DMX512 Lighting Explained
DMX512is a standard of lighting control that was developed by the
US Institute of Theater Technology(USITT). This standard was originally developed to control
light dimmers, but is currently being used to control just about every aspect of
lighting, from color changes, to light motion, to
fog machines, and even lasers.
DMX512 lightsare specially designed to work with this standard, although most any light can be made to work by using
dimmer packs or relays.
lighthas an address and "listens" to a control cable for commands that are sent to its address. Addresses are generally set on the
lightby a series of DIP switches. Note that one
lightmay have multiple addresses. For example, a
color changing lightmay have one address to set the mode of the
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 the
lightis set by DIP switches, the first address of the
lightis being set and the others will be offset from the first. For example, if a
lighthas 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. A
DMX512 lightwill have a
DMXdescription 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 one
lightmay 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 one
DMX512 protocolis capable of controlling up to 512 addresses per "universe", however most
controllersonly provide a subset of this. Each universe represents a separate control line. Each control line is connected to the
lightsin a "daisy-chain" manner, whereby the
controlleris 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 the
lightswill be compromised.
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, for
DMX512 is easy to use, is fast enough for most applications, and is capable of producing spectacular large-scale
DMX512's acceptance by the industry is shown by the large number of devices that are available that use the