7-pin DMX

[pudgeo2]

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?

[JD]

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.

[gafftaper]

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.

[icewolf08]

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.

[SteveB]

Originally Posted by pudgeo2

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?

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

[sound_nerd]

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.

[Footer]

Originally Posted by sound_nerd

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.

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

[icewolf08]

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

[len]

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.

[Footer]

Originally Posted by len

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.

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.