Revised Standard Grade Technological Studies
Applied Electronics
Contents
Introduction
Structure
Resources
Assessment
Detailed resource list
Component Electronic Systems
Electricity
Simple Circuits
Integrated Circuits: 555 timer
Modular Electronic Systems
Introduction: Electronics – a systematic approach
Modular boards
Analogue and digital signals
Problem solving in electronics
Switches
Truth tables
The comparator
NAND and NOR gate boards
Logic in Electronics
Switching logic
Binary numbers
Combinational logic
Pin-out diagrams
Practical tasks
Electronics Mini-Project
Introduction
Application of Technology
Example: Remote Controlled Buggy with Light and Sound
Computer simulation
Appendix 1: Infrared Remote Control
Remote controlled toy
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Standard Grade Technological Studies: Applied Electronics
Introduction
Electronics is a key influence in today’s society and is therefore a key area of study in
Technological Studies. This component unit should be studied early in the course after
pupils have some knowledge of systems.
Structure
This unit is split into three distinct sections:
 Component Electronic Systems
 Modular Electronic Systems
 Logic in Electronics.
These sections can be delivered in any order, with each approach having its own
advantages and disadvantages. Obviously there is some overlap between the units. For
example, logic appears in the Modular Systems section in the form of the inverter, the
OR, AND, NAND and NOR gates and as subsystem boards. Similarly, if the Modular
Systems section is delivered first then some areas of Component Systems are
mentioned.
The advantage of delivering the Modular Systems first is that it gives an easy
introduction to electronics; however, there is a danger that pupils will work through
this section and solve the problems without picking up a real understanding of
electronics.
Logic Systems naturally follows on from the Modular Systems section.
The advantage of delivering the Component Systems first is that the pupils gain a firm
understanding of electronics, components and circuits. This gives them a deeper
understanding, which helps in the subsequent sections. The disadvantage is that pupils
may find the theory contained in this section difficult early in the course, although as
they are General/Credit pupils the level should be well within their ability.
By delivering the Component Systems first, pupils will cover the use of multimeters
and prototype circuit boards that are used in the other sections.
If the Component Systems section is to be delivered last, then it will be necessary to
give the pupils some instruction in the use of multimeters, prototype circuit boards,
simple electronic theory and components.
The contents of this unit are set out comprehensively so that teachers do not require
the use of additional notes or textbooks. Pupils can move at their own pace in many
areas, but it must be stressed that these unit notes should not be used as an open
learning pack and it will be necessary to deliver many important lessons at crucial
times. These include an introduction to electrical theory (Ohm’s law, Kirchoff’s
second law, etc.), series circuits, parallel circuits, and an introduction to components
(recognition, use and characteristics).
Standard Grade Technological Studies: Applied Electronics
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Resources
The resources required to run this unit are the same as those being used in
Technological Studies at present. Some equipment may differ in type (for example
different meters, prototype boards and modular systems) and therefore the notes
provided will have to be interpreted differently.
The main resources are:
 a range of components
 prototype circuit boards (often referred to as breadboards)
 digital non-auto ranging multimeters
 a modular electronic system (for example E&L boards)
 circuit simulation software (for example, Crocodile Clips).
Circuit simulation software can be used for many of the activities but pupils must also
have experience of building physical circuits. This is necessary to experience the real
components as well as the problem-solving attached to building real circuits.
Teachers are encouraged to use other resources such as video and the interactive CDROMs that are available. Software that simulates Modular Systems is also available
and could be used to aid classroom management problems that arise from faulty
boards. A detailed list of resources is provided at the end of this introductory section.
Assessment
External
This unit of work and the exercises within will prepare the pupils for any electronics
questions that appear in the 90-minute exam at the end of the course. It will enable all
pupils to gain the knowledge and understanding required and give them suitable
practice in reasoning and numerical analysis.
Internal
The internal assessment of this unit requires pupils to carry out a structured
assignment. The assignment should take approximately three hours to complete but in
some circumstances this can be extended.
The pupils will be expected to:
 complete a specification from a given brief
 create appropriate diagrams to illustrate the problem parameters
 produce a graphical representation of a proposed solution
 perform a computer simulation of the proposed solution
 build and test the proposed solution
 evaluate the solution against the original specification.
It must be stressed that this is not like the existing main project report.
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Standard Grade Technological Studies: Applied Electronics
Example
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 that drives the pump motor constantly except when it is hot during
the day.
For this assessment problem, pupils would be expected to produce:
 a limited specification from the information in the brief
 a system diagram illustrating the parameters
 diagram(s) showing a proposed solution using modular boards or a discrete
component circuit
 a parts/component list from classroom resources
 a computer simulation using Crocodile Clips or other suitable simulation software
 a physical solution to the problem
 a small written evaluation comparing the performance of the solution to the
specification.
Further information on the internal assessment can be found in Appendix 1 of the
Arrangement Documents: Guidelines for Internal Assessment.
Standard Grade Technological Studies: Applied Electronics
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Detailed resource list
Relay
 Miniature 5 V DPDT (RS 376-981)
Component electronics systems
Low voltage power supply
Integrated circuit
 555 timer IC
Prototype circuit boards
Digital multimeter (non-auto-ranging)
Resistors
 100 R
 220 R
 270 R
 390 R
 1K
 Light-dependent (LDR) ORP 12
 Thermistor: ntc (RS 256-102)
Computer simulation software
 Crocodile Clips
Modular electronic systems
Modular circuit board systems
 E&L, or
 Alpha systems
Simulation software
 Control Studio
Potentiometers
 10 K (RS 375-304)
 100 K (RS 375-332)
Logic in electronics
Transistors
 BC 108
Modular circuit board system
 E&L, or
 Alpha systems
Diodes
 Light-emitting 5mm red
 1N4001 (RS 261-148)
Computer simulation software
 Crocodile Clips
Capacitors
 100 F electrolytic
 1 F bead
Low-voltage power supply
Switches
 Miniature push (RS 331-758)
 Miniature slide (RS 339-673)
Prototype circuit board
Logic probe
Lamp
 Holder (RS 564-891)
 MES lamp 6 V (RS 586-172)
 MES lamp 12 V (RS 586-201)
Buzzer
 Piezo flying lead (RS 203-0233)
Motor
 36 volt miniature
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Resistors
 220 R
Diodes
 Light-emitting 5 mm red
Integrated circuits (TTL)
 7400
 7408
 7432
 7404
Standard Grade Technological Studies: Applied Electronics
Component Electronic Systems
Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
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Contents
Electricity
Simple Circuits
Integrated Circuits: 555 timer
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3
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Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
Electricity
Introduction
Electricity is one of the most important forms of energy available to man. It affects
everyone’s lives in many ways. If you take time to think about your everyday life you
will realise that our lives are full of devices that depend upon electricity. These
devices depend on the electrical circuits inside them to work. The circuits often
change the electrical energy into other forms of energy such as heat, light and sound.
In this area of study you will learn how these circuits work and about the different
components within them.
Electric circuits
An electric circuit is a closed loop or network made up of electrical components such
as batteries, bulbs, switches and wires.
Switch
Battery
Lamp
Electric current
Electric current is the name given to the flow of negatively charged particles called
electrons.
e
le
c
tr
o
n
s
Current is measured in amperes, usually referred to as ‘amps’ (A). Current is the rate
of flow of electrical charges (called electrons) through a circuit.
Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
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Voltage
In most circuits a battery or voltage supply is used to drive the electrons through the
components. Voltage is measured in volts (V).
+
V
_
Current
Flow
R
Resistance
All materials conduct electricity. The materials that conduct electricity well are called
conductors and those that are poor conductors are called insulators. Metals are good
conductors while rubber and glass are good insulators.
A good conductor offers very little resistance to the flow of electrical current. In other
words, it lets currents flow with very little voltage being applied. Resistance is
therefore a measure of how much voltage is required to let a current flow. Resistance
is measured in ohms ().
Electron flow  conventional current
Scientists in the early nineteenth century decided the direction of conventional current
flow. It seemed to them that current flowed from the positive side of power supplies
to the negative side. It was not until the twentieth century that electrons were
discovered and the true direction of current flow was proved.
As stated earlier, electric current is the flow of electrons but often it is more useful to
consider electric current to flow in the opposite direction. This is called conventional
current.
So although it is technically wrong, for convenience ‘conventional current’ will be
used in the circuits and calculations throughout this work.
+
V
_
Conventional
Current
R
Conventional current flows from positive to negative.
One of the main reasons for maintaining this convention is that symbols and other
data based on conventional current have become standard.
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Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
Batteries and voltage supplies
Batteries and voltage supplies are the source of power behind all electrical circuits.
Without a power source, electrical circuits will not work. In your work (as in most
electronic circuits) all power sources will be low-voltage  this normally means
everyday batteries or a low-voltage power supply.
The low-voltage supplies and batteries will normally supply between three and 12
volts. Electronic components normally work on much lower voltages and so the
circuits must be designed carefully.
The symbols for batteries and voltage supplies are as follows.
Single battery or cell
Multiple batteries or cells
Voltage supply
6 volts
Note the positive and negative side of the battery:
-v
e
+v
e
Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
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Direct current (d.c.)
The voltage supplied by batteries or low-voltage supplies is direct current (d.c.). This
is the normal type of supply to low-voltage circuits. Alternating current (a.c.) supplies
are high-voltage  usually 230 volts. This is the normal supply in homes and schools.
Many portable electric power tools work from 110 volts for safety.
Resistors
Resistors are basic components in electrical and electronic circuits. They limit the
amount of current flowing in circuits or parts of circuits. Resistors are roughly
cylindrical and have coloured stripes. They also have connection wires sticking out of
each end.
The stripes indicate the value of the resistors. The colours represent numerical values
according to a special code.
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Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
Resistor colour code
Resistors are marked with what is known as a resistor colour code. Each band that
surrounds the body of the resistor helps identify the value (in ohms) and the tolerance
(in per cent). In most resistors only four colour bands are used.
The colour code chart for resistors is shown below. The colours are used to represent
different numbers, and in this way we are able to tell the value for each digit.
First and
second
colour band
Digit
Black
0
x1
Brown
1
x 10
Red
2
x 100
Orange
3
x 1000 or 1 K
Yellow
4
x 10 000 or 10 K
Green
5
x 100 000 or 100 K
Blue
6
x 1 000 000 or 1 M
Violet
7
Silver means divide by
100
Grey
8
Gold means divide by 10
9
Tolerances:
 brown  1%
 red  2%
 gold  5%
 silver  10%
 none  20%
White
Multiplier
Standard values
Resistors are supplied in a range of standard values: 1.0, 2.2, 3.3, 4.7, 5.6, 6.8, 7.5, 8.2
and 9.1. These standard values can then be multiplied by 10, 100, 1000, and so on.
Typical values of resistors are 220 R, 100 K, 680 R, etc. Some other popular sizes are
also available, such as 270 R and 390 R.
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4-band resistor colour code layout
4 Band Resistor Colour Code Layout
1st band
1st digit
4th band
tolerance
2nd band
2nd digit
3rd band
multiplier
Example
If the colours on the above resistor are:
1st band  red
2nd band  violet
3rd band  brown
4th band  gold
then using the table on the previous page, the value of this resistor is 270  and its
tolerance is 10 per cent. This is worked out as ‘2’ for the red first band, ‘7’ for the
violet second band and ‘times 10’ for the brown third band.
For most purposes you can ignore the tolerance. In the above example the
manufacturers guarantee that the resistor will not vary from the marked resistance by
more than 10 per cent.
Symbol for resistance
Although the symbol for ohms is ‘’ it is often shown as a capital R; that is, 270
ohms can be expressed as either 270  or 270 R.
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Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
Using the resistor colour code
Using the resistor colour code chart, record the resistance values of the following
resistors. Write your answers in your normal report notes/jotter.
1. 100 R  10
blue – violet – brown – silver
2. 3 K9  2
orange – white – brown – gold
3. 100 K  10
brown – black – red – gold
4. M2  5
brown – black – green – brown
Draw and note the colours of the resistors below. Use colour pencils to show the
correct colour bands.
Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
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Exercises
1. Using the colour-code chart, determine the colours of the first three bands of the
following resistors.
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Value
270 R
1 K5
33 K
1 M2
330 R
150 R
82 K
560 R
6 K8
750 R
390 R
2 M1
82 R
4700 R
9 K1
Colour
2. Using the colour-coding code, calculate the values of the following resistors.
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
10
Value
First three colour bands
red
red
red
yellow
violet
black
grey
red
red
yellow
violet
orange
red
red
orange
orange
orange
orange
green
blue
brown
red
violet
black
grey
red
brown
brown
green
green
brown
grey
yellow
brown
black
yellow
green
blue
orange
brown
grey
black
brown
grey
green
blue
grey
orange
orange
orange
yellow
red
red
brown
grey
red
black
violet
brown
orange
Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
Diodes
Diodes are devices that allow current to flow in one direction only.
Current can pass this way only
Anode
Cathode
Symbol for Diode
Current will flow through the diode only when the anode (positive side) is connected
to the positive side of the circuit and the cathode (negative side) is connected to the
negative side of the circuit.
Light-emitting diodes
A light-emitting diode is a special diode that gives out light when current is flowing
though it. LEDs are used as indicators to tell when a circuit (or part or a circuit) is
working. You can tell the cathode of an LED as it is the short leg and there is a ‘flat’
on the plastic casing.
-ve
As with the normal diode, the current can only pass one way.
Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
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Switches
Switches are useful input devices (or transducers) that have metal contacts inside
them to allow current to pass when then they are touching. There are several ways in
which the contacts in mechanical switches can be operated. The main types are 
push-button, toggle, key, slide, magnetic (reed) and tilt. These switches are ‘digital’
input devices as they can only be on or off.
Toggle
Slide
Key
Tilt
Rocker
Reed
The switches shown above are all single pole with single or double throws. These are
known as SPST and SPDT switches. The symbols are shown below.
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Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
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Microswitches
Microswitches are small switches that are useful for detecting motion. They are
especially good as sensors and limit switches. Typical systems that use microswitches
are traffic barriers and lift systems.
The microswitch above has a roller fixed to a lever that detects movement and throws
the switch. It has three terminals: common, normally open (NO) and normally closed
(NC).
The microswitch below is commonly used in schools.
3 -- NO
1 -- C
2 -- NC
Like most microswitches, this one can be wired in three ways.



C and NO: this is a normal on/off switch.
C and NC: this allows current to flow when the switch is not operated.
C, NC and NO: when wired like this it acts as a changeover switch.
These microswitches are single-pole double-throw (SPDT) switches.
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Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
Simple Circuits
Series circuits
The diagram below shows a typical use for an LED circuit, where the LED indicates
that the car radio/cassette is on. The diagram also shows a simplified series circuit
layout for the LED indicator. The resistor is necessary to protect the LED from
drawing too much current and ‘blowing’.
The diagram below shows the above circuit using the component’s symbols. This is
called the circuit diagram.
Switch
I
6V
LED
The components in this circuit are connected in series. This means that they are
connected up in a line, one after the other (or end to end).
Series circuits are the simplest to deal with as the same current flows through all of
the components. The voltage, however, is divided up between the components – more
of this later.
Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems
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