Circuits for magnetic pickups

[Darrell Norquay]

At 08:43 AM 7/31/96 +1200, Tony Bryant wrote:
>I'm using the following circuit for my inductive pickups:

The circuit I've seen using the LM3900 is:

                   +V                   
                   0                   R1 - 5M
                   |                   R2 - 200K
                   R1                  R3 - 200K
                   |    |\             R4 - 10M
                   |    | \            R5 - 5M
          P----R2--+----|- \
          I             |   \
          C             |    \__________
          K             |    /      |
          U             |   /       |
          P----R3--+----|+ /        |
                   |    | /         |
                   |    |/          |
                   +--------R5------+
                   |
                   R4
                   |
                   0    
                   +V


This was for use with a magnetic reluctor type pickup.  This will give
hysteresis, as well as a nice square wave out.  You might try a few hundred
pF cap across the pickup, and about a .01uF from the pickup side of R2 to
ground.  This may improve the input noise immunity.




regards
dn
dnorquay at awinc.com