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[Jerry Kirksey]

We are currently revamping a high school theater lighting system.  It's all strand using shownet protocol. We are replacing everything with Martin ELP ellipsoidals and Blizzard Oberon Fresnel Zooms which are communicating fine through the 5pin connection.  But we also are using four Blizzard Hotstik 5 CobII to wash the backstage.  Lo and behold, they are an $850 light with 3 pin only.  I cannot communicate with them through a 5pin to 3 pin adaptor.  Is this to be expected?  If so, is there a solution?

[Mac Kerr]

We are currently revamping a high school theater lighting system.  It's all strand using shownet protocol. We are replacing everything with Martin ELP ellipsoidals and Blizzard Oberon Fresnel Zooms which are communicating fine through the 5pin connection.  But we also are using four Blizzard Hotstik 5 CobII to wash the backstage.  Lo and behold, they are an $850 light with 3 pin only.  I cannot communicate with them through a 5pin to 3 pin adaptor.  Is this to be expected?  If so, is there a solution?

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[Paul Johnson]

5 pin DMX and 3 pin DMX are the same. The only issue could be if the cable has pins 2 and 3 swapped. Adaptors as in in-line and short cables are absolutely fine and very normal. I'd swap the 2 and 3 and try again.

[Tim Weaver]

5 pin DMX and 3 pin DMX are the same. The only issue could be if the cable has pins 2 and 3 swapped. Adaptors as in in-line and short cables are absolutely fine and very normal. I'd swap the 2 and 3 and try again.

What he said.

5 pin dmx just uses pins 1, 2, and 3 in the 5 pin connector. Wired the same way as the three pin. It's just as likely that you got a bad or miswired 5 to 3 adaptor. I have bought them by the case load and always get a few duds.


FWIW, I know that the DMX standard for 5 pin is supposed to use all 5 pins for two universes, but nobody is doing that today. It's easier to run network to the stage and break out into 20 or 30 universes over a single Cat cable.

[Brian Jojade]

What he said.

5 pin dmx just uses pins 1, 2, and 3 in the 5 pin connector. Wired the same way as the three pin. It's just as likely that you got a bad or miswired 5 to 3 adaptor. I have bought them by the case load and always get a few duds.


FWIW, I know that the DMX standard for 5 pin is supposed to use all 5 pins for two universes, but nobody is doing that today. It's easier to run network to the stage and break out into 20 or 30 universes over a single Cat cable.

I've seen consoles that use the 5 pins for 2 universes, but I've yet to run into a light that supported switching universes on the 5 pin cable.  Even worse, I've run into lights with 5 pin connectors that ONLY have 3 pins wired making universe 2 passthrough not possible. It's one of those standards that never really was implemented consistently enough to be usable.

Some places stick with 5 pin DMX so that there's no confusion in connecting audio and DMX connections.  Others use 3 pin so that their cable inventory is interchangeable.  Real world solution is to keep a pile of 3-5 and 5-3 adaptors handy so you can adapt as needed.

[Jeff Lelko]

Some places stick with 5 pin DMX so that there's no confusion in connecting audio and DMX connections.  Others use 3 pin so that their cable inventory is interchangeable.  Real world solution is to keep a pile of 3-5 and 5-3 adaptors handy so you can adapt as needed.

Yep, and I know you know this, but for those playing along at home - DMX and XLR are physically different cables.  One is meant for an analog audio signal and the other for a digital data protocol.  While throwing a mic cable into the light rig in a pinch might work (and we've all done it), it's not what any reputable lighting company should be doing as common practice. 

Barring the exception of 2 universes of DMX over a single 5-pin cable or other oddball scenarios, one can switch back and forth between 3-pin and 5-pin DMX without consequence.  The "right" way to handle this sort of thing though is to use a DMX splitter and run separate 3-pin and 5-pin daisy chains to avoid excessive junctions in the cable path.

To the OPs issue though, I'd suspect either a bad or miswired adapter, or something else entirely that just seems to be manifesting as bad DMX (a fixture setting perhaps?).

[Scott Hofmann]

[quote author=Tim Weaver link=topic=177765.msg1642571#msg1642571 date=1664820686
FWIW, I know that the DMX standard for 5 pin is supposed to use all 5 pins for two universes, but nobody is doing that today. It's easier to run network to the stage and break out into 20 or 30 universes over a single Cat cable.
[/quote]

From  "Recommended Practice for DMX512", page 18:
"Connection of pins 4&5:
The second pair in the DMX512 line is described in the DMX512 specification but its use is not defined. There are many devices and systems in the field that use the second pair, on pins 4 and 5, for various purposes. Some systems implement talkback using the pair as a return EIA485 line to the console or a separate fault and status display unit. Other systems may employ the two wires of the 2nd pair as direct control signals, for temperature indication for instance.

Most DMX512 devices, with in and out connectors for daisy-chaining, simply connect the first three pins; 1 to 1, 2 to 2 and 3 to 3. Not all devices also connect pins 4 to 4 and 5 to 5.

Talkback systems which utilise the second pair as a return line require special distribution amplifiers and custom bi-directional repeaters and isolators."

Apparently the used of the 2nd pair for another DMX512 universe was not envisioned by the people who created the DMX standard.

[Brian Jojade]

Yep, and I know you know this, but for those playing along at home - DMX and XLR are physically different cables.  One is meant for an analog audio signal and the other for a digital data protocol.  While throwing a mic cable into the light rig in a pinch might work (and we've all done it), it's not what any reputable lighting company should be doing as common practice.

XLR is a connector type, not a cable type.  DMX uses 3 pin or 5 pin XLR connectors.  The 3 pin XLR connectors for DMX are identical to the ones used for audio cables. 

The specified impedance for DMX cables is 110 ohms.  The operating frequency of DMX is roughly 250khz, whereas audio is 20khz or lower.  At lower frequencies, impedance matching of the cable is less important, but typical mic cables are around 100 ohms.  Pretty close to the DMX spec.

The official DMX spec with perfectly matched everything is 3000 feet.  Real world reliability issues with multiple fixtures start to happen when lengths exceed 1500 feet.

Using audio cables for short runs typically a non issue.  ie, if you've only got 100 feet of DMX line, mic cables are going to work just fine.

[Jeff Lelko]

XLR is a connector type, not a cable type.  DMX uses 3 pin or 5 pin XLR connectors.  The 3 pin XLR connectors for DMX are identical to the ones used for audio cables. 

Eh, you're not wrong, but I can't think of the last time I sent a stagehand off looking for some Belden DMXFLEX after telling him that the Belden 8412 he brought me isn't what I wanted  .  It's usually "send up a 50ft 3-Pin DMX" or "run an XLR over to that mic stand". 

Using audio cables for short runs typically a non issue.  ie, if you've only got 100 feet of DMX line, mic cables are going to work just fine.

This I disagree with though.  Proper impedance aside the shielding of the cable is also quite important for ensuring reliable data transmission.  I'd go so far as to argue that one of the biggest sources of glitchy light systems is the use of inferior/improper cable.  While yes, most of the time mic cable will work, it's bad practice.  If I spec a light system for a fly-in gig and the rental house delivers it with mic cable we'd be having words.  It'd also lead me to wonder what other corners are being cut...

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