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Tutorial
What Is DMX? A Simplified Guide.
10
Jan
Jan
DMX is a simple protocol language primarily designed for controlling theatrical lighting. Ok, I lost some of you already.
If you have an LED light that accepts DMX, you can control all of its functions with a DMX controller.
DMX Cables
DMX runs on DMX cable and is terminated with a 5-pin XLR, a 3-Pin XLR, or a screw terminal connector (Phoenix Connector). DMX cables only need three wires (a twisted pair with a shield).
Don’t let the different cable ends confuse you. By the definition of the organization that created DMX, DMX Cable should only be 5-pin, but that didn’t stop most of the lighting industry from exclusively using 3-pin DMX cables because pins four and five were never allocated. A 5-pin to 3-pin turnaround works because only the first three pins send data.
Running DMX
For this example, let us assume we have four of the same DMX lights we want to control with a lighting controller.
We need to run DMX from our lighting console to our four lights. Luckily, our lights hang close together, making it easy to link DMX. I run one DMX cable from the out-port of my lighting console into the in-port of our first fixture. I then run a short DMX cable from the out-port of my first fixture into the in-port of my second fixture. I continue this until all four of my lights are connected to DMX.
A DMX cable can carry 512 channels. Each channel offers increments of 0 to 255. By itself, DMX does nothing. Everything is up to the lighting fixture or device you are trying to control.
Let’s say our lights have three colors of LEDs, and the maker of this product has given us the option to control it as a three-channel (red, green, and blue) or a four-channel (red, green, blue, and dimmer).
Let’s keep this simple and say I set our lights to three-channel mode. I would set the mode on the light itself. Now I have four of these lights that I want to control individually. The first thing we will need to understand is addressing.
Addressing
I have 512 channels to work with and four lights that require three channels each. The first light I will address to channel 001. The second light to 004, the third to 007, and the fourth to 010.
I have 12 faders in front of me on my DMX controller. When I bring up the first fader, I will have red on the first light. If I want red on all lights, I need to bring up faders 1, 4, 7, and 10.
What if I were to address the fourth fixture to channel 9? It will still work, but when I bring up fader 9, the third fixture will be blue, and the fourth will be red because there is an overlap in their addresses.
So what happens if I make it a four-channel light? Then I need to change the addressing to 001, 005, 009, and 013. The first three channels will allow me to color mix by bringing up and down the intensity of my three colors. The fourth channel serves as a master dimmer that changes the intensity of the light’s output.
What if I want to control my four lights together in four-channel mode? I set the address of all four fixtures to 001. Now faders 1-3 will color mix all four lights, and fader four will be the master dimmer of all four lights. We can address the lights together as 001 and control them together because they have the same DMX traits. If you had a different light that offered the same 4-channel mode (red, green, blue, and dimmer), they too can be addressed and controlled with our four lights.
So What Do The 0-255 Steps Do?
0-255 steps do whatever the manufacturer of the fixture has determined. With the three-channel LED lights we’ve been using as our example, the increments determine the brightness of each color. Zero would be off, and 255 would be the brightest, with everything in between.
Suppose I make a one-channel DMX coffee maker that turns on at 50% and above to the DMX we’re running. I address the coffee maker to DMX channel 013, so I can control it individually from the four LED lights I’m separately controlling as three-channel fixtures. When I slowly bring up fader 13, nothing happens until I bring it past the midway point; at which point, I start brewing coffee. When I bring the fader down past the midpoint: the coffee brewer turns off.
While most people running DMX aren’t modifying their coffee machines to be part of their setup, the point is that 0-255 steps can be for a diverse set of functions and not just brightness or strobe speed.
Now, 512 channels of DMX may seem like a lot when working with 4-channel lights, but any concert or professional Broadway show greatly exceeds 512 channels. Consider moving lights. Some moving lights will require many channels to control. Some large fixtures can use up to 24 or more DMX channels each, so if you have a lot of moving lights, you can easily use up your 512 channels. Don’t worry! All you need is another universe.
What’s a Universe?
In DMX, 512 channels are called a universe. You can buy consoles with many universes to handle larger venues. Some smaller churches will sometimes opt for two universes- one for the house lighting and a second for the theatrical lights. Most of the time, this is not needed, but I thought you should know.
Can I Use Mic Cables For DMX?
When you say XLR, most people think of microphone cables. So, the common question is, can I use an affordable mic cable for running my lights DMX?
The answer is: we wouldn’t. Your typical mic cable has an impedance of 80 ohms compared to a DMX cable’s 120. Impedance is the effective resistance of an electric circuit or component to alternating current arising from the combined effects of ohmic resistance and reactance. So you may find your fixture strobing, flickering, or at a complete loss of signal if you use mic cables. Honestly, for short runs with minimal lights, you probably will not have any problem using regular mic cables, though we advise against even this.
Using A Splitter
In our earlier example of running DMX, our fixtures were close enough to link DMX. However, lights are often so far apart that it would be easier to run DMX from your controller than from the last light. In this instance, we would need a DMX Splitter. I would run DMX out of our lighting console into our splitter. We could then run DMX to our various groups of lights.
The recommended maximum number of lights you are supposed to link DMX together is 32. So a splitter is a must if you are running more than 32 lights.
Well, I hope this brief introduction helped you better understand DMX. Below I have linked some other helpful lighting resources.
