15.7 KHz RGBs to Component (YPbPr) schematic/IC?

Hm, that's interesting. I am working on something very similar.

This project takes 15.7 KHZ RGBI or CGA and outputs 31.5KHz analog VGA. This is for old computers to use new monitors. One thing that came up is that LCD TVs have component inputs and that they are compatible with

The operation to go from RGB to YUV is fairly simple to understand, it's just a matrix. You need to look for colorspace converter chips but the ones I've found are big, powerful and in crazy packages.

RGBI to YUV can be done in a handful of logic gates. RGB to YUV would need a handful of video amps and mixers of some kind.

Hey why don't you email me and we'll see what we can come up with.

Seems pretty simple to me. You aren't transcoding or converting anything. You aren't changing the timings, etc. You just need RGB to YPbPr.

You can look up the ratios of Y and Pb and Pr, and do this in a simple matrix with a handful of resistors and three op amps. Here is the formula:

I'd bet you a moderate-price dinner that you can find the matrix schematic out there on the WWW.

If it's analog, you could just use some op-amp sum & difference circuits. Calculate the resistor values from info on Charles Poynton's page:

Intersil has a DC restore chip, the EL4093... overkill for lo-res video, but cheap, IIRC.

And the venerable old LM1881 sync separator for timing.

...jerry

Thanks for your replies,

I have found a schematic here...

This takes RGB and converts it to YPbPr using op amps. However, this does not use the composite sync as input...only the RGB...how does the video get its timing? I know the R,G,B is combined to get a total luminance (Y), which in svideo and component contains the sync as well...but how would taking just R.G,B without sync work? Does each color component (R,G,B) contain its own fragment of timing, so that when combined to form Y it also contains all the sync too? The above link is for a pay and get schematic so I can't just post it...but it does all make clear sense to me...just not how it can make a Y that conatins sync without taking sync (composite in my case)as input....

Jerry

Sorry...wrong link sent before....

"Jerry Lynds" schreef in bericht news:gD80h.72885$E67.55124@clgrps13...

Hmm... IMHO this circuit converts YPbPr to RGB. Apparently Y is supposed to carry the sync. In this case the sync has is own output. I saw RGB signals in which one of the colors (don't remember which) carries the sync. For that way separating the sync from a composite video signal is the easiest part. It can be done by some old fashioned discretes but the venerable old LM1881 has also been mentioned already.

petrus bitbyter

That circuit I was looking at must have been for a sync on green (RGsB) input...crap...

You only asked about the video signals, not the sync signals. Impossible to answer your question without some real-world context.... Does your source have separate H & V sync? Composite sync? Sync on green?

Which type of sync does your destination want? Any combination can be converted to any other, but you have to specify exactly what you need.

Or at least what the source and target hardware are. I think there are a few variations of RGB and YPbPr. How the sync is encoded is the most likely variable thing.

some CGA cards had luminance/chrominance outputs, they could probably go straight to a "svhs" input.

I once hooked the lumiance to the composite in of a VCR and got a (monochrome) image on a TV.

but why would anyone want to keep a CGA card when a VGA card is backwards compatible ?

I have one somewhere that can even drive a CGA monitor....

Bye. Jasen

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I've never looked closely at TV RGB, but I think in the absence of separate sync (ie. composite) sync is often in the green channel.

I did mention in my first post I was using RGBs...analog 15.7 KHz rgb with composite sync as output. This needs to be converted to YPbPr for connection to a TV with component video. I pretty much just embarrassed myself with my last post about not uderstanding how the sync was getting into the Y...the circuit I was looking at must have been for a sync on green rgb input. That circuit was here...

But anyway...that circuit was helpfull in my understanding of how to use op amps at matrix the rgb to get Y, R-Y and R-B....but I still need to introduce sync...would another op amp do this to add sync to the green before R, G, B get combined to create a Y = 0.3R + 0.59G + 0.11B signal? Or even after?

Jerry

Elantec used to make some nice video sync separators, it seems Intersil have bought them.

You could try looking at

OK, so you are saying that your source equipment has four coax outputs: R,G,B, and composite (H+V) sync. Right?

Sorry, still not clear exactly what your destination equipment wants. Are you saying that it wants sync on Y? Separate composite sync? What, *exactly*?

How many connectors does it have? How are they labeled? You are unlikely to get any useful specific advice with only generic descriptions of your situation.

OTOH, you could identify the source/destination equipment by make and model and make everything much easier to decode here.

On a sunny day (Fri, 27 Oct 2006 12:02:26 GMT) it happened "Jerry Lynds" wrote in :

After. So once you have Y, and say it is 700mV pp, add 300mV composite neg sync. This then gives 1Vpp, and you need to drive into 75 Ohm likely, so you may want to go for 2V pp low impedance out with a 75 Ohm resistor. Usually works fine with some transistors, emittor followers, no ICs needed. I hope your TV is also 15.7 kHz, and not a VGA monitor. If it is a VGA monitor then you need to convert to double the 15.7kHz for example, and that is a whole other story, I have done that with DA / AD and FPGA, so I could play the old DVD player on the 19inch monitor.

"Jan Panteltje" schreef in bericht news:eht6fv$hqp$ snipped-for-privacy@news.datemas.de...

Jan,

Can you tell more about that conversion? I've got questions about an old monochrome monitor (15.67kHz) output to be connected to a VGA monitor.

petrus bitbyter

On a sunny day (Fri, 27 Oct 2006 19:56:08 +0200) it happened "petrus bitbyter" wrote in :

Hi, Petrus, yes, I used a Spartan2-200 FPGA, and 2 Philips ADC converters, lemme look (long time ago) TDA8708 8 bit flash. I did the BW only, but worked out the color, you can sample Y at any speed you like, and use a 2 to 1 CMOS 4053 and sample U and V sequentially at half that speed each. If you sample low freq you just get lower resolution ;-) Then you need 3 DA 8 bit converters, and I used r2r ladders. I used the FPGA dual port block RAMS (these allow read and write at the same time), to store a line in 64 uS, and then clock it out twice at double speed, would have to look up the Verilog code. The most challenging was to do a digital PLL 2x to multiply the H. (Jitter was a problem especially if fed from a VCR source). It also worked as a timebase corrector, but not 100% good, did not finish it. Had a sync separator IC first, but then just clamped the Y bottom sync with a simple diode and did the sync slicing in Verilog. Was just an experiment on the Digilab board. Doing it in HDL makes things more simple to change. When using a TV signal as source, as the OP does, then 1024 samples per line should be enough. That fits nicely in a Spartan2 block-RAM. I have tried several sample frequencies and configurations. You need some input filters if you think you have high frequency components in the input, and a low pass after the DA (R2R with high R is low pass enough ;-).

Actually I also used color in the timebase corrector, with composite in and out with this setup... color is tricky as your time resolution becomes critical (subcarrier phase), it is always once clock, even as I used the internal 4x FPGA clock multiplier to go to 200MHz... PAL is forgiving... Finally played the DVDs in the PC :-).

It is a fun project, maybe I should play with it again some day, but all went digital.... satellite... :-)

If you need code or diagrams maybe I can scan something in.

Actually it is a multi-pin din....and yes, it has R,G,B and composite (H+V) sync.

I apologize if I was being vague...I thought that was a pretty good description :( Anyways, the source is older video game systems such as a Sega Genesis or Sega Saturn. Pin outs here...

Component video found on every DVD player as output, and found as input on pretty much any brand name TV over 20" in the past year....

It just has 3 RCA connectors labeled Y, Pb and Pr. I am assuming sync is on the Y...as this circuit to convert from Component (YPbPr) to RGB uses a LM1881 to remove the sync from Y

I think this is starting to be more trouble than it is worth...

"Jan Panteltje" schreef in bericht news:ehtjr0$f71$ snipped-for-privacy@news.datemas.de...

Thanks Jan. It's about a monochrome display mainly used for 80 columns characters and only two steps of brightness except black. It can do graphics as every dot is programmable but it is slow. So AD will be overkill. I think some comparators will do. Problem may be how to synchronise the sampler with the dotclock. If you have material about the storage and recovery of the samples and the way you treated the sync I should be glad to receive it.

BTW My e-mail address is valid once you've removed the obvious additions. Petrusdotbitbyterathotmaildotcom works as well.

petrus bitbyter