Power line timebase

[Michael]

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?

[mister_e]

Yes it's possible and you can skip the additional external hardware. Just feed the 60Hz to a interruptible pin, a Timer CLK input or whatever else will do the trick

What do you want to do exactly?

[Michael]

Ok, sure...I've never used the internal timer before and yes the clock input would be the way to go...it would always increment that internal timer and then
I could look for a 1 second flag.

The T0CK input, right?

Right in front of me, yet like I said, have never used the timers before....forgot about that input pin.

I suppose you choose that pin in a register and the default is that it's incremented by the PIC crystal.

Great ! Thanks.

[Michael]

Just a matter of getting the 60hz sine wave squared up?

[mister_e]

you don't need to bother to much about that, use a simple resistor in serie (as current limiting) and look what's happen to the wave? Yeah, the PIC internal diode clamp it, most of the time, it's fair enough.

I have to go, but i may do something to help you to start. Which PIC do you plan to use?

[Michael]

I have some antique 16c65B's.

Thanks Mr E, you put me on the right path...it'll be fun to learn about the timer modules and interrupts.

Just though I'd take the 60hz off the secondary of my 6 volt transformer.

My crystal based worked fine but I don't like the temperature variations.