Quote Originally Posted by Darrel Taylor View Post
What size zeners are you using?

The INT input is Schmidt trigger, so it has to get above 4.0V to trigger the interrupt.
It may not make it, or cause a delay after zero-crossing that could affect the timing.

Have you tried it without the zeners?
Hello Darrel, I made a slight mistake in the above post, it's not full wave rectified. The circuit goes like this - Phase->1.5Meg->12V zener->1K->4.7V zener->3.3Meg->PIC

No I have not tried it without zeners yet. Will it be OK to remove the zeners from the above equation - the place where I am gets heavy voltage fluctuations - The variation could be from 170V - 280V AC (I am serious!)