DIY YUV to RGB converter

Nice circuit. It seems that with this circuit, a sync stripper, and a sync separator (LM 1881), it should be no problem to hook up a DVD player with a Y-Pb-Pr output to a computer display with an RGB input. The DVD player in question outputs a 480p signal on the component output and the display in question is an LCD panel with an internal scaler. Presently they are connected with an S-Video cable but I find the picture unsatisfactory.

Back to the point: it should be possible to create a YPrPb->VGA converter with less than $50 in parts.
 
I experimented with hooking up my computer monitor (Samsung SyncMaster 210T) to my DVD player. The DVD player has composite, S-Video, and Y-Pr-Pb component video outputs. The monitor has composite, S-Video, RGBHV, and DVI inputs.

In my first experiment, I simply attached the Y output from the DVD player to the G input on the monitor, and set the DVD player to progressive scanning output. The monitor understands sync-on-green, so it was able to show the picture. However, the picture was unstable and the frame was actually separated horizontally right in the middle of the screen. Some luck, but not much.

Next I used the LM1881 to pull the sync signal from the Y, and fed that to the H and V inputs of my monitor, with Y directly attached to R. This yielded a nice, stable, red image on the screen.

Next, I attached Y to all three R, B, and G inputs with the LM1881 feeding H and V. Now I have a stable black-and-white picture. Getting closer!

Now I just need to order some op-amps from Digi-Key to convert the color difference signal to proper RGB color, and I be in progressive-scanning nirvana. Thankfully the Samsung has a high-quality scaler.

:cloud9:
 
Did anybody ever get one of these things working? I've got a VGA diy projector and I'm looking at getting a progressive scan DVD player with YPrPb outputs as well as possibly getting HDTV cable in the near future, so one of these devices would be very handy. If I use this RGB converter and then use the LM1881 vertical sync to drive V and its composite sync to drive H, won't I have everything I need to make my VGA monitor happy? Any suggestions for the output capacitors on that RGB schematic? I assume that's to get rid of DC offsets so some pF value might work?

The only commercial product I've found is this:
VGA Box *YPrPb -> RGB/VGA* Ver. II but it's overseas and in the DIY spirit I'd like to build my own anyway :wave2:

Since I've never used anything HD, where exactly is the HD output resolution set? Is it a setting in the DVD player or does it output all formats at once and the HDTV uses the one it can handle? My projector's LCD is 1024x768 max so I'm guessing 720p and 1080i are out of my range and I'll have to settle for 540p, which is equivalent to a progressive PC resolution of 960x540, no? It appears that little dongle I linked has DIP switches that set the rez and vertical refresh so I'm confused on this point. :scratch:
 
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=64631&item=5770867419&rd=1
I saw this on eBay and it made me think about this whole conversion a little bit more. The guy makes it sound like you can directly drive a VGA monitor with this simple cable if the monitor supports sync-on-green, which mine does. It's sort of a mystery device as there appears to be no circuitry except maybe in the db15 shell, but how would it be powered?

Also, I was thinking that 540p would be my target resolution because my LCD projector is 1024x768 max and this would be 968x540p, but now that I think of it, if I sent that resolution to the LCD wouldn't it try to scale the picture to 4:3 ratio and make it look like crap?

For flexibility I will likely just build an HTPC and use it to scale DVDs and set the lcd resolution, though I'll have to find a way to input YPrPb into the PC if I order HD cable... shouldn't be too hard :D
 

ShagMan

Member
2005-04-26 8:30 pm
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OK, just for kicks, I took a VGA cable and a RCA A/V cable, and went to work... I tried it out on my 2001FP, and it actually did the sync correctly, so this monitor definitely has sync-on-green... HOWEVER... and I tried this with two different DVD players, same result... there's WAY too much green! I get some red and blue, but the green is much much stronger. Any ideas? Is this due to the sync/data that's being sent over the green cable?
 
You connected the Y to green, haven't you?
Y is B&W + sync picture.
Pb is Red
Pr is Green
It's S-Video with Red and Blue separated.

You have to get the green signal like this:

Green = Y - 0.51(Pr-Y) - 0.186(Pb-Y)

There is surely a(low quality) IC in the wire using the 5v line(from the TV, the input might output 5v from a pin)

elm-chan.org got what you need.

A YPbPr(named YCbCr, component) to RGB(VGA) converter:
http://elm-chan.org/works/yuv2rgb/report.html