Re: Controlling Holiday Lights

["Robert L Bass" <robertbass1@xxxxxxxxxxx>]

> PWM requires switching the light on and off
> very fast, otherwise you will see flicker instead of fade.

Anything faster than about 30 times per second you will see as a fade rather than flickering.  However, when using incandescent
bulbs the lamp doesn't actually turn off when power is cut.  Instead, the filament starts to cool down.  It takes a few ms to "go
out" and by that time the current has turned on again.  Triac based theatrical dimmers do what you're trying.  These vary in cost
partially with their load capacity.

> That is what I am building.  It isn't anything new.
> It is just phenomenally cheaper to build, plus I
> get exactly what I want.
>
>> might also want to Google the archives of CHA using "Christmas lights"
>
> Yup.  I've posted a few myself.  Such as
> http://www.computerchristmas.com/ just a few days ago and almost exactly
> two years ago.  :)
>
>> or some such.  There have been a number of interesting threads on the
>> subject every year since I've been posting (and that's a long time)
>
> Yeah, I've been around a while myself.  Looks like I just passed my 11th
> anniversary in this group.  :)

Heh, heh, heh...  You know, Sylvan, if I had taken note of the name in the headers I would have recognized you immediately.  :^)

> Oh, and BTW, I was doing the stage lighting thing nearly 30 years ago, and
> we didn't have any PWM equipment, much less computer control.  The light
> board in the booth was simply a remote control for large mechanical
> dimmers (motor-driven rotary variable resistors) in the 'cage'.

I've seen those backstage at a few "antique" theater houses over the years but never actually used one.  I've worked with 0-10V, a
few proprietary schemes, DMX-512 and MIDI.  We used MIDI to integrate lights with sound tracks for a few youth department functions.
I also used it to trigger strobes, foggers and fans at preset times before I installed a computerised control system.

> A scene change made all kinds of impressive whirring
> and buzzing noises, and the heat coming from that
> equipment would power a small town...

Sounds familiar.  We decided to upgrade the dimmer closet in a large church in CT a few years ago.  I acquired a replacement
transformer -- 440 / 208 WYE.  The transformer powered a 400-Amp breaker box which in turn powered the dimmers.  Even using triacs,
the air conditioned dimmer room (where the transformer was located) was always about 15 degrees warmer than the rest of the
building.  The real fun was installing the thing in the second floor dimming closet though.  It took five men to push and pull it up
the stairs.

> I find PWM incredible, especially since the introduction
> of low loss and high-power MOSFETS.  I almost cannot
> believe the way we set any light level on a 2000w fresnel,
> with comparatively no heat generation and noise.

Our system had 105 permanent circuits and about 15 open ones that could be attached to rental dimmers if needed.  Eight circuits
were 6kW each for running ACLs and such.  The rest were 1kW loads though with the gradual changeover to Source IV luminaires, we
were able to get the same light as a 1kW unit with ~600W.

One particular play for which I was the LD had something like 300 cues.  I'd plot the lights on my PC at home, configure the
"scenes" on stage, time all the cross-fades and then tweak each one until I was satisfied with everything.  At various times we used
a pair of fog machines, a bubbler (ala Lawrence Welk), half a dozen computerized strobes, various moving lights, four manual spots
and, once in a while, all of the FOH fixtures.  It was a fun place to go to church.

After doing that for a number of years a few other churches and schools asked me to work on their lighting systems.  I learned the
hard way an old saying, "Strand is also a verb."  Anyone who hasn worked as an LD will know what that means.

--

Regards,
Robert L Bass

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