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7-pin DMX

Discussion in 'Lighting and Electrics' started by pudgeo2, Nov 17, 2007.

  1. pudgeo2

    pudgeo2 Member

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    So I've been working in a shop for a large AV company. I was doing some house cleaning, when I came across a box of 6 & 7 Pin DMX. I know what 6 pin is used for (analog dimmers & RFUs), but does anyone know what 7-pin is used for?
     
  2. JD

    JD Well-Known Member

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    By DMX, you mean the old Canon style connectors? (XLR)

    As far as I know, DMX is only in 5 and 3 pin styles, but the Switchcraft / Canon / Neutrik connectors come in many configurations. 7 pins might be handy for 6 channel analog dimmers among other things. (6 chns & common, so you don't use the shell.) So, maybe they have been there for awhile.
     
  3. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    True DMX standard should have 5 pins and only 5 pins. Two of those pins usually aren't used. Sometimes manufacturers cut it down to three pins. Sometimes power is added and you have four pin scroller cables. But that's just messing around with what is convenient for their products. Seven Pin? My guess is that it's some sort of pre-dmx proprietary control cable or an analog cable as pointed out already. There was some time between analog control and when the DMX standard was adopted were every manufacturer had it's own sort of digital control. Another possibility is some sort of modern adaptation to make the old technology work with current cable?

    If you find an old Cinch Jones cable you'll see about 20 pins. They have a rectangular plug. Remember in the "bad old days" before DMX you needed a separate wire for every dimmer you were controlling.
     
    Last edited: Nov 17, 2007
  4. icewolf08

    icewolf08 CBMod CB Mods

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    Yes, the DMX512-1990 standard requires you to use a 5 pin connector and 5 conductor cable. There was talk about being able to expand the protocol for other uses that hasn't happened yet. Manufacturers realized that since only 3 of the 5 pins were being used they could save money by using 3 pin connectors and 3 pin cable. In many new devices you have both 3 and 5 pin connectors, so some manufacturers decided they would spend extra money, but the end user pay it anyway, so who cares.

    Is DMX due for an overhaul? Probably not. There is ACN which is starting to hit the market, but it is going to take a very long time before DMX goes away. DMX does just about everything we need it to do, and it has been installed in so many venues that upgrading will take a very long time. There are still people using analog dimmers that require Cinch Jones connectors, and they just hook their new console up through an A/D converter.

    The reason that DMX is not used for triggering scenery or Pyro cues is due to the protocol itself, and has absolutely nothing to do with the physical properties of the cable, etc. DMX is based on the RS-485 data protocol. The controllers sends out a repeating stream of information, consisting of a start code, and then 512 data blocks which are the levels for the 512 DMX "channels" that can be connected to one universe. Each device in the universe counts the blocks as they go by, and if the devices starting address is 100, it listens to block 100 through whatever and does what it is supposed to do. DMX has no error checking though, so if there is a bad block and it was connected to a pyro device, it could accidentally trigger the device. This is why protocols like MIDI are used for show control.
     
  5. SteveB

    SteveB Well-Known Member

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    Can't remember exactly, but it might be either ETC RFU cable (I think that's 6 pin XLR), or possibly Sensor to Console Link cable. Not sure why you would have Link cable in anything over 20ft, which would be sufficiant to go from a booth wall plate to a console, as generally it's hard wired to the racks. Might be for a touring system that wanted the Link system operational.

    SB
     
  6. sound_nerd

    sound_nerd Active Member

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    We use 7 pin xlr style connectors on all of our 6ch analog packs and controllers. It is much more durable than the midi type connectors that came standard on the packs. (LDS DS-3000 systems)

    The 6 pin? I have no idea.
     
  7. Footer

    Footer Senior Team Senior Team Premium Member

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    Could also be a 2 channel com system cable. Telex has 6 pin on all of there 2 channel packs.
     
  8. icewolf08

    icewolf08 CBMod CB Mods

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    6-Pin is generally used as RFU cable, and 2 channel Clear-Com.
     
  9. len

    len Well-Known Member

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    To be excruciatingly precise, the ONLY cable that is truly dmx is 5 pin twisted pair shielded. This according to the USITT standard updated a couple years ago.

    4 pin scroller cable is not dmx, although it is used in lighting. As is 3 pin xlr, and perhaps 6 or 7 pin. Or cinch-jones. And all the others. Theoretically, 3 conductor extension cords could carry dmx data. So while it is possible that any cable carries a dmx signal it is not truly dmx standard unless it is 5 pin xlr twisted pair shielded cable.
     
  10. Footer

    Footer Senior Team Senior Team Premium Member

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    The loop hole to the standard was that the manufactuers could put 3 pin on and call it DMX if they supplied an adapter, so people just put on the 3 pin and forgot about supplying the adapter. The real deal was that production houses did not want to stock an extra cable when they had plenty of 3 pin connectors and cable laying around.... even though hardly any of it was meant for data.

    Before anyone says it... RDM was originally thought to use the second pair but because so many fixture don't have access to the second pair they were able to cram RDM into the first pair along with DMX data.

    It has also been said that you can run DMX through a barb wire fence... would you want to... no... but you could.
     
  11. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Should anyone ever need to order 6pin XLR plugs and connectors, be aware there are two pin configurations, and they are not compatible with each other. One has the pins arranged symmetrically, the other does not. I believe the ETC RFU (Expression family) uses the non-symmetrical, and Telex and CLearCom use the symmetrical, but I might have that backwards.
     
  12. Footer

    Footer Senior Team Senior Team Premium Member

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    Doesn't the RFU have 6 pins but one pin is a center pin? I haven't have an ETC RFU for a few years so I can't really remember. I also remember the ETC link cable having a center pin or two. I do know that you can plug the DMX cable into the RFU output on ETC consoles, that tripped me up a few times when I let someone else run the DMX...
     
  13. JD

    JD Well-Known Member

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    The biggest disadvantage to DMX is that it works like a boss shouting orders who doesn't listen to anyone! If someone doesn't hear him right, they go out and do the wrong thing! (Thus BAD for Pyro.) Technically, this is known as "error check" which DMX does not have. As far as the extra pins go, people who write standards like to allow for things that sometimes don't happen. Ethernet has 8 pin connectors, and 8 conductor cabling but only uses 4 wires. So, some have adopted a 3 pin system with DMX and it works fine if you are using all 3 pin fixtures. Others have used the second pair for a second DMX universe, doubling the amount of channels it can handle. But it was said before. The standard is 5 pin, and anyone who uses the extras to do something like feed power is no longer on the standard, and probably asking for trouble!
     
  14. Logos

    Logos Well-Known Member

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    European Phillips audio gear used to use the Din plug with 7 pins and upgraded that at one point to the same size as a Canon 3 - 6 pin. It wasn't very popular. It was a real [email protected]#$%^d to solder.
    Riggers units on ETC boards used a 6 pin Canon plug for a couple of models. I think that has already been mentioned.
    Wasn't there a video application that used 7 pin Canon plugs in the sixties or seventies.
     
  15. kwotipka

    kwotipka Active Member

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    I hated those things.
     
  16. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    It's been touched on but not really clearly... The original purpose for those two extra pins was for information from the device to be returned back to the console. There are a few applications where this is going on right now but EXTREMELY limited.

    As for the future of DMX. It is on the way out BUT it will be VERY slow. ACN and Ethernet based control is coming very soon. While we wait for ACN to be fully adopted we are in a period of proprietary ethernet languages. New Consoles have been coming out with both ethernet and DMX jacks for a year or two... I believe EOS is the first to ONLY have ethernet jacks (right?) I'm not sure what intelligent gear has ethernet jacks just yet but it won't be long until it all does. There are a lot of advantages to the user of ethernet based control, #1 being the cable is far cheaper.

    My new theater is Strand based so it will "talk" Strand's proprietary ethernet language from the console to the dimmers and back. The Strand language goes out over the ethernet system of the theater to the DMX nodes. The nodes translate it into DMX and from there it's DMX cable to my gear. In the future my console and dimmers will be upgraded to speak ACN If I am able to purchase gear that speaks ACN there will be no need for the nodes, or the expensive DMX cable. Everything will speak ACN and connect via ethernet cable.

    To me, the best part of the future is RDM. With RDM we will no longer need to set DMX addresses. The gear will identify itself to the network and talk back to the console. You'll be able to plug in a bunch of gear hit a button and it will all find itself in the network. Much like plugging in a USB device to your computer today.

    When will we all have ACN? About the time Charc retires. ACN and RDM are realities that will be implemented soon. The technology is here and the manufacturers just have to go through the process of implementing it. However the question is, can your theater afford to switch when your DMX system is working just fine? Yeah that's what I thought. My guess is in about 5 years the vast majority of new purchased gear will no longer be DMX based. Gradually as systems go down ACN will replace DMX. So it'll take a good 15-20 years until most of us make the switch to ACN. Then it'll be another 15-20 years after that until the "cinch jones" club (little community theaters, schools, and churches) give up their ancient gear and upgrade to ACN equipment. DMX is dead technology... but she's going to take a REALLY long time to die so get used to her.
     
  17. icewolf08

    icewolf08 CBMod CB Mods

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    Though wireless is nice, it is kind of moot since you need to run power to the fixtures anyway, though I suppose we do have W-DMX...

    As for power and data in the same cable, for moving lights it is probably a bad idea. A mis-wired scroller cable can cause hundreds of dollars of damage. A mis-wired high voltage/data line would cause thousands of dollars of damage, and maybe some unwelcome pyro effects.
     
  18. avkid

    avkid Not a New User Fight Leukemia

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    Yeah, many people have tried power and data in the same cable for several different applications.
    I don't care what people say about PoE and it's possibilities, I am still not comfortable feeding my lights or computers with it.
    There's just something about electricity and 23 AWG copper that doesn't give me the warm fuzzies.
     
  19. Footer

    Footer Senior Team Senior Team Premium Member

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    Whats going to kill people with ACN is the fact that you can't daisy chain but have to do a point to point for each fixture. Couple that with the 300' limitation and there are going to be some issues. Fiber snakes will become the norm simply because they will have to. I HIGHLY encourage anyone who is wanting to get into any type of technical theatre to go get their CCNA. I should have mine (took the class, never had the time to take the test.... or I am just lazy.. you pick). I can not tell you how much having that class has helped me. When these networks get larger data systems are going to have to grow. I see in the future a gigabit fibre backbone going to each truss breaaking out into cisco switches that will take copper to the fixture. Ethercon connectors on everything... yadda yadda yadda.

    Also remember that HIGH QUALITY (Cisco...) switching gear is expensive. More then any opto-splitter. You can get cheap off the shelf switches for a few hundred, but the odds of it going down are pretty good. Very little of this stuff is meant for the road so things will have to be beafed up. Cisco designs most of their gear to get racked up in an air conditioned room and turned on and left on for 10 years. We do the exact opposite. We put things on a case, plug and unplug it hundreds and hundreds of times, throw the case in a 5 degree below zero truck, let it bounce around, pull it out at 6am, plug it in, and repeat. Common networking gear will break by the 3rd show. The cost of having a switch for every 24 or 48 fixtures is not going to be cheap, and people are going to be very slow to make the investment if DMX is still around. Ethernet works great for distrubution, I have 4 SN110 nodes on the show I am doing right now. When ACN gets to the actual fixture, things are going to get much more complicated.

    Clay Packy is now putting "future ethernet" jacks on all of their new Alpha wash/Alpha Spot gear, thats the first ones I have noticed. Many other companies are soon to follow. I see DMX jacks staying on most gear for at least the next 10 years. After all... there are still AMX jacks on the ETC 12 and 24 Packs and AMX died nearly 15 years ago. We still have serial jacks on our computers... these protocols never really die... they just fade away VERY slowly.

    oh... and I want the update for the SN110's for ACN to come out... NOW.
     
    Last edited: Nov 17, 2007
  20. kwotipka

    kwotipka Active Member

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    I have a question. Is this new control system true TCP/IP or UDP data? There are lots of video protocols out there for video that pass over CAT5 but is not legal network traffic. Problem is that TCP/IP has tons of overhead that delay the signals. I don't know if lighting is that picky. If it is TCP/IP, how may channels can you load this thing up with before it becomes an issue. It obviously isn't UDP because there is no error correction in that and you are back to the issues of DMX there.

    just wondering.

    kw
     

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