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5 pin DMX- 512 channels... or 1024?

Discussion in 'Lighting and Electrics' started by Lora, Jun 11, 2005.

  1. Lora

    Lora Member

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    Ok. So. I'm having a little discussion here with a very good friend of mine. He's managed to completely confuse me. I've always been told that a single 5-pin DMX cable is used to carry one lighting universe- that is 512 channels. But I'm told, that actually no, it carries 1024 channels- 2 universes. I can see how that would work, He says that: " It was originally intended to have the ability to carry 2 universes, using all 5 pins. Hence, when using 1 universe there are 2 spare pins."
    1 pin for ground.
    2 pins for universe 1.
    2 pins for universe 2.
    (= 5)

    And that makes perfect sense. So. If a desk allowed, could the cables I currently have carry 1024 channels?
     
  2. len

    len Well-Known Member

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    Nope. No matter whether 3 pin or 5 pin, a dmx line carries one universe. The reason for pin 4 and 5 is two-fold (or so I am told). One is to separate it from mic and other sound cords, and the other was a plan to be able to send data back to the desk, including lamp hours, temperature readings, update software versions for fixtures, etc. To my recollection, no fixture can do this via the dmx line. It is possible in some fixtures to do it from fixture A to fixture B, such as the HES X-Spot, but it is not available everywhere. Martin fixtures typically require a device called a wife, which uploads new software versions.

    The other reason it is not possible to carry multiple universes on one line is because there are no fixtures (to my knowledge) which can be set to different universes. If all the data were carried on one line, you'd have to have the ability to tell a fixture its address AND its universe number and I don't think that is possible.

    In sum, it may be possible to do it with 5 pin in a purely theoretical sense, but the reality is, no desk I know of, and no fixture I know of, can send or receive multiple universes and sort them out correctly.
     
  3. SteveB

    SteveB Well-Known Member

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    len has it pretty correct, but I'll chime in anyway.

    The 512 limit was imposed to allow max refresh of the signal before the dimmers thought the signal had been lost (Am I explaining that right ?). At a rate of 44hz. too much info in the data stream - I.E. too long a string, might show up as a lag, with notchy dimmer response.

    Remember that DMX was devised before it became widespread for fixture control. At the time it was unusual to see installations that had more then 1000 dimmers, thus even the largest of the older consoles usually only had 2 ports.

    In theory, a fixture doesn't care what group of DMX addresses it listens to. You could theoretically have a fixture wait to address 5434, and it would respond. The refresh rate would be VERY SLOW on the data stream, however and the fixtures would respond poorly - sort of like playing an on-line game on a dial up connection.

    SB
     
  4. len

    len Well-Known Member

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    Thanks for the more technical, and more accurate, explanation. Never considered the issue of refresh rates, etc. I learned something today.
     
  5. eamon

    eamon Member

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    Hi all


    All the above information is correct regarding dmx. here is a link to an excellent site that will provide oodles of info on the topic

    http://www.dmx512-online.com

    The other 2 pins(4&5) are currently unused at the mo. In recent months USITT has ratified dmx 512-A. This will upgrade the standard to allow pins 4 & 5 to be used. Specifically for reporting functions, upgrading software etc.

    hope that helps

    eamon
     
  6. Andy_Leviss

    Andy_Leviss Active Member Premium Member

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    If you want to learn the nitty-gritty on DMX, as well as all sorts of other control protocols, you can't do better than John Huntington's book Control Systems for Live Entertainment. The first part of the book is a detailed intro to all sorts of protocols, including an explanation of hexadecimal numbering so that he can actually go and explain the exact formatting of the data in the message, how the data's encoded in that particular protocol, etc. The second part ties all the different types of control systems (lighting, sound, motion control, video, etc.) together into real world examples.

    Not an easy read, at least the first part, but an invaluable reference.

    --A
     
  7. avkid

    avkid Not a New User Fight Leukemia

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  8. ship

    ship Senior Team Emeritus Premium Member

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    I'm more a fan of either DMX Protocol or Sandstrom's "Stage Lighting Controls." Found it in my case at least a better book than Control Systems, but the former was not bad either.

    Hog's have long had the Hog Remote sending power down pins 4&5 for it's use. While also feasable to use than split back into two seperate universes on two pair cable, you might also have data problems in that unless the two pairs of conductors are individually wrapped or twisted - normally not the case, you might have some signal errors in the line. Just an assumption on my part however as it's not my primary field.
     
  9. dt21

    dt21 Member

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    Hey I was told by some really old and wise techs that when they 1st came out with the 5 pin DMX cable it was intended that 2 universes could be send down the cable e.g. by using a Y slit…… disk 1 sends 1st universe thought pins 2 and 3. Disk 2 sends 2nd universe thought pins 4 and 5 and pin 1 is ground. So although the cable can send 1025 channels the refresh rate stays the same as 512 because it is using 2 data streams. So in the case you were saying of a disk having 2 outputs these could be send down one 5 pin cable. I’ve been told that it has been used in this way, you would have talk to the old times to find out more.

    This ability has been unused and forgotten. And these days some fixtures are doing away with 5 pin and using 3 pin e.g. MAC’s
     
  10. mbenonis

    mbenonis Wireless Guy Administrator

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    FWIW, the IPS line of dimmers by Entertainment Technology use pins 4 and 5 to send data back to a status monitor, such as dimmer temp, load size, error status, power consumption, etc. It a very useful, if antiquated, system especially if you can't get down to a dimmer physically to check it out.
     
  11. eamon

    eamon Member

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    hello dt21

    Just saw your post and see a few misguidedthoughts on some issues. There are two links to dmx related sites that are quite informative in above posts.


    USITT standard DMX connector is a 5 pin XLR connector. Not 3 pin. DMX currently use in a standard configuration only the 1st 3 pins. The main reason for a 5 pin connector being who plugged the DMX line into the back of the sound desk!!!
    Manufactures who use 3 pin conenctor primarily do so on a cost basis. Pain in the arse when a rental company forgets to include the adaptors.....
    There is obviously a greater abundance of XLR 3 pin connectors etc.

    PIn 1 Ground
    Pin 2 Data minus
    Pin 3 Data plus

    Pins 4 & 5 are currently not used. Some manufactures do utlise them in their equipment but I could not say who

    On sayiing that DMX 512-A has being ratified by USITT to allow the use of pins 4 & 5 for extra features. Again web links will provide more info.

    if you use a Y split in your DMX line you are leaving yourself open to problems from signal spikes to noise and the possibility of your signal being interrupted mid show... Not a good thing methinks

    As was said in a previous post re the amount of data a DMX cable carries is due to amongst other things the refresh rate. A standard DMX cable should carry only 512 channels(1 universe)

    hope that helps

    eamon
     
  12. Lora

    Lora Member

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    I don't see how a manafacturer would use three pin over five pin due to cost...

    by split, I think dt21 means that if you were sending 2 universes down one dmx cable... if that were to happen... then you could split them into 2 3 pin plugs with a common ground.

    so, from what you all say, it sounds like it can be done, but very rarely is?
     
  13. ship

    ship Senior Team Emeritus Premium Member

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    Think that you have it given the above questions as to both standards and potential gremlens in your system. It's two un-used conductors, do what you wish with them even wire your end connectors with a LED and light them up in using the extra conductors at least initially will have been within concept of "spare."

    I do see that most of us do not recommend doing this however.

    As for manufacturers installing three verses five pin, most will give you the option of which you want to use. The DJ market is still much sold on 3-pin thus no doubt a primary factor in it's continuing use. While the manufacturers follow the Protocal standard, they supply the product and normally will allow you to choose your end user complaince with it. It's a good idea to comply if for nothing else than it keeps the unshielded and crap microphone cable out of your long data cable runs from causing errors. On the other hand, that note about adaptors... now there is something that's constantly needing to be kept up in supply. Always have extra in emergency stock, and if tech person have at least one set in your tool box.

    Think some light boards are up to six or more universes of DMX now especially if they have to run a Catalyst system at distances over what Cat.5 is rated for. For some shows, I'm running dual 16-pair / 8-cir. DMX/Clear Com snakes to FOH. This means two circuits of Clear Com and 14 universes of DMX as needed. All might not be used - yet but the more technical, the more universes needed. One step short of doing either a lower speed of Cat.5 or going fiber optic. Fourth Phase I believe is already fiber optic for control.
     
  14. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Over here it has been common practice to control colour scrollers with pins 4 and 5 on a DMX line.
     
  15. avkid

    avkid Not a New User Fight Leukemia

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    Well,if they are doing that they not too wise or future oriented with DMX512-A slated to be the world standard in the near future.
     
  16. SteveB

    SteveB Well-Known Member

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    Ship wrote:

    "Think some light boards are up to six or more universes of DMX now especially if they have to run a Catalyst system at distances over what Cat.5 is rated for"

    The ETC Emphasis system has a capacity of 64 universes of DMX patched into 4000 console channels, all over Net2. 32,000 DMX channels or so. Just dump nodes on the network to gain access as DMX.

    I'm fairly certain other manufacturers can do something similar, as Strand, Martin, GrandMA, Hog, etc are all networked consoles.

    As to dt21's comments, I don't ever recall anybody planning on using the spare conductors for a 2nd universe. At least no reputable manufacturer that followed the DMX standards. I believe Martin tried for a very short time to send a control voltage over pins 4&5. The outcry made the effort short lived.

    I'm also aware that MANY manufacturers still ship with 3 pin on their ML's (Studio Spot CMY/Zooms comes to mind). Martin, for a while, even used a reverse polarity 3 pin, requiring shops to stock special Martin Only 3 to 5 adapters.

    SB
     
  17. dt21

    dt21 Member

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    so just let me get this right you would be sending DMX to the colour scrollers? and that is would be a 2nd universe? one for light dimmers and one for scrollers? so then you would be sending 2 universe down the 5 pin cable? like the techs from OZ said?

    just so you all know i wasnt talking bout sending 2 universe down the 1 line but sending 2 lines down 1 5 pin cable ie using all pins.
     
  18. avkid

    avkid Not a New User Fight Leukemia

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    The main reason it is popular is because many people think it's "ok" to use plain cheap mic cable, whereas us educated folk know that only high quality(in some cases gold plated connectorsv are used)3 pin XLR should be used for sending the more "delicate" DMX signals
     
  19. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Sorry for the confusion. With regards to the scrollers, pins 1 to 3 carry the DMX and power the motors with voltage supplied by pins 4 and 5. Poor use of the word control in this post.

    Was having a tiresome day yesterday!
     
  20. ship

    ship Senior Team Emeritus Premium Member

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    Normally on the best of scroller cable, it uses a four pin standard and not normal two pair wire.

    Pin One and Four are 14AWG wire for power to scroller. Think about your cable, you want to send how many amps of current how many feet to run a motor off normal data cable sized conductors? Pins two and three are data, and the shell of the plug/connector are attached to the shield that is also a ground. This data line is also individually shielded and twisted from the power conductors. One cable and plug, but very different cable than a two pair data cable. For this reason, it's probably not wise to use a five pin cable either.
     

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