DMX-512

Dimmer Protocol:  Intro to DMX-512
Preset boards use analog control signal to dimmers.
   Continuous signal between 0 v. and 10 to 28 vdc.
Computers are digital; store commands as binary digits.    Required D-to-A converters.
Analog: separate sets of wires for each dimmer, making huge numbers of control wires.
Multi-plexing: adding element of time so that signals sent in sequentially; dimmer reads only own signal.
   Requires only two wires for signals.
AMX-196 (Strand):  Analogue Multi-plexing, 196 channels.
DMX: Digital Multiplexing:
   Same two wires, more channels of control.

Principle
	* Each device assigned a distinct dimmer number.
	* Devices read their own signal as it comes by and holds until refreshed or changes on next cycle.
	* DMX address assigned manually, often through DIP switches.
	* All devices with same number read same "level".
An imaginary DMX-3:
DMX-512: USITT standard
   Digital Multi-plexing, 512 channels.
   An 8 bit serial system.
   Most manufactures quickly adopted as option
      or as only flavor.
Advantages:  Most equipment works well together.
   Amazingly flexible, can do a lot never anticipated; non-dimmer applications, moving lights, smoke machines, color scrollers, etc.
Disadvantages:
	* Only 512 addresses available; more through multiple DMX "universes".
	* Only 256 discrete steps available for each channel.
Not a problem for dimmers set in percent
DOES pose problems with Moving Lights.
Most moving lights use proprietary protocol with translators.
New protocol under developement, probably based on eithernet in 32 bit

Running DMX:
	* Utilizes a specific twisted pair cable.  Spec calls for 5 pin XLR.

2 are signal, 1 is shield, other pair are spares for talk-back
Unapproved applications also use 3 pin XLR, i.e. Mic cable
Rules:
	* Designed to be daisy-chained unit to unit.
	* Last unit must be "terminated" w/ 220 ohm resistor.
	* Cable lengths must kept under about 500 feet.
	* Repeaters, opto-isolators and opto-splitters and amplifiers needed for very large systems.

The next "generation": Ethernet
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©2000, Mick Alderson