Hi,
Thanks all for the congratulations
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Originally Posted by Steve_P
If you would like another 405 TV for test purposes, let me know. There's also a few people working on recreated 405 Line Colour transmissions - this could be very handy!
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I think I'd like to take you up on that offer (once I have a VHF modulator built), the Sony 9-90UB isn't exactly the cutting edge of 405-line technology, with AC-coupled video and no black-level clamping. Mine also seems to be having trouble with line and frame sync as well as the frame linearity problems noted (on 625-line off-air as well; it's not my electronics after all!) Another TV, or possibly a monitor, would prove very useful. (I used to have an ex-BBC Pye 2823C4Z 8.5" monitor many years ago, which suffered terminal LOPT failure and was scrapped, unfortunately. I still have the schematic for it and wouldn't mind another one.)
As for colour, well, the output of the PC is in colour to start with, so that shouldn't prove too difficult. It's on the list of things I'd like to investigate, along with getting it to do 441-line, 819-line and anything else I can think of. I'm not sure but I suspect an off-the-shelf NTSC encoder IC with a custom crystal might be all that's necessary for 405-line NTSC.
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Originally Posted by Trish
I take it that you have used something like standard resistor additions. One thing to consider is something like a clamp pulse to ensure the black level stays relatively constant.
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The 'summing R, G and B' bit is correct, one fixed resistor and a couple more with series presets adjusted to the correct ratios with the aid of calculator and digital multimeter. There's an attempt at black-level clamping; though as noted it won't make any difference with the Sony TV anyway. The next versions will be DC coupled throughout, which saves additional circuitry just to put back something which was there originally. (The outputs of the graphics card are 0.7V p-p with black at 0V.)
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Originally Posted by Steve_P
when is this going to be available?
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Plans are afoot behind the scenes to get an RGB+sync to mono composite converter sorted out which a) works better than my lash-up and b) minimises component count and so shouldn't cost much. As for the software, it's all already available - what I need to do is try to rationalise the installation and configuration process , investigate easier installation methods (such as the 'KnoppMyth' single-CD installer) then document the installation and configuration process step-by-step so it can all be installed assuming no prior experience of Linux. I ought to try to acquire some more graphics cards as well; at present I can only guarantee it working with my nVidia GeForce4 card as that's all it's been tested with. There's still more work to do, the problems with the overscanned user-interface and poor rendering of user-interface fonts need sorting out; as does getting it to work with a digital terrestrial card (I bought one but it arrived last week damaged and dead, I'm still awaiting a response from the supplier.)
Right, back to work... l;et's see if I can get the Sony TV working a bit better, it's not really showing off how good the output of the PC really is right now.
Regards, Kat