Negative logic debounce circuit

tonyStewart

Joined May 8, 2012
237
I'm looking for a circuit whose output stays on for a while after the input has gone, but in negative logic.

I know a 555 timer or an RC + transistor circuit works with positive logic, but I don't know what works with negative logic.

In other words, a circuit whose output goes LOW as soon as the input goes LOW, but stays LOW for a bit after the input goes HIGH (or Hi-Z).
Preferably, I'd want it to work with Hi-Z (without pullup resistors).
It should stay for 2-3 seconds.

It will connect to a button, which connects to ground when closed. I can't really make the button connect to power when closed.

This is how the timing would work:
View attachment 343027
Normally open switches with contact bounce only need a Cap across the contacts to debounce it. The external pullup R * C =T determines the transition time to 63%. If your threshold is 50% then use T= 1.2 * RC
 
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