Re: RS485 - XPL on the wire

["Mal Lansell" <mlansell@xxxxxxxxxxxxxx>]

The dmx interface hardware would only have to deal with those two byte
channel/level commands - not a full xPL message.  There would be a PC
service handling the xPL side of things in the same way that the CM12
service does for X10.

The heaviest load would be on the DMX side, where the data has to be
continually pumped out - this might be the best side to use the UART,
with the PC side (RS232?) handled through bit-banging.

IIRC, there's no all channels on/off command - the system consists
only of a stream of light level bytes.  Each DMX-controlled device
has to count the bytes until it gets to the one meant for itself, and
then uses that byte to set its own light level.  The count resets
when there is a pause (I forget how long) between bytes.

To produce the equivalent of all channels off, you would have your
DMX interface just send a stream of zeros (and yes, you would need to
reserve a channel for special commands from the PC).

As for dimmer packs - they are often available on Ebay.  Otherwise,
it looks like you can get 4 channels for around 100 pounds (e.g. the
Chauvet DMX35 dimmer).

If you want to DIY the whole thing, there is also a company making
DMX controlled dimmer chips (basically a pre-programmed PIC) that
handle all the timing for dimming via solid state relays.
www.artisticlicence.com

Of course, it's not just lights that are DMX enabled - you could turn
your house into a virtual nightclub!

Mal






--- In ukha_xpl@xxxxxxx, "Frank Mc Alinden" <fmcalind@b...>
wrote:
> Hi Mal
>             Just had a look at that Guys ASM code I  assumed that a
uart
> would be needed for the dmx output....He just bit bangs it out.....
>
> It looks like it could be done easily using a 16f876....my only
concern
> would be processing the incoming xpl message which in my setup is
interrupt
> driven...and can only process info after all channels has been
updated....I
> think it would also fit into a 16f88 (4k?) .....
>
> When you say that dmx units are a lot cheaper than cbus dimmers how
much are
> they ???
>
> Would people purchase Dmx units for their lighting control ???
>
> If i can pick one up cheap i would have a go at xpLling it........
>
> Also does dmx have an  All channels ON / OFF  command ??? if not
would some
> channel numbers have to be reserved for these functions
>
> Below is what i would assume to be an xPL Dmx command..???looks
ok ???
>
> *********
> xpl-cmnd
> {
> hop=1
> source= xpl-xplhal.mainpc
> target=aec-dmx.mainpc
> }
> dmx.basic
> {
> channel=20
> level=45
> }
>
> ****************************************************
>
> Frank
>