Re: Controlling Holiday Lights

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Mon, 23 Oct 2006 12:35:17 -0400, Marc_F_Hult
<MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote in message
<8hqpj29mh1i2k70271s621vs7kc8akksu6@xxxxxxx>:

>On Sat, 21 Oct 2006 17:31:24 -0600, sylvan butler
><ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxxxxxxxx> wrote in message
><slrnejlbec.c53.ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxx>:
>
>>On Sat, 21 Oct 2006 02:13:08 -0400, Robert L Bass <robertbass1@xxxxxxxxxxx>
>wrote:
>>> sylvan wrote:
>>>> I'm talking about the hardware, and you are talking about the protocols
>>>> to talk to the hardware.
>>>
>>> I don't see why you consider MIDI too slow to accomplish the task.
>>
>>I'm wanting the hardware to control TRIAC or SSR switches, eg a parallel
>>binary I/O port.  With that I can turn on and off a light (or anything
>>else) at a rate over 1000 times per second.
>>
>>This allows all kinds of creative fades to On, Off, or anywhere in
>>between at 100% the whim of my self-written software.
>
>1000 on-offs per second controlling 60 hz AC lighting yields:
>
>(1000/sec) /(120 zero-crossing/sec) = 8.33 control choices per second.
>
>As a practical matter, about one-third of those possible on-off signals will
>fall so early in the AC cycle that they wouldn't produce enough current to
>make visible light (although they would use up electricity).
>
>So as a practical matter, unless you first convert the AC to DC, you might
>have as few as 5 distinct illumination levels.
>
>This is probably completely adequate for most scene-control purposes where
>slow, smooth transitions from scene to scene are unimportant, but you are
>touting this "1000hz" approach as being as providing "all kinds of creative
>fades" and "anywhere in between" when as a practical matter, your "1000hz"
>approach is much cruder than even the simplest X-10 dimmer.
>
>And it pales in comparison to DMX-512 with 255 distinct values and the
dimmer
>curves and pre-heat values (i.e, non-linear relationship between input
>control value and phase value) are part and parcel of even moderately
>sophisticated implementations.
>
>Are you doing more work and accomplishing less with this technique? Or do I
>misunderstand something quite completely  -- wouldn't be the first or last
>time ;-)
>
>... Marc
>Marc_F_Hult
>www.ECONtrol.org


255 levels * 44 changes * 120 zero-crossings/sec =  1,346,400 hz
= 1.35 mhz = frequency needed to bit-bang a phase-controlled AC dimmer with
the same number of intensity levels and time resolution as DMX512.

(Assuming phase control. The arithmetic for amplitude control is a bit
different and bumps into other limitations such as flicker.)

sylvan is asking about doing this from a PC bus with off-the-shelf LPT cards
so, presumably requires a real-time OS that runs on conventional x86 PC
hardware such as Windows CE, Labview RT, QNX, BeOS, VxWorks,
RTLinux/FreeRTOS/Linux2.6.18+ and so on.

(I wonder what use the 100 MB release of Windows PE 2.0  might have for HA if
the 24-hr run limitation could be overcome/thwarted?  Not RT, but small
enough for simple installation and use without a hard drive.
http://www.microsoft.com/technet/windowsvista/deploy/winpe.mspx )

... Marc
Marc_F_Hult
www.ECOntrol.org