Switch Debouncer With Auto Repeat

This circuit produces an output pulse when SW1 (pushbutton) is depressed. It also becomes a hysteresis gate oscillator. D1 and R2 add asymmetry. The DBRT (delay before repeat time) is caused by the oscillator start-up conditions: C1 has to change from zero to the upper gate threshold rather than to the lower threshold.

The auto repeat time:

t=[(R1+R2)(C1+C2)(Gate Hysteresis)]/Vsupply

Gate hysteresis ~ 1 V for 74HCT14

DBRT=0.7T (upper gate threshold hysteresis)


Upper gate threshold ~ 2.3 V for HCT14

R1 <>

R2 <>

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