>I am working on an automotive timing circuit that uses a toyota reluctor
pick
>up. It's output is a pseudo sine wave that changes in frequency and
amplitude
>as the rpm changes. The ideal point to in the wave to send a position
>interrupt is as the wave passes zero. I've tried running it through an op
amp,
>letting the wave swing from a 5v pedestal, and computing the midpoint
between
>the two peaks but this eats up too much time is an "after the event has
come
>and gone" solution. Anybody have a suggestion?
>
>Bruce


Don't amplify it as a voltage.  Use a current to voltage converter.
That's even a simpler circuit..   Magnets moving past coils create
current. (evidenced by the messnier effect, since a superconductor
has no resistance, there can be no induced voltage!)

This also as the effect of minimizing the effect of the pickup
inductance since it's working into a short. It ruins the Q, making
the transducer much more wideband, and removes almost all
of the self-resonance problems.

We made this mistake with magnetic heads for credit cards too.
The voltage mode circuit is hideous, and has to be tweaked to
a range of frequencies.