Electrical Issue: PIC input false triggering, Signal Noise suspected.

[mark_s]

@mark_s
I would add that moving the reed switches a few inches away but leaving all the wiring as is would likely cause the reed switches to stop functioning but that is OK as it would allow you to determine if mark_s's theory holds true.

If you still have false trigering then it was because of either the magnetic coupling or possibly vibration.

At least that is what it seems you were getting at with your suggestion (or am I missing your point Mark?)

Dwight,

Yes, just move the reeds temporary to see if they are triggering. If that is causing the problem, maybe just by rotating the reeds 90 degrees would solve the problem? Abecker made two statements that are key - "It worked superbly on the bench" and installed with the reeds disconnected, it quit triggering. So it's probably interference entering the cable or the reeds closing?

Abecker should take note when it is triggering. On acceleration the motor will be drawing the most current. On deceleration it could be generating inductive spikes back into the power supply. Does it false when the train is not moving?

Brings back memories, my dad had a large H0 gauge train table when I was a kid. We couldn't wait for him to get home from work
so we could run it.

[abecker]

Mark,

I'll address the second remark in this reply. The first time I discovered the problem (and it did occur consistently) I would have to say there is no acceleration or deceleration possible because the speed control is set and remains at a preset DC voltage (I have no means of attenuating the speed control, electrically or mechanically.) Knowing this I suppose it is safe to conclude that there is a considerable inrush of current when the control relay closes.

As I recall from the first real run the PIC firmware closed the "Run" relay contacts and the trolley moved a few inches in the correct direction. Then operation jumped to the next logical state which was sensing the trolley position and stopping at the station. The only problem being, it was not near enough to the reed switch to activate it using the magnet below the car.

You ask a very good diagnostic question which I have not tried yet. I should test for false triggering without the trolley (dc motor) running but voltage applied to the track and overhead wire. This should rule out any influence of those objects. Lately I have been asking myself the uncomfortable question as to whether I have been wrongly suspecting DC motor EMI of causing the problem. This test would help eliminate the transmission sources from the cause.

I hope my work later today will shed more light. Thanks for your insights.