Embedded Systems & Firmware

What is the phenomenon called in which a mechanical switch's contacts bounce, turning on and off many times in a short period when pressed?

  1. ALatch-up
  2. BCrosstalk
  3. CContact bounce (chattering)
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Answer: C. Contact bounce (chattering)

When a mechanical switch closes, the metal contacts bounce and turn on and off for a few milliseconds. A microcontroller reads its pins very fast, so counting naively would register one press as several. The bounce is removed in software by waiting and rereading, or in hardware with a capacitor or Schmitt trigger to smooth the waveform. This processing is called debouncing.

  • A. Latch-up is a CMOS fault where large current keeps flowing.
  • B. Crosstalk is signal leaking from an adjacent wire.
  • C. Correct. A single press may read as several.
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