4.7. Debouncing Mechanical Switches
Mechanical switches bounce for a few milliseconds before stabilizing in their new position. Meaning, the
switch will open and close repeatedly (bounce) when switch is changed to closed position. If the switch is
used as an event or an input where each transition is considered a new input then the designer is
required to debounce the switch before using the switch value in the rest of the system.
There are numerous approaches to debouncing a switch output. Here are four typical approaches to
debouncing:
RC Circuit Debounce
The most basic approach is to use a Resistor and Capacitor (RC) circuit to debounce switches. This
method uses the time constant (τ=RC ) to slow the circuit eliminating the bounce. R and C value
will be selected based on duration of switch bounce. Here is the simplest form:
The drawback of this approach is that “Out” transition from low to high may be too slow for use in
digital circuits. Flip Flop Design
SR Flip Flop Variation
This method uses a variation of SR Flip Flop to debounce a switch output as shown below:
+5V
GND
A
B
OutVccGND
Out