I think I have smoked the MCU input that I was using for tach input. I made a mistake in my wiring:
That D9 input is supposed to be 5 V tolerant, but I guess it can't tolerate 6-7.5 V at unlimited current.
I was hoping to use that input and a timer as a frequency counter to determine RPM. This worked fine with a signal generator on the bench. However, I'm picking up the signal from the line that goes from the contact points in the distributor to the spark coil, which I was thinking this would be a 0-6 V (nominal) square wave. But, now I'm wondering if there might be some high voltage there as the points open and the field collapses, and if my little 10 nF bypass capacitor and the Zener will be sufficient.
That D9 input is supposed to be 5 V tolerant, but I guess it can't tolerate 6-7.5 V at unlimited current.
I was hoping to use that input and a timer as a frequency counter to determine RPM. This worked fine with a signal generator on the bench. However, I'm picking up the signal from the line that goes from the contact points in the distributor to the spark coil, which I was thinking this would be a 0-6 V (nominal) square wave. But, now I'm wondering if there might be some high voltage there as the points open and the field collapses, and if my little 10 nF bypass capacitor and the Zener will be sufficient.