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National Diploma In Engineering
Data Communications
Electronics B NIII
Assignment no. 2
A/D and D/A Convertors and Display Devices
Weighting 20%
Name: Malcolm Brown
Class: NDD2
Tutor: Ken Hughs
Contents Page
Task 3
A/D and D/A Convertors 4
Analogue and Digital Signals 4
Analogue / Digital Conversions 5
Analogue to Digital Convertors 6
Digital To Analogue Converter 8
Glossary Of Terms 10
Visual Display Devices 11
Seven-Segment Displays 14
Dot Matrix Displays 16
Bibliology 18
A/D and D/A Convertors
Explain two methods of converting analog signals to digital signals and compare
them. Explain one method of digital to analog conversion. Choose two A/D
convertor devices from the catalogue and list their characteristics,
performance, cost, applications etc.
Display Devices
Describe how LED and LCD display devices operate - ie explain the principle
behind their operation. Describe the features of the 7-segment, star-burst and
dot matrix displays. Choose some devices from the catalogues and describe them.
You are required to produce a written report on your work. The report should be
in standard report format and comprise of a front page with title, contents page
summary, introduction, main body of the report describing the task and how you
met the requirements of the task, circuit diagrams etc. and conclusions.
Appendices may be placed in the report if necessary.
The report should be word processed and presented in a plastic folder. Your name

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class and subject should be clearly visible.
A/D and D/A Convertors
Analogue and Digital Signals
Analogue Signals - Signals whose amplitude and/or frequency vary continuously
eg. sound. Fig 1.1 illustrates an analogue signal:-
Fig 1.1 Illustration of an analogue signal
Digital Signals - Signals which are not continous in nature but consist of
discrete pulses of voltage or current known as bits which represent the
information to be processed. Digital voltages can vary only in discrete steps.
Normally only two levels are used ( 0 and 1 ).Fig 1.2 illustrates a digital
Fig 1.2 Illustration of a digital signal
Analogue / Digital Conversions
In todays electronic system it is often necessary that the overall system may
not be entirely analogue or entirely digital in nature. Thus a digital system
may be controlled by input signals which are the amplified analogue outputs,
perhaps of some measuring transducer (termister, LDR). Similarly a digital
system output may be required to control the measured analogue system via
analogue control values.Interfacing is therefore required between the analogue
and digital subsystems and it is necessary to be able to convert an analogue
signal into a digital equivalent signal and visa versa. A/D and D/A convertors
are therefore used.
An analogue signal cannot be represented exactly by a digital signal and must be
sampled at sufficient intervals for all relevant information to be retained.
Sampling theory states that at least two samples must be obtained per period of
the highest frequency component. If the highest frequency component is fs then
the period of the sampling signal is given by:-
T < 1/2 fs

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