>
> I have just re-joined the list as I have a project to build a
> 9 zone external light controller (UK,
> "230"v), driven from PIRs, push buttons at each exit door etc.
>
> Planning to use a 16F877 running at 20mhz, zero-crossing
> detection, phase angle firing to give 'soft
> start' (and 'soft stop'?), opto-isolated triacs etc.
>
> All that pretty much as discussed in the archives at various
> places, thanks guys.
>
> The Question(s) :
>
> Am I expecting too much?

No, but you might think about keeping all of your AC syncing and gating on
one PIC and the logic for your sensing and timing on another. I am not one
of those people who says to spread PICs all over the place just to make
programming easier, but you will have to constantly time your gate signals
with the ZC's - the timing of which can occasionally vary as utility
providers switch generators on & off line, etc. It's just the most effective
way to keep this function set at the highest priority.


> Are there issues I am overlooking?

Here's one - what about crosstalk - @ 230V, every device gate will see some
effect from nearby gating, which takes the form of fast transients that
exceed ratings for many triac's DV/DT rating. Along the dsame lines - with
sensitivity varying with gating in different quadrants, you may want to
think of using SCR's instead. To run that many channels, work fast to get up
to speed on snubbing and determining the optimal gate pulse
shape/pattern/duration for your devices.

D. R. probably has the most experienc in multi-channel phase angle control -
just  listen carefully to his responses - He's helped me out of a couple of
stickies..


CL

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