While I know its difficult to make a linear DPSS, I feel you folks have been badly ripped off by so called analog lasers. I brought a ADAT (yeah, so called old school technology) and after so minor debate about how to wire a a ILDA cable (more on that later) hooked up to a couple of different projectors. Max adat color signal is 2.5 volts, so you'd think on a 0-5 input that would mean at least some illumination coming out of the lasers. Wrong!
I was beginning to think I had a bunch of dead ADAT channels until we put the signal on a scope. (nice scope Spec!) So I went off to the shack to get some parts to build a gain/loss box. Magicly, suddenly the blue/green worked. It seems you have a huge KNEE voltage around 3.3 volts (I could live with .6 to 1.2 volts for various reasons ) before turnon and a very small linear range. Not to mention the timing issues between blue, green, and red.
The folks at SELEM alomsot universally used Marconi's MAXY modules, so red is not a issue here, they turn on around ~ 1.2 volts. Now my ADATs are set to lag color about 3 points worth, due to the fast PCAOM, but still many of the results were darn ugly. Also many people were dependant on Pangolin for their image size and offset, this is a no-no in the field, its fine for home or planetarium work, but you need KNOBS. Digital systems chop resolution when they reduce image size ...........
So I propose a few things.
One. The SELEM board , aka a couple of differential to single ended and single ended to differtial converters, a lead/lag network for color correction and offset/size knobs with the capability for both gain and loss, and a small test square built in for sanity. The test square consists of a 7473 dual JK flipflop and a 555 wired as a walking ring counter, set for a 30 hz square. This board needs to be somewhat standardized. David Zurcher is building Bill Benner's color adjust circuit for evaluation. There is a commercial DSP solution available in Europe, but its way out of price range for a hobbyist.
Two, the photon lexicon standardized risetime measurement, done with a standardized, published ,digital pulse circuit and a standardized common small area photodiode like a bpw34 and a dual trace scope. Thus we can compare different manufacturers and know what range of lead/lag we need. There will have to be some rules attached to this, like how to define the pulse envelope, ie most of you here have no experience with FWHM, ie full width half maximum measurements. FWHM is not always a good measurement, anyways, as we need to know fall times too.
Three, we need to make sure we all wire the same ILDA connector on our projectors for SELEM/FLEM I traditionally use the pin 25 gound when running single ended, this was BAD when trying to interchange signals with almost everyone else, who had variations of single ended ground on their color and used signal minus tied to signal ground for single ended graphics. I'm glad I made up a hackable cable before I left, and it got hacked many, many, times. Most people didnt have knobs because of the differential signal issues.
FLAMES and SUGGESTIONS WELCOME
STEVE ROBERTS