DMX 512 – What is it Really

DMX512 - What is it Really

Basically, DMX512 or just DMX is a way to control things from a central control device. Officially, this is now an ANSI standard developed in 1986 by the United States Institute for Theatre Technology or USITT to replace analog control of dimmer systems. It has gone through many revisions to become an industry standard, it is now “ANSI E1.11 – 2008 (R2013)” maintained by Professional Lighting and Sound Association or more commonly know as PLASA. DMX stands for “Digital Multiplex with 512 individual pieces of information” unless you are on Jeopardy or need to win a bet you can forget this right now, but the question comes up a lot. It was initially based on an existing standard of the time EIA–485 so, much of the electrical parts of DMX are the same.

With that out of the way, the important stuff, how to use it successfully.

Today DMX can control a bunch of devices like dimmers, LED lighting fixtures, moving lights, fog machines and other environmental effects and special use tools. We now can even run DMX over an Ethernet network, more on this in future posts. Because it has no error correction (the information is not guaranteed to arrive exactly right) it can not be used for critical environments where safety is a factor such as pyro, motorized sets, etc. There are four main areas to focus on when setting up a DMX control system.

Addressing

We hinted to the fact that DMX has “512 individual pieces of information”, each one of the 512 pieces of information is known as a channel and a group of 512 channels is called a universe. Within each channel there are 256 steps of control, in most cases this relates to intensity but could be movement or some sort of internal selection within the device. Each device has a start address, imagine the street where you live as the DMX universe and the houses are devices. Each house has an address so the mailman knows where to deliver the packages, in the same way, devices need an address so the controller knows where to deliver the commands.

Most modern devices use more that one DMX channel, so the start address would be the first channel the device will use. So in the below example we have four devices:

DMX-Setup

To set the address some devices have a number display (the easy way), some units have binary dip switches (the hard way). Usually, the user manual will have a chart to tell you what to set the dip switches to, or there are a couple of apps that will help with this:

Cabling

Traditionally DMX cabling uses a 2 conductor shielded 120-ohm cable with a 5 pin connector. However many brands on the market are now using 3 pin XLR connectors, this opens the door for microphone cable to be used. There is a great debate about this and its implications, but we will not get into it for now (maybe in later posts). For now here is a good set of recommendations

  • Use only DMX cable (CAT5 and CAT6 network cable are also an option now)
  • 5 pin or 3 pin connectors – need to work within the manufacturers design
  • Limit the number of units on a single run to 32 units (EIA-485 Spec)
  • Limit the total length of cable to 3200 feet in a single run (EIA-485 Spec)
  • Use a 120-ohm terminator on the last device (these are readily available)

All DMX devices have an input connector (Male) and an output or thru connector (Female) and are connected together by “daisy chaining” them. This means you connect the controller to the input of the first device, then connect the second device from the output connector of first and so on till you get to the last unit. On the last unit, we will plug in your terminator to the output connector.

Controller

The controller can be a lighting console, a computer running software or a computerized console. Either way, this is the unit that will send the commands out to the devices and where you will interface with your system to make changes. The controller will be set up to know what DMX channel the devices are listening to so it can send the commands to the right place. With older controllers each fader will be a channel, this gets a little cumbersome when you start using LED’s and moving lights with all the different parameters that can be controlled. Software based controllers will take all this into consideration and present different controls tailored for each parameter type (color, movement, etc). No matter what controller you are using they all act as the Post Office, from our earlier example, sending packages to specific addresses.

Device to be controlled

These are the units that will receive the commands from the controller and make changes based on them. For example, if it’s a dimmer, it will change its intensity; if it’s an LED fixture it could change its color. DMX uses 256 steps for making these changes so, a value of 0 is 0% intensity or Off and a value of 255 is 100%. This value is like the volume on your TV, click the up button and the volume is increased by one click, it went from a value of two to a value of three (or if you are like me with an old TV, from two bars to three bars). Some devices will also have a selection of options that can be controlled with DMX, for example, the range to set an LED fixture to strobe could be between 20 and 30, so we would set that channel to a value of 25 (the fixture should be strobing now).

Here are a couple of resources you may find useful

Now you can amaze and astound your friends with you new found knowledge of DMX. Go out in the world and spread good things and make the place you live better.

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