On 19 Apr 2004 at 21:48, Chris Miller wrote:

> I have attached a PDF of my input circuit.  C1 is 1uf C2 is 33pf C3 is
> 1000pf R1 is 500ohm and R3 is 4.7K.  This circuit seems to work well
> on my old design but I do not have a PCB version of my PIC project to
> test it on yet.  I do have a wire wrapped version which fails
> miserably.

One thing to try is a much lower pull up than 4.7K to prevent false triggering.
In an indistrial control circuit I made that sits next to a 3 phase motor I use
470R pullups on all switch inputs. That means ~10mA at 5V. The device
supplying the input pulse must be able to sink this current. Opto-couplers are
not a magic solution for cases like this either...they may only take 1mA or so
to trigger which can easily be induced.

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Brent Brown, Electronic Design Solutions
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Ph/fax: +64 7 849 0069
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eMail:  brent.brown@clear.net.nz

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