Re: Specifying a relay to control lights etc.

On 22 Oct 2007 01:49:49 -0700, scouselad
<allanlewis99@xxxxxxxxxxxxxx> wrote:

Hi,

I'm doing a project on home automation and, as you might expect, I'd
like to control a lighting circuit (standard filament bulbs, most
likely) via a digital light sensor and a micro-controller. Obviously,
to control the mains supply, I'll need some sort of relay. However,
I'm not sure how I could emulate a "dimmer" control in this way. For
example, I considered using PWM (which my micro-controller can produce
automatically), but I'm not sure if a relay can respond that fast. I
understand that solid-state relays (SSRs) respond much faster than
electromagnetic and electromechanical relays, so I'd like to use an
SSR if possible.

Basically, I'd like a device that I can give some variable input so
that it will vary the amount of AC mains voltage across my light bulb
(or heater, or fan, etc.). It would be nice if there was something
that will take digital input (perhaps PWM) but all I've found so far
in that department is the Crydom MCTC range, which are a little too
expensive (~£80/$160) compared to small SSRs (~£4-10/$8-20). However,
I'd be happy with something that takes analog input if it saves me a
lot of money.

---
From your description I assume that you want to be able to set, and
have the device keep the ambient light level constant in, say, a
room, regardless of the effects of external light streaming in
through windows or from adjacent rooms.

That is, if there was no external light streaming into the room the
lamp would be at its brightest, but as more and more external light
illuminated the room the lamp would dim in order to compensate.

Is that right?


--
JF
.