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R-C switch debouncing

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I tried it (the Schmitt inverter RC debouncer) and it works great. Ended up using 4.7K, 1K and 1µF. And yes, the chip I used (a xxxLS14) is a hex inverter. Much easier than a 555, although I still want to try that too.

hi CZ,
Ref the inverting and non inverting Schmitt de-bouncer circuit.

Consider what the output of an second inverting Schmitt would be if you connected this second inverting Schmitt to the output of the first one.

That is two inverting Schmitt buffers in series,,, it would be exactly the same a single non inverting Schmitt output, this should answer your original post.
 
Thanks, Eric. Yes, I knew that; what was bugging me was not knowing exactly what the switch was doing in that configuration. I wasn't getting that it was generating a negative-going pulse, which was then inverted to what I needed. The diagrams in that 2nd PDF that you provided helped a lot. (Still can't find the link to that; do you have it handy?)
 
Thanks, Eric. Yes, I knew that; what was bugging me was not knowing exactly what the switch was doing in that configuration. I wasn't getting that it was generating a negative-going pulse, which was then inverted to what I needed. The diagrams in that 2nd PDF that you provided helped a lot. (Still can't find the link to that; do you have it handy?)

Look at the 4th link on this link.
Fairchild application 140 - Google Search
 
Thanks, but that's not the document I was looking for; it's an app note called Pulse Generation and Signal Conditioning Circuits Using Configurable Multifunction Logic Gates, published by ON Semiconductor. Not whether you or someone else posted a link to it here. Very useful paper.

There, I found it (pretty easy to find with a title like that!).
 
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The circuit you posted at the top is quite poor, it needs R1 to be greater than R2 by about 10:1 which gives pretty poor RC time constants.

I have modified the circuit to show a much better way to do it, it gives almost a 1:1 time constant for the RC and can be used as a pretty effective debounce directly into a logic input as it provides a low impedance signal right at the logic input.

**broken link removed**
 
The circuit you posted at the top is quite poor, it needs R1 to be greater than R2 by about 10:1 which gives pretty poor RC time constants.

Well, thanks for letting me know that.

All I can say is 1) what I have was taken from an app note which I trust is fairly authoritative, and 2) it works plenty well enough for me.
 
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Well the guys that write app notes don't necessarily know the best ways to do things. Some of them are just academics that got themselves employed by a big electronics company. ;)

You might also note they got the shape of the discharge curve wrong in the discharge/charge curves too. They might have given that appnote to the new boy to do... :eek:
 
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