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'[OT]: There are more things in heaven and earth, H'
2002\05\21@093956 by Bob Barr

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On Tue, 21 May 2002 21:49:47 +1200, Jinx wrote:

>>    Bouncing at bottom contact will produce 0 - 0.5 Vdd noise.
>>    Bouncing at top contact will produce 0.5 - 1 Vdd noise.
>
>Exsqueeze me ?
>
>Noise coming from the switch will be 0-5V regardless. It
>must be as a consequence of the contacts touching or
>otherwise the switch wouldn't be a switch, unless it came
>from the Pisspoor Switch Co catalogue

Isn't that a division of DirtCheap Enterprises? :=)
A real favorite of purchasing managers worldwide.


Regards, Bob

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2002\05\21@102615 by Bob Ammerman

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The point made here is that the top contact can only pull the PIC pin
between 0.5 Vdd (when open - ie: the 'resting' state due to the R-R voltage
divider) and 1.0Vdd (when closed).

Similar logic results in the same thinking for the lower contact - 0 to 0.5
Vdd

If the thresholds of the Schmitt are guaranteed to be > 0.8Vdd and < 0.2Vdd
then this will debounce quite nicely, with 0.3Vdd margin.

Still, I don't like the complexity -- I'd certainly just use a single R to
Vdd and have the switch pull the pin  low - then use software debouncing.

But ... if I had to be absolutely, positively sure that the switch couldn't
bounce (like if it controlled power in a nuclear reactor or some such) then
I might be more comfortable with this hardware solution.

Bob Ammerman
RAm Systems

{Original Message removed}

2002\05\21@124131 by Mike Singer

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Bob Barr wrote:

>On Tue, 21 May 2002 21:49:47 +1200, Jinx wrote:
>
>>>    Bouncing at bottom contact will produce 0 - 0.5 Vdd noise.
>>>    Bouncing at top contact will produce 0.5 - 1 Vdd noise.
>>
>>Exsqueeze me ?
>>
>>Noise coming from the switch will be 0-5V regardless. It
>>must be as a consequence of the contacts touching or otherwise the
>>switch wouldn't be a switch, unless it came
>>
>>from the Pisspoor Switch Co catalogue
>
>Isn't that a division of DirtCheap Enterprises? :=)
>
>A real favorite of purchasing managers worldwide.

  Wow !!! Thanx fellows, I've got a nice, almost forgotten feeling,
I used to have at Komsomol meetings in Soviet Union :-)

  Mike.

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2002\05\21@162409 by Jinx

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> I might be more comfortable with this hardware solution.
>
> Bob Ammerman

I'll tell you where I went wrong - I kept thinking pushbutton

(note to self - look at SPDT diagrams in front of you. Sorry
Mr S)

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