Re: Dimming

[Nigel Orr <nigel@xxxxxxx>]

At 20:43 06/11/00 +0000, you wrote:
>I find X10 clumsy and unreliable.  I have been able to utilize a triac,
an=
d
>a variable resistor plus some other stuff to dim a light, but using a
>variable resistor defeats the point... what I need to be able to do is
dim
>the light using something like a PIC.

There are various options, digital or analogue control, or complete
homebre=
w...

Digital, probably most expensive, usually easily expandable, easy
interface=
=20
to PC, off the shelf.

Analogue, 0-10V or similar fed to a controller which handles all the triac=
=20
stuff.  Maplin have a module for about =A320 that looks like just the
ticke=
t.

Homebrew, you can run a PIC via a dropper resistor from the mains, and
take=
=20
a dropped, rectified, unsmoothed (phew!) mains signal as an input to=20
determine the zero-crossing points, then use an output to drive a=20
triac.  If you want the PIC to have a wired interface to some other=20
controller, it would need to be opto-isolated, or else you would need to=20
use an isolated power supply and something like an HCPL-3700 for
sensing,=20
instead of a dropper resistor etc.

That last paragraph may mean nothing to you, it could be called overly=20
concise... which of those 3 would you like to do?

>  I don't know how to do this, as at
>requires precise timing with the mains frequency, as far as I know.

You need to determine the zero crossing points, but you re-synchronise
to=20
each one of them, so the timing after that point isn't very critical.

Nigel


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