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DMX-512, THE BASICS

No other protocol has become as ubiquitous in the lighting field as DMX-512. Since its creation in 1986, it has simplified and enriched our jobs by giving us the freedom to design unique, automated shows. When it comes to lighting, we have full control over the what, when, where and duration of a unit’s performance.

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No other protocol has become as ubiquitous in the lighting field as DMX-512. Since its creation in 1986, it has simplified and enriched our jobs by giving us the freedom to design unique, automated shows. When it comes to lighting, we have full control over the what, when, where and duration of a unit’s performance. Additionally, thanks to the protocol’s uniform standard of transmission, we are not limited to one manufacturer’s proprietary control devices. The same technology controls most lighting equipment available today.

Even most classic plug n’ play icons have been revisited and equipped with DMX compatibility. As prices continue to drop, more of us can afford to purchase DMX fixtures, even on a shoestring budget.

What is DMX-512?
DMX, or Digital Multiplexing Data Transmission, is a standard protocol by which lighting controllers and control desks can communicate with lighting equipment. Its creator, the United States Institute for Theatre Technology, Inc. (U.S.I.T.T.), originally developed the protocol for dimmer packs. Today, DMX-512 allows many types of fixtures from different companies to be used together easily.

The number 512 represents the number of channels one DMX cable can carry.

Each one of these 512 individual channels can be set to a value ranging from 0 to 255. For example, if a dimmer function is addressed to channel 1 and the level of channel 1 is raised to 255, the dimmer function will transmit full power (functioning at 100%, full dimming). The same applies for other functions such as color and gobo. This is what we call intelligent lighting: the ability to control, via data link- DMX cable-, all the personality traits, or functions, of a fixture. Each of these traits is assigned to a distinct channel, and channels are assigned values between 0 and 255. The function controlled by a particular channel is determined by the fixture, and will be found in the owner’s manual of your particular unit.

What is addressing?
Each intelligent light's range of controlling DMX channels must be set manually. Each light's DMX address corresponds to the first of the light's channels. For example: If you have two intelligent lights that use five channels each, you set the DMX address of the first light to 1 and the second to 6. In that configuration, the first light is using channels 1,2,3,4, and 5; and the second is using 6,7,8,9, and 10. You may also have to set up your intelligent light console for the type of lights you have and program their DMX addresses on the console before you can control them.

Planning addressing
You may want to do a little planning before you start addressing your lights. Put your lights in a logical order; it will help you figure out which light is which later. Next, find out how many DMX channels each type of light you have uses (The light's manual should tell you this). Now that you know which channel each light’s address begins with, you can figure each light's DMX address (except when your controller banks channels*). Take the first light's DMX address, add the number of channels it uses, and you have the second light's DMX address. Then, take the second light's DMX address, add the number of channels it uses, and you have the third light's DMX address. Do this until you have all the DMX addresses for your lights figured out and written down.

*Some controllers give you settings automatically and some controllers use banks of channels. Some DMX controllers bank all fixtures in 16 channels so your first fixture would always start on channel 1 and your second fixture will always start on channel 17 if you use a controller with banks of channels such as the CHAUVET® DMX-55. Controllers such as the CHAUVET® ShowXpress TM, that don’t utilize banks, allow you to use all the channels. Always go by the controller’s settings, not the fixture’s.

Setting dipswitches
Read your fixture's manual to find out how to address your light. Many intelligent lights use binary dipswitches, while others lights may use a small display and buttons to set the DMX address. When using dipswitches, there is always a minimum of 9 dipswitches. Some units have extra dipswitches for added functions such as stand-alone, invert, and focus.

Each dipswitch refers to a binary code and has a value as listed below:

Dipswitches must be on and correspond to the start channel values for each unit (Exception: if your controller works in banks*). This is when your math skills will come in handy, as it may be necessary to do some calculations to figure out the proper dipswitches to turn on. If the first light starts at channel value 1, we only need to place dipswitch #1 (Its assigned value is 1) in the “On” position. Let’s say our second unit starts on channel #4. Look at the table. You’ll need to turn on dispswitch 3 only because it has an assigned value of 4, but our third unit starts on channel #7. Which dipswitch (s) should be placed in the “On” position? You need the values to add up to 7, therefore, you should place dipswitches 1, 2 and 3 in the “On” position, as they have a combined value of 7 (1+ 2 + 4). Our fourth unit starts on channel value 10, so it will be necessary to turn on dipswitch 2 and 4 (Based on dip 2 and 4 having a value of 2+8=10).

Wiring and electrical details
Once you have figured out which dipswitches to turn on, it’s time to connect your DMX cables to transmit data from the controller to a unit, and from each unit to another unit, daisy chain-style. Any installation must meet the requirements of EIA-485, meaning that the use of suitable, quality cable is particularly important to provide safety, shielding and prevent transmission interferences*. Such cables include:

*Mic cable is NOT suitable. Analog cable is not an acceptable replacement for long-term use! These cables will degrade over time and are more conducive to interference and prone to failure in the long-term.

At the speed DMX works, correct wiring practice is important. Always arrange wiring to ensure that the data source is at one end of the cable. Never use a Y-connector instead of a DMX splitter in applications where signal splitting is necessary.

Wireless DMX
The ability to transmit and receive DMX signals without wires is a newer development in the technology that allows designers more flexibility in fixture placement. By utilizing a transmitter and receiver, DMX signals can be transmitted without requiring a cable run. A single transmitter can also run more than one receiver, allowing designs that incorporate split trusses to be “wired” effortlessly.

Line termination
All DMX lines must be correctly terminated for reliable operation. If not, a loss of signal may occur. Some fixtures have a built-in, switchable, line-terminating resistor. In this case, make sure that only the last item in the chain has its terminating switch set to the “On” position. If the last item (farthest from data source) does not have a terminating switch, then an external line-terminating plug is needed.

This article was submitted by CHAUVET ® staff To keep abreast of the latest, visit
http://www.esta.org http://www.chauvetlighting.com