I am designing a TV transmitter as given in the link below:


My question is, where from do I give the video input? For the audio input, I can simply connect an audio jack to the audio out pin of the motherboard. What do I do about the video? Video output from the motherboard is trough the VGA pin. How do I tap out the video signal from the computer and feed it to this circuit? Please provide any simple technique.


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  • \$\begingroup\$ A single connection is almost always composite. \$\endgroup\$ – Ignacio Vazquez-Abrams May 15 '16 at 12:15
  • \$\begingroup\$ "The transmitter circuit is compatible with PALB and PALG systems." Its designed for a PAL modulated signal such as you would get from a camera output \$\endgroup\$ – JIm Dearden May 15 '16 at 12:15

Computers have used many interfaces to send video information to a monitor. Early in home computing, many used composite video. However this had a bandwidth limit of about 4MHz for black and white and 3.8MH for color. If you search through this patent you will come across some bandwidth limitations. These are the types of signal the device you linked to is expecting.

Very soon, demand for both color and higher resolution obsoleted the composite approach which was replaced by CGA. And that was replace by other formats like VGA. And that was replace by other formats like HDMI which is digital.

While VGA is still analog, there are many incompatibilities between VGA and composite. In a composite signal, color, brightness and video synchronization are all encoded into 1 signal. In a VGA cable, the colors Red, Green, Blue all have their own pairs of wires as well as the horizontal and vertical synchronization signals. Also the scan rates are different. Where as PAL and NTSC composite signals scan the screen at 50 and 60 times a second respectively. VGA can scan up to 70 times a second.

Possibly the most incompatible difference is the number of dots that can be displayed. As stated above a black and white composite signal display about 4 million dots per second. That would be about (4,000,000 / 60) 67,000 dots per screen for an NTSC signal. A VGA signal can put about 288,000 dots on a screen.

So, regardless of the effort or interface device, the resolution limit of a PAL or NTSC monitor will render certain applications (for example, reading 80 column text) impossible to implement.

  • \$\begingroup\$ Eh, I wouldn't say impossible. I had my computer connected to a tube TV at 800x600 before, and while I wouldn't consider using it long-term I wouldn't call it "impossible". It's just a matter of what tradeoffs you're willing to put up with. \$\endgroup\$ – Ignacio Vazquez-Abrams May 15 '16 at 13:23
  • \$\begingroup\$ Agreed. If you were to transmit images or video it should work with the expected loss of detail. But if you were displaying 80 column text I would not expect usable results. \$\endgroup\$ – st2000 May 15 '16 at 13:47
  • \$\begingroup\$ @st2000 When the Apple II first came out in 1977, it had only 40 column text. But users wanted to use it for serious word processing, so various third-party manufacturers came out with 80-column cards (and eventually Apple did too, for the Apple //c). The Apple could only generate composite video and RF outputs. The text resolution of the 80-column display was actually quite usable, as shown in this somewhat over-exposed photo of a monitor screen. Not too shabby for composite video. \$\endgroup\$ – tcrosley May 16 '16 at 0:35
  • \$\begingroup\$ Yes this is correct. I assumed the OP would use color. The color carrier limits the dot rate to 3.8MHz. Faster dot rates would be translated into colors, not dots. \$\endgroup\$ – st2000 May 16 '16 at 12:14

You want to get a VGA to RCA (composite) video converter like this one which sells for 14 USD. The description says it is compatible with PAL systems which is what the transmitter expects as one of the comments mentioned since you are in India.

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