This simple adapter can be used to convert Y/C video (S-video) to a composite video. This adapter is useful in cases where your video output device has only S-video output but your signal source accepts only composite video input. This circuit works with both PAL and NTSC video standards.
This circuit can be quite easily build inside a the S-video connector case if a physically small size 470 pF (ceramic) capacitor is used. Larger capacitor values will also work, but cause picture to become "softer". The voltage rating of capacitor can be 10V or more.
This circuit works in practice quite well even though the circuit operation is not ideal. This means that impedances and signal levels not matched exactly right, but near enough to work accetably. The picture quality you get from this circuit is is good, but not as good as with best possible composite video output circuitry.
What if my PC graphics card has a 7-pin S-video connector instead of 4-pin ?
The four pin S-video connector as shown above is the standard connector for carrying S-video. Those seven pin connectors seen on some PC graphics cards are non-standard connectors for carrying S-video. The use of the pins on those seven pin connectors is not standardized and can vary from manufacturer to manufacturer. (For some strange reasons some manufacturers in PC industry just keep constanly breaking the industry standars and create lots of confuzion to users when doing so).
Generally the four pins on those 7-pin connectors on the same places as the standard four pin S-video connector have practcly always the same fuctionality as those pins in S-video connector. The other three pins can have then some extra signals which are not part of S-video (usually some pins of those carry composite video and some control signals, but the use of those three extra pins vary quite much). So if you encounter 7 pin connector for S-video, then forget the three center pins... just use the four on the standard positions. The circuit shoudl work with those connectors as well.
http://www.epanorama.net/circuits/svideo2cvideo.html
