ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 2 [All]   Go Down

Author Topic: Y cable with DMX?  (Read 884 times)

Kirby Yarbrough

  • SR Forums
  • Sr. Member
  • *
  • Offline Offline
  • Posts: 386
  • Reston, Virginia
Y cable with DMX?
« on: February 27, 2017, 09:20:02 am »

Pardon my elementary question: can I use a 3-pin Y cable to split DMX signal coming from a controller?
Logged

TJ (Tom) Cornish

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3491
  • St. Paul, MN
Re: Y cable with DMX?
« Reply #1 on: February 27, 2017, 09:39:59 am »

Pardon my elementary question: can I use a 3-pin Y cable to split DMX signal coming from a controller?
It might work depending on length of your run and if you use terminators (in this case no terminators would be better than multiple terminators), but that's not really the right way to do it.

You want a DMX splitter/opto-isolator such as this: https://www.sweetwater.com/store/detail/DataStream4?adpos=1t1&creative=175866237996&device=c&matchtype=b&network=g&gclid=CO_V_-bAsNICFR65wAodRQIEhw
Logged

John Fruits

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 396
Re: Y cable with DMX?
« Reply #2 on: February 27, 2017, 10:56:41 am »

Doug Fleenor says no.
http://www.dfd.com/primer.html
It's also sort of like using mic cables, it might work......until it doesn't.
Logged
"The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs.  There's also a negative side."-Hunter S. Thompson

Scott Hofmann

  • Full Member
  • ***
  • Offline Offline
  • Posts: 208
Re: Y cable with DMX?
« Reply #3 on: February 27, 2017, 05:24:37 pm »

Pardon my elementary question: can I use a 3-pin Y cable to split DMX signal coming from a controller?

The answer is NO.
Logged
Scott Hofmann

duane massey

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1319
Re: Y cable with DMX?
« Reply #4 on: February 27, 2017, 08:32:34 pm »

Uhm, NO.
Logged
Duane Massey
Technician, musician, stubborn old guy
Houston, Texas

Don T. Williams

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 293
  • Midas Pro 1 & 2, M32, dbTech T12, T8, S30, DM12
    • Q Systems Music & Sound
Re: Y cable with DMX?
« Reply #5 on: February 28, 2017, 12:07:59 am »

It really doesn't work.  I've had lots of customers try it and called me in when it didn't work.  I have never heard of it working correctly!  DMX is not at all like audio.  Opto-isolator splitters are not that expensive and solve your problem.

They also work when mixing fixture types (some don't play well with others), and when the strings of fixtures get larger.  I've read that 32 fixtures is the limit, but I know of situations where a lot fewer fixtures didn't work until they were isolated/split.
Logged

Lyle Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1084
Re: Y cable with DMX?
« Reply #6 on: February 28, 2017, 01:27:17 am »

Doug Fleenor says no.
http://www.dfd.com/primer.html
It's also sort of like using mic cables, it might work......until it doesn't.

It will work better than people are suggesting, but I wouldn't plan to work that way.  If doing this keep your legs short.

For me, this is in my emergency workarounds bag of ideas.

Not the "right thing", but not nearly as dodgey as the mythology suggests.

DMX runs on RS485, and anything you can get away with on RS485 will work for DMX.
Logged

TJ (Tom) Cornish

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3491
  • St. Paul, MN
Re: Y cable with DMX?
« Reply #7 on: February 28, 2017, 09:18:04 am »

It will work better than people are suggesting, but I wouldn't plan to work that way.  If doing this keep your legs short.

For me, this is in my emergency workarounds bag of ideas.

Not the "right thing", but not nearly as dodgey as the mythology suggests.

DMX runs on RS485, and anything you can get away with on RS485 will work for DMX.
Agreed.  It probably will work in some situations, but having the right tool is so inexpensive, it seems silly to work very hard to avoid spending $130 to do it the right way.
Logged

duane massey

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1319
Re: Y cable with DMX?
« Reply #8 on: February 28, 2017, 09:19:01 pm »

I have installed over 30 of these over the past 5 years, and have not had a single issue:
http://www.usledsupply.com/shop/dmx-splitter-1-8.html
Logged
Duane Massey
Technician, musician, stubborn old guy
Houston, Texas

Kemper Watson

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 265
Re: Y cable with DMX?
« Reply #9 on: March 03, 2017, 07:07:59 am »

I have installed over 30 of these over the past 5 years, and have not had a single issue:
http://www.usledsupply.com/shop/dmx-splitter-1-8.html

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

Tim McCulloch

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 16553
  • Wichita, Kansas USA
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.
Logged
"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Lyle Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1084
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 »
Logged

Lyle Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1084
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 »
Logged

Bob Charest

  • Lab Lounge
  • Hero Member
  • *
  • Offline Offline
  • Posts: 629
  • Westbrook ME, USA
    • Bob Charest Band
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
Logged

Tom Bourke

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1427
    • http://www.cwalv.com
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.
Logged
I have a mild form of Dyslexia that affects my ability to spell.  I do use spell checking to help but it does not always work.  My form of Dyslexia does not affect my reading.  Dyslexics of the world untie! <a href="http://www.cwalv.com" target="_blank">http://www.cwalv.com</a>

Scott Holtzman

  • Hero Member
  • *****
  • Online Online
  • Posts: 3266
    • River Delta Audio
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.



Logged
Scott AKA "Skyking" Holtzman
River Delta Audio, Cleveland OH
www.riverdelta.rocks

Lyle Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1084
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.
Logged

Marc Paolella

  • Newbie
  • *
  • Offline Offline
  • Posts: 10
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.
Logged
Pages: 1 2 [All]   Go Up
 


Page created in 0.075 seconds with 16 queries.