Circuits for magnetic pickups
Terry Sare
Terry_Sare at dell.com
Thu Aug 1 19:30:06 GMT 1996
To cancel the voltage induced in both line you would probably need to
ground the sensor side. Use a twisted pair to the sensor to have a
balance line, otherwise common mode noise cancellation will not be as
effective. You should also have some degree of hystresia in this as it
is a high input impedance and will pickup non common mode voltage and
oscillate.
TS
______________________________ Reply Separator _________________________________
Subject: Re: Circuits for magnetic pickups
Author: owner-diy_efi-outgoing at coulomb.eng.ohio-state.edu at dell_unix
Date: 8/1/96 1:23 PM
>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
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