Double DMX terminators?

[ACTSTech]

The architect of our project just had the electrician call me with a question I don't have the answer to, and neither does he, so I'll throw it out to the experts.

If the DMX signal runs to an active splitter but only three of the four outputs are in use, should the fourth output be terminated?

If there are both 3 and 5 pin outputs on the splitter, should any unused output be terminated?

If the lighting instrument has both 3 and 5 pin on it, do you terminate both?

Do you terminate a wall jack that isn't in use?

My brain is melting from all the specifications I'm trying to read through on other things and I can't think straight at the moment. My initial thoughts are that the only thing that needs to be terminated is the last instrument, but if it has both 3 and 5 pin, whatever line you're using would be what needs to be terminated as you wouldn't use both for any reason, but then I thought if we ran a 5 pin in but a 3 pin out to the next instrument that's only 3 pin, would I need to terminate the 5 pin at instrument 1 and then terminate the 3 pin on instrument 2? Sorry I'm having mental problems, maybe they switched my coffee to decaf...

 

[derekleffew]

On a splitter, unused outputs do not need termination.

If an end-of-line fixture has both 3- and 5-pin ins and outs, either (and only one) output should be terminated regardless of input.

 

[MNicolai]

In opto-isolated splitters, the outputs are each their own silo. Lack of termination on any output without fixtures on it will not create a problem for any other branches of the system.

If a fixture has dual pinouts on it, you also do not need to terminate unused outputs. The digital signal transmission length between the bridged connectors is not significant enough that reflections are created that come back down the DMX line and create interference -- and electrically the connectors are bridged together so for the last fixture in the signal chain, if you terminate either the 3-pin or the 5-pin connector you have terminated the entire signal chain.

The only no-no is that if you have a fixture with dual 3/5pin connectors on it, from a single fixture you cannot use both a 3-pin cable to loop out to one branch of fixtures and then another 5-pin cable to branch out to another, creating a "Y" split in the signal chain.

 

[RonHebbard]

@ACTSTech I'll try to reply in your order:
If your source (LX Board) only has one DMX output, and that output is driving into your active splitter, if the splitter has a hard-wired parallel output in addition to its four actively optically isolated outputs, terminating the looped through / output terminates your source. After that, each of your splitter's four outputs is another source and each requires termination.
If your LX board has more than one output, it's already acting internally as an actively isolated splitter.

Terminating your active splitter's unused 4th output is optional and should have no effect on normal operation.

If your splitter has four isolated outputs with each output feeding parallel connected XLR 3's and 5's, ideally you're only using either the XLR3 or 5 of any given isolated output; terminate the one you're using, XLR3 or 5 and NOT the unused connector, one output / one terminator, done deal.
If you're using both the XLR3 and 5 of the same isolated output, terminate one or the other, not both.
Ideally I'd only use one or the other. IF you whipped me and MADE me use both, I suspect I'd terminate the end of the LONGEST run / the run passing through the most devices. I've neither an honest answer nor any guarantees for using both the XLR 5 and 3 on the same isolated output.

If a lighting instrument has both XLR3's and 5's, they're almost certainly connected / hard-wired in parallel within the instrument.
If the instrument housed internal active splitting electronics I'm sure its manufacturer would be PROMINENTLY bragging / promoting this feature. Again; one output / one terminator, done deal. Some lighting fixtures / DMX controlled devices (Color scrollers, irises, foggers) sense when they're the last device on a line and provide auto termination; again manufacturers would LOUDLY proclaim this feature.
@jfleenor Care to comment?

Wall jacks: Are they sourced directly from your LX board, from a looped / through output of your splitter, from one of your splitter's four isolated outputs? If you told us the source of the wall jack, and if it is the only output of its source, or the last output of its source we'd have a better chance of providing a correct answer.
Toodleoo!
Ron Hebbard

 

[derekleffew]

If the instrument housed internal active splitting electronics I'm sure its manufacturer would be PROMINENTLY bragging / promoting this feature.

I'd argue the point about "PROMINENTLY bragging / promoting this feature". We saw in these forums where a VP of R&D for a (the) major manufacturer "forgot" that they'd implemented this feature on some of their fixtures. https://www.controlbooth.com/threads/the-dmx-termination-plug.9116/post-105412

Some lighting fixtures / DMX controlled devices (Color scrollers, irises, foggers) sense when they're the last device on a line and provide auto termination; again manufacturers would LOUDLY proclaim this feature.

I know of no "Color scrollers, irises, foggers" that detect when they're last in line. Some of one manufacturer's fixtures and dimmer packs have this feature. How does the device sense when it is last? A special panel mount female XLR that contains a switch to engage a terminating resistor when a male is plugged into it. That's it. No fancy electronics, just a dumb mechanical switch. The receptacle BTW was made by Neutrik at the behest of ETC. https://www.controlbooth.com/threads/the-dmx-termination-plug.9116/post-109084 https://www.controlbooth.com/threads/the-dmx-termination-plug.9116/post-284421

 

[ACTSTech]

If your LX board has more than one output, it's already acting internally as an actively isolated splitter.

If your splitter has four isolated outputs with each output feeding parallel connected XLR 3's and 5's, ideally you're only using either the XLR3 or 5 of any given isolated output; terminate the one you're using, XLR3 or 5 and NOT the unused connector, one output / one terminator, done deal.

If a lighting instrument has both XLR3's and 5's, they're almost certainly connected / hard-wired in parallel within the instrument.

Wall jacks: ...from one of your splitter's four isolated outputs

Thanks everyone. I think that I'm overthinking everything, but my brain is not working right (which is normal...)

The board will be driving two universes. U1 will run to the old dimmer racks and that's that. No issues there. U2 will run to a splitter which will branch out to the FOH positions. Proposed splitter (to be determined) will have four isolated outputs with each output feeding parallel 3 and 5 pin. I only want the 5-pin to be used (I don't really need the 3-pin, but I can't argue with the architect yet...) so the 3 pin will be unused. 5 pin out of the splitter via DMX cable to 5-pin wall jack.

I assumed the wall jacks don't need termination, only the last instrument on each line, and I wouldn't try to use an instrument as a Y, that's why I was confused by them saying that I need a terminator on EVERY out of every line or instrument. Thanks for making me seem less stupid.

 

[Jay Ashworth]

I'd argue the point about "PROMINENTLY bragging / promoting this feature". We saw in these forums where a VP of R&D for a (the) major manufacturer "forgot" that they'd implemented this feature on some of their fixtures. https://www.controlbooth.com/threads/the-dmx-termination-plug.9116/post-105412

I know of no "Color scrollers, irises, foggers" that detect when they're last in line. Some of one manufacturer's fixtures and dimmer packs have this feature. How does the device sense when it is last? A special panel mount female XLR that contains a switch to engage a terminating resistor when a male is plugged into it. That's it. No fancy electronics, just a dumb mechanical switch. The receptacle BTW was made by Neutrik at the behest of ETC. https://www.controlbooth.com/threads/the-dmx-termination-plug.9116/post-109084 https://www.controlbooth.com/threads/the-dmx-termination-plug.9116/post-284421

I gather that a similar thing happened with 75ohm video termination on BNC connectors back in the eighties, when you cared about this sort of thing - somebody's devices would automatically terminate if you didn't have something plugged in to the loop through, and that was how they did it: they could sense that there was a plug physically plugged in to the loop through.

If you plugged a blank BNC connector in there, it would determinate and look like hell.

I have a bit set that says that I know that because I actually tested it, but it was probably 1988 at the time, and I don't remember the details anymore.