> I assume power ( HOT ) thru 4,7Meg  resister should be connected to
> one of pic pin then how do I synchronize it. I still do not clearly
picture
> it. Thanks for your help.

My comments re driving levels being too low for the optocoupler used still
apply but I didn't read your comments on driving closely enough - as noted
by others, random PWM to an AC  bulb will lead to unexp3cted results. I
stsill suspect a major problem is the amount of drive.

To detect zero crossing you CAN use a high value resistor bweteen mains and
a PIC pin but this is EXTREMELY unwise for safety reasons - especially where
your family is potentially (pun only slightly intended) being connected to
the other end.
Much safer is to use a second opto coupler to detect mains zero crossing

Phase ----RRRRR---|>|-----Neutral
                                |        |
                                --|<|--  Opto diode.

This requires a high voltage capable R of suitable rating. Using a mains
rated capacitor in series with the opto (and a resistor as well) will give
less power dissipation. There are other ways to get mains zero crossing info
such as small step down transformer, current transformer using a toroid etc.
Using an opto with zero crossing function built in will make the task easier
again.

If you DO use a high value R directly from mains you must make sure that all
low voltage parts are treated as if at mains potential and be SURE that the
resistor will withstand mains voltage - ideally use two in series with each
mains rated.


ST electronics have an app note for the ST6 used as a mains lamp dimmer and
no doubt many other people do too.


regards



            Russell McMahon

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