DMX Relay

I want to try to build a DMX relay, but I really don't know where to start. I've never used Arduino before, but I have been around a lot of electronics and a lot of programming so I want this to be both a learning project, and a usable project.

In my school's theatre we have many DMX cables to control all our house and stage lights, the lights can be controlled from two different locations. the vestibules or the lighting booth, and in order to change which location the lights can be controlled, we have to physically go plug, and un plug the wires and switch the patch around. In order to avoid this, I have been trying to think of a relay that takes both of the DMX lines from the booth and the vestibules and "decides" which one to relay to the lights. The way i was thinking is if there is no signal from the booth (the light board being turned OFF) then route the signal from the vestibules to the lights, and if the DMX cable from the board is active, then route the signal from the booth to the lights.

I hope this makes sense, I'm not sure how else to explain it. This is to avoid having to manually flip a switch or to manually un plug and plug back in different DMX cables.

I know you can buy things that do this, but the reason I am looking to make it is because I really want to get into arduino, and to save money.

So there are two DMX signals coming from the vestibules and the lighting booth, and I want to make an arduino and program it to "patch" one cable through to the lights, or the other depending on a set of parameters.

I was hoping you guys could shed some light on this because I have been looking around and thinking and thinking about it and haven't come up with much anything.

Thanks

Good project idea... the commercial dmx mergers around over $1000 (but also offer other useful features, two desks at once, LTP/HTP etc)

I would consider building a circuit with a mechanical relay at the place where the 2 DMX cables get patched (dimmer room?). The relay would physically switch the +/- conductors of the dmx cables, defaulting to the important cable (biobox?) if there is a fault, the relays Normally Closed position would ensure a failsafe.

You could install some buttons (connected arduino inputs) at the 3 locations, run some cheap cable permanently, write some code that controls the relay (DPDT could switch both pins of the DMX signal, GND could be common), almost wouldn't need an arduino..

Having the circuit auto-switch might be a lot more complicated, you could have an arduino setup to receive DMX, there's a few libraries already written, but I haven't seen any code that accept 2 dmx sources at once.

Maybe a simple voltage sensing circuit, detects which signal is active?

Anyway, just a few suggestions!
dargs

dargs:
Good project idea... the commercial dmx mergers around over $1000 (but also offer other useful features, two desks at once, LTP/HTP etc)

I would consider building a circuit with a mechanical relay at the place where the 2 DMX cables get patched (dimmer room?). The relay would physically switch the +/- conductors of the dmx cables, defaulting to the important cable (biobox?) if there is a fault, the relays Normally Closed position would ensure a failsafe.

You could install some buttons (connected arduino inputs) at the 3 locations, run some cheap cable permanently, write some code that controls the relay (DPDT could switch both pins of the DMX signal, GND could be common), almost wouldn't need an arduino..

Having the circuit auto-switch might be a lot more complicated, you could have an arduino setup to receive DMX, there's a few libraries already written, but I haven't seen any code that accept 2 dmx sources at once.

Maybe a simple voltage sensing circuit, detects which signal is active?

Anyway, just a few suggestions!
dargs

Yeah they are quite expensive, and I have pretty much figured how to do it mechanically without an adruino, but what I am trying to avoid is having to physically flip a switch. Its not so much that it is accepting the DMX sources, more what I was thinking, like you later said, just sense if one line has a voltage signal, and "patch" it through if it does.

I know there are ways to "test" the dmx signal, i found this link Make a DMX tester. which shows you how to create a tester with LEDs to display if it is working, so that might help..

I'm just having a hard time wrapping my head around it because I also don't know the limitations of arduino and things like that. i guess what im thinking of is having (the DMX line is a 5 pin) pins 2 and 3 go into arduino for both lines where the board.. i guess checks the voltage, and if it has voltage it just continues that out to a single DMX line..

Let me know if that makes sense, I might just be completely crazy and wrong.

Hi Kyle,
DMX is primarily a 3 wire system (all be it two and ground -RS485)
if you have the full complement of 5 wires ran to each location then in theory you could use the spare conductors/wires to switch the relay at the patch panel.
You would simply have to plug into a location to remotely take control of the system from there.
i would try putting a link between the spare unused pins, this link would then provide a link between a common connection and the routed relay at the patch panel. the relay would then link the DMX data line from the desk to the system.
OR use an Arduino to do the logical part, but you will still end up needing a relay/physical switch to route the DMX communication lines