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Dmx splitting

Discussion in 'Lighting and Electrics' started by Alfonso, May 8, 2018.

  1. Alfonso

    Alfonso Member

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    Hello I was wondering if its possible to run dmx into a terminal strip and wire multiple lights to the terminal strip instead of using a dmx splitter ?
     
  2. Van

    Van CBMod CB Mods Premium Member

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    In short, no. In long, you could but it would cause massive chronic migraines. The signal will get reflected back at to the block at different times and play Hell with the time. Buy a DMX opto-splitter you can find them stupid cheap if you're on a budget or buy a good one from Fleenor and never have to worry about your DMX Slitting again.

    You can make a run of Dmx and split it off at each fixture, as close to the fixture as possible, but again, each connection point is going to create a flucuation in the signal and wind up causing you issues, eventually.
     
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  3. Mac Hosehead

    Mac Hosehead Active Member

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    It's not standard practise, but you might get away with it. If it works during rehearsal but fails during a performance, was it worth it?
     
  4. jfleenor

    jfleenor Active Member

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    How many lights are you trying to handle? Remember, there's a 32 fixture maximum per line of DMX.

    Thanks Van! We actually have a new splitter aimed at the DJ market; our 124 splitter. It's four-way DMX/RDM, and MSRP is $412.

    *Whispers a secret* And we'll have a new splitter debuting in the next month or so in the same vein.
     
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  5. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    @Alfonso A few thoughts and queries for you:
    First query, how many lights are you thinking? Two, fifty or several hundred? For talks sake, let's target 30 as a maximum number without a proper splitter with individually / independently driven outputs.
    Consider running your DMX to your first fixture and then extending in parallel to your second fixture continuing on in parallel again to your third fixture or next DMX controlled device. When you reach the last device in your parallel connected chain install a 120 Ohm 1/8 Watt resistor across contacts two and three as a terminator to improve signal to noise and reduce reflections.
    Toodleoo!
    Ron Hebbard.
     
  6. TimMc

    TimMc Well-Known Member

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    The quick answer is NO. Not just NO, but HELL NO.

    DMX is one-way serial data. If you corrupt that data (reflections are the most common) there is no way to un-corrupt it without doing the DMX the right way.

    There are cheap DMX splitter/isolators from ADJ, Chauvet, etc... or get the Real Deal from Fleenor.

    Doug Fleenor once said (paraphrased) "people fly me all over the world to tell them to not put more than 30 fixtures on a DMX string and to put the mic cables on microphones; use real DMX cables for lights."
     
  7. Chris Pflieger

    Chris Pflieger Active Member

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    Not to argue with the expert, but does that still hold true? Given that new devices are typically using 1/4 or 1/8 unit load transceivers...
     
  8. jfleenor

    jfleenor Active Member

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    It's still the golden rule. Of course, DMX is relatively robust for a lighting protocol... and people can work loopholes into it if they understand what they're working with. But rules are created for the lowest common denominator, and not everyone is working with the newest and fanciest of gear all the time.
     
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  9. Brentgi

    Brentgi Active Member

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    I think it'd be a great experiment actually. Remember to take video footage and report back with your findings.
     
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  10. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    Good points. Its the new build and dmx house lights that make me wonder about this. If all new 1/4 or 1/8 load drivers on house lights, is it worth saving a separate DMX run? I haven't yet - too easy and cheap to put in an extra 4 port node - and probably easier to diagnose problems - but the possible option exists.
     
  11. RickR

    RickR Well-Known Member

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    I'm still looking for the transceiver load data to show up on fixture data sheets. If it's not on paper it's not guarenteed.
     
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  12. Glenn Parke

    Glenn Parke Member

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    Its definitely worth getting an optical splitter. One advantage is that it isolates different branches from voltage spikes.
    Here's one example, mind you is was 25 years ago.
    I was in Fl working in a conference center in charge of all the A/V. We were using an old ETC Expression console, that daisy changed into a string of several dimmer racks and 10 Wybron scrollers and also a Dmx to analog converter for some old dimmers.

    After a concert was over, I left some Par 64s up for worklights with scrollers with a Majenta color. After cooking the gels for some 20 to 30 mins, I forgot to dim the par cans before resetting the scrollers. A double release on the console and all the scrollers went back to their home position, while they were very hot, not recommended.

    Next time I fired everything, the scrollers tried to move but couldn't. This sent a voltage spike through the whole DMX line and wiped everything out, even my console.

    After investigating and research, the DMX inputs on all the equipment had a common input IC chip, which acts as a DMX repeater. I was able to buy some replacements IC chips for about $32 and was able to fix everything. Fortunately, the IC chips acted like a voltage suppressor and saved the console and rest of the equipment.

    Of course the scroller strings had to be replaced. Lesson learned.

    A DMX optical splitter was soon purchased afterwards.
     
  13. Malabaristo

    Malabaristo Active Member

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    I say stick to your current practices--not for the sake of DMX itself, but for RDM. Most DMX houselights require RDM for configuration, and RDM gets less reliable as you add more devices to a line. You probably could put 256 units with 1/8 load drivers and (if all your wiring and terminations are perfect) have them all receive DMX properly. However, you'd never get RDM to work properly.
     
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  14. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    Ist not the 256 I think about. Its when I have 30 and at last minute need to add 4 in that area. Mostly trying to avoid a lot of redesign.
     
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  15. JD

    JD Well-Known Member

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    The 32 fixture rule is not as solid as you would think. Somewhere in between 20 and 40 fixtures, you will run into problems. A lot has to do with what quality an lengths your DMX run is. Junky cable and you probably won't make it to 32. Using proper cable and termination you will safely hit 32. Will adding a 33rd fixture crash the rig? Probably not, but a number has to be picked as a guideline and 32 is a nice number!
     
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  16. danTt

    danTt Well-Known Member

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    I believe? that RDM actually adds a second device "load" to the chain. So an rdm enabled fixture counts as two devices, not one. If you have 1/8 load drivers I'm not sure how that translates.. if it's functionally a 1/4 load driver? It's been a while since I delved too deeply into this though, Distribution tends to be cheap enough these days that I'd prefer to have shorter isolated chains and limit that fallout if a cable starts acting up.
     
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  17. Lyle Williams

    Lyle Williams Active Member

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    You can also think about wireless. If you go wireless (certainly doesn't suit everyone) then the wireless becomes the splitter.
     
  18. Chris Pflieger

    Chris Pflieger Active Member

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    Actually, a 32 unit load is a hard and fast rule of the RS-485 spec.
     
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  19. Chris Pflieger

    Chris Pflieger Active Member

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    It doesn't.

    With RDM, the RS-485 transceiver actually gets to transmit every now and then, and the load is only a receiver load.
     
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  20. Chris Cotter

    Chris Cotter New Member

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    No do not. Never parrallel DMX wiring! Does the light have DMX IN and a DMX out? If so always daisey chain and terminate last light in chain . [email protected]
     

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