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
Figure 1. A simple de-bouncing circuit.