Re: Specifying a relay to control lights etc.
- From: scouselad <allanlewis99@xxxxxxxxxxxxxx>
- Date: Tue, 23 Oct 2007 01:17:25 -0700
On Oct 22, 11:58 pm, John Fields <jfie...@xxxxxxxxxxxxxxxxxxxxx>
wrote:
On 22 Oct 2007 01:49:49 -0700, scouselad
<allanlewi...@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
Exactly. I have already bought a light sensor (an Intersil ISL29003)
with I2C output that I intend to control from a Microchip 16F877 or
similar - setting up that system is really another task entirely. What
I'm looking for is something that I can give a variable input (either
PWM or some digital input - I2C would be nice - or just an analogue
voltage level) causing it to adjust the power delivered to the light.
I know I can do this by adjusting the firing angle of a triac, but I'm
not sure of the circuitry involved to make to control fully
electronic. I've found lots of similar "dimmer" circuits on the net,
mostly using triacs, but they all have a large potentiometer to
control the dimming. What I want to do is use a circuit like that but
with an electronically-controlled potentiometer. Again, I know that
digital pots exist, but I don't think they will take UK mains voltage
(220-240V).
I hope that's clarified things.
.
- Follow-Ups:
- Re: Specifying a relay to control lights etc.
- From: John Fields
- Re: Specifying a relay to control lights etc.
- References:
- Specifying a relay to control lights etc.
- From: scouselad
- Re: Specifying a relay to control lights etc.
- From: John Fields
- Specifying a relay to control lights etc.
- Prev by Date: Re: Receiver sensitivity and IF bandwidth??
- Next by Date: Re: Power Supply Rectification and Smoothing
- Previous by thread: Re: Specifying a relay to control lights etc.
- Next by thread: Re: Specifying a relay to control lights etc.
- Index(es):
Relevant Pages
|
