CYGN-B

[mixedgas]

What does a Danube Board do?

Steve

[lasermaster1977]

What does a Danube Board do?

Steve

One of the great Laserium choreography numbers was to the "Blue Danube" and consisted of slow, graceful variations of the classic rotating, RYGB, Lissajous figures and cycloids of slightly out-of phase 1:1 sine/cosine signals, coupled with quadrature DC RYGB movements, moving to the music. I'm betting the Danube board was related to this.

[laserist]

The Danube board generated a slightly variable 100 Hz sine wave that was controlled by a 0-10V input voltage. It generated fixed 100 and 50 Hz sine waves. The combination of the fixed and variable wave forms generated Lissajous loops and "eights". When the 0-10V signal approached 10v the variable waveform was driven further from 100 Hz causing the loops and "eights" to "tumble". (It was modified to generate a low frequency quadrature signal pair that was used for z axis rotation and as an offset with the introduction of the Mark VI projector.) When Laserium premiered in 1973 Ivan and Charlie used army surplus signal generators to do the Lissajous figures and had 4 friends each with x/y faders to control the four image sizes. Laser Images couldn't afford 5 or 6 laserists per show. So consequently the Danube card and the 351 (later 352) data system were developed. There's actually very little about the choreography of The Blue Danube in "Laserium I" that involved a lot of adjustment of the frequency of the Danube board. Most of the choreography involved a constant fixed rotation for each image channel, master x/y gain that was enhanced by the fixed rotation, and individual image gains. There was a nice fairly tight lumia background effect that was produced with a clear plexiglas wheel with clear epoxy (mixed so bubbles formed in the epoxy) smeared around the wheel. Charlie made these in his garage. The process was "top secret".

[Greg]

(It was modified to generate a low frequency quadrature signal pair that was used for z axis rotation and as an offset with the introduction of the Mark VI projector.)

I wonder if anything further is known regarding that modification, as that sounds like a very useful modification.

So that's a cat's meow. The project includes the original slotted can chopper. I certainly noticed the change from this to the aom. It was like an insanely fast chopper, but with no trails. I thought it a sad loss at the time. There was a number in Laserock2 that, the way I saw performed, used slotted can chopper, CYGN-A, and the 351 gains and offsets scheme to, shall I say, be specific in a beautiful way about something one might not expect such a simple combination of signals to be so specific about.
Previously posted video of 351 visualization here:
https://www.youtube.com/watch?v=fkQeG4tbIYc

Photo shows a reformatting of some of what I got from Steve.

[laserist]

The Danube loops and eights were generated by clock/divider circuits. (2 pairs of divide by 16 and then divide by 2048/4096 counters. One had a pulse synchronizer that could insert a 0 to 20 KHz clock in one pair.) Those circuits sent square wave pulse trains through integrators to convert to triangle waves and then low pass filters to convert to sine waves for output. The rotation sin/cos outputs were generated by taking the 50 Hz output and phase shifting it 90 degrees to generate a quadrature cosine signal. Then the sine and cosine signals were then sent to two sample and hold circuits that were clocked to generate the Danube rotation/revolution outputs.

In looking at the Danube schematic to make this post I found I made an error previously describing the board's function. The 100 Hz "A" signal is the fixed frequency and both the 100 and 50 Hz "B" signals were slightly variable. By clocking the sample and hold circuits with the equivalent of a 50 Hz "A" clock the rotation/revolution signals had a theoretical resolution of 4096 points.

[ronhip]

Seems cruel talking about the schematic and how it works without looking at it in front of you. So... for your edification, I present you with that schematic (I had to break up the PDF in 2 parts of less than 5MB each for the forum software...)

Included is some pretty good documentation.

Ron

[mixedgas]

Thank you for the educational PDF.

Always wondered how that effect was SOOOOOO stable.

Steve

[laserist]

Thank you for the educational PDF.

Always wondered how that effect was SOOOOOO stable.

Steve

I think the thing that defines a laserist is the ability to see those subtle things other people miss. I had nothing to do with the design of the Danube card, but on behalf of those who did, thanks Steve.

[Greg]

Here is a previously unreleased photo of the mark VI projector in the McLaughlin Planetarium no later than 1982. Unfortunately the hood is on.

[Greg]

Exciting update: Communication has occurred with someone who operated the Laser Images choreography control desks. A possibility exists some very interesting lost knowledge may yet be recovered.