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Teacher Resource Bank
GCE Electronics
Changes to Content
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Teacher Resource Bank / GCE Electronics / Changes to Content / Version 1.0
CHANGES TO CONTENT
Unit ELEC1 - Introductory Electronics
Topic areas removed
•
•
•
10.9 – Capacitors – Moved to ELEC2.
10.10 – RC Networks (dc only) – Moved to ELEC2.
10.11 – 555 Timer – Moved to section ‘Timing subsystems’ ELEC2.
Topic areas added
•
•
Design and simplification of combinational logic systems
(from previous specification – unit ELE2, 11.1).
Specific changes to sections
Topic
Changes from old specification
System Synthesis
minor clarification of 10.1.
Voltage (V), Current (I) ,
Resistance (R), Power (P)
minor clarification of 10.3.
Diodes
10.4, clarification about calculations expected.
Resistive Input transducers
10.5, reference also to logarithmic scales.
Transistors and MOSFETs
no changes from 10.6.
Output Devices
10.7, with addition of seven segment displays and
minor clarification.
Operational amplifiers
minor clarification of 10.8.
Logic gates and Boolean
algebra
Design and simplification of
combinational logic
systems
10.2 from ELE1, with the addition of 11.1 from ELE2.
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Teacher Resource Bank / GCE Electronics / Changes to Content / Version 1.0
Unit ELEC2 – Further Electronics
Topic areas removed
•
•
Design and simplification of combinational logic systems – Moved to ELEC1.
Filter circuits – Moved to ELEC5.
New Sections/Topic areas
•
•
Capacitors – (from previous specification – ELE1, 10.9).
dc RC networks – (from previous specification –ELE1, 10.10).
Specific changes to sections
Topic
Changes from old specification
Capacitors
10.9 from ELE1 with minor clarification.
dc RC networks
10.10 from ELE1 with no changes.
Sequential logic
subsystems
10.11 from ELE1 with description of operation of 555
monostable and astable.
11.2, removal of NAND gate monostable and
astable.
Counter subsystems
no changes from 11.3.
Timing Subsystems
The operational amplifier
Amplifier subsystems
Power amplifier
subsystems
2
gain-bandwidth product from 11.4 with ideal op-amp
properties and the use of negative feedback.
voltage gain from 11.4, with op-amp circuits from
11.5, 11.6, 11.7, the differential amplifier and
clarification.
11.9, power gain calculations and more detail of
what is expected.
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Teacher Resource Bank / GCE Electronics / Changes to Content / Version 1.0
Unit ELEC4 - Programmable Control Systems
New topics
•
•
•
Microcontroller assembly language replaces QBasic.
Robotic systems.
H-bridge driver.
Specific changes to sections
Topic
Changes from old specification
Control systems
no changes from section 12.1.
Microprocessor
subsystems
no changes from 12.2.
Programming
Input subsystems
Output subsystems
Interfacing subsystems
Robotic systems
flowcharts from 12.3, QBasic replaced by assembly
language.
ADCs from 12.5, optical switches, optical shaft
encoders from 12.7, adding reference to Gray code.
DACs from 12.5, with stepper motors, 7-segment
and dot-matrix displays from 12.7.
tri-state buffers and data latches from 12.5, Schmitt
triggers from 12.6 and the addition of the H-bridge
driver.
new section, including some of the material on
neural networks from 12.4.
Additional notes
These notes should be read in conjunction with the specification.
Control Systems
This section considers control systems in general, candidates are expected to be
able to analyse a given control system into the main functional blocks as shown in
the diagram in the specification.
Control systems can be categorised as open loop, when no information is available
from the output indicating whether an action has been completed correctly, or closed
loop systems, when information from the output is available. This information can be
combined with the input to the control system in two ways:
1
2
it can either be subtracted from the input, negative feedback, resulting in the
output being directly controlled by the input,
it can reinforce the input, positive feedback, leading to the output usually only
having two possible states.
Candidates should analyse control systems, electronic and non-electronic, that are
familiar to them, identifying both open and closed loop systems together with whether
negative or positive feedback is involved.
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Microprocessor subsystems
Almost all industrial and commercial electronic systems contain microprocessor
control systems. The reason is obvious, it reduces costs: the functionality of a piece
of equipment can be readily modified by a manufacturer simply by upgrading the
software within the microprocessor controller, the same microprocessor controller
can be used in a very wide variety of equipment.
It is therefore vital that all students of electronics are exposed to microprocessor
control systems and their use.
While there are many economic and social benefits of microprocessor systems,
candidates should also be aware of possible adverse effects of dependence on such
systems.
Although most microprocessor control systems are now fabricated onto a single IC,
specialist systems will use discrete elements, candidates should be aware of the
basic components of a microprocessor control system and the function of each
element.
Microprocessor systems with RAM, ROM, I/O ports, buses etc all fabricated into an
IC are known as microcontrollers. As technology advances, the number of
microcontrollers available increases year on year as does the functionality offered by
each device. It would not be possible to keep up to date with such developments
within an examination specification and so it was decided to focus on the
fundamental concepts of microcontrollers and develop skills that are transferable to
future devices. As a result, this specification assumes a generic microcontroller with
a Harvard architecture and the following specification:
•
•
•
•
•
•
•
•
•
a clock speed of between 1 and 20 MHz;
an accumulator or working register, W, through which all calculations are
performed;
a program counter, PC;
three 8-bit bi-directional ports - PORTA, PORTB and PORTC;
three data direction registers TRISA, TRISB and TRISC, to determine
whether the bits of each port are inputs or outputs;
for the data direction registers, if a bit is set to 1 then the port bit is an input, if
the bit is set to 0 then the port bit is an output;
a status register for which bit 0 is the carry flag, C, and bit 2 is the zero flag,
Z;
a clock prescaler, which can be set to divide the clock frequency by 2 to 256;
an 8-bit timer register, TMR, which is incremented on each rising edge of the
clock prescaler pulse and which sets bit 1 of the status flag when it is 0.
Programming
Since almost all modern electronic systems contain programmable devices it is
essential that all candidates are able to analyse a process or operation into a
sequence of fundamental operations, and then represent these fundamental
operations into a diagrammatic form. While there are several diagrammatic systems
available, this specification continues to use flowcharts for this purpose.
For the foreseeable future, microcontrollers will continue to have various forms of
Assembly Language, even though high level interpreters are usually available. It is
not be possible to cater for all of the high level interpreters within an examination
specification and so it was decided to focus on the fundamental concepts of
microcontrollers and develop skills that are transferable to future devices. As a
result, this specification requires candidates to be familiar with a limited range of
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Teacher Resource Bank / GCE Electronics / Changes to Content / Version 1.0
assembly language microcontroller instructions. These instructions are listed below
and will also be available on the Data Sheet included with the examination paper:
•
•
•
the memory is made up of registers, each with its own separate location, R;
K is used to represent a literal, which can be a memory location (e.g. 29h), a
label (e.g. display) or a value, (e.g. FAh);
standard arithmetic and Boolean operators, e.g. add K to W etc as in the table
below:
none
stack <=PC
PC <= K
PC <= stack
none
none
Clock
cycles
1
2
none
2
Increments the contents of R
Decrements the contents of
R
(R) <= (R) + 1
(R) <= (R) - 1
Z
Z
1
1
K
K
K
K
K
Add K to W
AND K with W
Subtract K from W
OR K and W
XOR K and W
W <= W + K
W <= W • K
W <= W - K
W <= W + K
W <= W ⊕ K
Z,
Z,
Z,
Z,
Z,
C
C
C
C
C
1
1
1
1
1
JMP
K
Jump to K (GOTO)
PC <= K
none
2
MOVWR
MOVW
MOVRW
R
K, W
R
Move W to the contents of R
Move K to W
Move the contents of R to W
(R) <= W
W <= K
W <= (R)
Z
Z
Z
1
1
1
Mnemonic
Operands
Description
NOP
CALL
none
K
No operation
Call Subroutine
RET
none
Return from Subroutine
INC
DEC
R
R
ADDW
ANDW
SUBW
ORW
XORW
Operation
Flags
Candidates will not be expected to remember the details of this generic
microcontroller as sufficient information will always be included on the Data Sheet
and in the questions. However, they will need to understand the concepts and the
application of such instructions to microcontrollers.
Candidates will be expected to be familiar with the following representations of
hexadecimal numbers:
FA16, FAh, &HFA, 0xFA
In general candidates will be required to either write a subroutine for one of the
operations listed within the specification or to interpret a piece of code written with
this instruction set.
Candidates are also expected to be aware of both the use of hardware interrupts and
polling of input ports to trigger events, and should be able to consider the advantages
and disadvantages of each method.
Input subsystems
This section is concerned with devices that can be used to enter information into a
microcontroller system. There has only been one addition to this section from the
previous specification, and candidates are now required to be able to explain the
benefits of using a Gray coded shaft encoder compared to a binary coded shaft
encoder.
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Output subsystems
This section is concerned with devices which can receive information from a
microcontroller system. It has been decided to continue to use a summing amp
based DAC in this specification rather than move to R - 2R type devices. The use of
the summing amplifier follows on directly from the AS module work of ELEC2.
Candidates should know about multiplexed 7-segment displays and their advantages
over non-multiplexed displays. Candidates should be aware of the relative merits of
both LED and LCD seven segment displays as well as the overall limitations of such
displays for showing a wide variety of different characters. Candidates should be
aware how these limitations can be overcome by the use of multiplexed dot matrix
displays.
Most microcontroller operated machines require a motor as an output device. This
specification requires candidates to be aware that there are two main types of motor,
conventional and stepper and candidates should be able to describe the essential
differences in operation between these two types of motors.
Candidates are required to be able to describe the use and operation of stepper
motors and be aware that there are both bipolar and unipolar stepper motors and
these can each be 4 pole or 6 pole devices.
Interfacing subsystems
This section is similar to ELE4 in the previous specification. The Schmitt trigger has
been restricted to inverting circuits and, as before, these should be based on opamps.
The control circuits needed to drive both LED and LCD 7-segment multiplexed
displays and LED dot matrix displays should be studied by the candidates. It is
expected that examination questions involving these displays will often show these
displays driven from the output ports of a microcontroller.
Candidates will be expected to be able to describe the associated circuits needed to
drive both conventional and stepper motors, though again it is expected that, apart
from MOSFET switches, this will be accomplished from the output ports of a
microcontroller.
New to this section is the H-bridge driver circuit for conventional motors. Candidates
are expected to be able to recall the circuit and describe its operation.
Robotic systems
Recent years have seen a dramatic growth in the use of robotic systems, particularly
in industrial and military applications. While there are the headline catching robots
like the Mars Rover and cruise missiles, the vast majority are simply systems which
may or may not be mobile but which are able to have some awareness of their
surroundings and, through training, can act upon that information. This growth in the
use of robotic systems is set to increase as technology increases.
This section of the specification gives candidates an opportunity to gain a general
awareness of the diverse use of robotic systems as well as likely future
developments. It also provides a focus for this unit on programmable control
systems.
Candidates should be able to describe the essential components of robotic systems.
All robotic systems need sensors. These can range from simple switches which are
actuated when the robot touches something, through ultra sound or microwave echo
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location to full video recognition. Candidates will not be expected to have any depth
of knowledge of these sensors, but be aware of some possible types and their uses.
In order for a robotic system to interact with its surroundings, it must have actuators
that it can use to move, grasp etc. Candidates will have already studied both stepper
and conventional motors as part of this specification but they should also be aware
that robotic systems can also use both hydraulic and pneumatic actuators. Again
candidates will not be expected to have any depth of knowledge of these actuators,
but be aware of some possible types, their applications advantages and
disadvantages.
The information arriving from the sensors will need processing, and instructions will
need to be sent to the actuators. This is the job of the control system. In most cases
this will take the form of a microprocessor control system which candidates will have
already studied as part of this specification.
All robotic systems need sources of power. For fixed systems this does not
represent a problem since it is easy to provide all the power required from the mains
electricity supply. However, for robotic systems that are mobile, the source of power
can be a major issue. Candidates should be aware that all mobile robotic systems
need some way of storing energy, which in most cases will be batteries. Candidates
should be aware of at least two different types of rechargeable battery, e.g. Leadacid, Nickel-Metal-Hydride, Lithium-Ion, etc and the relative merits of each type.
Candidates should also be aware of the increasing use of fuel cells, particularly those
based on alcohol, and the advantages and disadvantages of these compared to
conventional rechargeable batteries. Again candidates will not be expected to have
any great depth of knowledge of these power sources, but be aware of some
possible types and their relative merits.
Candidates are required to be able to analyse a process into its fundamental
operations and write subroutines to perform basic tasks. It is envisaged that many of
these processes will relate to robotic systems and so there is little additional material
to cover for the section on designing control algorithms for a robotic system to
achieve a given objective. However, candidates will benefit from having given some
prior consideration to such examples as: a robot, moving forward, receives
information from its sensors that there is an obstacle ahead.
Any autonomous robotic system will have been programmed / trained to deal with a
wide variety of situations it is likely to encounter. However, it is inevitable that it will
encounter situations that it has not previously met. In order to be able to learn, the
techniques used within Artificial Neural Networks, e.g. Back Propagation are likely to
be employed. Candidates should be aware of at least one of these ANN techniques
and should also develop a reasoned opinion as to the ability of such systems to
sustain artificial intelligent behaviour.
Candidates will need to be aware of suitable applications of robotic systems as well
as the social and economic impact of such systems. Clearly, with the technological
developments of each passing year, the capability of robotic systems will continue to
develop and candidates should develop a reasoned opinion of possible future
developments.
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Unit ELEC5 – Communication Systems
New topics
• DAB radio
• Audio systems (filter circuits and power IC amplifiers)
Specific changes to sections
Topic
Changes from old to new specification
General principles
12.1, with minor clarification.
Audio systems
Radio communication
Radio receivers
Digital communication
filter circuits from 11.8 in ELE2, plus the use of audio
power IC amplifiers.
modulation, channel spacing and bandwidth from
13.2, plus an outline of DAB, and clarification of
what is expected.
simple receivers, tuned circuits and superhets from
13.2, with minor clarification.
13.4, with clarification, reference to the Schmitt
trigger and addition of the concept of packet
switching.
Mobile communication
no changes from 13.3.
Optoelectronics
13.5 with minor clarification.
Additional notes
These notes should be read in conjunction with the specification.
General principles
This section is largely unchanged from the previous specification and considers
communication in general terms. Candidates are required to understand the purpose
of communication and are expected to analyse a generalised communication system
into its constituent parts and represent these in block diagram format. A vital
component of any communication system is the medium linking the transmitter with
the receiver, candidates will be expected to recall the four main communication
media for electromagnetic radiation (twisted pair cable, coaxial cable, optical fibre
and free space) and compare their relative merits of each.
The demand for communication continues to rise annually and candidates are
required to understand and apply the relationship between bandwidth and the
capacity to carry information. This insatiable demand for communication has seen
the end of a transmitter being linked to a receiver by a unique transmission medium.
In almost all transmission systems many transmitters are linked to many receivers by
a single transmission medium and it is important that candidates understand this and
are able to describe the main methods of signal multiplexing.
It is an unfortunate fact that as information passes from a transmitter to the receiver
along a transmission medium, it will suffer attenuation and the addition of noise,
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distortion and cross talk. Candidates are expected to recall and describe the
differences that these effects have on the information signal. The larger the noise
signal compared to the information signal, the more difficult it becomes to extract the
information. Candidates are therefore required to appreciate this and also calculate
the signal to noise ratio of the signals in decibels.
Audio systems
This section is new to the communication systems module. Audio systems are an
integral part of communication and so it was decided to move much of this material
from the Further Electronics module of the previous specification in order to further
balance the modules at AS level.
Communication systems rely on being able to filter signals in order to extract the
information. This relies on circuits and components whose properties are frequency
dependent. One such component is the capacitor; candidates should be able to
calculate capacitive reactance and the breakpoint frequency of both high and low
pass passive filters when combined with resistors.
Passive filters always result in a loss in signal strength. This can be avoided by
incorporating the passive filter into an op-amp circuit. The use of an op-amp enables
circuits to be constructed which not only cut treble and bass, as with passive circuits,
but also boost the treble and bass response. Candidates are required to draw,
analyse and explain the operation of such first order filters as well as calculating
component values and breakpoint frequencies.
In order to turn the information signal into sound it is necessary to increase the power
of the signal and feed it to a loudspeaker. This requires an audio power amplifier.
Discrete component amplifiers are considered in ELEC2 but, in modern
communication systems, such discrete component power amplifiers are rarely used.
Manufacturers prefer to use integrated circuits containing power amplifiers, since
they are usually cheaper and offer better performance for the cost than their discrete
equivalents. Candidates will be required to describe and explain the use of such
common audio power IC amplifiers.
Radio communication – General Principles
Much of this section is the same as in the previous specification, although the
emphasis has changed from candidates being able to describe to being able to
explain a process. The majority of radio communication is now digital and a wide
range of different modulation techniques are used. However, all modulation systems
rely on either altering the amplitude or frequency (phase) of the carrier wave. It was
therefore decided to concentrate on these fundamental methods and leave the more
complex modulation methods for further study.
Candidates need to be able to explain the need for a carrier wave as part of the
frequency division multiplexing of the radio spectrum. Amplitude modulation (AM) is
one of the fundamental modulation methods and candidates are required to explain
this process and draw diagrams to represent the modulated waves both in the time
and frequency domains.
With the ever greater demand for radio channels, the bandwidth of radio
transmissions is important and candidates need to explain and calculate the
bandwidth requirements of AM signals.
Frequency modulation (FM) is the other fundamental modulation method, candidates
need to explain the process of frequency modulation and also draw diagrams to
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represent the modulated waves. FM signals have the potential to occupy a large
bandwidth and candidates need to describe and calculate the practical bandwidth
requirements of such signals.
It is considered important that candidates know which modulation methods are used
on which bands, with AM being used on the lower frequency bands and FM on the
higher frequency bands. In order to prevent public radio stations overlapping, their
bandwidth and frequency are governed by international agreement. Candidates
need to understand and explain the relationship between channel spacing and signal
bandwidth.
Within the lifetime of this specification, many of the public AM and FM radio stations
will be replaced by Digital Audio Broadcasting, DAB, radio. It is important, therefore,
that candidates know the frequency bands used for DAB transmissions, together with
an understanding of the methods of multiplexing and the data rates used.
Radio receivers
This section is essentially the same as in the previous specification. Although there
have been many advances in radio receiver design, most still rely on the principles of
the basic radio receiver or the superhet receiver.
The basic radio receiver considered is essentially a ‘crystal set’ radio. The AM radio
stations Radio 4 (LW) and Radio 5 (MW), together with other local radio stations,
enable candidates in most parts of the country to construct and use these basic
radios. This helps them focus on the function of each of the sections of the simple
radio, together with the design of the tuning circuit.
Candidates need to be able to calculate both component values and resonant
frequencies of such tuned circuits and draw the resonance curve of parallel LC
networks.
Such basic radio receivers suffer from many deficiencies, and candidates need to be
able to explain how these can be overcome with the use of a superhet receiver.
Candidates will need to be able to draw a block diagram of a superhet receiver and
describe its principle of operation.
Digital communication
Digital communication offers significant advantages over analogue communication,
which explains why more and more communication systems are becoming digital.
Candidates need to be able to compare the relative merits of both digital and
analogue communication systems.
There are many different digital modulation techniques currently in use, but this
specification focuses on the four fundamental methods:
• Pulse Amplitude Modulation (PAM)
• Pulse Width Modulation (PWM)
• Pulse Position Modulation (PPM)
• Pulse Code Modulation (PCM)
Candidates need to be able to describe, using diagrams, each of these techniques
and also explain, with appropriate calculations, how the sampling rate and resolution
determine the required bit rate of the digital signal.
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While digital transmission of information can reduce distortion and interference, care
must be taken to ensure that the signals are transmitted and received correctly.
Candidates are required to discuss the relative merits of half/full duplex and
serial/parallel communication links. It is important that the transmitter and receiver
remain synchronised and candidates need to be able to describe the relative merits
of synchronous/asynchronous transmission and the use of start, stop and parity bits.
Modern communication networks, e.g. the Public Service Telephone Network and the
Internet, rely on packet switching and candidates are required to describe the
concepts of this technology.
Almost all communication systems rely on multiplexed serial transmission of
information. Shift registers are used to convert serial data to parallel data and vice
versa and candidates need to be able to explain their operation and draw appropriate
timing diagrams. Similarly candidates need to be able to describe and explain the
use of a multiplexer together with designing logic diagrams for 2 to 1 and 4 to 1
multiplexers.
The theory of the Schmitt trigger is covered in ELEC4. Candidates need to be able to
explain qualitatively the important role that Schmitt triggers play in communication
systems in the regeneration of digital signals.
Mobile communication
This section of the specification is the same as it was in the previous specification.
Although mobile technology has moved on considerably, the basic concepts remain
the same. The country is still divided into cells and in the centre of each cell is a
base station. The base station communicates with each mobile phone by radio
signals. Because of the high frequencies and low power of the radio signals, the
same radio frequencies can be used again and again in other cells, so increasing
significantly the number of transmission channels.
Candidates need to understand the fundamental principles of cellular mobile
communication and be able to calculate the maximum number of mobile phones that
can be supported in a given cell.
With the number of mobile phones now exceeding 40 million in the UK, they have
clearly had an impact on everyday life. Candidates should be able to describe such
situations.
Optelectronics
Although copper cables are capable of carrying signals at over 1Gb/s, the distances
over which they operate are relatively short. For high speed data transmission over
long distances optical fibre cables have proved themselves to be efficient and
reliable.
Candidates need to be able to describe how optical fibres are constructed and their
mode of operation.
As the signals travel along the fibres, they are attenuated and suffer dispersion.
Candidates need to describe the effect that this has on the signals.
In order to achieve large distances, laser diodes are used as transmitters and
sensitive photodiodes (PIN diodes) are used as receivers. Candidates need to
describe their use with optical fibres.
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