• Dan Koellen AI6XG

The Digi-Disco, a 1970's Light Controller

This is a light system that I designed and built in 1978 to control large flood lights of different colors, synchronized to disco music played during dances. At that time I was working with a popular local radio personality as a technical assistant when he DJ'ed dances during this time of Disco dance music. Prior to this controller, stage lights with different colored gels were used. The lights were switched on and off mechanically. This controller eliminated the mechanical switches and enabled the lights to synchronize to the beat of the Disco tunes. The lights could also be put in chase mode that was popular at that time. Also a VU meter type mode could be used.

The circuit used TTL logic gates, an ADC built from analog voltage comparators and the ubiquitous 555 timer. All very plentiful and relatively inexpensive in 1978. The circuit did not use optoisolators between the mains switching triacs and the control circuitry. Optoisolators were very expensive in 1978 so the decision was made to sacrifice the cheap open collector TTL 7406 drivers. After an initial sacrifice that generated a generous amount of magic smoke, careful power circuit isolation prevented further sacrifices. But a tube of extra ICs were always at hand just in case! Don't do this with your designs, there is no reason not to use optoisolators today. Don't skip this mandatory safety design protocol.

140420 EN Retronics
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This article first appeared in Elektor Magazine Jan/Feb 2015 issue.

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This is the German version that appeared in Elektor Magazine June 2015 issue

The console manages the operation of the light show; the wear and tear seen here shows the console was used quite often. In the lower right corner, Phase is the identity I used when working sound and lights for the dance gigs.

The circuitry contained in the console was built on a perforated board. Black soot from the 7406 catastrophic failure can be seen in the top center. To the left is the tube of replacement devices that was brought to each gig.

The remote box contained the triacs to switch the lights. At the bottom are the sockets for connection to the light bars; the console cable plugged into the socket on the bottom left. The transformer supplied stepped down AC to the console.

The hand drawn schematic for the Digi-Disco. Phase Sound and Light Consultants was the entity identification I used at that time.

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