Re: Controlling Holiday Lights

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Sun, 22 Oct 2006 12:58:11 -0600, sylvan butler
<ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxxxxxxxx> wrote in message
<slrnejnfq3.u01.ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxx>:

>I know that.  I'm building the instrument that is controlled, not the
>controller...
>
>> that a "change" can be a command such as "Begin fade from scene 125 to
>
>And the instrument which actually implements the fade is what I am
>building.  Unless it uses HUGE variable resistors with HUMONGOUS heat
>sinks to dump the waste heat, it will use PWM (Pulse Width Modulation)
>to actually fade the light.  PWM requires switching the light on and off
>very fast, otherwise you will see flicker instead of fade.

<snip>

<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.

Are you referring to reverse-phase AC control using MOSFETs as "PWM"?

Dimming of AC lamps is conventionally done by turning on the current to the
dimmer after the zero-crossing rather than at the zero crossing. This is
conventionally described as "phase control", not " Pulse Width Modification",
whether TRIACs, back-to-back SCRs, IGBTs, or (rarely?) MOSFETs are used as
the semiconductor control elements and whether the switching is conventional
or reverse phase.

Or are you talking about lamps or LED's  operated on DC?
Is so, there are DMX512->PWM and 0-10vdc analog-> PWM converters that
modulate DC.

There are of course many DMX512--> AC dimmer and 0-10vdc --> AC dimmers

I've wired parts of my house with 10AWG for ceiling-mounted DC lamps. At
present, I have 24vdc ->> 0 to 12vdc dimmers which are under DMX/0-10vdc
control and have begun investigating high-power LED's (the lamps are still to
pricey for me at this time). LEDs are an arena for PWM in home lighting,
especially when combined with RGB lighting control so that color as well as
intensity can be controlled. High-power LED controller ICs are emerging eg
from Maxim.

... Marc
Marc_F_Hult
www.ECOntrol.org