Re: Controlling Holiday Lights

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Mon, 23 Oct 2006 03:03:53 GMT, shb*NO*SPAM*@comporium.net (Si Ballenger)
wrote in message  <453c2f0d.127164656@xxxxxxxxxxxxxxxxxx>:

>On Sat, 21 Oct 2006 19:23:20 -0600, sylvan butler
><ZsdbUse1+noZs_0610@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
>>Very.  12 on a standard parallel port, but only 8 of those are 'fast'.
>>That's why I was asking about multiple parallel boards.  :)
>
>You may want to look into getting the SIIG parallel port cards
>like below. One assumes you have chosen an OS and software that
>will support your high speed timing requierments.
>
>http://www.provantage.com/siig-lp-p02011-s4~7SIPC00Q.htm

sylvan was asking about cards with four LPTs (the one cited only have two
ports).  In any case, LPT ports seem to be an inefficient way to get 4 x 8 =
32 'fast' TTL outputs.

In bygone days, the LPTs were convenient because they were supported by the
OS. As Si implies above, attempting to control multiple LTP's in real time
deterministically at 1000hz with a PC without a real- time operating system
would cause one to see many more flashes and other glitches owing to OS and
software timing problems in the PC than anything caused by the hardware.

I presume that sylvan gets his "1000hz" requirement from 120 zero-crossings
per second * 8 positions  per zero crossing = OFF + 8 other intensity values.
Pretty crude. Not sure why he would go this route. Conventional dimmers do
much better than that -- eg DMX512 nominally has 255 intensity values, some
X-10 implementations nominally 32 different values,  etc.

... Marc
Marc_F_Hult
www.ECOntrol.org