Newsgroups: rec.arts.theatre.stagecraft
Subject: Re: quick & dirty DMX interface?
References: 
"Mr R@t [2.33xu2]"  writes:

> apologies if this has been done to death before [I have already searched the
> net but not found anything which does not break the bank]
> 
> is it possible to get an RS232 to DMX adaptor for not much money - or even
> to make one?
> 
> We are toying wiht the idea of making cheap DMX controller from old PC's
> running either DOS or [probably] linux. I can write the software and am as
> for hardware I am not frightened of soldering irons - spent 4 years in the
> broadcast industry as an engineer...

You can find technical information on DMX-512 and links to circuits at
http://www.epanorama.net/lights.html#dmx512
There are some converter links, ut nit exacty RS-232 to DMX-512 interface.

> I saw someone here refer to RS485 DMX - is it then the same protocol as used
> for broadcast kit, so I can just use KK systems convertor or similar?

DMX-512 is the standard interface and protocol used used in
the theatre and entertainment industry. DMX-512 allows control systems to
communicate with dimming systems, automated luminaires, color scrollers 
and with other equipment.
The standard is developed by USITT at
1990. The standard is extremely simple. The interface is electrically
RS-485 bus where there is one transmitter all the timke transmitting and
multiple receives along the bus. The wiring for what DMX-512 is designed to
is 120 ohm shielded twisted pair wiring. DMX-512 is designed to use 5-pin
XLR connectors, but some implementations use 3-pin XLR connectors. The
protocol used in DMX-512 bus is similar to normal serial communications
(like RS-232 with 8 data bits + 1 stop bit) and operates at 250 kbps speed.

I don't know if "KK systems convertor or similar" will work, I have
not used those or don't�have data on those. Most propably it is not 
suitable for this application if it is designed for somethign else.

> I found some convertors but they were hundreds of pounds, come on surely the
> components used aren't *that* expensive???!?

The components are not that expensive. The reason why
those are that expensive is that they are low volume
special products (makes of them want to make some
money out of few units).

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/