Originally published at checkeredhat.com
DMX is the most common method for controlling intelligent stage lighting. DMX stand for “digital multiplex”. What that basically means is that a number of signals are sharing the same cable at the same time.
DMX uses a five pin XLR cable to carry the control signal from lamp to lamp in a daisy chain fashion. Each fixture is assigned a particular series of addresses to answer to. Often this is done by setting dip switches. I use an app for Android called DMX Calc to make sense of the dip switches.
Almost all DMX fixtures require more than one channel to operate. You set the fixture to the first channel and the fixture will answer to however many channels it needs after that. For example, if you set a fixture that requires nine channels to channel 1 it will be listening to channels 1 through 9.
It is possible to have a number of fixtures answering to the same channels. It’s important not to mix and match fixture types when you choose to do this. All the fixtures assigned to the same channel should be of the same make and model. When DMX addresses are shared all of the fixtures on the shared address will respond identically.
Each DMX “universe” is equal to 512 channels. Many lighting consoles allow for control of more than one universe. This allows for the independent operation of more lights than would be allowed by the ceiling of 512 channels of a single universe.
If fixtures overlap in addressing unpredictable results will occur. Attempts to control one fixture will cause strange behavior in the fixture whose addresses overlap. This is called crosstalk. It’s important to carefully plan so that crosstalk does not occur.
You can find out how many channels each fixture uses by consulting the users manual that came with it. This information is usually contained in a table called “DMX protocol”. This table will also reveal what each channel controls and what effect various settings will have. A channel can control color, brightness, gobos, speed,movement or even laser pattern.
Any number of types of controllers can be use to send signal to the fixtures. These range from small interfaces which control less than a full universe, to software interfaces, to enormous boards capable of controlling many universes of lights with preprogrammed movements.
Programming DMX involves setting your channels to the way you want them and then saving them to a “scene” for later recall. For example, if I had two LED pars pointing at a spot on stage I could tell one of them to have both it’s red and green LEDs at 50%. I could tell the other one to have it’s blue LEDs at 100%. At that point I could save the scene to the first memory position on my controller and recall it whenever I needed it.
A scene does not contain any motion. If my lights were “movers” each scene would contain only one position. If I wanted the lights to point someplace else I would have to program another scene with the new position. I could do this multiple times and save each one to another memory slot. Then we could tell the controller to cycle between the different scenes as a “chase” or a “pattern”.
Most controllers allow you to program them to run a number patterns in a row as well. A number of patterns being run in a row is called a “show”. As you can see, programming an entire show could be a very complicated and time consuming process.
I hope this sheds a little light on the subject of DMX. Take your time and plan out what you want to do. Research your fixtures and your controller. With a little patience you should be able to make the show you see in your mind into reality.
If you have any questions please leave them in the comments below. Good luck!