Dimmer

[Darrel Taylor]

P.S. I am using full wave with few high value resistance connected to phase and zeners to drop the voltage further.

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?