Grand Wagoneer cruise sensor as VSS

[shimniok]

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.

[babywag]

http://www.ifsja.org/forums/vb/showthread.php?t=70106
Related reading...

[Six_Shooter]

I'm pretty sure people have used those sensors with GM ECMs directly without issue. Change the road speed constant to match the 8 PPR signal and the vehicle speed should be correct.

On top of that, if you still wanted to use the Arduino, you can connect directly to it without dividing the signal first, since you can do all of the scaling in software, and also change it from a sine wave to a square wave output.

[babywag]

I'm pretty sure people have used those sensors with GM ECMs directly without issue. Change the road speed constant to match the 8 PPR signal and the vehicle speed should be correct.

On top of that, if you still wanted to use the Arduino, you can connect directly to it without dividing the signal first, since you can do all of the scaling in software, and also change it from a sine wave to a square wave output.

I asked several years ago in regarding to changing the 7747 .bin, nobody knew what to edit.
So if you have the info? what needs to be changed?

[EagleMark]

There is no Parameter in 7747. Any speed stuff goes to and from DRAC.

[Six_Shooter]

There is no Parameter in 7747. Any speed stuff goes to and from DRAC.

Yes, a DRAC would work well here, would have to calculate the proper setting for the jumpers, but that's where using the DIP switches is great, to be able to adjust easily.

I saw no mention of what ECM was being used, and since the 4PPR setting swas mentioned I assumed MPFI or late model PCM that uses the 4 PPR sensor natively. The 7747 uses a 2 PPR VSS natively.