A Simple Guide to DMX

DMX512 is a communication signal used to control what are commonly referred to as Intelligent Lights by universal or specific DMX controllers. It started out as USITT DMX512, then was abbreviated to DMX512 and is now most often called DMX.
The abbreviation DMX512 stands for Digital Multiplex Signal that can control up to 512 channels. This language was created by the United States Institute for Theater Technology (USITT) to simplify and unify theater lighting systems. Before DMX was created, the only lighting control system was analog which required one individual wire to be run from the controller to each light fixture or dimmer pack.
It is important to understand that DMX is a communication signal only and does not supply power to the fixtures. All DMX light fixtures and dimmer packs require their own power supply.
DMX is now recognized world wide as the standard communication language for theater and night club lighting and now even some fog machines.
A DMX system has 4 basic parts: A controller that creates and sends the signal, the cable that carries the signal and the light fixtures or dimmer packs that receive the signal. These are all connected in a Daisy Chain manner with the controller at the beginning of the line, the light fixtures and dimmer packs in the middle and the light at the end of the line acts as a signal terminator.
Connecting a DMX system is easy if you follow these three steps.
1. Link the controller to all light fixtures and dimmer packs with high quality cables.
2. Set the DMX address on each fixture or dimmer pack (usually, but not always necessary).These 2 steps do not have to be done in this order, but you must not power up any part of this system until the controller, all light fixtures and dimmer packs have been connected and addressed.
Let's talk about DMX cables...

I recently received and email from a blog monitor that said... "There are MICROPHONE cables and there are DMX cables and one can NOT be used for the other". That's a very strong statement. Very "Black and White". Unfortunately, it's also very untrue. That statement would be like saying that Chevy's are for taking your kids to school and Ferrari's are for racing and one can not be used for the other. I have seen many people race Chevy's successfully and I have also seen a few Ferrari's in the school pick up lanes.

I don't know exactly why people make those black and white statements about DMX cables. Perhaps they merely lack real world experience in the field. If they had real world experience, they would know that there were companies like NSI making digitally controlled lighting boards and dimmer packs with signals carried thru 3 pin XLR cables long before the term DMX was ever heard of here in America. (NSI calls their proprietary signal MICROPLEX and they still use it today).

What do you think those digital signals were carried thru back before the late 90's when DMX was introduced to the commercial market here in America? MICROPHONE CABLES. That's all we had back then, that's what was used and that's what worked for years. Perhaps some cables marked "DMX Cable" might perform better than some cables marked "MICROPHONE Cable", but it can also be proven that some mid to high grade MIC cables work better than some DMX cables and if you and your audience can't tell the difference, who cares?

What does matter is which pins the wires are connected to on the 3 pin XLR plug. At High Energy Lighting (CheapLights.com), we currently buy "MIC" cables and "DMX" cables from over 22 different suppliers. Regardless of how they are marked, we test samples from each different "MIC" and "DMX" cable model to make sure they work in a DMX chain before we ever offer them to our customers.

Here's an interesting fact... In the ten to fifteen years that we have been selling cables for transmitting digital signals for light processors, we have never had any cables returned by customers saying they didn't work as a DMX cable, unless the cable actually had a physical defect, such as a wire not connected to the plug or a cut in the wire. That's a great statement to be able to make!

Here's a few more interesting facts...

1. "DMX" was created in 1986, but not widely used or known. At that time, the popular method for transmitting signal to dimmer packs was zero to ten volts.

2. "DMX" was revised in a major way and started gaining recognition in 1990. (But not in America).

3. The first DMX lighting controllers were displayed at the American LDI Lighting convention in 1999 by LitePuter.

4. "DMX" was introduced as the "Standard" digital signal for the World Wide lighting industry in 2000.

Damaged cables and their connectors are the main cause of DMX system problems. Bad solder joints and corroded connector plugs can easily interfere with the signal and prevent proper operation.DMX cables should never be installed in the same conduit or junction boxes as power wires. You wouldn't even want them running side by side on a temporary basis.
Never attempt to use a Y cable or splitter other than a true DMX splitter.
Although a five pin XLR connector started out as the official connector for DMX, the three pin XLR connector has always been the standard in the U.S.A. and is quickly becoming the the most popular everywhere.
Both connectors do the same thing. Pin #1 = ground, pin #2 = negative signal, pin #3 = positive signal. On five pin XLR connectors, pin # 4 and #5 are usually not used.
Each light fixture and dimmer pack must have an address in order to receive data from the controller. Assigning an incorrect address to your light fixture is as fatal as putting the wrong address on your electric bill payment. In both cases the lights won't come on!! DMX address mistakes are a big cause of problems with new systems and new human operators. Bad addresses on fixtures cause problems such as gobo change instead of mirror movement, color change instead of gobo change, or no response at all.Setting DMX addresses is sometimes very simple by following manufacturer instructions and sometimes very difficult when no instructions are available.
Most DMX light fixtures have nine DIP switches used to set the address of that fixture.
dmx switch 2
Address values are easy to remember. Starting on the left and moving right, each dip switch has a value twice as large as the switch at its left.
dmx switch 3
The address for a DMX light fixture equals the sum of the value for all dip switches in the ON position. In the picture above,
the address selected is 1.
Here are a few more examples...
dmx switch 4Address is 2
dmx switch 5Address is 3
dmx switch 6Address is 7
dmx switch 7Address is 21
The rule for setting an address with DIP switches is to start with the largest number of a DIP switch and work your way down through the lower numbers. To set an address of 35 you would first flip on DIP switch # 6 for a value of 32, then flip on switch #2 which makes the total value now 34, then flip on switch #1 which makes the total value now 35.
You might find these little switches easier to manipulate with a small screwdriver or a writing pen.
This is where the confusion starts. Many intelligent scanning lights use 4 channels; 1 for the gobo wheel, 1 for the color wheel, 1 for left to right mirror movement and 1 for up and down mirror movement. So why does the second fixture need to be addressed 13 instead of 5? I can't tell you why they do it, but almost all manufacturers make DMX intelligent lights that OCCUPY more channels than they USE. If you don't have a good owners manual that clearly identifies the addresses of the second, third and fourth units, you can follow the same procedure that we do when we test a new light.Connect only one fixture to the controller with only one DMX cable. Set the address of this fixture to 1. Turn the power on the controller and fixture and test each slider on the controller to identify which slider activates each item on the light fixture. After you have made a note about each slider and its activity, turn the power off for the fixture and the controller. Run a second DMX cable to one more fixture and set its address to 1. Power up all items and test the sliders again. Both fixtures should do the same thing at the same time. You can have as many fixtures as you like daisy chained together and all set to address #1. This is the simple way to test and run multiple intelligent lights.
If you want to have each light doing something different from the others, you must address them each differently. This is when you need to know how many channels the light OCCUPIES. To do this, turn the power off for the fixtures and the controller. Go to the second fixture and set its address to 2. Power up all items and test the sliders again. If both fixtures don't work properly and in sync, turn all power off and advance the address of the second unit by 1 and try again. If this still fails to operate properly, power down and advance the address of the second fixture by one again. Keep doing this until you find that the second unit works in sync with the first.
If you know that your light fixture OCCUPIES 6 channels then your first fixture will be address 1, your second fixture will be address 7, the third fixture will be address 13.
When setting DMX addresses, the design of your DMX controller and each light fixtures channel function need to be observed. For instance our CX-5 has 12 sliders for light operations while our DMX-STEP-ONE has 8 . Each is very convenient for some intelligent lights, while inconvenient for some other lights with fewer channels.This problem can be overcome by setting DMX addresses imaginatively.
Lets say you have one intelligent scanner that uses channel 4 for left / right mirror movement and channel 5 for up / down mirror movement. You have another light that uses channel 5 for left / right mirror movement and channel 6 for up / down mirror movement. By advancing the address of one fixture, you will have the same slider controlling left / right mirror movement on both lights. You can play with the addresses of every light fixture to make sliders on your controller operate as you would like.
In theory all DMX signals must be terminated. I can tell you from personal experience that most of the systems I have operated were never terminated and still worked fine. Termination does reduce signal errors caused by reflection at the end of the DMX daisy chain. Almost all (if not all) light fixtures on the market since 1999 have a built in terminator.