Circuits for magnetic pickups

[peter paul fenske]

Hi Oliver

>On older transmissions GM used a PM generator as the Vehicle Speed Sensor.
>It outputs a sine wave and about 4000 pulses per mile.

This tends to give a sine wave whose frequency is proportional to
speed oliver. It ranges from about half a volt to ten volts depending
on vehicle speed. Magnetic field and all that


>
>The later model transmissions (it is Getrags I am particularly interested
>in) they use a hall sensor of some kind that is triggered by a slotted
>disc on the axle. That signal is run to the ECM/PCM which drives the
>speedo at the usual 4000ppm.

Hall effect devices generally deliver a square wave either five volts
or 12 volts in amplitude.
>
>Now, I would like to use the new transmission on an older car, so I
>would have to run the Hall sensor signal into a microprocessor that
>generates the proper speed signal from it.

I would just use a resistor network to slightly attenuate the hall output
and perhaps a low pass filter(parallel cap) and a series cap to generate
a zero crossing for the ECM.


>Any help would be appreciated!
>
>Best regards,
>
>-Oliver

Well oliver there are prob better answers out there. but dats all my sens
GL: peter