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Simple De-Bouncing Circuit

The contact bouncing is not a problem when we use switch or relay to turn on a lamp, motor or another load. But if the switch is used to give an input to a digital counter, a personal computer, or a micro-processor based equipment, then we must consider the contact bouncing. Because the contacts need a few milliseconds to stop the bouncing but the digital circuits can respond it in microseconds, then the information that being read may be wrong.
 

A simple hardware de-bounce circuit for a momentary N.O. push-button switch is show in Figure 1. This circuit uses an RC time constant to swamp out the bounce. An RxC value of about 0.1 seconds is typical. Note the use of a buffer after the switch to produce a sharp high-to-low transition.

       　Figure 1. A simple de-bouncing circuit.

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