'Mains lighting control'
Whats the best way of controling the brightness of mains lights? I saw a
lamp a while back that consisted of a frosted perspex tube with two
coloured mains lamps in it. They were then faded in and out to produce
various coloured lighting in the room. I liked the idea but I thought I
could do better with a PIC and make it user controllable (such as speed of
change and pattern). I was thinking of triac control but I have never had
to do this in the past. Can someone suggest some code or control method
that would be appropriate.
Personal Web Pages: http://web.ukonline.co.uk/members/tim.kerby/
There's an application note on the Microchip web site on triac
dimming of lights. Also, I've designed a product based on the 16c74a
that does this. See the ShoeBox dimmer at http://www.dovesystems.com .
Phase angle control is the easyest way to control the volume of a light
(incandessent) if you need to use flouressent then consider the HF ballast
from phillips they take a 0-10v signal same as many commercial dimers.
A consideration with phase angle control is the ammount of noise radiated and
conducted this needs to be controled with capacitive and inductive filters.
Low voltage lamps were described in a recent mchip seminar using pwm and a
single FET these make a simalar ammount of 'noise' but due to the switching
frequency it is simpler to filter.
|I am involved with our church's annual Singing Xmas Tree, where we have
an choir put on a concert in a 6 level
tree shaped pyramid. We use Xmas tree lights in 4 colors and some
special channels as well, all on dimmers. Commercial dimmers all seem
to have that 30 volt turn on where you can't dim to or start from '0',
because of the diac diode built in to most dimmers. I built a 555 ckt a
few years ago, that starts its time period each ac zero crossover and
then C/R times from 0 to 8.33333ms (1/2 of each 60 cycle) and then
triggers a 25 amp triac. The problem is we now want to remote the
control pots and I now need dc control rather than R/C time constant
control as we want to run the controls ~200 ft away from the
triacs/power boards. The pic seems like a good vehicle for this. One
other consideration, I don't mind the concept of running analog wires/dc
voltage for each control if it is much simpler, but it seems to me, I
could run RS422 signals as well on two wires. Rather than re-inventing
the wheel (fun but takes time), can any of you help me. Surely this has
been done many times before - theater lighting etc. I have no problem
with the electronics, making PC boards etc. but don't (yet) have much
pic experience. Tks for your time.
I've found useful information regarding TRIAC in the SGS-THOMSON web
in the technical literature area:
Under Processors & Peripherals and under Thyristors you will find notes
from basics on firing TRIACS up to elaborated circuits with ST
microcontrollers that you can convert to your PIC.
Montaigne, Mike <MITVMA.MIT.EDU> wrote: PICLIST
> I am involved with our church's annual Singing Xmas Tree, where we
> have an choir put on a concert in a 6 level tree shaped pyramid.
> We use Xmas tree lights in 4 colors and some special channels as
> well, all on dimmers. .... we now want to remote the control pots
> and I now need dc control rather than R/C time constant control as
> we want to run the controls ~200 ft away from the triacs/power
> boards. .... it seems to me, I could run RS422 signals as well on
> two wires. Rather than re-inventing the wheel (fun but takes
> time), can any of you help me. Surely this has been done many times
> before - theater lighting etc.
Yes, it's been done before; take a look at the DMX512 mini-FAQ at:
=== Andrew Warren - ix.netcom.comfastfwd
=== Fast Forward Engineering - Vista, California
Tks Andy, I printed that out.
Simple light dimmers are C/R time from '0' crossover to trigger triac.
Theater (analog) dimmers are 0-10V control & 0-10V ramp into comparator
to time from '0' xover.
Even if controlled by DMX or other serial link, still electronically
noisy because of A.C turn-on.
Why not (using micro) always start on '0' crossover and leave out 1/2
The more 1/2 cycles you leave out (alternate odd and even so load is
balanced), the dimmer the light.
Would this work? I've never seen it, but I may be re-inventing the
Regarding lamp dimming by including only selected full
half-cycles, I believe you'll get a lot of flicker on the lamp. This is
especially the case if you want a large number of levels. Our Shoebox
dimmer (http://www.dovesystems.com) maps the 256 levels of DMX to 33,333
possible turn-on times in each half cycle. If you want ten lamp levels
(and don't care about relative lamp intensity or DC component), you could
select to send 1 to 10 half-cycles every 83mS, resulting in a flicker
rate of only 12 Hz. This would be quite visible.
On Fri, 16 Jan 1998 16:13:55 -0500 "Montaigne, Mike" <AECL.CA> montaignem
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