DMX Questions

[dmoore]

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[n1ist]

The DMX data pair is pins 1/2 with pins 7/8 as the ground and pins 3/6 as the almost-never-used secondary pair.   While I guess you could feed DC on the other pairs, it would be a non-standard application, and I would double-check that anything you plug in has those pins isolated.  Also, some devices may not pass those pairs from the input to output connector.

RS485 is typically a 120-ohm bus; the difference between terminating at 100R and 120R is minor.

The 32-node limit isn't a hard one; it depends a lot on cable length and the types of driver and receiver chips used on the devices (some are good for 256 nodes).  You can probably go a little over the limit without problems,  A splitter, wireless RX, or the third connector on a LE all regenerate the signal, so the count starts fresh.
/mike

[hbomb341]

Mike GOOD Info - THX!!!

Harrison

[austindave]

Just to (maybe) clarify something Mike says...

"A splitter, wireless RX, or the third connector on a LE all regenerate the signal, so the count starts fresh."

So with Lynx equipment, the ONLY way you could exceed the 32 node limit would be if you custom-built a cable in a star configuration - where you made a single output fan out to 32 separate Lynx device inputs (all wired in parallel)... You'd have to go FAR out of your way to run into a problem with RJ's designs.

--Dave

[RJ]

Let me clarify that back a little.

The Dmx out on the express do not amp the signal on both outputs. Only on the "DMX Out 2" So you could daisy enough to get into problems using the dmx out #1. The Line Drivers I use are low load and rated at 64 devices on the bus but this is under perfect conditions with very short runs so I normally say stick to the 32 limit and come off a DMX output if you need more. 

Dmx does not function well if you split the cable into multiple cables do to the reflection and signal phase. This is why we use hardware splitters to split the dmx into multiple paths. I have had a few users misunderstand and try this. How do I know. Cause it didn't work well and they asked for help. In all cases removing this fixed it.

Hope that helps keep anyone out of problems.

[RJ]

Yes with the DMX pair passed through. The DMX OUT #2 is the output of a one channel splitter for the users convienence. It was cheap to add and gets rid of all the splitters in the yard.

RJ

[austindave]

Thanks for the explanation RJ. I wouldn't have guessed that the two outputs would be different.

So for signal integrity "safety" sake, if possible, we should try to daisy-chain off the DMX Out 2 output & only use the DMX Out (1) for limited runs? Or in a fan-out configuration, leave DMX Out (1) disconnected every few nodes deep in the tree, relying on DMX Out 2 to "re-generate" the signal every now & then?

Thanks again,
Dave

[BigVettePimp]

Real quick ques for RJ. Will the LE support having 12v run through 3/6 to power a few RGB dmx units.
Thank you.

[rrowan]

Real quick ques for RJ. Will the LE support having 12v run through 3/6 to power a few RGB dmx units.
Thank you.

Nope its a 120/240v AC controller

Rick (Not RJ) R.

[RJ]

The express does not mind but I would not do it on the SSR4's
The MR16 does not pass all the pins through but 7&8 are fine on them to use.

RJ

[RJ]

No the DMX Out 2 is a regenerated signal and no pass through.

The DMX in passes all pins to the DMX OUT  ... Only DMX OUT 2 does not.

RJ

[BigVettePimp]

RJ
Thanx for the extremly fast response and for all the work you do.

[Kwajtony]

Thanks for the explanation RJ. I wouldn't have guessed that the two outputs would be different.

So for signal integrity "safety" sake, if possible, we should try to daisy-chain off the DMX Out 2 output & only use the DMX Out (1) for limited runs? Or in a fan-out configuration, leave DMX Out (1) disconnected every few nodes deep in the tree, relying on DMX Out 2 to "re-generate" the signal every now & then?

Thanks again,
Dave

This is a good question, I believe (maybe incorrectly) that you would need to terminate DMX each time you did not use the DMX Out 1?

[RJ]

Normally you use DMX out and daisy chain your units together. There is no reason to use DMX out 2 unless you are going off in a different direction with a seperate DMX cable on the same universe. Or if you have more than say 20 units on this run and want to amp the signal for another 20 or so.

Yes if you do not use DMX OUT then it is the last unit on the DMX chain so you need to terminate. Using DMX out 2 does not relieve you of this. The unit can have two cables coming off it and still be the end of the chain if using DMX out 2.

Hope this is clear enough and requires no more clarification.

RJ