NTSC S-Video signal levels

[GoingFastTurningLeft]

The LCD panel in my D.I.Y. projector has a contrast control but no brightness control. It runs off Composite NTSC. I crank up the contrast and the brights are OK, but dark scenes get "lost".

What I figure I could do is use the S-video output of the equipment I'm using with it. Take the Luma (Y) channel and amplify/filter/whatever to it to raise what "black" is - basically make an box that gives me a brightness control. I'd then convert the S-video down to composite for the panel. I know how to do that, that's not the problem.

I'm having trouble coming up with the actual technical specs of this signal. All the articles I pull up are way too general. Anyone know where I can look?

[haklesup]

Try a data sheet for a chip that works with that kind of video.

A quick look at digikey and searching on Video turned up ICs in the Analog Front End and Decoder categories with lenghthy datasheets and a scan of a few showed at least some discussion of the signals you are working with.

For example this encoder is used to output video from DVD players, some of the charts near the end devine voltage and other parameters you might be after.
http://www.analog.com/UploadedFiles/Dat ... 2_7173.pdf

Datasheets also frequently reference application notes which might have more of what you need in one spot.

http://www.analog.com/en/cList/0,2880,7 ... 43,00.html
Scroll down to the Video topics. Looks like AN-205 is a hit and some others may be of interest.

[GoingFastTurningLeft]

Thanks a lot, i'll have to take a look at them. It looks like application notes are the way to go when you're trying to work with a new kind of signal, since it shows you what you're working with and how to do it.

I found an application note from Maxim about some op-amp or something that discussed AC coupling and clamping, and included a diagram of all the signals.

http://pdfserv.maxim-ic.com/en/an/AN3303.pdf

The S-video Luminance channel goes has a -300mV sync pulse, with a signal that goes +700mV to 0V. I played around with some capacitors and resistors and I could make it get darker, but if you didn't use a big enough capacitor, you would lose the sync signal and the picture would roll.

Maybe the approach here would be to split the signal into the sync and luma signals, alter the luma signal, then sum them back together.