Circuits for magnetic pickups

[Tim Drury]

>If anyone get a good pickup going (no extra pulses) that uses the simple
>op-amp, let me know. I would love to remove the lm1815 from the design. I am
>far into the routing of the board, but I have a couple of extra amps in the
>LMC6494 that I am using for O2 buffers. So I you guys get some good thig
>working, shoot me some mail.

Sandy,

I always got good noise immunity by doing this:


                        |-------- gain ----------
                        |                        |
   [pickup]-----------------  +                  |
       |                          opamp  >---------
       ---------------------  -
                  |
                  |
                 GND

This circuit uses an op-amp like a comparator (high pos-feedback).
But what is important is using the other lead from the pickup as
a ground reference and feeding it into the negative side of the
op-amp.  Any noise in the system (eg. ignition) will appear on 
both leads of the pickup and be cancelled out inside the op-amp.

Here is something to consider:  Does it matter where you ground the
lead?  At the sensor, or at the op-amp?

-tim