Tech Support and Application Notes
By John Vellone
Composite video the oldest and most common type of video interface for sending or receiving an analog video signal to or from a television set. Originally indroduced with the advent of the first B&W television, composite video is also known as the Radio Standard’s code RS170. RS170 is a B&W video signal which consists of luminenece and contrast component. When Color TV was introduced the Radio Standards committee imposed that the new color composite signal be reversly compatible hence the new color composite signal known as RS170A now introduces a color burst component to the composite video signal. The composite video signal known to us today has a combined color,luminance and conttrast component to it.
Separate Video, more commonly known as S-Video, and sometimes incorrectly referred to as “Super Video”( because its arrival coencided with the arrival of the Super VHS or S-VHS) and also known as Y/C, is an analog video signal that carries the video data as two separate signals, luma (luminance) and chroma (colour).
The 4-pin mini-DIN connector is the most common of several S-Video connector types.
Here is the pinout of the S-video connector shown from the end with the FEMALE PINS (picture is a view on the equipment back/front panel):
Pin 1 Y ground Pin 2 C ground Pin 3 Y (luminance+sync) Pin 4 C (crominance)
S-video to composite video adapter
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 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.
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