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Compu Live VI Appendix
watch on your TV, in a lighting fixture you set the channel that you want your fixture to display the
information for. This is known as the DMX address.
In other words, if I set my lighting fixture to channel 21, then my fixture’s DMX address is 21. Both
expressions are common in the lighting world.
Example
Imagine we have a DMX dimmer that controls a simple light bulb. This dimmer is set to DMX address
21, so the lighting fixture will only receive the information from channel 21 and ignore the rest.
We have a controller that sends a signal through a DMX cable and this cable goes into a decoder (the
DMX dimmer) that receives the signal. So if the controller sends the “turn on” information on channel
21, the dimmer will turn on the light bulb.
Conventional lighting fixtures (simple dimmers) require 1 channel of information only. However,
intelligent lighting fixtures require more than 1 channel to work. For example, if I have a lighting fixture
that requires 5 channels of information, and its DMX address is 21 (again, address is the first channel
used by the fixture), then this fixture will use channels 21, 22, 23, 24, 25. The decoder knows that the
fixture needs 5 channels of information, so it will decode 5 channels only and ignore the rest. The
controller knows the fixture uses 5 channels also, so it will send 5 channels of information.
Example
Imagine you have a very simple robotic moving head that uses 5 channels:
1. pan
2. tilt
3. color wheel
4. gobo wheel
5. dimmer
You set your moving head to address 21 and you tell the controller that you have this particular moving
head on address 21. The controller then knows that channel 23 corresponds to color wheel, for
example. If you want to change the color of the light beam, you tell the controller what color you want,
the controller automatically sends this information through channel 23, and the lighting fixture reacts
accordingly.
Typically, intelligent lighting fixtures use 1 channel (sometimes more) for every function they can
perform (color, gobo, prism, dimmer, etc). Some robotic moving heads use over 20 channels, some
simple scanners only 4 channels, etc.
3. The protocol
So far, we’ve been referring to “information” traveling through DMX cables from the controller
into the fixture’s decoder. This “information” is nothing but a number between 0 and 255. This number is
called the DMX value for a particular channel. Then, the DMX signal is nothing but a series of DMX
values along 512 DMX channels.
Example
Back to our 5 channel simple robotic moving head; channel 3 controls the color wheel, which has 25
different color combinations. The color displayed will depend on the DMX value on channel 3 (as it is
being sent by the controller) as follows:
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