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I have assembled this project http://cb2.qrp.gr which was lot of fun, but I have a TV with a composite video input only. Now I know there are ICs out there that can convert from RGB/HSYNC/VSYNC to composite video (PAL/NTSC), like the AD725, but I would like to investigate how such a conversion can be done in discrete components, if this is not too difficult to do. Is that possible and what parameters should I investigate? Note that the project has already a black and white composite video output, but I also need the colors to present.

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  • \$\begingroup\$ see the block diagram for the AD725. you need to build the equivalent. \$\endgroup\$
    – Jasen
    Nov 19 '19 at 9:55
  • \$\begingroup\$ from a distributor this part is about 8 bucks, but available on the gray market for much less, \$\endgroup\$
    – Jasen
    Nov 19 '19 at 10:00
  • \$\begingroup\$ Define "not too difficult" for you? It sounds like you have not done any research about the subject. Just look at PAL video signal specifications, and determine yourself if it is too difficult, compared to purchasing a integrated chip that already does the task. \$\endgroup\$
    – Justme
    Nov 19 '19 at 10:13
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SCART can carry either RGB or composite video, depending on which pins the source chooses to drive.

But if you have RGB, then there is no easy way to convert it to composite video. Conversion requires turning the RGB into luminance (monochrome) and chrominance signals, then modulating the chrominance signal on top of the luminance (in a way that is specific to either PAL or NTSC).

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  • \$\begingroup\$ SCART can carry both RGB and composite at the same time. It is even necessary as the composite pin is used as the sync signal for RGB video. \$\endgroup\$
    – Justme
    Nov 19 '19 at 11:12
  • \$\begingroup\$ however, in this case, (with the CB2) the composite pin only carries a monochrome signal. \$\endgroup\$
    – Jasen
    Nov 20 '19 at 5:47

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