DMX Cabling for beginners

You bring up a perfectly valid point that I feel is worth a sticky for a posting.

Despite the fact that there are standards, some companies, for some reason, choose to ignore standards and do it however they feel to do it. As a results, it is necessary to increase one's knowledge and know how to deal with things. In your excellent example, knowing how to deal with a fixture or fixtures that are polarity reversed.

In this example, adaptor cables need to be made AND LABELLED. As well, fixtures need to be LABELLED. Actually, even better would be to modify the leads on the fixture to comply with standards, which would be a hell of a lot less frustrating. That's what I would do, at least. Not having to remember which light is wired bass-ackwards at showtime set is a lot less stressful. Now you have to track polarity and adaptor cables. It's bad enough we hvae an interchangable/adaptable 3/5 wire system for MyDMX, but then coupled with polarity reversed issues, now it's just too much garbage to deal with and too many other goofy parts to carry around.

Some ADJ controllers have a polarity reverse switch, but this is more critical if globally things are backwards. In many cases, it will simply change what is having the issues, which in and of itself may be a key troubleshooting feature to discover such problems.

I'm planning on ordering some Elation fixtures soon. These come with a 5-wire DMX. I'm highly motivated to void the warranty and install 3-wire connectors for DMX to put things all on my single 3-wire DMX standard. But modifying 8 fixtures and hence 8 ins and 8 outs, with not much time before a show, I'm not anxious to dig right into that project so fast!

Wouldn't it be nice if light makers would simply just GO with the agreed upon standard? It worked for MIDI, it works for microphones, it works for a lot of other things(unless you're Cisco and seem to feel that you need to keep re-inventing things that don't need to be re-invented just to dictate market movement). If people would stop fighting standards, we'd have a lot less problems!

Thanks for the reality check. I think everyone should read your posting just to be made aware of this stupid inconstency. It's a good bit of knowledge to keep readily available, especially when dealing with non-familiar lights.

Actually I agree with this. I will use a couple lights from American DJ for example. I have a couple American DJ-Startec Arc Beam 150s. Most DMX fixtures with 3 pin XLR connectors are wired this way:
Pin 1: Common
Pin 2: Data -
Pin 3: Data +

The Arc Beam 150 is wired like this:
Pin 1: Common
Pin 2: Data +
Pin 3: Data -
(Reversed)

So before I had my Elation DMX-Branch 4, I had about 4 DMX cables as polarity cross-over cables. This had proved to be very difficult in setting up for gigs because it took more time. Now what I did probably voided the warranty on my DMX-Branch 4, was I swapped the pins on output 4 so that way I can use regular cables. Set up now takes less time because I use outputs 1-3 as normal polarity and output 4 as reversed polarity. No polarity cross-over cables to deal with, just regular DMX cables to run everything.

Well, I would have used a reverser cable at an output on the DMX Branch/4 instead of cracking it open. But, as I get more comfortable, I would be making my changes on the fixtures.

Here's my logic:
Right, it's your gear, you know it. Well, I work with crew on a fairly regular basis. I don't expect them to remember such nuances. I want them to grab lights and grab DMX cabling and get going and it works. You plug it in, it works. Of course, there are ways around this via some labelling and training, but come showtime, you know people choke all the time. That's why I'd modify the fixtures instead.

Regardless, your way is perfectly valid and good and yes, you voided your warranty. Still, depending on how you do your stage, this sounds like a nice fast and conveneint solution for you, which again, if it works, then it's got to be right, right? Sure is!

Clearly, you're in control over your gear, and doing your "reversed fixtures" on a reversed port for their runs is a great solution. You know what might be cool? The DMX Branch 4 and Opti Branch 4 having polarity reversing switches installed on a per port basis? Now that would be cool! Although, I bet it wouldn't be super practical for most folks.

All I can say is that this is a good idea as well.

I'm hoping to purchase 8 Elation Opti Tri Par's, which use a 5-pin DMX. I want to modify these to use 3-wire so I don't need to deal with 5-wire stuff. Of course, using my OptiBranch/4, it's not an issue, I have 3 and 5 wire outputs, but all my other stuff is 3 wire. My current plans include 3 to 5 wire adaptors in both directions(2 each) and 6 3-foot 5-pin DMX cables.

Again, there is a standard. Why can't everyone just agree to it and follow it? It would make things a LOT easier for everyone.

I am in the process of getting a factory in London to manafacture 100 - to + and + to - adaptors as I am sure this would help out.

One thing that may be helpful to all is that make sure all your -/+ lights are first in the loop then add the +/- to the last bit. That way you'll only need one adaptor for the whole loop.

I would be interested to know what is the "standard standard"! I know ADJ MyDMX won't work my SmartScan SSC2 or SoundLAB scanner 2 without a reversal adaptor. MyDMX works with Acme Dyanmos without an adaptor...

All very confusing for the up and coming DMX programmer! I remember this problem in the 1980's with Showcad and Showcad plus.

You can easily change the wires with a soldering iron, cup of tea (or coffee if in the US!) you'll swear a bit but it takes about five minutes to change one end of the lead...

The problem is people trying to save a buck. 3 pin DMX shouldn't exist at all since it is not part of the standard, standard says 5-pin and 5-pin only. You can thank DJ's for that. In an effort to save even more money, people started using XLR vs DMX and then start to wonder why they have issues. Again, standard says 5-pin, 120 ohm cable. Not 3-pin, 600+ ohm cable.

As for different lights not working with certain things, you have introduced a whole ball of wax unto itself. DMX has baud rates and transmission speeds. Now the latest standard (DMX512A-2004) says everything is set to a certain baud rate and transmission speed. Certain old fixtures again don't like higher speeds and baud rates, so they flicker or don't act correctly.

Moral of the story, you can blame basically all the mishaps on someone trying to save a buck somewhere, be it cheaper cable, DMX drives, etc. If everyone simply followed the standards like higher end companies do, there wouldn't be issues.

Well, I won't argue your logic on how you're dealing with your scenario. There's no defacto right way to handle this sort of thing. If your lighting rig allows, I definately agree on your concept to put the reversed lights together. I also think putting them at the beginning or end to avoid excessive cross-over cables is also a good idea. Then again, maybe doing an entirely sepparate run might be the way to go when using a DMX splitter/repeater unit.

I forget exactly what the standard is, but I know all my lights that I currently have in inventory adhere to it. According to a quick research session, it appears Pin 1 is ground, pin 2 is - and pin 3 is +. I often get Pins 2 and 3 reversed in my mind, but in my wiring, I simply go pin to pin and all the cables are fine.

Really, I think it's irresponsible and negligent for manufacturers to make this type of mistake. It's so easy to ensure the connectors are wired properly that there's really no excuse for doing it wrong.

I also agree with what you're saying about this being a very frustrating and confusing issue for not only newbies, but seasoned veterans as well who MORE STRONGLY expect their lights to be wired properly. As I've said, I'd be inside the fixture and changing it at the connector.

I also agree that it doesn't take much effort to make your own adaptor cable or adaptor. While I don't take coffee or tea, the more valid point you make is that this effort isn't all that difficult or time consuming. But now you have to specially mark the cable so you don't confuse it with the properly wired cables.

Standards exist for a reason. I think it's time they were universally followed. It works for MIDI, it's becoming more standardized for XLR(many European hardware, especially older gear is wired Pin 3 hot, which you fix on a tech bench)

I have had several lights from old Roulette's and Showscan 1's that were the size of a London bus right up to ADJ LED Scan Plus's. I don't think I have ever seen a fixture with a 5 pin plug/socket. I have a few lasers and that's about.

One good thing with 3 pin is that it's cheap and can be picked up in the local Maplin.

However it does create problems for everyone. I would imagine that companies like ADJ, Martin and others must get lights returned with an assumed fault even though the fixtures are perfectly ok. I know, I have returned lights myself thinking there is a fault!

The motto is "Check, check, check your fixture instructions"

Cheers

Alan

So far in my inventory, all my DMX equipment is 3-pin. I do have an Elation OptiBranch/4, which is a DMX splitter/repeater, and it supports 3 and 5 wire operation, which is a nice way to go. My future purchase of 8 Elation Opti Tri Pars, those utilize 5-pin connectors.

Now, a controller like my DMX Operator has a poliarity reverse switch on it, which I've never needed to use. This is a super handy feature for diagnosing +/- reversed fixtures. Similarly, having a cross-over cable or adpator, from how you're presenting things, is practically a must-have in your toolbox. I have to take the position of agreeing with you because even though it may be a one-off learning thing, no tool to check means endless frustration because you'd lack the tools to otherwise handle this.

I totally agree and have been saying this: Check your fixture instructions.

I say it for other reasons, but it's still valid. I've been using that to tell people to read manuals to see if features they want are supported how they want them, with sound active in DMX mode being a primary inquiry.

You also bring up a good scenario: how many perfectly good lights are being returned due to them being wired in reverse at the plugs? Again, standards exist for a reason, and they need to be followed.

Now, in my scenario, I do test all my new lights with my existing gear within the best of my abilities well before events. I've so far not run into any DMX wiring issues. Even so, I think I may go ahead and build myself a short DMX cross-over cable, just to have handy. I doubt I'll ever need it, but I'll feel better having it handy. Since I only use my own gear, it's not as essential to have this sort of thing. For those using lights from who knows where or lighting companies who may have to integrate in act-supplied lighting, this is a MUST HAVE element.

I also think that this whole concept is not really a beginners issue per say, but something beginners need to be aware of. This is more of a "once you understand the basics of DMX, now here's a bit of sludge to keep in the back of your mind." I sure know I will now.