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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

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Key term

How are the segments of a seven-segment display labelled?

Key term

Which segments light to show the digit 7?

Key term

What is a common cathode seven-segment display?

Questions from this subtopic

Each one with the model answer underneath.

  1. 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. 2

    Which segments light to show the digit 7?

    Model answer

    Segments a, b and c light to show a 7.

  3. 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. 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. 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. 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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