DMX Ghosting??

[djsteviec]

We had 11 fixtures on one DMX loop. Ranging from Robe moving heads, Abstract Twisters, Martin Destroyers, 518's and Wizards.

 

We then added 17 LED parcans and 4 ceiling mounted scans. We simply continued on the DMX link from the last head. Trouble is, I am trying to reprogramme them all, and I am getting inteferance on the robe moving heads. They are ClubSpots250. They just don't want to do what the controller is telling them. If I unplug the new ring of fixtures, they work fine.

 

There isn't a DMX terminator in the last unit, does this sound like its the problem? Wouldn't there be more interference than just on the Robes??

 

 

Thanks.

 

Steve.

[david.elsbury]

You're running rather close to the "32 device limit" (actually 31, cos the desk counts as a device) on your DMX chain.

I would suggest terminating, and also a splitter to split the rig in half, one to the Robe's and one to the LED parcans.

 

 

 

A concurrent post has been automatically merged from this point on.

 

Failing that, it's entirely possible one of your cables is faulty, either mis-wired, has one wire not connected, or whatever. Can you take down all the cabling and test it? Or swap it out peice by peice?

[djsteviec]

"32 device limit"... hadnt heard of that. What is that?

[david.elsbury]

http://www.google.com/search?client=opera&...-8&oe=utf-8

[mrcog]

DMX Loop?!?! DMX ring?!?!

 

DMX shouldnt be brought back into the system. It should go from the desk into the fixtures until the end of the line and then terminated. Apologies if thats not what you meant.

 

Also have you checked that the DMX adressed arnt overlapping each other? That could be causeing problems.

[KevinE]

If you're using a 2nd hand masterpeice, have you made sure there's no old DMX slot patches in there that may be confusing things?

 

2nd the advice on the terminator, this is surely crucial on a rig this big.

[Martijn de Groot]

You have to count the console/controller and in this case it is 33 fixtures, which is 1 to many.

To have proper control, don't use more than 15/16 fixtures in 1 DMX line/universe, dimmers are controlled by a processor which counts as 1 device.

Starting at the beginning:

- What type of console/controller are you using?

- how many DMX outputs/universes can you run from it

- how many fixtures are in the rig? (32) means 2 universes.

- how long is the length of DMX cable running?

- do you have devices with active DMX, or is it just DMX in and hard-wired thru?

- are all device with 5 pins connectors?

- do you use a proper DMX-terminator?

- do you have devices running from the same adress?

- is your softpatch matching the adresses of the fixtures?

come with the answers and I will try to help you from there

[jayselway]

I agree with all the above.

 

First thing I'd do, is get a DMX Splitter, then run two or three DMX lines into the rigs, depending on how far the bits are from each other. :blink:

[Neil Hampson]

The 32 device limit is derived from the RS485 protocol, upon which DMX512 based. I have not come across the controller counted as the first device before, but in any case I would have moved to a second universe long before I got that far.

 

I am possibly speaking out of turn here but if you use a DMX splitter, I believe the splitter acts as a repeater allowing a further 32 devices from each spur of the splitter. I'm sure someone here could confirm this as I've never done it before on DMX, I have used similar products in industrial control using RS485 though.

[Tomo]

The "32-limit" refers to the number of DMX (RS485) chips on the line.

 

So the controller has one chip, and each fixture also (hopefully) has one chip.

 

I have seen a few 'cheaper' fixtures that use a direct-on-line opto-isolator. Those are very bad news, as they tend to be equivalent to 5 or 6 proper DMX chips.

 

However, three things to remember:

1) DMX *must* be run in a 'daisy-chain' fashion. Passive Y-splits, rings, loops etc are extremely bad news.

2) Termination is quite important - many systems seem to work fine without one, but they are really working 'on the edge' - a slight change to circumstances can make it suddenly misbehave.

3) While the 'limit' is 31 fixtures, this is really under 'perfect' conditions.

 

Perfect conditions never happen in real life!

- I try never to go above 20 fixtures on a given wire.

 

DMX-splitters give you multiple copies of the input, and each output should be able to drive a further 31 fixtures. Again, I try not to go above 20 on one wire!

 

So given that your existing system worked fine, I'd suggest buying a DMX splitter, plug the existing DMX line into one output and the the new fixtures into another output.

[bradley]

I had this problem at school. We added a DMX splitter and it worked fine. Also make sure you are using DMX cable and not plain XLR. We also reinstaled the software we were using. Hope it helps.

 

Bradley

[djsteviec]

I still haven't had a chance to get a terminatr yet, but will do this week. If that doesn't work, Ill move on to the next possibility.

 

Thanks for all of your input. I will be back and will let you know what happens.

[jayselway]

You can make one really cheaply if you haven't got easy access to someone who manufactures them :P