I have tied the PIC ground to neutral, and an EXTINT pin to hot through a
4.7M resistor, and gotten good zero cross detection.  I have then timed
over for the desired phase angle, and pulsed a logic triac directly from
another io pin.  Works great, few parts, spiffy.  Mchip has an app note on
the zero cross method, and as someone else mentioned, motorla's data book
has good info on triac driving, also teccor's had good tutorial.

>         We are working on a lighting controller but we need some info and
/
> or code on Zero Crossing, Phase Control and Interfacing Triacs. We would
> prefer code for the 16C84 but that doesnt really matter as we can convert
it.
>
>                                 Thanks from
>                                         David Dobbs
>
>
>
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>                 Just to let you know we have a web page at
>                       ' http://www.innotts.co.uk/~dobbs/ '
>
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>