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Pro Production: Understanding DMX Lighting Control

The foundation and essentials of an industry standard

By Craig Leerman March 28, 2013

There are a variety of protocols used that have been used over the years to facilitate communication of the control signals between a lighting console and fixtures and dimmers and effects.

Before moving lights and LED fixtures, analog protocols were used to send intensity information to dimming racks. These systems sent a DC voltage signal ranging from none or 0 volts (off or 0 percent) to 10 volts (full or 100 percent) and were commonly referred to as 0-10 volt systems.

While analog voltage systems do allow smooth fading and control of stage lighting they have a few drawbacks. The first is that a separate wire is required for every dimming channel in the system, as well as a common neutral wire. Large lighting systems would require big heavy multi-channel snakes from console to the dimmer racks.

Another big drawback to these systems were that control consoles were very limited, offering few submasters and little to no programming features. And manufacturers didn’t always agree on connectors, so consoles from one manufacturer might not be able to connect to a dimmer from a different manufacturer.

When intelligent fixtures arrived on the scene, it was obvious that using a 0-10 volt protocol was not going to be the best choice so manufacturers developed their own protocols and consoles to control their lights.

For a while, it was common practice for a lighting operator to have two consoles at a show, one for the par cans on the dimmers, and a second one for the movers. Implementing additional intelligent lighting from multiple manufacturers would have required a separate console for each type of fixture.

In 1986, the United States Institute for Theatre Technology (USITT) developed a digital control standard called DMX512. DMX (or Digital Multiplex) offers 512 control channels over a single 3-5 wire shielded cable. For the first time any manufacturer’s console could control any dimmers or fixtures that used the DMX standard.

Today, DMX512 is used to control dimmers, LED fixtures, moving lights, fog and haze machines, and special effects like confetti launchers. Because the DMX protocol does NOT have any form of error correction, it must not be used to control pyro or any stage equipment or effect that could present a hazard if it was to be triggered unexpectedly.

The cabling standard for DMX512 offer not only a main or primary data path, but also a secondary data path. This is used by some manufacturers for relaying information from a device back to a console, like the temperature of the fixture or other status monitoring. In most cases, the second data pair is not used.


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About Craig

Craig Leerman
Craig Leerman

Senior Contributing Editor, ProSoundWeb & Live Sound International
 
Craig has worked in a wide range of roles in professional audio for more than 30 years in a dynamic career that encompasses touring, theater, live televised broadcast events and even concerts at the White House. Currently he owns and operates Tech Works, a regional production company that focuses on corporate events based in Reno.
http://techworksreno.com/

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