Switch Bounce and Other Dirty Little Secrets

Switches can do some really odd things. Most engineers learn this dirty little secret soon after connecting a switch or a relay to a digital system. Switches don't make and break cleanly on the time scales of digital systems. Instead, a typical switch makes multiple transitions during the tens of milliseconds required to open or close, due to effects that include age, operating inertia, mechanical design, and the microscopic condition of the switch-contact surfaces. Commonly called "switch bounce," this behavior is an inescapable fact of life.