Hello,

        I'm relatively new to the PIC scene.  I want to use a PIC16F870 to measure
the rpm of a rotating shaft (0-15,000rpm).  There is a passive speed sensor
in the shaft that puts out a sine wave whose frequency is proportional to
shaft rpm.  The amplitude of the signal increases with increasing
speed.  The max. voltage of this signal is 70V peak-peak.
        I'm using PIC Basic Pro to program my PIC.  I'm thinking about counting
the number of pulses over a specified amount of time (measured using
TIMER0) and converting to rpm.  Of course I'll have to do some averaging
and stuff like that.  Extreme accuracy is not important.  +/- 5% would be fine.
        I'm assuming putting a 70Vp-p signal to one of the digital I/O pins would
be bad?  How do I get around that?  Just a simple voltage divider?  What's
the voltage range the I/O pins can handle and still register as a HIGH or LOW?
        Any comments on potential pit falls or better ways to do this would be
appreciated.

Thanks,

Gary

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