Circuits for magnetic pickups

[Oliver Scholz]

Hi all,

regarding the recent discussion of magnetic pickups I have a question:

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

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.

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.

Now the question: Does anybody know the waveform of the signal?
Is it sine, square, ??? Which circuit would be recommended to buffer it?
Also, how many pulses does it generate per revolution of the drive wheel?

Any help would be appreciated!

Best regards,

-Oliver