S-Video to Composite: Difference between revisions

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A basic S-Video to composite convertor can be made by a simple short of the two signal wires, and the two ground wires of the S-Video.  Looking AT an S-Video plug (IE with pins) with the rectangular notch of plastic at the bottom, pin 4 is the pin at the top right, pin 3 is the top left, pin 2 is the bottom right, pin 1 is the bottom left.
S-video is basically just composite video, but split up into its chroma (colour) and Luma (brightness) parts, which both operate at different bandwidths. The pin allocation is like so:
*1 - ground
*2 - ground
*3 - luma
*4 - chroma


In the simple bodge the results are useuable if absolutely necessary, but gives poor colour quality, and a ghosted image.
It comes in a horrible format from computer graphics cards, and other consumer devices. This isn't really useful for YSTV, so we have a few ways round using it:


Pin 4 and 3 are connected straight to the signal pin of composite. Pin 2 and 1 are connected straight to the ground pin of composite.
* The kramer convertor. This device is the preferred solution. The kramer converter performs Automatic gain control on the chroma and luma, based on the size of their respective sync pulses, before combining them. This solves many odd syncing issues with equipment.


In the better, but more complicated, version a capacitor is used.  The value of this capacitor can be anywhere between 400pF and 10nF according to the web link : [http://www.epanorama.net/circuits/svideo2cvideo.html http://www.epanorama.net/circuits/svideo2cvideo.html].  One bought from Farnell used 420pF, Ystv has lots with 470pF capacitors.
* The bodge cable. This is a direct join of pin 3 to 4, and then 1 to 2. This means that no AGC is done, and the output signal isn't amplified to the correct level. The 3/4 mix goes to composite signal, and the 1/2 mix goes to composite ground.


In the complicated version pin 4 (the crominance) is NOT connected straight to the composite signal pin. Pin 4 is connected to the capacitor, the other terminal of the capacitor is connected to the composite pin.
* The less bodge cable. This method is the same as the bodge cable, but first, chroma (pin 4) passes through a capacitor of 0.4nf to 1nf, before joining to the luma signal. This, in theory, stops any interesting termination problems from appearing, although, in practice, we haven't noticed any difference when compared to the basic bodge.


Pin 3 (the luminance) is connected straight to the composite signal pin.  If a physically small capacitor is used then it can just about be contained within the plug case, this is of course a more durable method than having it exposed.
As always, when using bodge cables, please test them first, as the plastic s-video connectors aren't the most sturdy things around...
 
As with the simple bodge, the complicated bodge has pins 1 and 2 connected straight to the compostie ground.
 
Notes are that this will supposedly take an S-Video signal and convert it to a PAL or NTSC compatible composite signal. 75 ohm shielded cable should be used, failing that it should be shielded audio cable.

Revision as of 17:43, 5 January 2012

S-video is basically just composite video, but split up into its chroma (colour) and Luma (brightness) parts, which both operate at different bandwidths. The pin allocation is like so:

  • 1 - ground
  • 2 - ground
  • 3 - luma
  • 4 - chroma

It comes in a horrible format from computer graphics cards, and other consumer devices. This isn't really useful for YSTV, so we have a few ways round using it:

  • The kramer convertor. This device is the preferred solution. The kramer converter performs Automatic gain control on the chroma and luma, based on the size of their respective sync pulses, before combining them. This solves many odd syncing issues with equipment.
  • The bodge cable. This is a direct join of pin 3 to 4, and then 1 to 2. This means that no AGC is done, and the output signal isn't amplified to the correct level. The 3/4 mix goes to composite signal, and the 1/2 mix goes to composite ground.
  • The less bodge cable. This method is the same as the bodge cable, but first, chroma (pin 4) passes through a capacitor of 0.4nf to 1nf, before joining to the luma signal. This, in theory, stops any interesting termination problems from appearing, although, in practice, we haven't noticed any difference when compared to the basic bodge.

As always, when using bodge cables, please test them first, as the plastic s-video connectors aren't the most sturdy things around...

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