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Old 03-20-2011, 11:23 AM   #1 (permalink)
glug
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Join Date: Mar 2011
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VSS signal not being recognized?

I'm really impressed with mpguino. Thanks to everyone who has made it happen! I am so close to having my own duemilanove build working, but I need some help..

The snag is the VSS signal. I have verified that I am getting a nice, clean sine wave (at all speeds, at least up to the 35mph I have tested), but it seems it isn't being properly processed. It only starts to register VSS at speeds above 35 mph, and then increases too rapidly.

I think there is something wrong with the behavior of the VSS code as it relates to my signal. The injector pulse width measurement seems fine. I am debugging with the serial port output.

This is my second build. The first was on breadboard, and it had the same problem. My initial build had 100K resistors, and I assumed that was the issue. My perfboard version has 50K. I feel that the circuit is correct.

I am running mpguino.pde version 0.75 with arduino 022. I assume that is okay due to the at328. I tried the "required" 0011, but this sketch is too large to compile, and that version does not support the at328. I also tried 0016.

I have recorded (on an audio recorder) the VSS sensor output - both the raw sensor output, and also at pin 14/0 (after the resistor and diode). It's a great looking sine wave of approximately 10 hz per mph (approximately 36,000 pulse/mile). When sampling at pin 0, the bottom of the waveform is a bit flattened.

I considered that my arduino may have a bad pin 0, so I tried another duemilanove with the same result. Other code is reading signals on pin 0 just fine.

At rest, the sensor has an impedance of 1.25K.

The vehicle is a 1990 Ford F-250 truck, and my VSS source is the "RABS" sensor in the differential.

I have tried a variety of pulse/mile settings. At this point, I'm not sure where to go next. I know the vss code is quite mature, so I don't think I should need to tear into it.

Thanks!

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