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Continued from December 2007 CTI Newsletter

Eight Universe Main-Backup Switch 

By Larry Dunn, City Theatrical Head of Engineering

A 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.

DMX 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.  

All 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.

In 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.

We 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.

We 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”. 

Questions?  Please call or email City Theatrical's Sales Manager, Andrew Nikel.

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