Hi, I made a chain positioner powered by a stepper motor. One arduino mega feeds a pulse train to advance the chain a certain speed and distance. Another mode of operation is scrolling or jogging the chain to its starting position. When in pulse ready mode, it allows a second arduino uno to tell it to start the pulse train; when the pulse train is finished, it hands control back to the arduino uno.
Everything works great, except occasionally it starts on its own or does a second unwanted chain advancement. I put a scope on the pins and found 5 volt peak to peak oscillation at about 16KHz rate on the arduino power rails as well as all input and output pins. The stepper controller, when enabled, not even moving, emits a 16KHz square wave when the scope probe is brought near the stepper controller. I have disconnected all wiring from the stepper controller to the arduinos, the connections are through opto-isolators anyway, grounded the machine and all power supplies, changed power supplies, etc. Also tried 0.1 uF capacitors everywhere.
Any other ideas to suppress this noise? The project would run great except for this interference. Thanks for any input about this problem.