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Solution:
The Latch as a Contact-Bounce Eliminator:
A good example of an $\overline{\mathrm{S}}-\overline{\mathrm{R}}$ latch application is in the elimination of a mechanical switch contact “bounce.”
When the pole of a switch strikes the contact upon switch closure, it physically vibrates or bounces several times before finally making solid contact.
Although these bounces are very short in duration, they produce voltage spikes that are often not acceptable in a digital system. This situation is illustrated in Figure (a).
An $\overline{\mathrm{S}}-\overline{\mathrm{R}}$ latch can be used to eliminate the effects of switch bounce as shown in Figure (b).
The switch is normally in position 1, keeping the $\overline{\mathrm{R}}$ input LOW and the latch RESET.
When the switch is thrown to position 2, $\overline{\mathrm{R}}$ goes HIGH because of the pull-up resistor to VCC, and $\overline{\mathrm{S}}$ goes LOW on the first contact.
Although $\overline{\mathrm{S}}$ remains LOW for only a very short time before the switch bounces, this is sufficient to set the latch. Any further voltage spikes on the $\overline{\mathrm{S}}$ input due to switch bounce do not affect the latch, and it remains SET.
Notice that the Q output of the latch provides a clean transition from LOW to HIGH, thus eliminating the voltage spikes caused by contact bounce.
Similarly, a clean transition from HIGH to LOW is made when the switch is thrown back to position 1.