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Switch Bounce

<^< Input Conditioning | Course Index | Switch Debouncing >^>

Switches contain two metal contacts, made of brass. When switched off, these contacts are held apart, separated by an insulator - air. To switch on, these contacts are slapped together by some lever mechanism, aided by a strong spring. Now, metals are springy. When the contacts hit each other, they bounce apart, hit each other again and may continue to do this a number of times before coming to rest in contact with each other. All of this happens very quickly. We normally do not notice it, and it causes no problem.

When the switch is part of a switch unit, this bouncing causes a series of changes in output, as shown in the diagram.

We can show these changes on a voltage/time graph:

<^< Input Conditioning | Course index | Switch Debouncing >^>