> -----Original Message-----
> From: Herbert Graf [mailto:mailinglist@FARCITE.NET]
> Sent: 23 September 2003 15:37
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE] (automotive) frequency trigger
>
>
>         The opto-isolator WOULD be the "safest" way to go,
> however I agree with you, taking that much current from the
> line might cause problems (it probably wouldn't but I
> wouldn't chance it myself). I have done something similar and
> I used the "high impedance" idea, a 1M resister going into
> the PIC I/O. The protection diodes on most PIC I/O pins
> SHOULD protect you enough. This technique is OK for a one
> off/personal project, however if you are going into volume
> I'd recommend other techniques (i.e. an NPN transistor). TTYL
>
> --


Did you drive 12v (via the 1Mohm) directly into the pic? Isn't that out of
spec? or did you use ~ 2M & 1M ish in a potential divider to give the pic
~4v

jon

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