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DMX lighting consoles
As the console starts sending a new set of 512 channels, every fixture has to lock in with that new beginning, and then keep track of the channels.

DMX Lighting Control: History, Design, Do’s and Don’ts

The DMX standard is very simple. It is a network consisting of a controller and one or more slaves. In lighting speak, that would be a console and one or more fixtures.

If you have any type of modern lighting in your house of worship, then it is most likely controlled via DMX. More specifically, DMX512. That’s because it is the most ubiquitous type of lighting control since the early ‘90s.

As the name DMX512 implies, it transmits 512 channels of data. It does this very fast. In fact, it operates at 250,000 bits/second.

Let’s take a deeper dive into DMX, by discussing the history, design and the do’s and don’ts associated with the lighting control protocol.

History

In the early days of electronically controlled lighting, all fixtures were individually lamped, and used a dedicated dimmer to regulate their brightness. The lighting console typically controlled each dimmer via a 0-10Vdc signal. If you had a six channel dimmer, then you needed a cable with six separate wires in it, besides other wires, that ran from the console to the dimmer.

In many cases, this was hundreds of feet of cable running from where the console was, behind the audience, to the dimmers back stage. Again, no big deal for six dimmers.

As shows grew, though, so did the number of dimmers. They grew to the point where there were hundreds to thousands of dimmer channels in a show. This meant large numbers of cables, with the many wires in them.

Because of this, companies started designing consoles and dimmers that could communicate via serial wire, like a mouse that is used by your computer. At first, each company did their own thing, though, it wasn’t long before the industry changed their line of thinking, recognizing the need to work together. Eventually, there was agreement for the need of a common standard across all manufacturers so that, for example, the console from Company A could talk to the dimmer from Company B.

From that, DMX was then born.

The first DMX512 standard was released in 1986. Over the years that followed, a few revisions were made, but it remained relatively the same.

Design

The standard is very simple. It is a network consisting of a controller and one or more slaves.

In lighting speak, that would be a console and one or more fixtures. Electrically, it uses a single cable of at least three wires. This configuration is daisy chained, starting from the master controller, and going to each fixture, until it reaches the last one.

DMX chart

As the name DMX512 implies, it transmits 512 channels of data. It does this very fast. In fact, it operates at 250,000 bits/second. And it repeats all 512 channels of data, at typically 25 times per second. But it can be as often as 44 times per second.

Think of it as one person (console) standing at the end of a long tunnel, shouting out numbers. All the other people (fixtures) are positioned in small doorways along the tunnel, listening for their specific number in the sequence.

So how does each person know which numbers are theirs?

Each fixture needs to have a starting address assigned to it, when you set up your rig. This is typically done using the menu on the fixture. Along with that is choosing the mode in which you want to operate the fixture. For our example, let’s say it is a simple RGB (Red, Green, Blue) LED fixture. It needs three channels of data, out of the 512 available. Let’s say we set it for a starting address of 4, because some other fixture is using 1-3.

As the console starts sending a new set of 512 channels, every fixture has to lock in with that new beginning, and then keep track of the channels, as they get transmitted. Our fixture in the example has to essentially throw away the first three channels, but when the fourth, fifth and sixth come, it needs to capture those. It then applies them according to its design, typically it is 4-Red, 5-Green and 6-Blue.

It’s rather simple, and as long as you address all your fixtures correctly, it should all work.

But what things can cause it to not work?

Do’s and Don’ts

1. Only daisy chain the wiring. Never leave a fixture with two cables, essentially splitting the path. Some fixtures come with both 5-pin and 3-pin connectors.

DMX connections

It is perfectly fine to come into the fixture with a 5-pin cable and leave using a 3-pin, or the opposite.

But don’t leave with two cables using both 3-pin and 5-pin.

2. The max total length of wiring should not exceed 1,300 feet. I’ve never come close to that.

3. No more than 32 fixtures on a daisy chain. Too many, and the signal degrades.

4. Terminate the daisy chain with a terminator. It is nothing more than a connector without a cable, and a 120ohm resistor, soldered across the two data pins (2-3). In many cases, you can run without it. But recall our example of the person shouting down the tunnel. Sometimes the tunnel can have an echo at the end. Those reflections cause the people listening to have trouble hearing the numbers. The terminator is like a damper and stops those reflections.

5. Use only DMX cable. You may get away with using microphone cable, but eventually it will act up. More than likely, it will be fine during rehearsal, but when a room full of people with cellphones come in, it won’t. As I said earlier, it is transmitting at 250,000 bits/second, which is a much higher frequency than your lead vocalist is singing at.

What works for singing, doesn’t work for data.

Follow these simple guidelines and I expect your rig will be reliable and free from worries!

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