Re: Re: Dimming

[Nigel Orr <nigel@xxxxxxx>]

At 17:31 07/11/00 +0000, you wrote:
>Nigel - can you suggest a Maplin part number? I think that =A320 per
>lamp is a little too much - a triac plus a few other components cost
>under a pound...

Yes, assuming limitless design time available, you could do the whole
thing=
=20
(excluding enclosure) for under a tenner including optoisolated control=20
etc, but I assumed you were in the same boat as me- too many ideas, too=20
little time.  CK23A is the Maplin part number, ZAX27 is the
manufacturers=20
number, there's a data sheet on Maplins website, price is =A329.99, not
=A3=
20=20
as I had thought.

> > You need to determine the zero crossing points, but you re-
>synchronise to
> > each one of them, so the timing after that point isn't very
>critical.
>
>How could the PIC determine the zero crossing points?

'Depends'.  If you want the pic on the 'live' side, and optoisolate your=20
data interface, you can use some mix of a dropper resistor, zener and=20
diode.  If you want the PIC to be on the 'data' side, and optoisolate your=
=20
triacs and zero crossing input, use something like an HCPL-3700, or
maybe=20
even a plain optoisolator (connected backwards) and suitable components.

If you have a look at the piclist archives (maybe http://www.piclist.org ),=
=20
this has come up fairly often, a search for 'zero crossing' or 'mains=20
control' would probably help.

Nigel


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