I thought I'd redo a pic stopwatch that I did and rather than crystal control, use the AC line frequency as a timebase. (It's not a portable stopwatch).

I really would like some hints on what I can do.

I keep thinking no matter what, I'm going to have to have an external chip to convert the 60hz to 1 hz (or whatever)....but do I?

I really don't have much experience with what a PIC can do "in the background"...but it seems limited to it's own peripheral hardware (tmrs, usart, etc).

Are there any creative ways that I could monitor the line frequency and yet still have the continuous program running doing all the math and led display functions etc. ?

Like I say, I suppose a counter or 2 as an external timebase is probably where I will end up? (There was a chip CD4566 that was a 60hz to 1 hz timebase but no longer available).

Any ideas?