DMX-512 is a Digital Multiplexing standard which allows the control of 512 dimmers using a serial communications bus. Despite its numerous limitations, it has flourished around the world as a theatre and stage lighting standard.
The standard is maintained by the United States Institute for Theatre Technology (USITT) which publishes the DMX-512 standard. This evolved to become the ANSI/TIA/EIA-485-A-1998 standard. The standard was published in 1986 under the name DMX512/1986; ESTA (Entertainment Services and Technology Association) began revising the standard in 1990 which was then Issued by ANSI in 1994. However a revision was released in 2000 under the name DMX512/1990 and again in 2000 as DMX512-A/2000. The A-version of the specification can only be applied to equipment with active electronics conforming to this standar
The first dimmers/fixture functions were controlled by levers on the dimmers/fixtures. During a show, it could take several people to move these levers and someone else to coordinate them. This kind of control was quite cumbersome. Later, control wires were run from each dimmer/fixture to a control console. If you had 300 dimmers/fixtures, you had to have 300 control wires!! To improve this, manufacturers started using digital signals sent down one control cable.
At first, each manufacturer used their own protocols, meaning that different manufacturer's equipment could not be combined. Finally, DMX-512 was adopted as the standard lighting control protocol. Standard DMX is based on 512 individual channels, which can be set to a level between 0 and 255. If a dimmer/function was addressed to be on channel 1, and the level of channel 1 was brought up to 255 (100%), the dimmer/function would be sending out at full power. A colour/gobo or other function may also be assigned a number from 0 to 255. DMX-512 requires only a single channel with a 3 or 5 pin connector to connect many devices. Data is sent serially using a pair of wire (the third pin on the connector is the ground).
One key advantage of DMX is that the cable is less bulky, cheaper, and less cumbersome than a multi-conductor cable. It's widespread use now means that there are many device that use the standard, all of which interwork.
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Prof. Gorry Fairhurst, School of Engineering, University of Aberdeen, Scotland.