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2 boards to one dmx line?

Discussion in 'Lighting and Electrics' started by benintights, Mar 15, 2004.

  1. benintights

    benintights Member

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    I'm interested in purchasing a new board to run both conventional lights and intelligent ones. If I plan to wire my entire system using dmx, is it possible to take the signal and split it so two boards can send a signal down the same line? What I would like to do is to have a pc controller for my moving lights, and a fader-board for my stationary ones. Is this possible using a dmx-splitter? Or can I have two boards daisy chained together while allowing them to be controlled seperately? Any suggestions?

    Thanks,
    benintights
     
  2. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Hmmm - my initial thought would be NO. Although I would not be confident in my reasoning. If you are going to have one dedicated controller to run intelligent lighting and another to run the rest, wouldn't it be easier to just to have two seperate runs?

    I am sure that someone will provide a real answer but I thought that I would have a crack at it.
     
  3. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Hiya,
    If you wanted to run one board and split that signal using a DMX splitter--yes you can do that...however if you want to "loop" or combine two different consoles into ONE signal--ehh--yes and no sorta. An iso-splitter works in one direction only. I believe if you tried to loop thru a console(separate in brands) thru wiring, and combine two signals into one--they would give you sporadic and wild results as the various commands of each would interfere with the other. What you need is a DMX COMBINER. These do exist...they combine and isolate commands into one DMX line, but I have never used them or know a ton about them. Check with Doug Fleenor Designs website....I know he has a few combiners/mergers. But I'm not sure if those units are for backup board purposes or to actually run a show off of. Controlbooth Member DMXTools on here may also have more insight on this too...

    http://www.dfd.com


    Another way to link two consoles is thru MIDI...provided both are MIDI capable. You would only have ONE line of DMX going out to your splitter and various toys, but you would use TWO consoles to do stuff with them. One would be set up as the MASTER console, and the other as the SLAVE console which feeds into the master console. FWIW--I believe the merger/combiner uses a similar set up.

    -wolf
     
  4. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Well you do learn something new every day. Never heard of these things. I knew that the iso-splitters were unidirectional and imagined that the combining of 2 different sens via a Y lead would not be the greatest of ideas and could possibly damage one or both of the units. I know that this is a pontial problem with using Y leads to take a stereo signal into a mono signal because the Left and Right channels will have different voltages at different times and one channel has to potential to over power the other, damaging the output devices. The risk is very low but another problem is it affects the actual sound. I didn't know this until someone pionted it out to me by lifting one of the channels. The soultion was very simple and cost about $20 in components and case etc and I am sure that there may well be a garden variety gizmo that you could put together yourself. Would like to hear if I am on the right track with this line of thought or not. Probably not - but hey, I'm willing to learn :idea:

    Other than termination, that really is the extent of my DMX knowledge.
     
  5. BenFranske

    BenFranske Member

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    Depending on what you choose for your computer controller and boards you may be able to loop through one or the other. For example, if you are using Martin's LightJockey (the PCI card version) there are both DMX inputs and outputs. You could take the DMX out of your conventional board and input it to the computer DMX in, program the computer to loop those signals PLUS the computer moving light control back out the DMX output and to your dimmers and intel. lights.
     
  6. Nephilim

    Nephilim Active Member

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    It's probably better in the long run to use two seperate runs. Do you really want to be daisychaining your dimmers and your intels? (I guess that depends on where your dimmers are).
     
  7. DMXtools

    DMXtools Active Member

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    I went the opposite way. I invented my "DMX-lator I" to get my microplex dimmers onto the same DMX board I use for my intels. Running dimmers and intels through two separate boards made no real sense when most scenes were combinations of intel and dimmer lighting... it just made extra work for me and increased the chance that I'd screw up a cue.

    That said, if you insist on running two separate boards, it's probably better to go with two separate cables. DMX combiners are available, but they aren't cheap.

    A combiner is absolutely necessary to get two boards on one cable (unless one of the boards has combiner functions built-in). DMX-512 was designed for a single transmitter (the board) and multiple receivers (dimmers and intels). There is no provision for multiple transmitters. Because each transmitter thinks it's the only transmitter in the DMX universe, it sends whenever it wants. Both transmitters not only could, but would transmit at the same time. They'd interfere with each other and nothing would get through properly.

    A combiner consists of two or more DMX receivers, one transmitter and some memory shared between them. Assume a 24-channel board for the dimmers and a 192-channel controller for the intels. On the output side, to keep things simple, we'll put the dimmers on channels 1-24 and the intels from channel 25 up. Receiver A takes the DMX signal from the dimmer board, strips off the packet header and puts the data into memory locations 1-24. Receiver B takes the DMX signal from the intel board and puts the data into memory locations 25-216 - channel 1 from the intel board goes into location 25, channel 2 into location 26 and so on. The transmitter creates a new packet header, then sends the data from memory locations 1-216 as a brand new DMX packet.

    There's some really critical timing stuff going on in the combiner, because this is all happening simultaneously - the receivers don't "take turns" because each board's transmitter thinks it's the only one - it doesn't know there's somebody to take turns with. The transmitter in the combiner can't wait for the receivers to stop, because chances are they won't.

    Getting the snaky timing right isn't easy, either in terms of the hardware or the software to do it, so combiners can get kind-of pricey. Unless you're running a few miles from the booth to the stage, a second cable run is much more cost-effective.

    John
     
  8. Nephilim

    Nephilim Active Member

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    Then again, the only boards that I've used for both conventional and intel lights had two universes.
     
  9. Skawillow

    Skawillow Member

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    I purchased a soundtec DMX Merge.

    I have a number of heads which I have programmed to use higher DMX channels that I control via PC and combine with a manual 24 channel DMX desk running 2 * 12 way packs and it works fine providing use ensure you don't split the line and you correctly terminate.

    Mark
     

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