Dmx Thru Wiring

[SanTai]

The small RGB led light thread and using TRS connector and if there were support for it in the standards. It is not what I want to discuss here, I would like some more info on something that were lightly touched in that thread but I believe it is OT(in that thread) so I started this thread for it.

How should you wire the DMX throu connection and how is it done in commercial fixtures? High and low end?

If I for some reason need a one channel dmx relay, don't have one lying around and are on a thight budget. I might build something like this: Velleman nv which is a kit costing around 30€, but it only got a DMX in and not a throu.

How should it be done? What does the standard say and how is it most often done?
A female XLR in parallel with the board?

 

[JD]

Most simply connect 1 to 1, 2 to 2, and 3 to 3, and branch off to the board in a simple Y connection. This is an imperfect method and it is best to keep the wiring as short as possible. The board itself should not have a terminator on it. (4 to 4 and 5 to 5 if you are using standard 5 pin. No pcb connection on those.)

Each time this is done, some degradation occurs and it is one of the reasons no more than 32 units should be on any given run. Use opto-isolators with multiple outputs to gain numbers higher than 32. (Star topography.)

Some units buffer the signal and actually have separate in/out connections on the PCB. Sounds good, but actually causes another problem: If one unit goes down, everything downstream is lost. Can't think of any I've opened up where it was that way.

As for the connection between pin 1 and the case, Some connect it directly, but it is better to put a 10 ohm resistor between the two. This helps prevents the data cable from becoming part of the ground circuit between fixtures. If your project case is plastic, no need. If you do use a resistor, purchase a fuse-able resistor and cover it in a small section of fiberglass sheath. That way if there is a catastrophic ground fault, you will not set your DMX cable on fire. (Most important on fixtures with an electrically grounded case.)

 

[derekleffew]

...How should you wire the DMX thru connection and how is it done in commercial fixtures? High and low end?...

See this post, and the entire thread.

The VL3000 line is about as "high end" as one can get (pardon the pun/mixed metaphor) and it uses an I/O assembly similar to this:

Blue Point Engineering Inc. - DMX Controllers / Hardware
as does almost every DMX device I've ever seen (unless it's separate panel-mount connectors wired in parallel with a stub-out).

 

[sblair]

The small RGB led light thread and using TRS connector and if there were support for it in the standards. It is not what I want to discuss here, I would like some more info on something that were lightly touched in that thread but I believe it is OT(in that thread) so I started this thread for it.

How should you wire the DMX throu connection and how is it done in commercial fixtures? High and low end?

If I for some reason need a one channel dmx relay, don't have one lying around and are on a thight budget. I might build something like this: Velleman nv which is a kit costing around 30€, but it only got a DMX in and not a throu.

How should it be done? What does the standard say and how is it most often done?
A female XLR in parallel with the board?

The proper way to do it to bus the In and Thru connectors together directly and then connect off that for the DMX feed for your device. In effect this creates a small 'Y' inside the product, but very short stubs are fine (i.e. less than foot or so). This is how most all professional grade moving lights are built (as is the VL I/O board shown above).

Buffering the signal and regenerating on the output is a very bad practice as someone else mentioned. Another issue doing that causes is it will block RDM and any other bidirectional communication.