post your eye melty abstracts here

[AnAnonymousParty]

Those were done using a image generator designed back in 1977. (CYGN-B for the LII folks) It had 3 quadrature sin/cos osc. built up using 555 timers feeding Johnson counters that had 1% resistors to build up discrete sin/cos outputs.

What was the idea behind that, if you don't mind my asking? I can think of several reasons:

Was it to ensure a sine wave of consistent quality?
To have constant 90 degree phase shift across the frequency range?
To be able to to vary the phase shift?
Or was it for frequency stability?

Reason I ask is because, besides being just basically curious, I'm interested in hearing about how others have solved the problem and what the design considerations (requirements vs tradoffs) were. I've designed/built voltage controlled sinewave quadrature oscillators but didn't need to resort to anything like that. I get constant phase shift over a fairly wide frequency range and not much sine distortion. I'm using parts that, while getting harder and harder to find now (OTAs), ought to have been common in the 70s-80s. While I can't vary the phase shift in these circuits (and I typically don't want to) I have other VCQOs where I can vary the phase shift, albeit at the expense of phase shift dependent on frequency. I've considered using a counter/eprom/DAC combo, and might since I don't feel it would violate my 'all analog' policy if I'm driving the counter from an oscillator that can be varied via a pot.

[swamidog]

All right, all right, I give up. What's the secret?

it is a static frame of a dot grid. i used rend2frame to clone it four times and then i mirrored the clones on the x and y axis.

i scaled the source frame up to about 3.5, applied a perspective of 0.3, added some xy rotational transforms on sine curves, then added a post color modulation and intensity event.

i used a world rotate to the four clones so the whole thing would spin.

quick and easy.

[DZ]

Finally hooked the console up to my color projector to play around a bit. Color data is coming from a QM2K, X and Y are completely analog. 2nd from the last pic I used the ILDA test pattern for the color data. The last pic I used the "gray scale" test frame.

[swamidog]

Where's the video??!!!!

finally hooked the console up to my color projector to play around a bit. Color data is coming from a qm2k, x and y are completely analog. 2nd from the last pic i used the ilda test pattern for the color data. The last pic i used the "gray scale" test frame.

[DZ]

Where's the video??!!!!

Oh geez! You are never satisfied! I tried to get a video last night but it turned out pretty bad. I'll have try again, eventually...

[laserist]

What was the idea behind that, if you don't mind my asking? I can think of several reasons:

Was it to ensure a sine wave of consistent quality?
To have constant 90 degree phase shift across the frequency range?
To be able to to vary the phase shift?
Or was it for frequency stability?

Reason I ask is because, besides being just basically curious, I'm interested in hearing about how others have solved the problem and what the design considerations (requirements vs tradoffs) were. I've designed/built voltage controlled sinewave quadrature oscillators but didn't need to resort to anything like that. I get constant phase shift over a fairly wide frequency range and not much sine distortion. I'm using parts that, while getting harder and harder to find now (OTAs), ought to have been common in the 70s-80s. While I can't vary the phase shift in these circuits (and I typically don't want to) I have other VCQOs where I can vary the phase shift, albeit at the expense of phase shift dependent on frequency. I've considered using a counter/eprom/DAC combo, and might since I don't feel it would violate my 'all analog' policy if I'm driving the counter from an oscillator that can be varied via a pot.

I think the idea was a combination of factors. First and foremost someone wanted to play. We like creative people. Second they intended to build more than one, and do it relatively inexpensively. So they implemented three quadrature sine/cos oscs, and a quadrature triangle osc - each with amplitude and frequency modulation without any relatively expensive analog devices or burr brown chips. The early boards were wire wrapped. (I have one of those – whoever wire wrapped it was an artist! Figure 242 resistors/diodes/caps, 9 transistors, 20 chips, and a couple of trim pots on about 20 square inches of board space.) It was a clever design. The guy who designed it did the amplitude modulation by varying the input voltage to the CMOS chips making up the Johnson counters. Still there are lots of ways to skin a cat – this one had the advantage that almost every component was available from your average Radio Shack. (If that’s an advantage!)

The earlier analog quadrature osc was done conventionally and had a bit of phase shift due to the way fine frequency control was implemented. Perhaps the original intention was to replace the analog version, but they had different qualities so it's rare not to see both on Laserium equipment.

[AnAnonymousParty]

The early boards were wire wrapped. (I have one of those – whoever wire wrapped it was an artist!

And a lost art, at that. I'd like to see that.

The guy who designed it did the amplitude modulation by varying the input voltage to the CMOS chips making up the Johnson counters.

Interesting.

Creative people, the real secret.

Am I correct that you are involved with the shows at the STL Sci center? I've been planning a trip into town to check it out.

[DZ]

At around 2 minutes you'll enjoy the sweet squealing noise of good 'ole G-120's!

http://www.youtube.com/watch?v=rIudCpdMqrQ

[laserist]

snip
Am I correct that you are involved with the shows at the STL Sci center? I've been planning a trip into town to check it out.

Yes, I'm that guy...

We just started doing Laserium Light Years last night. The Science Center wanted a show with more recognizable music than Timesteps, Pepperbox, & Adagio (from Concerto Grosso OP. 6 NO. 9) Arcangelo Corelli – John Tilp may have had just that goal in mind when he chose the music for Light Years:

Speak to Me / Breathe / On the Run - Pink Floyd
Rock Around The Clock - Bill Halley & the Comets
Heartbreak Hotel - Elvis Presley
Roll Over Beethoven - Chuck Berry
Twist & Shout - The Beatles
Light My Fire - The Doors
Good Vibrations - Beach Boys
White Rabbit - Jefferson Airplane
Purple Haze - Jimi Hendrix
Golden Slumbers / Carry That Weight / The End - The Beatles
Jumpin' Jack Flash - The Rolling Stones
Dance To The Music - Sly & the Family Stone
Rocketman - Elton John
Baba O'Riley - The Who
I've Seen All Good People - Yes
Departure / Ride My Seesaw - Moody Blues
Stairway to Heaven - Led Zeppelin
Karnevil #9 / 1st Impression part 2 - Emerson, Lake & Palmer

[Jem]

Wow!, there's some epic tracks in there :-)

Particularly lovin’ the final ELP track ;-)