the names have been changed to...

[laserist]

http://forum.rfeda.net/archiver/tid-375311.html

[mixedgas]

The digital Z rotator schematic is now a trade secret.

Sorry guys. I've given nearly everything else away, and helped many of you, in many ways. Analog rotation is expensive, took ages to develop, and that I'm NOT giving that away.

I've angered many of my professional friends with helping here. I'm not giving away the "Holy Grail". Its cost me work over the years and lots of personal profit to help the industry grow. I can't afford to do that any more in this economy. Heck, I cant even afford to upgrade to a QM2000 from a QM32.

You wont find the zip file on line.

The actual 12 bit digital rotation multiplier core comes a 1970s Radar vector display design article, takes 4 chips to make and costs less then 60$ for the core.
It comes from a Sperry aircraft radar. The circuit as published had major glitches at exactly 90, 180, and 270 degrees. It took a while to deglitch.
The chips are still available.

Steve

[Badpip]

Cool idea with digital controlled analog circuitry... But with todays prices on DSPs, is it really worth the trouble anymore?

It will have a delay, but it only be a micro second or two... Then again, so will an old analog design (slewrate of the opamps).

/Thomas

[mixedgas]

DSPs are pain in the neck to develop for.

Steve

[polishedball]

Is this rotation the same as shear on a UGC?

[Photonbeam]

My old school hardware rotator. Signal path is analog, but the sin and cos tables are on eprom so the rotation can be stopped without drifting. Two channels - each with axis select, rate, fwd/rev/stop/reset buttons, mixer section with gains and offsets, zoom, joystick, ext Z in. I bought the schematics from designer, Bart Johnson (Laser Displays) around '79 or '80 and transferred to PC boards - which I still have.

[DZ]

Wasn't there a z rotator schematic in the Lightshow Handbook? Based on the AD534?

[polishedball]

Wasn't there a z rotator schematic in the Lightshow Handbook? Based on the AD534?

Yes but really was a scaler

[mixedgas]

What I have does not need sin/cos eprom tables nor vcos nor CORDIC. It does it a different, analog, way using an array of 6 resistors wired in a tapped hexagon of all things, some opamps, and some DAC chips. EEs whom have looked at the schematic, say: " THAT WILL NEVER WORK," but it works well.

Not only can you rotate, but you can generate waveforms with it, by applying a bias or a ramp or other waveform to one of the analog inputs and then applying a digital word to the angle inputs.

Wickedly clever...


Steve

[mixedgas]

Is this rotation the same as shear on a UGC?

Not really, the multiplier scheme in the UGC has only a small amount of twist available.

The UGC math appears to be a simplified subset of a geometric corrector designed for CRT microfilm projection. Greg and probably some one else, whom I cant remember, re-engineered the daylights out of it to simplify it and reduce the number of chips. Greg's board is way different from the CRT board, using some really neat combinatorix to reduce the number of math functions about 10 fold. Its far superior in many ways. I would not be surprised to find LSDI simply started from scratch.

I used to have one of the crt correctors, it was 24" by 24" and full to the brim of pots and high quality metal can chips.

UGC works using the difference and sum of squares of the input signals. For shear its using the fact that sin of x for a small x is really close to x, as well as other math. It really can't rotate more then a few degrees before severe distortion sets in.

Steve