From: Subject: S-video to composite video Date: Thu, 22 Nov 2001 09:03:36 +0100 MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_NextPart_000_0084_01C17334.91E6A4F0"; type="text/html" X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4522.1200 This is a multi-part message in MIME format. ------=_NextPart_000_0084_01C17334.91E6A4F0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Location: http://www.hut.fi/Misc/Electronics/circuits/svideo2cvideo.html S-video to composite video

S-video to composite video adapter

This simple adapter can be used to convert Y/C video (S-video) to a = composite=20 video. This adapter is useful in cases where your video output device = has only=20 S-video output but your signal source accepts only composite video = input. This=20 circuit works with both PAL and NTSC video standards.=20

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=20 case if a physically small size 470 pF (ceramic) capacitor is used. = Larger=20 capacitor values will also work, but cause picture to become "softer". = The=20 voltage rating of cpacitor can be 10V or more.=20

This circuit works in practice quite well even though the circuit = operation=20 is not ideal. This means that impedances and signal levels not matched = exactly=20 right, but near enough to work accetably. The picture quality you get = from this=20 circuit is is good, but not as good as with best possible composite = video output=20 circuitry.=20

Here is the pinout of the S-video connector (picture is a view to = female=20 connector on the equipment end):=20

3D"S-video = =20

1   Y ground
2   C ground
3   Y (luminance+sync)
4   C (crominance)

What if my PC graphics card has a 7-pin S-video connector instead of = 4-pin=20 ?

The four pin S-video connector as shown above is the standard = connector for=20 carrying S-video. Those seven pin connectors seen on some PC graphics = cards are=20 non-standard connectors for carrying S-video. The use of the pins on = those seven=20 pin connectors is not standardized and can vary from manufacturer to=20 manufacturer. (For some strange reasons some manufacturers in PC = industry just=20 keep constanly breaking the industry standars and create lots of = confuzion to=20 users when doing so).=20

Generally the four pins on those 7-pin connectors on the same places = as the=20 standard four pin S-video connector have practcly always the same = fuctionality=20 as those pins in S-video connector. The other three pins can have then = some=20 extra signals which are not part of S-video (usually some pins of those = carry=20 composite video and some control signals, but the use of those three = extra pins=20 vary quite much). So if you encounter 7 pin connector for S-video, then = forget=20 the three center pins... just use the four on the standard positions. = The=20 circuit shoudl work with those connectors as well.=20

Can the circuit used in other way ?

If you try to connect the circuit in opposite way so that you have a=20 composite video signal which yoiu want to feed to S-video input then you = might=20 wonder would this circuit work also in that way. The answer is that the = circuit=20 sort of work also in this way. If you connect a comoisute video source = to a=20 S-video input of your TV using this circuit, you will get a full color = picture=20 on your TV screen. The downside of this is that the picture quality will = be=20 worse than if you were using the real composite vidoe input of your TV. = The=20 reason for this is that after the circuit the color information is still = in the=20 brighness signal, you you see some interference on the screen caused by = color=20 subcarrier which gets to the screen. This all means that you can use = this=20 circuit as last change in situations where you don't have a composite = video=20 input. The picture quality is degraded, but propably still usable for = some not=20 so demanding applications. A real well working solution would be much = more=20 complicated than this circuit.=20

Tomi Engdahl <Tomi.Engdahl@iki.fi>

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