Multiple Consoles on a single DMX line
- Thread starterg15
- Start date
In all likelihood it simply won't work. You will have two RS-485 transceivers trying to drive the same line, and unless you have them perfectly synchronized the downstream devices won't even be able to identify the start of a DMX frame. You might get some garbage that the receiving devices will react to, but you certainly won't have any kind of control.
RS 485 is widely used in industrial applications, so the transceivers are designed to be highly tolerant and usually have overcurrent and overvoltage protection built in, so it's very unlikely that any damage will be done.
RS 485 is widely used in industrial applications, so the transceivers are designed to be highly tolerant and usually have overcurrent and overvoltage protection built in, so it's very unlikely that any damage will be done.
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Yes, it won't work. See the metaphoric description of DMX in the wiki--one can't have two sources yelling out information, the receivers will get confused as to whom to listen to.
However, there are devices that can combine two (or more) inputs into one output. Either on an HTP basis: DFD DMX512 Combine Unit; or on a priority basis: DataLynx.
However, there are devices that can combine two (or more) inputs into one output. Either on an HTP basis: DFD DMX512 Combine Unit; or on a priority basis: DataLynx.
In general, the backup console/processor is listening for its tracking partner (primary console/processor) and making sure that it is still up and in control. When it detects the primary console/processor is not communicating with it, it will start outputting DMX.
While two consoles/processors are connected to the line, only one is transmitting at a time.
JD
Well-Known Member
There's always the $3 solution... a DPDT switch! Don't laugh! If you're only going to run one console at a time it works! (as in a "live" one, and one for backup.)
I even tried it with two live boards, switching back and forth to see what would happen. I am sure there was some disturbance as one or two frames got lost, but with the conventional dimmers, I was hard pressed to even see a flicker.
Fleenor's SW1 Passive A/B Switch is slightly more than $3
, but yes, it's another solution.I built one of these back in the mid-'80s to use with my Prestiges. Practically a necessity, and being an AV company, they were big on charging half-price for backup gear.
In another venue I got tired of unplugging and plugging cables, so built one to transfer control from the Prestige in the booth to the Patchman on stage.
sure, i'll admit they're great as a 2 scene preset, but trying to record and play back any type of cue is just so much harder than it needs to be.
/hijack
on topic:
the smartfade can be setup so that fader 1 controls the level of everything in the dmx input stream, while the rest of the faders remain channel faders
/hijack
on topic:
the smartfade can be setup so that fader 1 controls the level of everything in the dmx input stream, while the rest of the faders remain channel faders
Bah I new I should have split those posts off into a QotD last night >:>
Synchronize
Active Member
zuixro
Active Member
Even when nothing is changing, the controller is still spitting out DMX. DMX is literally just a string of bytes, the intensities of channels 1 through 512, so if you had 10 lights patched starting at channel 10, the stream would look something like this:
[Start] 0 0 0 0 0 0 0 0 0 FL FL FL FL FL FL FL FL FL FL 0 0 0 0 0 0 0 0 0 0 [And onward to channel 512]
If the controllers were perfectly synchronized, it might work. Probably wouldn't be reliable though. Besides, at that point you should probably just run another cable.
If they're on separate universes there's no issue. In fact most large scale productions run a conventionals board and a movers board.
My venue actually has two (well, three, but that's because someone ****ed up) male DMX wall-mount outlets, all on the same chain - one in the booth and one down in the house. Obviously we can't use both at once - though if I had any actual power I might want to set up one of those priority-based dmx mergers so that I could set up an aux board in the house without having to go turn off the board in the booth when some silly person leaves it running.
00AVD
Active Member
If you have multiple male inlets and no patching / switching in place, then it's not wired correctly. It may work fine most of the time, but you shouldn't rely on kludges like that.
A DMX line should have exactly two connections - a male at the "sending end" and a female at the "receiving end". Anything tapped onto the line in between the ends is a mistake.
A DMX line should have exactly two connections - a male at the "sending end" and a female at the "receiving end". Anything tapped onto the line in between the ends is a mistake.
RS-485 (the signaling protocol used by DMX) is a multi-drop protocol. Every node on a DMX chain except for the physically first and last is "tapped onto the line between the ends"--active splitters notwithstanding. It is perfectly acceptable according to the underlying standard to have the sending device located in the middle of the chain as long as proper biasing and termination are implemented.
Of course that last bit brings a bit of a wrinkle. If the sending device winds up in the middle of the chain, both ends of the chain should be terminated, and the sending device should *not* internally terminate. I'm not sure which if any consoles do that [edit: internally terminate the 'head end' of the DMX line, I mean, which is not generally required for linear single-transmitter topologies].
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