Re: Controlling Holiday Lights

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Mon, 23 Oct 2006 17:55:36 -0600, sylvan butler
<ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxxxxxxxx> wrote in message
<slrnejqljo.a3i.ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxx>:

>On Mon, 23 Oct 2006 11:49:44 -0400, Marc_F_Hult
<MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote:

>
>> I presume that sylvan gets his "1000hz" requirement from 120
>>zero-crossings per second * 8 positions  per zero crossing = OFF + 8 other
>>intensity values.
>
>Not even close.

Then please do post how you chose 1000 hz.


>> Pretty crude. Not sure why he would go this route.
>
>I'm not.
>
>> Conventional dimmers do much better than that -- eg DMX512 nominally has
>> 255 intensity values, some
>
>Think of it as me building a DMX512 or X10 dimmer.  How does it actually
>create the varying intensities?  By turning on and off the light many
>times per second.  That's what I'm doing.

No.  DMX512 does not "turn[] on and off the light off many times per second".
DMX512 can set a new, 0-255 dimmer level up to 44 times a second, but it is
the dimmer that turns the conduction of a TRIAC or back-to-back SCR ON
depending on the phase at each half cycle. A TRIAC cannot be "turned off"
during 0< a < 180 and 180 < a <360 degrees. It turns _itself_ OFF at 0 and
270 degrees whether we like it or not.

If you are turning ON the light many times per second, how do you synchronize
with line frequency? If you don't, what happens if you turn on the light when
it happens to be at 0 or 180 degrees compared to when it happens to be at 90
or 270 degrees?

... Marc
Marc_F_Hult
www.ECONtrol.org