1.2 – Electronic Sub-Systems.
11.
A control system is required to run an industrial boiler, it has the
following specification. A motor supplies oil to the boiler. If the boiler
overheats or produces too much smoke it is to be cut off and an alarm
sounded.
a)
Design a control system, using any of the following systems blocks.
Light Sensing Unit, Debounced Switch Unit, Temperature Sensing Unit,
OR gate, AND gate, Pulse Generator Unit, Rain Sensor, Buzzer Unit,
Lamp Unit, Transducer Driver, Inverter, Motor, Solenoid, Latch.
[7]
55
GCSE Electronics.
Unit E1 : Discovering Electronics
b)
Having built the system it is found that with the boiler at normal
temperature and no smoke being produced the pump does not run.
However if the light sensor is covered the pump does run.
i)
Suggest a reason for this.
.........................................................................................................................
[1]
ii)
There are two possible ways this could be overcome, suggest
what these may be.
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
c)
.........................................................................................................................
[2]
Name an input sensor and an output unit that you might find on a
record player.
Input Sensor
=
..........................................................................
Output Unit
=
..........................................................................
[2]
56
Topic 1.2 – Electronic Sub-Systems.
Solutions to Homework Questions.
Solutions to Homework Questions 1:
1.
An analogue sensor is one which can provide as its output, a voltage
signal which can have a value anywhere between 0V and the maximum
voltage of the power supply. The output tends to change slowly with
time.
2.
A digital sensor is one which can provide as its output, a voltage signal
which can have only two values 0V and the maximum voltage of the
power supply. The output tends to change rapidly with time.
3.
a)
Any two from Switch Unit, Magnetic Switch Unit, Rain Sensor.
b)
Any two from Light Sensing Unit, Temperature Sensing Unit, Input
Voltage Unit.
c)
Buzzer Unit.
a)
The light sensing unit, uses light as its input and produces at its
output a changing voltage signal which represents the amount of
light shining onto the sensor. The unit is analogue and changes
tend to take place slowly as the light intensity changes.
b)
The lamp unit is an output device which takes an electrical signal
and converts it into a visible indicator, that the electrical signal is
present.
c)
The temperature sensing unit uses temperature as its input and
produces at its output a changing voltage signal which represents
the temperature of the sensor. The unit is analogue and changes in
output voltage tend to occur slowly as the temperature of the
sensor varies.
4.
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GCSE Electronics.
Unit E1 : Discovering Electronics
d)
The magnetic switch / reed unit is a digital input sensor which is a
switch operated by a magnet. When the magnet is close to the
switch the contacts close and complete the circuit. When no
magnet is present the switch contacts are open.
Solutions to Homework Questions 2:
1.
The transducer driver or transistor switch is needed as an output
device in order to boost the current available from the processing
sections of electronic subsystems to drive high current loads like
motors and solenoids.
2.
a)
b)
3.
58
OR Gate.
A
B
Q
0
0
1
1
0
1
0
1
0
1
1
1
A
B
Q
0
0
1
1
0
1
0
1
0
0
0
1
AND Gate.
The NOT gate or inverter, has just one input and one output. Its
function is to invert or reverse the voltage level of the signal coming in
to the gate. In other words if a logic ‘0’ is present at the input a logic ‘1’
will be present at the output. If a logic ‘1’ is present at the input then a
logic ‘0’ will be present at the output.
Topic 1.2 – Electronic Sub-Systems.
4.
The voltage comparator, compares two voltages and gives an output of
full supply voltage when the input signal is bigger than the reference
signal, and an output of 0V when the input voltage is smaller than the
reference voltage.
5.
The pulse generator unit gives and output which is constantly changing
from 0 to maximum supply voltage and back to 0V without any input
being present. It is used mainly to drive counter units and provide a
signal capable of making a lamp flash on and off.
6.
The Latch unit is very much like a memory unit. It will remember an
event taking place, even if the event lasts only for a few tenths of a
second. The unit will remain in its ‘on’ state until it is manually reset, or
is reset by another electrical system. Its main use in applications like
burglar alarms etc.
7.
The delay unit as its name implies, delays an electrical signal for a fixed
length of time. In other words short events can be made longer for
example, an outside light which can be switched on as you leave the
house and it will remain on for long enough for you to lock the door
before going off by itself.
8.
A
C
Transducer
Driver
Buzzer
Unit
B
a)
INPUT
|
PROCESSING
|
OUTPUT
59
GCSE Electronics.
Unit E1 : Discovering Electronics
b)
c)
9.
i)
A
=
ii)
B
=
Rain Sensor or Light sensor
&
&
Light Sensor or Rain Sensor
iii)
C
=
AND Gate
Warn someone who has washing on the line that it is raining.
a)
Debounced
Switch
AND
Gate
Transducer
Driver
Buzzer
Unit
Pulse
Generator
b)
Light
Sensor
OR
Gate
Debounced
Switch
AND
Gate
Pulse
Generator
60
Transducer
Driver
Buzzer
Unit
Topic 1.2 – Electronic Sub-Systems.
c)
10.
i)
Latch unit
ii)
The latch would have to be connected between the output of
the OR gate and the input to the AND gate so that once the
light sensor output goes high or the door was opened the
signal from the gate would be latched on, keeping the input to
the AND gate high, and hence letting the pulse generator
signal pass through to the buzzer and therefore keep the
buzzer going until the latch was reset.
a)
Debounced
Switch
OR
Transducer
Gate
Driver
Motor
Temperature
Sensor
b)
Light
Sensor
AND
Gate
Temperature
OR
Sensor
Gate
Transducer
Driver
Motor
Debounced
Switch
61
GCSE Electronics.
Unit E1 : Discovering Electronics
11.
a)
Light
Sensor
Inverter
Transducer
Driver
Motor
Transducer
Driver
Buzzer
OR
Gate
Temperature
Sensor
b)
c)
i)
The light sensor is providing the inverse logic output to that
required. e.g.. ‘0’ instead of ‘1’.
ii)
1.
2.
Turn light sensor board around.
Add and inverter after the light sensor but before the
input to the OR gate.
Input Sensor
=
Needle / Stylus
Output Unit
=
Loudspeaker / Earphones
Now its time to look at some exam questions.
62
Topic 1.2 – Electronic Sub-Systems.
Examination Style Questions:
1.
Here is a list of electronic sub-systems:
latch
motor
light sensor
tilt-switch
Add the correct sub-system to complete the following statements.
(a)
A ................................ is an analogue input sub-system;
(b)
A ................................ is a processing sub-system;
(c)
A ................................ is an output sub-system.
[3]
2.
There are three types of electronic subsystem, known as Input, Process and Output.
Here are three subsystems:
Subsystem
Type (Input, Process, or Output)
Lamp unit
Light Sensing Unit
Comparator
For each one, decide which type it is.
Add the word Input, Process or Output to show what you have decided.
3.
[3]
Here is a system to warn someone that it is raining.
X
Y
Z
(a)
Which one of the following is the best sub-system to use as block X ?
A.
Light sensing unit
B.
Temperature sensing unit
C.
Moisture sensing unit
D.
Pressure sensing unit
Answer = ……….
(b)
Which one of the following is the best sub-system to use as block Y ?
A.
NOR gate
B.
Counter
C.
Time delay
D.
Transistor switch / transducer driver
Answer = ……….
[1]
[1]
(c)
Name a suitable sub-system for block Z
………………..
[1]
63
GCSE Electronics.
Unit E1 : Discovering Electronics
4.
Here is the block diagram for a bicycle theft alarm.
The owner ‘arms’ the alarm by turning a key operated rotary switch.
When someone moves the bicycle, a tilt switch activates the alarm.
A
C
D
E
B
The following sub-systems are available to be used in this bicycle alarm.
Transducer driver
Rotary switch
AND gate
Tilt Switch
Buzzer
Which subsystem will be used for:
(a)
block A;
........................................................................
(b)
block B;
........................................................................
(c)
block C;
........................................................................
(d)
block D;
........................................................................
(e)
block E?
........................................................................
[4]
64
Topic 1.2 – Electronic Sub-Systems.
5.
Here is the block diagram for an electronic alarm system:
(a)
(b)
How many process sub-systems are there in this system ? .............................
[1]
What job does the latch do in this system ?
.............................................................................................................................
.............................................................................................................................
[1]
(c)
What job does the transducer driver do in this system?
.............................................................................................................................
6.
.............................................................................................................................
[1]
Here is the block diagram for an egg incubator alarm.
A buzzer should pulse on and off when the incubator gets too cold.
The following list gives the subsystems which may be used.
Push Switch
Transducer Driver
Light Sensing Unit
OR Gate
AND Gate
Temperature Sensing Unit
Pulse Generator
Buzzer
Complete the block diagram for the incubator alarm.
[5]
65
GCSE Electronics.
Unit E1 : Discovering Electronics
7.
Here is part of a block diagram for a house alarm.
The owner sets the alarm by turning a key operated switch.
When someone then opens a window, a micro-switch operates and the alarm sounds.
Block A
Block B
Block C
Buzzer
Microswitch
(a)
The following sub-systems are used in this alarm:
Key switch
Transducer driver
AND gate
Micro-switch
Buzzer
Which sub-system will be used for :
(b)
(i)
block A?
....................................
(ii)
block B?
....................................
(iii)
block C?
....................................
[3]
It would be a better system if the alarm stayed on once a door or window was
opened.
(i)
What type of sub-system could be added to keep the alarm ON once it
sounds?
Answer : ..........................................
[1]
(ii)
Mark an “X” on the above diagram to show where this extra subsystem should be fitted.
[1]
66
Topic 1.2 – Electronic Sub-Systems.
8.
A burglar alarm is needed for a shop. An output should switch on and off
continuously when the front door is opened.
An incomplete diagram is shown below:
Select 5 suitable subsystems from the following list to complete the block diagram.
[5]
Micro-switch
Buzzer
Light Sensing Unit
Temperature Sensing Unit
Transducer Driver
OR gate
AND gate
Pulse Generator
9.
The block diagram shows a design for a house alarm.
The alarm is set if someone opens a door.
(a)
Name a suitable input sub-system?
........................................................
[1]
(b)
What job does the latch do in this system ?
.............................................................................................................................
(c)
.............................................................................................................................
[1]
What job does the transducer driver do in this system?
.............................................................................................................................
.............................................................................................................................
[1]
67
GCSE Electronics.
Unit E1 : Discovering Electronics
10.
An intruder alarm is required for a bed-room.
The following sub-systems are available.
Not all of them will be needed.
AND gate
transducer driver
buzzer
(a)
OR gate
comparator
inverter
micro-switch
light sensor
Choose from this list:

A processing subsystem which gives a high output only if both of its
inputs are high is ..................................................

An analogue input sub-system. .....................................................
[2]
(b)
The block diagram shows a possible design.
The alarm is set be turning a key-operated switch.
If someone opens the door, a micro-switch operates and the buzzer sounds.
Block A
Block B
Block C
Buzzer
Key
Switch
Choose from the list at the top of the page a subsystem to use as :
 Block A ..........................................................
 Block B ..........................................................
 Block C ..........................................................
[3]
68
Topic 1.2 – Electronic Sub-Systems.
(c)
This system has a major design fault.
(i)
Identify this fault.
............................................................................................................................
[1]
(ii) Name an additional subsystem which is needed to correct this fault.
............................................................................................................................
[1]
(iii) Put an “X” on the diagram opposite to show where you would place
this sub-system.
[1]
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GCSE Electronics.
Unit E1 : Discovering Electronics
Self Evaluation Review
Learning Objectives
My personal review of these objectives:



Use the following sub-systems as
part of a block diagram;
Input units: light, temperature,
rotation, magnetic, moisture,
sound, pressure pad/switch, and
pulse generator.
Output devices: lamp, buzzer,
motor, solenoid, and LED.
Signal processing: inverter, AND
gate, OR gate, latch, time delay
and comparator.
State the function of a transducer
driver.
describe possible applications of an
electronic system from a block
diagram;
produce a block diagram for a
system to solve a given problem;
design and test electronic systems.
Targets:
1.
………………………………………………………………………………………………………………
………………………………………………………………………………………………………………
2.
………………………………………………………………………………………………………………
………………………………………………………………………………………………………………
70