Charles, I did see your post with that code before posting this. Some of it's description seems ambiguous to me, but that's likely my own fault. PRELOAD value for example... I don't know what my shortest tach half cycle is, and then in code comments it says "depends on clock speed", but I don't know what to change if using a 4MHz Xtal. Seems a lot to work out when I only need to measure the time between two pulses. The current program is cycling all the time as said in my first post, or the power LED wouldn't work... as I also said, it's a POV display. I'm not using any pause commands at all. Timing is done by counting program cycles so there is opportunity to multitask. The alternator does sound like a good idea, even if it doesn't have the right output as described, the output of the regulator wouldn't reach it's full voltage until idling. With the right resistor divider, I assume I could produce a logic high or low state on a pin so there would still be no halting program execution.