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| Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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20th May 2020, 4:49 pm
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#1 |
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Octode
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
Posts: 1,885
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Converting "ttl" RGB to YPbPr
Hello, it's been a while since I got the soldering iron properly hot but I've now got a soldering bench of sorts together after moving house last year.
My first mini-project is that I have some old vintage micro computers that I'd like to connect up to a video capture card. The capture card I have takes in component video (I thought it was RGB when I bought it!) and the BBC Micro machines I have put out RGB at roughly TTL levels (not actually digital as there is a palette enhancer in there which allows mid-levels but roughly the signals are about 0..3V out on RGB and Sync). I've looked and there doesn't seem to be any cheap and cheerful converter so I started breadboarding something last night which sort of worked but was very smeary. I've now spent a bit of time with a pen and paper (read until 3am trying to remember how to do simultaneous equations) and some more time in LTSpice (read randomly changing resistors until it looks close enough). So blathering on aside - does the attached look sane? I want to keep it as simple as possible and power it from a single 5V rail (which is available). Preferably using as few components as possible (I have a lot of BC337's in stock). The accuracy of the colour doesn't need to be perfect as but it should preferably pass luminance to a good bandwidth so that 80 character text shows up nicely if possible. [The capture card claims to be HD but I suspect it will apply filtering to what looks like a PAL signal and smear stuff] So what do you guys think - daft idea? Are there cheap solutions to do this already that I'm being dim and missing? D [See the zip file for a higher resolution picture] |
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20th May 2020, 7:28 pm
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#2 |
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Octode
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
Posts: 1,885
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Re: Converting "ttl" RGB to YPbPr
Well I thought I'd have more takers for that one!
It works! I've bread boarded it up and it worked first time which I think is a first for me. The pictures attached are from the capture card - it actually looks much better on a real monitor (Sony with component inputs). Next project might have to be a scan doubler - the capture card is being "clever" and its de-interlacing, or something, is doing some sort of averaging of colours between lines: (the rainbow effect should be on every other line on the transition from E to A but the capture card is making mud!) Anyway I thought I'd answer myself incase anyone else has the same requirement! D |
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