DMX512 Lighting Explained |
DMX512is a standard of lighting control that was developed by theUS Institute of Theater Technology(USITT). This standard was originally developed to controllight dimmers, but is currently being used to control just about every aspect oflighting, from color changes, to light motion, tofog machines, and even lasers.DMX512 lightsare specially designed to work with this standard, although most any light can be made to work by usingDMX512controlleddimmer packs or relays. |
In the
DMX512method, eachlighthas an address and "listens" to a control cable for commands that are sent to its address. Addresses are generally set on thelightby a series of DIP switches. Note that onelightmay have multiple addresses. For example, acolor changing lightmay have one address to set the mode of thelamp(on/off/sound activated), another address to select the color, and a third address to set the speed at which it changes the color. When the address of thelightis set by DIP switches, the first address of thelightis being set and the others will be offset from the first. For example, if alighthas three addresses and the DIP switches are set to address 15, the light will be using addresses 15, 16, and 17. |
When a command
is sent to its address, the
lightwill respond to that command. ADMX512 lightwill have aDMXdescription table that describes what every command does. For example, a value of 0 might turn off the light, 10 might make it red, and 255 might make it blue. Note that more than onelightmay be set to the same address. If this is the case, when a command is sent, all of the lights with that address will respond. In this way, many lights can be controlled in synchronization using only oneDMX512 address. |
The
DMX512 protocolis capable of controlling up to 512 addresses per "universe", however mostcontrollersonly provide a subset of this. Each universe represents a separate control line. Each control line is connected to thelightsin a "daisy-chain" manner, whereby thecontrolleris connected to the first light, then the second light is connected to the first, and the third is connected to the second, etc. The last light in the chain must be terminated with a small plug in resistor device to keep the signal from reflecting from the end and interfering with the transmitted signal. If it is inconvenient to run the control line in one straight run,DMX512 splitters exist. It is important to use these rather than to just make a "Y" cable, as the signal levels will not be correct and the reliability of thelightswill be compromised. |
The
DMX512 protocolis designed for speed and simplicity. Therefore, no error checking is done, and as such,DMX512is not appropriate for controlling potentially dangerous equipment such as pyrotechnics. However, forstageandtheater lighting,DMX512 is easy to use, is fast enough for most applications, and is capable of producing spectacular large-scalelight shows.DMX512's acceptance by the industry is shown by the large number of devices that are available that use theDMX512 protocol. |
For more information about
DMX512, visit theUSITTweb site at http://www.usitt.org. Also, Ujjal has an excellent in-depth tutorial on his web site at http://www.dmx512-online.com. |
