Circuits for magnetic pickups

[Tim Drury]

I used the circuit shown in http://spbted.gtri.gatech.edu/hpe/ignitor.gif.  It is a +5V only
circuit with adjustable threshold.  The diode on the input filters the negative voltages
(tooth moving away from pickup).

If your having problems with noise try using both ends of the pickup in a differential-pair
configuration and feed them into the + and - inputs of the opamp.  Any noise will show
up on both lines and be cancelled out in the opamp.

-tim