Electric Noise PIC problem

[Tobias]

Dave
Thanks for the reply. I was away from my PC for a few days. The first schematic was the new version of the board being built. I changed input pins just for the hell of it to see if I could isolate the problem. I screwed up and made the first example schematic a cross between the new and older problem version.
The problem board schematic is attached. I had the WOT going into PortB.0 and On/Off on B1.

I just don't understand what in the hell is going on. When On/Off is pulled low, it activates the code and there is start up routine of about ten seconds. When WOT is pulled low it starts the timers. The two circuits are pretty much identical (WOT and On/Off) Yet the WOT looks like it is losing a signal and restarting the timer routine.

R22 and R25 (on the problem board/second attachment) are pull downs to help eliminate false triggering. I populated another board, the problem child one today and shipped it out to be tested on a car this weekend. I removed R22 and replaced it with a 10uf cap. I tested it out on the scope using a 16v input cycling at even 50 hz and it keep the WOT pin pulled low. So this weekends test should help me figure it out.

[Jerson]

Has the behaviour got anything to do with RB0/INT being used as an interrupt in your program? Maybe you can poll RB0 to confirm if this is what is causing the malfunction.

[Tobias]

Good question, originally I was using it as an interrupt but then I changed it over to a Do While Loop that executes the timer function while WOT is Low. I thought maybe I wasn't doing something right on the interrupt side so I went to the Do WHile

[mr.sneezy]

Hi,
Many many years ago I did the development for a GoKart (the racing kind) datalogger and instrument system, based on a HC11 In the R&D phase we spent more time in EMI suppression than in any other part of the design. We tried dozen of supression thechniques before we had a device that would run for more than half a lap once mounted on a Kart... Spark ignition environments are just EMI hell !

[Tobias]

EMI is the bitch of it all. I have a MSD ignition on my bench with a coil and test plug. The ignition and the coil is just like in the race car. I can fire up the MSD and have the board right next to the coil and all is fine, in the car it fails. The problem I am running into is that the wiring on every car is unique too. Some guys aren't even running a ground wire to the battery...they rely on the chassis to carry the load. I do have hope in that there are other electronics like data acq boxes that do work.

[Jerson]

I do not have too much of exposure to car electronics, but the one time I did work on a car was with the central locking. Rev the engine and all hell broke lose. The fix was to plant a simple half wave diode rectifier followed by a smoothing cap to supply my board followed by the normal regulator stuff. Along with this, there were some kind of coils fitted on the spark plugs that reduced the noise immensely.

Maybe I was plain lucky that my board worked after those changes or maybe it can lead you onto something.

[Dave]

Tobias , Once again, Where are the pullups for the inputs? And what is the purpose of R22 and R25? The schematic looks the same as before...

Dave Purola,
N8NTA