Spurious Interrupts

[danlee58]

I'm using a SuperPro in an automotive application. One function is to calculate RPM by measuring the period of a sine wave. I use a zero crossing detector to generate an Interrupt. The interrupt sets & clears a timer to determine the period.

When I run it on the bench connected to batteries, all looks good. When I install it in the vehicle, my interrupt runs with no action on the pin. This spurious operation corrupts the measurement, and the device doesn't work right.

Could my interrupt procedure run in response to some error condition?

How can I determine why the interrupt procedure is running?

[danlee58]

I found the problem. It was a ground loop, that was introducing noise into my zero crossing detector.