[sdiy] Passive debouncer

[Scott Gravenhorst]

patchell <patchell at silcom.com> wrote:
>    What I do to debounce switches is use an RC filter with a 74HC14 schmitt
>trigger.  You need the hysteresis to complete eliminate the bouncing.

Yep.  RC passive stuff alone makes for pretty crappy debouncing and can
introduce it's own weirdness by allowing the signal to slew through logical
no-man's land for too long.  Bear in mind that digital logic circuits are
really high gain analog amplifier circuits and if the input is in the right (er
wrong) range, the output is likely to toggle wildly because of amplified noise.
 The hysteresis fixes this.  I've used CMOS R-S flipflops when the switch in
question is a SPDT used as a logic 1 / logic 0. 

>Peter Grenader wrote:
>
>> I'm trying to use a mechanical switch as an option to advance a sequencer
>> count (manual tuning).  I'm getting about 15 million steps for each touch of
>> the switch due to it bouncing.  I don't want to run this into an active one
>> shot, for reasons I don't need to go into.  Was hoping I could make a real
>> simple passive rc on the faceplate, at the switch itself, to take care of
>> it.  Tried hanging one at the wiper of the switch, didn't work.  POssibly my
>> values didn't cut it.
>>
>> any suggestions?
>>
>> thanks in advance,
>>
>> Peter
>
>--
> -Jim
>------------------------------------------------
>* Visit:http://www.silcom.com/~patchell/
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>* -Yogi Yorgensen
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>

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