[mythtv-users] VGA to Component adaptors

Cory Papenfuss papenfuss at juneau.me.vt.edu
Wed Apr 27 11:20:34 UTC 2005

> There is a thread on nvnews about the component out in Linux, but no real 
> conclusions yay or nay. Someone here (Cory?) built his own, but I never did 
> get all the details. Seemed pretty simple from what I remember.
 	Ooops... I just re-read what I was accused of accomplishing.  The 
circuit I built converterted RGBHV (i.e. VGA) at 480i frequencies to 
*composite* (and s-vid).  It wasn't component.

 	The RGBHV->component is a much easier circuit, though.  There are 
lots of instructions on the 'net for how to build a transcoder for that. 
The toughest part is figuring out which gain matrix is correct for 
RGB->YPbPr... there seem to be a few different ones floating about.

 	Also, one minor caveat that I think most people happily 
ignore is that component video is supposed to have bipolar sync signals. 
Unlike the TTL-like signals of RGBHV, component sync is supposed to be 
nominally zero, go negative for a bit, then posititive for a bit, then 
back to zero.  It keeps the DC level of the sync signal zero so DC 
restoring circuits aren't necessary.

 	I don't recall any of the DIY transcoders doing that, but they 
seem to work all the same.


* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *

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