Control/Dimming DIY DMX Splitter/Repeater

[DanBlaze]

Hey guys,

So I'm running into issues at my high school right now with DMX signal. Sometimes our moving heads do not respond properly (they don't turn off when told to, colors don't match what we tell them to, etc). We have traced the issue down to weak signal. (The line goes 25ft to get into the ceiling, then its a 120 ft to the first moving head, and then 10 feet to the second, another 15 to the third, and 10 feet to the last moving head, which is giving us the most problems.) Now, I've been looking into DMX repeaters/splitters, and they seem to be quite expensive. I am very handy with a soldering iron, and I don't think making my own would be terribly difficult, but I want to consult you guys first. Do you have any recommendations on schematics for DIY DMX repeaters? Would something like this work? I am open to ideas.

DMX booster

I appreciate your help!

 

[metti]

This shouldn't be a problem but it would be a lot easier and not that much more expensive to buy something like the Enttec D-Split for a hundred bucks which would do what you want.

 

[Footer]

170' is not really that far for DMX. A repeater would be useful for a 300'+ Run. I have ran DMX over a 500' cable without issue. What kind of cable are you using? Is the run terminated? Are your fixtures "jittery" or you just getting the wrong colors? When the color reaches its destination, does it shake? Do the fixtures randomly pan/tilt? What makes you think its weak signal?

 

[Synchronize]

One thing to look at first is your cable. If corners were cut when the cable was purchased and cheap cable was used, that could be your problem. If mic cable was used, especially for that home run, that could be your problem. Mic cable, while it will transmit a data signal, is not designed to transmit a data signal. Usually one will not run into issues with 10 or 20 foot runs with a couple fixtures in the chain, but once you start getting into hundred foot runs with many fixtures in the change you start loosing quality. Even if the cable that was purchased and installed was sold as "DMX Cable" it could be no better in quality than mic cable. A lot of places will sell mic cable as DMX cable using the excuse that "It will work."

You should also look at signal speed coming out of the console. I know I had trouble with some MACs and an ETC Element once. It all came down to slowing down the data transmission speed.

New, good quality, DMX cable can be purchased from Full Compass at $.47 per foot. Thats the best price that I've found so far. It would probably cost less to purchase new cable than a splitter. I say purchase a splitter because I would recommend not attempting to build your own. Theres not that much too them but doing it wrong could result in frying your board and every fixture on every line.

Another thing that just popped into my head is line termination? Is your data line properly terminated? If not some wonkey things could happen.

 

[derekleffew]

I highly doubt it will solve your problem. I also doubt "weak signal" is the issue. How did you arrive at that determination? On large shows, DMX is regularly run 400-500' without issue. Notice that Dr. DMX has no "DMX boosters" or similar listed at Doug Fleenor Design. I'm sure if this were a problem, he would already have something to address it.

What make/model are the console and fixtures?
Are you using cable that meets the specs for DMX transmission, or microphone cables?
Is the line terminated?

It's likely you could buy the Enttec D-Split or this for less cost than building your own DMX booster.

EDIT: DanBlaze, forgive the repetition. It appears four people were simultaneously answering within five minutes. Take particular note as to how similar the answers are.

 

[dramatech]

I agree with the other folks posting, that your problem is probably not a weak signal. Other possibilities are posted, and you should try them one at a time.

Just for the future, if you really want or need a DMX booster, and not a full blown splitter, There are quite a few available at an inexpensive price, but sold as RS485 boosters. They will require changing some connectors and possible power supply issues.
I have used some Pretty good quality boosters, that I purchased surplus for $20 each. I used them for isolation on the input of a homemade scroller spitter/power supply. They work great, but beware you will have to have a pretty good understanding of RS485 and DMX, in order to wire them correctly.

 

[n1ist]

The guys over at the Christmas lights forums have splitter designs (both isolated and not). You should be able to find schematics and even buy blank boards. The animated lighting world is now mainly DMX, though predominantly with RJ45 connectors.

One more thing to check - is your DMX run terminated at the last fixture?
/mike