Hi,

I'm researching how to convert RGBS (sync) video output to YPbPr. From Wikipedia:

Y carries luma (brightness or luminance) and synchronization (sync) information. Y = 0.2126 R + 0.7152 G + 0.0722 B.

I have a RGBS signals coming out of a video encoder chip (CXA1145).


How can I - in the most simple way - generate Y from my RGB signals? I'm thinking about transistors on a breadboard, but I'm not sure how. I don't know how to add three weigthed signals together, and then 'inject' the sync signal into the result.

It seems that I can also use op-amps, but I would prefer to use transistors. Can somebody point me in the right direction. I'm looking for pretty basic advice, as I'm quite the newbie

 

This type of circuits are way complicated for a n00b.
You are better off buying a converter.

RGB does not carry sync. For RGB sync line is separate.

 

This type of circuits are way complicated for a n00b.
You are better off buying a converter.

RGB does not carry sync. For RGB sync line is separate.

Hehe, yes I know I'm in over my head. But I'm totally motivated. I already have a RGBS to VGA converter + upscaler, so I can play my old video games. I'm in search of enligthenment here

R,G,B and Sync are on separate lines (RGBS). Should I use voltage divider circuits on each of the RGB signals (for weighing), and then add them together, using op-amps or transistors, to get Y? (In theory)

 

What about this approach? (Attached image). I use voltage dividers for the weighing of the three color lines, and then a summing amplifier to add them together. At the end there is a voltage inverter to invert the voltage from the summing amplifier.

I suspect the resulting Y signal would have to be amplified... And also I need to inject the sync signal. But first things first: does the attached schematic look legit?

 

Have you looked these?

 

Have you looked these?

Yes - thank you. I can't get the linear IC from my supplier. But most importantly I want to find an approach I can understand, and build up in steps. That is why I start with just the 'Y'

 

Yes - thank you. I can't get the linear IC from my supplier. But most importantly I want to find an approach I can understand, and build up in steps. That is why I start with just the 'Y'

Ron_h from this site have made a great effort on rgb to ypbpr:
http://forum.allaboutcircuits.com/threads/signal-math-with-op-amps.79779/

... And I have collected a few other rgb to ypbpr schematics from around the web, and posted to another forum: http://www.smspower.org/forums/viewtopic.php?t=15048

What I'm looking for here is not a complete guide to building a circuit. Just some feedback on my little handdrawn schematic on how to get Y without sync, from rgb signals, using voltage dividers and op amp...

I have realized this thread is started in the wrong part of the forum. I'm sorry for the confusion. Can I move it to general electronics?

 

Well, I'm not much on exerting effort to re-invent the wheel so, since there are many circuits out there that do what you want, I see no good reason to come up with another. But if you want to to do that, have fun.