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Re: Superboard Colour RGB and composite interface
Posted: Wed Jul 31, 2019 3:10 am
by Steve Gray
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.
Re: Superboard Colour RGB and composite interface
Posted: Mon Sep 14, 2020 11:21 pm
by Scott Larson
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?
Re: Superboard Colour RGB and composite interface
Posted: Tue Sep 15, 2020 4:03 am
by Mark
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!
Re: Superboard Colour RGB and composite interface
Posted: Sun Sep 20, 2020 11:36 pm
by Scott Larson
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.
Re: Superboard Colour RGB and composite interface
Posted: Mon Sep 21, 2020 12:47 am
by Steve Gray
Sorry about that, i have both books and got them confused...
Re: Superboard Colour RGB and composite interface
Posted: Mon Feb 13, 2023 3:29 am
by Steve Gray