> Hi,
>
> I've found very good article on Circuit Cellar's September 2004 issue
> named
> "DMX-512 Control - Build a USB-to-DMX-512 Converter".
> (Circuit schematics and programs can be found the authors web-site:
> http://www.kalbermatter.ch/index3.htm) Also I can supply pdf article on a
> demand.
>
> Previously i've been trying to implement picmicro based transmitter for
> dmx
> controller but after showing this article i've decide to implement
> usb-to-dmx controller. But i've a problem with this article the author
> mentions "galvanic isolation"  for protecting pc against over voltages.
> How
> can integrate such a protection to the existing circuitry?
>
>
> After reading this magazine article i've searched some on google for
> pc-based lighting control softwares and saw very sophisticated one named
> eCue programmer (from www.ecue.tv). It has very powerful sound2light
> feature
> that will activated via hardware dongle. I want to implement such a
> complicated lighting control interface for my own use. My IDE choice will
> be
> LabWindows/CVI, i've some experience with it, but i need some techinal
> help
> for developing sound to light conversation...
>
> Any help would be very appreciated,
>
> Thanks in advance,
> G=F6khan SEVER.


This is a typical FTDI based design where the PC is responsible for
generating the DMX and transmitting it through the USB. I think it can be
difficult to get the timing correct when sending a high number of channels
at full speed. There are some open source projects on
http://www.sourceforge.net that use similar devices. Other USB to DMX
devices (such as the StarPort at http://www.dovesystems.com plus many
others) have a processor (such as a PIC) interpreting commands from the
USB and then generating (and receiving) DMX independently.

On isolation, analog devices has a new isolator with a built in DC to DC
converter that's pretty neat. However, the DC to DC is only 50mw, which
would not be enough to drive a 485 transmitter into a terminated load. It
could run a receiver, though.

The new draft of DMX calls for transmitters to be ground referenced and
receivers to be floating, which would eliminate ground loops. So,
isolation at the controller is probably not desirable.

Another interesting isolator out there uses capacitive coupling to get
across the isolation barrier. It requires a floating power supply, though,
which is probably the most expensive part of an isolated input. An idea
I'd like to play around with, on the receive side, is to just capacitively
couple the DMX down to a ground referenced receiver with clamp diodes on
the inputs. 60 (or 50) Hz common mode would be dropped across the
capacitors while the 250kbps transitions would come on through. Haven't
had a chance to play with it, though.

Harold


-- =

FCC Rules Updated Daily at http://www.hallikainen.com
-- =

http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist