Continued from December 2007 CTI Newsletter
Eight Universe Main-Backup Switch
By Larry Dunn, City Theatrical Head of Engineering
DMX main/backup switch is a device that allows switching a DMX network
between the main controller and a second backup controller so that in the
event of a controller failure the show can be continued on the backup unit.
main/backup switches have been used in critical installations since DMX was
first implemented. Prior to the
development of the CTI 5300 8
Universe Main/Backup Switch, DMX main backup switching options were
divided between custom made one-off units that were built around
“adapted” hardware such as serial printer switches, some smaller manual
switch units, and active systems
that handled up to 4 universes.
of these options had some perceived drawbacks; the smaller manual units were
not big enough to handle the large multi-universe shows that were becoming
common, the custom made units were expensive and did not always meet the
construction standards for critical use, and the active systems removed an
element of control from the show technicians which many seasoned
professionals were uncomfortable with.
the early spring of 2004 we were asked if we could provide a main backup
solution with a single switch for a multi-universe DMX lighting system.
From our research with lighting shops and Broadway electricians we
learned that such a unit should feature a single reliable mechanical switch,
should support up to 8 universes of DMX512, and should fit in the smallest
possible 19” rack-mount enclosure.
began with the switch, and developed a custom aircraft control grade sealed
rotary switch that is made specifically and exclusively for this unit.
Then we designed the DMX input and output circuitry as a single
precision-routed multilayer printed circuit board with shielded input and
output layers for reliable signal isolation, and we mounted the switch and
all the connectors directly to the PC board, so that the unit had no
internal wiring or extra connections between the DMX inputs and DMX outputs.
then packaged the finished circuitry in a 1 unit high (1-23/32”) 19”
rack mountable 16 gage steel enclosure with machined aluminum handle/guard
brackets mounted on each side of the switch to allow easy installation or
removal from a rack and to serve as protective guards for the switch.
The result is a reliable and durable unit that can switch between the main and the backup sources of up to 8 universes of DMX with a single positive and satisfying “thunk”.
Please call or email City Theatrical's Sales Manager, Andrew