I am using the Parallax Propeller to start and stop timers for an auto racing timing system. Out of 250 cars there were timing issues with about 10 or so. It was very random and hard to diagnose. I knew that somehow the input pins were somehow reading high and causing timers to start and stop. I also knew that it was very quick because one chip polling via a loop didn’t show the pin was high and another chip polling at 12.5ns detected it. After creating a pin test program and using a scope I found the problem. When switching on, a well pump pressure switch caused the pin to read high. It wasn’t every time either. (Although the scope was showing the interference every time). The pump was cutting on and off about every 5 minutes. About 75% of the time when the relay clicked on it caused the pin to read high. The scope was showing upwards of 2.4 volts. This is enough to make the pin read high. I am not switching the relay via the microcontroller. The relay is in a separate room in the building but still causing interference into my timing system.
I’m very inexperienced but I have a good knowledge of electronics. This high voltage stuff (the pump is powered with 220VAC) is not my thing though. The power supply for the microcontroller is connected in the same electrical panel as the well pump. I have tried using a 12 volt battery instead. No success. I have tried using capacitors on the power supply without success either. When checking the pressure switch I found that the 220 ground wasn’t connected. After connecting the ground it seemed as if it helped, but it still showed reading high about one time in 40 minutes with the well pump switching on and off about every 5. So I think connecting the ground helped but didn’t solve the problem.
Like I said I’m inexperienced, and don’t really know where to start. I have thought about taking a start capacitor off of a 220 air compressor and putting that on the load on the pressure switch. Would this help? Any other ideas on how to fix this problem?