Logic Gates may be used to remove oscillations or unwanted pulses (bouncing) produced by mechanical switches and relays during the mechanical switching process.  Below is an example of a switch debouncing circuit that utilizes NAND gates.

Figure 1. Bounce-free Mechanical Switching with NAND Gates

Figure 1 shows a circuit that uses two NAND gates to stabilize the output of a mechanical switch or relay. The output of the circuit as shown is '0'. Thus, at this point, X1 is '0'.

When the switch is thrown from '0' to '1', the 1.2 k-ohm resistor pulls up Y1 to '1', but this does not cause the output of NAND A to change, i.e., it remains to be '1'. Thus X2 is still '1'. However, the switching action causes Y2 to be pulled to ground, causing the output to switch from '0' to '1'.  This causes X1 to also switch to '1'.

Since at this point, Y1 is still '1', the output of NAND A switches to '0', which keeps the output at logic '1'.  In effect, the switching action of the mechanical switch was transformed by the two NAND gates into a clean digital transition from '0' to '1' at the circuit's output.

Throwing the mechanical switch back to '0' causes Y1 to go to '0' and Y2 to go to '1'.  This causes the output of NAND A to go to '1' and the output of the circuit to go to '0' since both X2 and Y2 are now '1'.  Again, the mechanical switching action was transformed by the circuit into a clean digital transition from '1' to '0'.