DMX Layout Help

[DIY Guy]

So this year I am going to give DMX a try.

What I would like to do is come out of the DMX dongle into a splitter and head in 3 different directions.

I've seen reference to DMX splitters from RJ, RPM and wjohn-- what are you guys using? As far as I can tell, RPM's is available, but there is mention of isolation (or lack thereof)? Not sure if this is something I need to worry about?

From the splitter I'm going 1) to the eves where I will have two Ren48LSDs chained, and the first pic of the first controller will have the start address set. I'll leave the TERM jumper open on the first Ren48 and short the TERM pins on the second.

The second output will go to a chain of three 24LVs. Again, the first pic on the first board will have the start address set. I believe I have to remove the 120ohm resistor adjacent to the Comm In/Out RJ45s on the first two 24LVs, and leave the resistor installed on the last board.

The third output will go to a chain of three ss24's. Same scenario as above (i haven't looked to see where the 120ohm resistor is on those)

And.. if there's time.. I want to try setting up some lights on the fourth output using n1ists stick splitters.

Is it possible to install a splitter right after the dongle and again at the location of the boards (ie put another splitter at the 24LVs so I don't have to remove the 120ohm resistors). Something tells me that at the very least, this is a bad idea, but figured I'd ask.

Am I on track?

Thanks!
Tim

[rokkett]

Ok, just a couple of quick comments. The Renard board designs are not set up the same as a typical DMX serial bus.. Each input and output is a separate serial bus with only two devices - a transmitter and a receiver. You should always leave the termination resistor on for Renards.

Secondly, the Renard DMX code is going to positionaly auto-address the Renard devices in each of your serial circuits coming out of the repeater.

Every PIC in your layout would programmed with a starting address of 1 with the exception of the first PIC on the first 24LV - I would use a starting address of 97 here. And the first PIC on the first SS24 - where I would use a starting address of 169 here.

This will consume 240 of the 512 addresses available within a single DMX universe and uniquely address each channel.

If you add additional splitters, you will need to also set the starting address of the other boards, as you will be removing the positional auto-addressing functionality of the Renard hardware design.

[DIY Guy]

Thanks Rokkett. Glad to hear I don't have to remove the resistor.

So there is no issue adding another splitter.. That is to say, splitting the output of another splitter?

[mschell]

A splitter does nothing but repeat and re-time the RS485 signals going out on the wire. However, it does introduce a small amount of latency (delay) in the signal. So you can certainly stack a splitter after another splitter, but understand that you could eventually get things out of "sync" based on the number of splitters in the chain.

With the small number of channels you've mentioned here, I don't think you'll have a problem.

[DIY Guy]

Thanks, Mark. Sounds like it should be a relatively simple ordeal!

What splitter are you guys using?

[dmcole]

What splitter are you guys using?

I currently have a Lynx DMX splitter I built in 2008 and used in both '08 and '09. I own an RPM Splitter board that I may or may not build up and use this year; I won't be daisy-chaining them, just a question of whether I will need three legs or four legs to my distribution network (I have never been able to get four legs to consistently work on the Lynx; three is fine).

My sense is that RJ is not going to offer the Lynx splitter in the future, expecting people to "split" DMX legs with either the Lynx Wireless system or with the new Smart String distribution hubs.

HTH.

\dmc

[mschell]

I also have 1 or 2 Lynx Splitters from last year or the year before.

I may not have as much need for them as I have in the past, since I plan to use j1sys's ECG-DMXRen8 board this year, with 8 separate outputs.

But having a splitter handy to re-time the signals is always a safety net.

Note that in most cases, unless you're going long distances, have a very noisy environment or other factors, splitters usually aren't that necessary, for DMX or for other protocols.

I have had 19 AL controllers out in the yard without a splitter to be found and they all worked fine. It's still RS485 and similar to Renard protocol.

[DIY Guy]

Thanks guys. THe only reason for the splitter is to eliminate some extraneous runs of cable (eg running up to the attic, then back down to something else).

Just convenience really. I wanted to make sure I can do it. There were also posts regarding the 120ohm resistor on the rens, but apparently I don't have to worry about it!

Ordered a couple of RPM's splitters. Looks like I only need one, but building one of anything is usually not much less than building a couple.. so what the heck :)

Tim

[rokkett]

DIY - Just remember that the starting addresses will need to be set on the first PIC for each controller board that will be connected directly to the splitter. The DMX guys are all like, "Duh, of course!" but the Renard guys are like, "What?!? DMX does not auto-address?" :)

[DIY Guy]

Will do, Rokkett, thanks.

I am going to put the start address on a little sticker an stick it on the PIC so I don't get confused.