The Jeep Grand Wagoneers with cruise control have an inline vehicle speed sensor (VSS). I finally pulled mine to have a look at converting it for use with GM TBI, instead of having to buy an expensive VSS.
It outputs 8PPR. The signal is a sine wave when viewed on an oscilloscope while spinning the sensor with a cordless drill. Amplitude ranges from 0.1 Vp-p to 3 Vp-p at max drill speed. In other words, frequency and amplitude increase with rotational speed. I don't know how much higher the amplitude goes.
So, the GM VSS needs a buffer right? I think this buffer device is converting the sine wave to a digital square wave of fixed amplitude (5V). Does that sound right?
Hopefully so. I prototyped a simple circuit to do just that. To get 4PPR out of 8PPR, simply run the output through a flip flop in a divide by 2 configuration.
So, the next step is to try the circuit with an Arduino (or something), log data and verify that I've dealt with glitches I was seeing earlier, and also output the speed so I can compare it to the mechanical speedo while driving.
I'll post updates here.
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