iDMX-1000
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the Virtual Controllers radio button. Use the Select
Unit Id drop down menu to select the address of your
iDMX-1000. Since “multiple of 16” unit addressing is
being used, only the most significant digit of the
address can be selected.
Pick a DMX address for the device that does
something visible like pan. If the pan DMX address is
4, this would be circuit 4 on the LOR network side.
Move the slider for DMX channel 4 and the fixture
should pan from left to right. If it does not, try
changing the Polarity Switch on the iDMX-1000.
Refer to the Experimenting with the Hardware Utility
section for more information.
General DMX Discussion
DMX512 (Digital Multiplex) was initially developed by
the US Institute of Theater Technology in 1986. It is
a very simple system that uses the RS485 electrical
protocol to transmit packets of up to 512 bytes. If you
are only using DMX channels 1 to 256, then the
packet only needs to be 256 bytes. The data rate is
250,000 bits per second. The data packets are
transmitted back-to-back as quickly as possible.
The maximum length of all cable in a DMX512
network is between 1,000 and 1,500 feet, depending
upon the number of DMX fixtures daisy chained. The
maximum number of ‘loads’ (usually fixtures) in a
daisy chain is 32. It is important to use good quality
cables and make sure the network is terminated.
‘Terminated’ means placing a 120 Ω¼ w resistor
between pins 2 & 3 of the cable of the last DMX512
device in the network.
iDMX-1000
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The DMX512 specification calls for the use of 5-wire
cables using XLR-5 connectors. These cables tend
to be very expensive and two wires in the cable are
almost never used. It is also inconvenient for
theaters to keep separate sets of cables for DMX
and audio. For these reasons, most DMX512 fixtures
you will see use 3-pin XLR microphone connectors.
Adapters that convert between XLR-3 and XLR-5 are
readily available. Microphone cables without
termination will work in environments with short (100’
or so) cable lengths. Trial and error works here.
Each byte in a DMX512 packet corresponds to a
DMX channel. The first byte is channel 1, the second
byte is channel 2, … The bytes can have values
from 0 (minimum intensity) to 255 (maximum
intensity.) How this ‘intensity’ is used is up to the
DMX fixture. It could be the actual intensity of the
light, or it could be that 0 means ‘all the way to the
left’ and 255 means ‘all the way to the right’ for a
lighting device with a moving mirror.
DMX fixtures usually have many channels assigned
to them. You generally set the base address
(channel number) of the fixture, and then that
address and perhaps the next 7 are also assigned to
the fixture. Here is a partial channel assignment for a
theoretical light scanner:
Channel Value Function
1 000-255 Pan, Left ►Right, 128 = center
2 000-255 Tilt, Up ►Down. 128 = center
3 000-005
006-128
129-240
241-255
Shutter closed (no light)
Shutter open (0-100%)
Variable Strobe (slow ►fast)
Shutter fully open (max light)
4 000-025 White