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.
Y-ground------------------+
+---------- RCA/composite ground
C-ground------------------+
Y-------------------------+
+--------- RCA/composite video
C------------||-----------+
470pF
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 cpacitor 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.
Here is the pinout of the S-video connector (picture is a view to female connector on the equipment end):
1 Y ground 2 C ground 3 Y (luminance+sync) 4 C (crominance)
If you try to connect the circuit in opposite way so that you have a composite video signal which yoiu want to feed to S-video input then you might wonder would this circuit work also in that way. The answer is that the circuit sort of work also in this way. If you connect a comoisute video source to a S-video input of your TV using this circuit, you will get a full color picture on your TV screen. The downside of this is that the picture quality will be worse than if you were using the real composite vidoe input of your TV. The reason for this is that after the circuit the color information is still in the brighness signal, you you see some interference on the screen caused by color subcarrier which gets to the screen. This all means that you can use this circuit as last change in situations where you don't have a composite video input. The picture quality is degraded, but propably still usable for some not so demanding applications. A real well working solution would be much more complicated than this circuit.