Comparator

[Rafaelcl2]

Does anyone know how to use the comparator of pic 16f877?. I need a zero crossing detector , for when a sine wave cross the zero , the Pic starts counting and when another sine wave cross the zero , the pic stops the counter.
Thanks.

[Ttelmah]

The PIC16F877, doesn't have a comparator module....
The 16F877A does.
The easiest way to do what you want, is probably to wire the output to load a flip-flop, and the output of the second compator to clear it. Then use the output of the flip flop, to gate the sigal to count.

Best Wishes

[Rick]

How do I use the comparator as a zero crossing detector in C , using PIC16f877A?.

[Ttelmah]

The same way as any comparator. You would need to have the AC voltage 'biased' so that the 'zero' point represents a voltage inside the comparator's range, and then feed this voltage into one input, and the DC voltgae corresponding to the 'zero' level into the other.

Best Wishes

[Rick]

I've never use a comparator before , could you please explain me how it works. I need fist to setup the comparator , using setup_comparator() function . when I choose wich pins are gonna be the input of comparators , is that righ? So how it works , Where do I choose that the comparison is gonna be with 0?. And when the Sine cross the zero , is a output pin(where do I choose it?) gonna turn logic 1?

Thanks so much for you Attention.

[PCM programmer]

Look at the CCS example file, EX_COMP.c for sample code.
It's in this directory:
c:\program files\picc\examples\Ex_Comp.c

Also study this thread:
http://www.ccsinfo.com/forum/viewtopic.php?t=26861

[Rick]

Which simulator do u guys use to simulate a comparator? I can't find PIC16f877A or other PIC who has a comparator at Proteus.

[vsmguy]

Should not a schmitt trigger and a small inexpensive PIC do a zero crossing detector just fine ?