VSS Signal assistance?

[wagonman76]

On vehicles that are having trouble with the VSS signal, does the VSS go through the ECM or VSS buffer? And if so, is the signal being tapped after that?

I know at least on mine, the signal from the VSS itself isnt very friendly. Depending on the vehicle, it goes either through the ECM or VSS buffer to clean up the signal, and then feeds the pulses per mile to the gauge cluster and cruise control module. I tapped into that and didnt have any problems once I got my wiring right.

[starquestPilot]

Originally Posted by wagonman76

On vehicles that are having trouble with the VSS signal, does the VSS go through the ECM or VSS buffer? I know at least on mine, the signal from the VSS itself isnt very friendly...

Starions: The signal to the ECM is not pre-filtered. It's a very bouncy/noisy 0-5v signal created by a magnet/reed switch combination at the speedometer.

[dcb]

Just a heads up, I think I made some progress this morning after the NASA guys got me thinking

Basic strategy,

keep track of the number of vss pulses (already do that) and accumulate the vss pulse lengths.

every 1/2 second compute the instant mph from the accumulated pulse lengths/number of vss pulses and reset.

I did a quick road test an instant mph is looking a lot better in the metro. Will release a new version when satisfied with it and when I integrate it into instant mpg.

[ac7ss]

Here is the waveform supplied to me from DCB. Placing a filter circuit in there will clean up the extra high speed pulses (small peaks) that may trigger false signals.

[dcb]

There are no known false peaks being picked up though. The chip has built in a differential between ON and OFF detection and there is debouncing to boot. As well as the pulse count seems accurate over large distances, so what are you trying to fix? The extra hardware won't buy you anything at this point.

[dcb]

I would add that as evidence that the fully processed signal is about as good as it is going to get is evidenced by the fact that when you average the readings over 1/2 second it now seems to be spot on and pretty smooth.

So it is accurate over distance, it is accurate on the 1/2 second scale, things will get progressively worse at less than 1/2 second for sure.

[ac7ss]

Likely, the downslope and upslope are causing the difficulty. They may be triggering a longer / shorter duration between pulses depending on the trigger level. If the average over a half second is good. there is not likely to be a problem in the long term. If one wanted to play with it on their own, there are a few ways to normalize the signal. But if, as you say, the 1/2 second average is good, that is the best solution.

[dcb]

Originally Posted by ac7ss

Likely, the downslope and upslope are causing the difficulty.

Well, if you like, around position 1159760 in that file, the speed should be pretty steady, but I think you will find that the large verticals are not evenly spaced, likely due to mechanical "slop". The data is all there and you were the one who said it was "easy" You might have to look at more than one pulse though.

Originally Posted by ac7ss

of course, if we had a trace output of the anomalous pulses it would be easy to determine the easy way to screen them out.

[forgottenmindset]

I just uploaded the v.72 code and the vss instant speed is awesome it is so fluid now, EXCEPT

when I get to 40 mph

then it waits until about 60 mph before it starts counting backward

1, 10, 30, 40, 40, 40, 40, 40, 39, 38, 37


CRAZY

where in the code can I tweak this to get it right?

[dcb]

Hmm.... Maybe

change:
  addEvent(enableVSSID,2 ); //check back in a couple milli
to:
  addEvent(enableVSSID,1 ); //check back in a couple milli