osiweb.org

Scott Larson wrote: ↑Wed Jul 31, 2019 1:02 am I always wondered how OSI did NTSC color. It looks like the circuit relies on the slight delay of a 7404 to jab the subcarrier at the right phase to produce a color. That can't possibly work.

The 540b circuit was “borrowed” from Don Lancaster’s video cookbook... it works. The 630 board doesn't do colour composite as far as i can see, it only incorporates the invert feature.

My 600d Colour board will not do composite. I wanted something that would provide RGB as the highest quality source, which could be converted in many ways. You can upconvert it to hdmi, or feed it directly to scart, or convert to s-video and composite... whatever you like. I will try to document the different solutions. I could make a little adapter board for composite if there is demand.

Steve Gray wrote: ↑Wed Jul 31, 2019 3:10 am

Scott Larson wrote: ↑Wed Jul 31, 2019 1:02 am I always wondered how OSI did NTSC color. It looks like the circuit relies on the slight delay of a 7404 to jab the subcarrier at the right phase to produce a color. That can't possibly work.

The 540b circuit was “borrowed” from Don Lancaster’s video cookbook... it works.

Yes, but how? Did it rely on the delay of the 7404 to modulate the color subcarrier? Or should I get a copy of Lancaster's book to find out?

As I understand it, the OSI generated colors by selecting the phase delay of the color subcarrier during video output as compared to the reference carrier supplied after the horizontal sync pulse. The OSI540B schematic shows this. The propagation delays of the 7404 were used to do the phase shift.

I found Don Lancaster's book online https://www.tinaja.com/ebooks/tvtcb.pdf look at page 203 on.

Its amazing this all works!

The OSI 440 board had a schematic for an optional 2-bit color RGB open collector drive to interface to the guns of a CRT!

Shoot, I just bought a used copy of Lancaster's "Cheap Video Cookbook" and of course it has absolutely nothing about color. I wish Steve had been a little more specific about which book he was referring to.

Sorry about that, i have both books and got them confused...

Wow, long time. Seems covid put a lot of plans on hold including my 600D colour board. Walter and I built a board and tried to get it working but had some difficulty. Shortly after I had a mishap and suffered a detached retina in one eye, followed by surgery, then my mom passed away, and then Covid hit. Since then I have just not been able to get back to the project until now. Yesterday Walter and I worked on it again and got some results. The board works! I did get the labelling of the DIP switch colours wrong which caused some initial confusion but we finally figured it out. So we connected the board output to a VGA connector and then to my Dell monitor that supports 15kHz. Walter's machine had a version of my customized CEGMON ROM which we used to test. I found that the 330ohm resistors seemed to make the video a bit dim so they may need to be adjusted, or it could be my monitor (more testing is needed). Below are some photos: