Specifications

“Lighting Systems Made Easy” Page 30
Current lighting designs have expanded to include a lighting control network design. Although
instrument selection colour selection, lamp placement dominate the design process, the light-
ing control system also requires careful planning. Lighting consoles control dimmers and a
wide range of automated devices. Control communication must be standardized if equipment
from different manufacturers is expected to operate within a network, controlled by a lighting
console. The lighting industry has adopted DMX-512 as their standard control protocol. Un-
derstanding DMX-512 is vital for anyone involved in the design or installation of lighting sys-
tems.
Although the adoption of a standardized control protocol is accepted by today’s manufacturers
this was not always the case. Prior to adopting DMX-512 as a control standard, manufacturers
used their own propriety control signals. This meant Manufacturer “A’s” lighting board would
only work with manufacturer “A’s” dimmers. The lighting industry became frustrated with the
lack of compatibility between different dimmers and control console manufacturers. Manufac-
turers adopted the DMX-512 control protocol, as the control “language” lighting consoles would
use to “talk” to their dimmers to appease the lighting industry.
The development of DMX-512 was based simply upon the control of dimmers by a lighting
console. The original developers did not envision the wide range of devices that DMX-512
would be controlling today. Although adequate to meet the demands of dimmer control the
DMX-512 protocol is often pushed beyond its original expectations by automated lighting
systems. However DMX-512 still remains the common protocol widely used in today’s enter-
tainment lighting industry. DMX-512 is multiplexed digital lighting control protocol with a signal
to control 512 devices. The term device is used because today’s lighting consoles could con-
trol scrollers, non-dim relays, moving lights, a graphical light in a computerized virtual reality
set or dimmers. DMX-512 comprises digital signal codes (zero or one). When a transmitting
device (e.g., lighting console) sends its digital codes, the receiving device (e.g., dimmer) trans-
forms these codes into a function command (e.g., dimming to the specified level). With digital
systems, signal integrity is compromised less over long cable runs, compared with analog
control. When a 0/1 digit is sent and received as a 0/1 digit, the device will perform the desired
task. The signal is transmitted on two wires twisted together, referred to as twisted pair. The
connectors used are 5 pin XLR, although the current DMX standard only uses pins 1, 2 and 3.
Pin 1 is the signal common shield, pin 2 is data – and pin 3 is data +. The signal is comprised
of a voltage rise, between 0 and 5 volts, carried on the twisted cables. The DMX transmitter
creates a rise of voltage on one cable, at a specific timing, while there is not voltage rise on the
opposite cable at the exact same time. The receiver looks at the two incoming signals on pins
2 and 3 then compares the differences. A voltage rise on one wire and the inverse on the other
will be seen as a differential and therefore deciphered as a digit. When both signals are identi-
cal (having an identical voltage rise on both cables at the identical time) no difference is recog-
nized and no digit deciphered. If interference were accidentally transmitted alone the line, it
would impart no response as long as the interference was identical on both lines. The proxim-
ity of the two cables assists in distributing interference identically on both wires. The signal
driver, within the lighting console, transmits 512 device codes in a continual, repetitive stream
of data. To obtain control of devices beyond 512, additional outlet ports are added to the
console. The added ports will operate in multiples of 512, port 1 will control devices 1 through
512, port 2 controls devices 513 through 1024, etc. The receiving device is addressed with a
number between 1 and 512 so it will respond only to data that corresponds to its assigned