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Author Topic: Y cable with DMX?  (Read 898 times)

Tim McCulloch

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Re: Y cable with DMX?
« Reply #10 on: March 06, 2017, 02:41:05 pm »

Doug Fleenor says "people spend thousands of dollars flying me all around the world to tell them: use real DMX cables and don't daisy-chain more than 24 fixtures - use a DMX splitter/isolator."

So to parse Mr. DMX's statement:

NO.  A BIG, FAT NO.
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Lyle Williams

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Re: Y cable with DMX?
« Reply #11 on: March 06, 2017, 04:34:13 pm »

Doug Fleenor says "people spend thousands of dollars flying me all around the world to tell them: use real DMX cables and don't daisy-chain more than 24 fixtures - use a DMX splitter/isolator."

So to parse Mr. DMX's statement:

NO.  A BIG, FAT NO.

Inside many (most?) fixtures the "DMX daisy chain" wiring is implemented as a y-split.  The two XLR connectors are wired together, and a single set of wires runs to the controller board.

When you don't wire lights to the "rules" the assumptions embodied in the rules (cable type, max distance, number of fixtures, etc) can go out the window.  Many implementations don't need anything like 400m AND 32 fixtures though.

« Last Edit: March 07, 2017, 04:51:28 am by Lyle Williams »
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Lyle Williams

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Re: Y cable with DMX?
« Reply #12 on: March 07, 2017, 04:44:31 am »

One also has to give consideration to when it is OK and not OK to be dodgey.

The established rules for things like DMX allow a system to be built and maintained by different people over time.  They don't need to be aware of previous anomalies and system-specific constraints.

Any sort of permanent installation should play by the rules.  The next person along shouldn't have to "discover" the Improvised Electronic Devices (IEDs) you have left behind.

If you are throwing something together for an evening and through poor planning (or a lost box of equipment) a y-split or two will save the show, go for it.  You know what you have done, you will troubleshoot it and get it working, nobody else needs to get their head around it, and in six hours it'll all be torn down and packed up never to be spoken of again.  :-)
« Last Edit: March 07, 2017, 04:52:25 am by Lyle Williams »
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Bob Charest

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Re: Y cable with DMX?
« Reply #13 on: March 07, 2017, 04:17:03 pm »

Inside many (most?) fixtures the "DMX daisy chain" wiring is implemented as a y-split...

Hi Lyle,

I'm certainly not the most experienced guy around, but, of the four brands of LED fixtures I've owned for our band, I've not seen just a y-split. DMW in & DMW out connected to a circuit board. We first started using DMX controlled LED lights in 2006 with Wiedamark, then some Chauvet gear, a company that was in CA that went broke, and now have Blizzard Pucks.

Is it really that common? Yikes, I wouldn't want to have to deal with that.

Best regards,
Bob Charest
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Tom Bourke

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Re: Y cable with DMX?
« Reply #14 on: March 07, 2017, 11:53:30 pm »

Inside many (most?) fixtures the "DMX daisy chain" wiring is implemented as a y-split.  The two XLR connectors are wired together, and a single set of wires runs to the controller board.
Yes they are wired that way, the difference is that the "Y" inside the instrument has just a short leg to the chip that reads the DMX off the bus.  That short leg to to the chip does not create reflections that are a problem.  That is very different from putting a "Y" cable in a random spot with instruments and long cables.  In that case you end up with reflections that may or may not cause problems.
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Scott Holtzman

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Re: Y cable with DMX?
« Reply #15 on: March 08, 2017, 12:26:53 am »

Yes they are wired that way, the difference is that the "Y" inside the instrument has just a short leg to the chip that reads the DMX off the bus.  That short leg to to the chip does not create reflections that are a problem.  That is very different from putting a "Y" cable in a random spot with instruments and long cables.  In that case you end up with reflections that may or may not cause problems.


It's more complicated from that.  The chip itself is a high impedance connection but the fixture has a balun in it to properly couple to the ~110 ohm bus impedance.



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Lyle Williams

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Re: Y cable with DMX?
« Reply #16 on: March 08, 2017, 08:02:50 am »

Remember that wavelengths at 250kbit/s are quite big.  If your legs aren't long, reflections are not going to be significantly out of phase.
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Marc Paolella

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Re: Y cable with DMX?
« Reply #17 on: March 12, 2017, 07:50:02 pm »

I use this as well, going on 4 years now. At $35 it's a no-brainer

I use this (Chauvet Data Stream) and it is a solid and wonderful product that gives you a lot of flexibility with routing DMX:

https://www.bhphotovideo.com/bnh/controller/home?O=&sku=751524&gclid=Cj0KEQiAgJTGBRDLr5_az_Ouk44BEiQAIxaA4mfYW2O7ZH9icAHg7jx3PuayGF9TCU3xTo9BggYV5B0aAmKV8P8HAQ&is=REG&ap=y&m=Y&c3api=1876%2C92051678762%2C&A=details&Q=

Worth every penny.
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