MSgpio.com read only forums (Jan.15,2018)

Hi,
I just wanted to share some of my GPIO build that may be useful. Currently the system is stable and working well in my daily driver thanks to Lance and other forum member's help!

1) Dealing with the VSS signal has given us all fits in one form or another. My solution was to simply use a factory GM DRAC to deal with the raw VSS\OSS signal, then dump the square wave output into the GPIO thru a simple voltage divider with a 5v Zener diode as a voltage limit clamp for safety. I mounted the unit inside the GPIO enclosure. Just about any year DRAC (or VSS Buffer) will work as they all put out a nice square wave. The early one I have is an “open emitter” and requires a pull-up resistor. Apparently they were made from the mid 80’s to late 90’s and can be had for next to nothing in the bone yard

2) The 4.7 ohm PC resistor needed a solid, safe home since I didn’t want it floating around in the harness. I simply mounted it under the AMPseal connector and broke into the output trace on the GPIO board. It barely gets warm when passing maximum current and stays cool during driving.

Rob

rxl158,

Very nice! The DRAC ("Digital Ratio Adapter Controller" found in many GM vehicles from 1992+) are a nice find. In addition to providing a nice square wave output, they also slow the signal frequency considerably (a typical result would be a VSS input of 96000 pulse/mile, and a DRAC output of 2002 pulses/mile), resulting in less interrupt overhead in the code from handling the VSS signal. There is more information on these here: http://614streets.com/drac.html

Thanks for posting this info!

Lance.

Just spent some time fixing my vss using a nte 995 sine wave to square wave converter. It was a bit of a fight due to noise but it works. It's almost the same as a lm 2907 chip.

Rukavina,

I am glad you were able to make something that works for you. VSS noise is such a pain for so many users. In theory these speed signals are always perfect, but in reality they never are. And when you have a 'zero-crossing detector' sensitive to voltage swings near ground, even low levels of noise cause problems. I am happy you will now be able to leave these problem behind!

Lance.