DMX through XLR

[shaferboy]

Hello, I'm a TD at my high school (all student crew, I'm a Junior) we have two Martin 812 Roboscanners and I want to hook them up. We have no DMX patching ability on our electrics, or in our catwalks but we want full control of them. Since we have mic outputs in these locations is it possible for me to plug the XLR in the back of the board (Strand 300 Series) and daisy chain them once the signal get's to the electric. If this is not an option, how could I do this?

 

[Floobydust]

Generally, yes you can. Try and see but just make sure they're not connected to your sound board before you plug anything in.

 

[Les]

It'll work unless or until it doesn't. I wouldn't personally do it because this sounds like a potentially long run on cable that is very susceptible to issues to begin with. The thing about mic cable (not to mention install-grade mic cable) is that it can work fine for a while and then one day just decide to be a pain. You'd just have to hope that it isn't mid-show when it decides to go haywire.

As far as routing real DMX; it could be a hassle and is generally very building-specific in terms of difficulty and staying compliant with both USITT and NEC. Have you thought about using wireless DMX?

 

[shaferboy]

I've chatted with some people down at Hollywood Lighting, and they said at the moment the technology is spotty at best. If we get them working for even a second, my director will want them working all the time.

Also when you say "long run on the cable" do the cables wear down with excessive use, ie running DMX through them?

 

[Les]

I've chatted with some people down at Hollywood Lighting, and they said at the moment the technology is spotty at best. If we get them working for even a second, my director will want them working all the time.

Same could be said for running mic cable. Do you have a DMX-out on your dimmer racks? If so, how close are they to the electric you want to get to? Nothing wrong with temporarily running a line from the deck as long as you make note of it for anyone operating the fly's (if applicable). Getting to the cats may be a different story. Cable could be fished through, but that opens a can of worms when it comes to using cable in conduit, etc (NEC), as well as working at height.

 

[shaferboy]

Our booth and dimmers are approximately 100 feet away from either of the points we would be hanging the fixtures. It's all audience between the dimmer room and the stage. Ours dimmers are in a little concrete room across the hall from our booth

 

[MarshallPope]

As has been said, the answer is a "yes, but." I personally run DMX through the sound snake at my church to a handful of LED fixtures on stage, using all mic cable. No, it isn't ideal at all, but I've yet to have problems with it, and it keeps me from having to find an extra $100 to run cat5 and buy real DMX-capacity cables. I fully expect it to decide not to work one day, but it isn't mission-critical in my situation, so I'm OK with that. Just know that you are doing something that may or may not work for you whenever it wants to.

I refer you to the sign posted above our copier, which is extremely appropriate to non-compliant DMX:

Warning
This machine is subject to breakdowns during periods of critical need.

A special circuit in the machine called a CRITICAL NEED DETECTOR senses the operator's emotional state in terms of how desperate he or she is to use the machine. The CRITICAL NEED DETECTOR then creates a malfunction proportional to the desperation of the operator. Threatening the machine with violence only aggravates the situation. Likewise, attempts to use another machine may cause it also to malfunction. They belong to the same union. Keep calm and say nice things to the machine, Nothing else seems to work.

 

[len]

Here's a couple other issues you might run into:

1. Running data that far on a microphone line might cause interference. An amplifier/splitter might be useful.
2. The board might not have the correct profile.
3. Martin 812 (IIRC) run on Martin protocol, which means that pin 2 and 3 are swapped. So you need a cable that will swap those two wires, but DO NOT switch them back between the 2 fixtures. Or you could open the fixtures and do that internally, but that might be more work.
4. The 812 isn't very bright. Don't expect much from it.
5. If the mirrors ever get cracked, don't buy them from Martin. They're ridiculously expensive. You can get dichroic mirrors made at a glass shop for about 1/5 the price.

 

[scotteckers]

Here's a couple other issues you might run into:

1. Running data that far on a microphone line might cause interference. An amplifier/splitter might be useful.
2. The board might not have the correct profile.
3. Martin 812 (IIRC) run on Martin protocol, which means that pin 2 and 3 are swapped. So you need a cable that will swap those two wires, but DO NOT switch them back between the 2 fixtures. Or you could open the fixtures and do that internally, but that might be more work.
4. The 812 isn't very bright. Don't expect much from it.
5. If the mirrors ever get cracked, don't buy them from Martin. They're ridiculously expensive. You can get dichroic mirrors made at a glass shop for about 1/5 the price.

Ask your maintenance/IT staff if they have some extra CAT-5 or CAT-6 cable around, as many schools often do. You can use this to run DMX to your lighting position. I have definitely used "microphone cables" to run DMX to TEMPORARY fixtures before, but be careful (see notes above as to why!). Also consider spending more time in English class! Good luck.

 

[Fountain Of Euph]

I would vote Wireless DMX. I have used it for several years and NEVER had a problem. As for the sound thing- I have done it with LED's, but it hurts, and is probably not the best idea. The insulation on the cables may not be good enough for the High Fi data transfer you need. It can also mess with your sound setup, causing static in the sound and and erratic behavior in the lights.

 

[JD]

If your mic line is run through conduit with other mic lines, and you won't need it to be used for audio in the future, you might want to consider using the old mic cable as a fish and tie / pull a piece of Cat5 through the pipe. Cat5 works great for DMX (much better than mic cable) as long as it is running through pipe. Another option would be to use the old mic cable as a fish, but pull Cat5 and a fish line trough it. Then simply use the fish line to pull the mic cable back through the pipe and you will have your cake and eat it too! Conduit with data lines is a best case scenario code wise. Since there is no power lines in the conduit (there better not be!) you don't have the heat/wire limit.

 

[BobHealey]

It can in theory work, until it doesn't. Big things to do are to keep DMX out of the audio device inputs and phantom power out of the DMX. I've gotten lucky with some 30 yr old mic lines driven off a net3 node passing through a neutrik patch panel, and a very interesting home made kludge of a stage box before hitting the jack i need. The stage box has all remote mics terminate as XLR males, and all lines to the booth originate as XLR females, and a toggle switch to internally connect the two.

Make sure you check the polarity of the Martins in the manual. Since the 812 is old enough to speak Martin in addition to DMX, it will most likely need pins 2 and 3 swapped going in to the first fixture. What controller have you used with these in the past, or does no one remember using them ever?

 

[len]

I would vote Wireless DMX. I have used it for several years and NEVER had a problem. As for the sound thing- I have done it with LED's, but it hurts, and is probably not the best idea. The insulation on the cables may not be good enough for the High Fi data transfer you need. It can also mess with your sound setup, causing static in the sound and and erratic behavior in the lights.

Not a bad idea in the best of circumstances, but
a) the OP is a student with likely no purchasing authority
2) see #a
d) hard to justify for 2 movers which were discontinued at least 10 years ago.

 

[itie]

Make sure you terminate the "dmx/mic cable" at the end of the fixture. In the past I've used mic cable when in a bind or when running dmx wasn't possible like in your situation. Usually I didn't see an issue if the runs where under 250ft. Once I hit longer runs I started having certain channels not behaving right. If you start to see a need for dmx in your electrics more often your best bet is to follow the advice of running the right cable through the conduit. Cat5 works well I would even look at getting a dmx splitter once it hits the electric so you don't have to daisy chain as much. Enttec makes a decent one for high school budget.


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[MikeJ]

I would try it using your existing mic cable, as long as you are sure of where the cable run goes, and where it ends up at both ends, that way you have no chance of crossing signals with other gear. It will either work or it won't. Its already there so it does not cost you anything but time if it does not work out. If those old fixtures do need pins 2 and 3 swapped(look it up to be sure), just grab a polarity swap/phase reverse XLR adapter. You might have some in your audio gear, or you can make one out of an old cable, if you can solder, or probably get one on amazon or guitar center for $3-4.

If it kind of works, but the fixtures act funny, a terminator may help. You can buy these, but if your school has electronics classes, ask that teacher to help. All you need is a 1/4 watt 120ohm resistor across pin 2 and 3 of an xlr connector. If you high school is anything like mine, you should be able to scavenge XLR connectors from dry-rotted mic cable that have been lying around since 1967 or so.

 

[jcslighting]

Like most folks in a low/no budget situation, I too have used mike cable for DMX with decent success. A couple notes not already mentioned - make sure the mike line does not have pin 1 grounded to the connector body. I had a sound guy lend me a cable that was wired that way and the DMX devices failed to do anything. The second thing is that you never know unless you try it. If the runs are short enough you should be in good shape as long as the cable is in good shape. Also, make sure you terminate the DMX run at the last fixture. An unterminated line can cause goofey issues farther back up the chain. Good Luck!

 

[shaferboy]

Thank you for all of your replies