First and foremost DMX512, which is often just referred to as just DMX stands for Digital Multiplex with 512 pieces of information. I know I know, it has a dry name but it's for good reason. To understand why DMX exists in the first place let's take a look at the innovation in entertainment lighting.

Lighting started out very simple. This image was from 1928, lighting used to be controlled using these large panels that required manual operation. If you wanted to turn a light on you had to flip a switch. As you could imagine this was very inefficient. With the advancement of electronic technology, electronic dimmers were created that could provide computerized dimming of many channels of light at once. This led to another problem, each manufacturer had a different protocol and the systems were not cross compatible with one another. As the industry grew and shows became even more complex the need for cross compatible equipment was even more important.

In order to fix this problem the USITT engineering commission sponsored a session at their annual conference. And by the end they had started a project to develop a lowest common denominator control protocol that would be able to communicate with everything. And in turn lighting manufacturers would have to support it in their products. Thankfully it was widely adopted and is the most widely used control protocol today.

Now that we know why DMX exists in the first place let's explore how it works under the hood. 

The DMX protocol is actually very simple; it is divided into two discrete components. We have the address and then the value associated with that address. The DMX512 protocol has, well, 512 addresses each of which can have a value between 0 and 255. 

You might be wondering why the values are between 0 and 255 and not 0 and 100. This has to do with the underlying data type. In computers we use bits to represent data, those are either 1s or 0s. In order to do anything useful with bits we need to combine them into larger groups to hold any meaningful data. The next step up is a byte, which is a grouping of 8 bits together. And if we do 2 to the power of 8 we can see that is where 255 come from. The 512 addresses together make up what is called a DMX Universe. 

DMX uses a 5 pin connector. You may have come across a 3 pin connector in the past, however, these are not permitted to be used according to the DMX specification but that doesn't stop people from using it anyways. The two main differences between the cables are future features and impedance. There are currently unused pins on a DMX connector that are reserved for future expansion and features. These have been used bi-directional communication but hasn’t been widely adopted yet by the industry. But arguably the most important reason to use a 5 pin connector is that the cable it is attached to has the proper electrical characteristics. While it may seem that the 3 pin cables work, you will run into issues with longer cable runs.

One important feature of DMX is that it is able to be daisy chained. This means that you can connect many devices together in one chain with the output of one fixture going into the input of another fixture. This works great in theatre especially since we normally have lights lined up in a line anyways and it is easy to jump from one fixture to the next.

Once we have connected our final fixture to the DMX daisy chain we need to terminate the end. Some devices have a terminator built in but if they don’t you can always purchase one online. DMX termination is very important. Imagine if you are in a large room and you yell, you will expect to hear an echo of yourself. This is what happens in the DMX cable without termination, the signal gets reflected back and can confuse the devices connected to it. This can cause instability, flickering, and other issues. 

Lights have come a long way and often time has many parameters that we can control such as pan, tilt, color, iris, gobo and much much more. Each of these parameters are controlled by one or more addresses. Since the DMX protocol sends all information to all devices it is up to the receiving device to take what it needs. We set the starting DMX address for each light by either using a digital display for newer devices or a DIP switch for older devices. 

Now we need to generate a DMX signal to feed to all of our devices. Light boards are what we normally use to control lights. These devices contain an operating system that allows us to program what we want our lights to do, and then convert those commands to the DMX signal. I personally use a desktop software called ETC Nomad, and its corresponding box that generates the DMX signal. You will notice that this box has two plugs, which corresponds to two DMX Universes.

This brings us up to the big limitation of DMX which is that we are limited to 512 addresses per universe. And with intelligent lighting fixtures these days using many addresses they run out of data very quickly. The solution for this issue is to keep adding on more and more universes. 

Thankfully there have been new protocols developed to distribute many universes of DMX over one cable, however, they are still required to be converted back into DMX before being plugged in.