CCEA A-Level Technology and Design 8900
Material Selection and Wood
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Plastics
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Product Analysis and Design Communication
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Electronic Control SystemsOption A
Microelectronic Control SystemsOption A
Mechanical and Pneumatic ComponentsOption B
Mechanical and Pneumatic SystemsOption B
Designing and Manufacturing ProductsOption C
Product Design in Industry and SocietyOption C
Product Development
Product and System Design and Manufacture
Microelectronic Control Systems
Seven-segment, LCD and dot matrix displays
- 3 things to know
- A2 1
Overview
Seven-segment labelling, common anode and cathode displays, decoders, multiplexing, LED bar arrays, LCD modules and dot matrix displays.
What you need to know
Answer each one before you reveal it.
Which segments light to show the digit 7?
What is a common cathode seven-segment display?
Questions from this subtopic
Each one with the model answer underneath.
- 1
How are the segments of a seven-segment display labelled?
Model answer
The segments are labelled a to g, running clockwise from the top, with g as the middle bar. Many displays add a decimal point.
- 2
Which segments light to show the digit 7?
Model answer
Segments a, b and c light to show a 7.
- 3
What is a common cathode seven-segment display?
Model answer
All the LED cathodes join at one pin connected to 0 V. A segment lights when its anode is driven to logic 1.
- 4
How is a common anode display driven differently from a common cathode display?
Model answer
The common anode connects to the positive supply. Each segment lights when its pin is pulled low, to logic 0.
- 5
Why does each segment need its own series resistor rather than one in the common lead?
Model answer
A single shared resistor would let the brightness change with the number of segments lit. Separate resistors keep every segment's current the same.
- 6
What does a BCD-to-seven-segment decoder do?
Model answer
A decoder converts a four-bit BCD input into the pattern of segment outputs for that digit. A counter can then drive a display through it.
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