VGA to TV or Composite video output

betwixt said:

It might be posible to do it of the resolution is only 640x480 pixels and you are prepared to see it without color. For any other resolution or in color you need a scan converter which will iinvolve at least one IC and some memory. It would be cheaper to buy one than make one.

Brian.

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Audioguru said:

I guess India still uses old analog TV (ours is high-definition digital today). Is it NTSC or PAL or Seq... (the French system)?

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betwixt said:

The old French system is SECAM but almost all European countries now use HD or SD digital systems.

That circuit will only work if the horizontal and vertical scan rates at the VGA output are the same as the analog TV standard, that's why I said it would be 640 x 480 pixels, it's only the base VGA definition that uses compatible rates. It is possible to use nothing more than a resistor network to get composite video (subject to the scan rate) but to get color the modulator IC is needed as shown.

Brian.

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betwixt said:

I think that's the simple resistor circuit I used before but I had it as a schematic rather than a layout. All it does is sum together the Red, Green and Blue signals in the correct proportions and 'sits' them on a pedestal made from the sync pulses. Please note it requires a standard 75 Ohm video load (normally inside the TV) and if you look at it without the load conected it will be completely wrong.

I stress again, you must use the lowest VGA resolution of 640x480 pixels, it will not work at higher resolutions because the sync speeds and polarities will be wrong.

Brian.

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