The S - R Latch as a Contact-Bounce Eliminator

The S - R Latch as a Contact-Bounce Eliminator


Contact bounce is a common problem that occurs when a mechanical switch or button is pressed or released.Instead of making a smooth and instantaneous transition from open to closed or  vice versa , the contacts may rapidly make and break contact several times before settling into a stable state.    

Case 1:

When the first switch connects to terminal A , the voltage at terminal B is zero. However , due to the bouncing phenomenon associated with the switch , the voltage at terminal A fluctuates several times before stabilizing at 5v.

 Case 2 : 

When the second switch connects to terminal B , the voltage at terminal A is zero. The voltage at terminal B undergoes several fluctuations before settling at 5v.


To avoid the issue of contact bounce in a switch , the A and B terminals are connected through a active HIGH input S- R latch(NOR gate based S-R latch). Additionally , the outpus of terminals A and B can be obtained through the Q and Q'.



Truth Table of the Active High input S - R Latch

  • The Q output represents the stable output received when the switch is connected to  the A terminal without experiencing any bouncing.

  • The Q' output represents the stable output received when the switch is connected to  the B terminal without experiencing any bouncing.





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