Amiga RGB to YPrPb convertor

[rkauer]

Ian give you a good hint on where to source -5V. So here goes another couple:

1- use the 79L05 instead full-sized 7905. Less heat, less space taken and enough current (100mA at max);

2- check my old design where I want to fit the board inside the old A520. There you'll find a chip who makes stable negative voltages from positive +5 or +12V.

Nice work! I'd been looking for an RGB to YPbPr converter lately, and in the end found a ready-made commercial one, model CSY-2100 "SCART to Y-U-V Converter". I got mine from Jaycar electronics, but Google tells me there are other stockists out there too.

Input is a SCART connector, using the following pins:
Red: 0.7 Vp-p, 75 ohms
Green: 0.7 Vp-p, 75 ohms
Blue: 0.7 Vp-p, 75 ohms
Composite video (also works with Csync signal only): 1 Vp-p, 75 ohms

Output is 3 RCA jacks:
Y: 1 Vp-p, 75 ohms
B-Y: 0.7 Vp-p, 75 ohms
R-Y: 0.7 Vp-p, 75 ohms

The spec sheet says it's compatible with PAL, PAL M, PAL N, NTSC, NTSC 4.43, and SECAM. Power (0.5 A @ 7.5 V) is from an external adapter; internally it runs off +5 V.

I'll probably change the connectors on mine for better integration with the other hardware I have, but it works fine for now.

Silicon Chip magazine listed a schematic for a similar circuit (I went to Jaycar originally to buy a kit for one of these, rather than the CSY-2100, but they didn't stock the kit and it would have been more expensive anyway). Here's the teaser for the article:

http://www.siliconchip.com.au/cms/A_102648/article.html

Note that it assumes sync-on-green but there is a user-submitted mod which adds a separate composite sync input:

http://www.siliconchip.com.au/cms/A_104857/article.html

[Matt020]

Is it possible to explain the difference between YPrPb and s-video. Not in terms of how it works technically, but the difference in output and how it appears on a LCD or Plasma TV. Is there a display difference?

[MagerValp]

Basically, component video is sharper - theoretically as sharp as RGB, but on the Amiga there's a (very slight!) loss when converting from RGB to YUV color space. In S-Video the chroma component (U+V) is bandwidth limited, and is only suitable for SD content- it's barely able to keep up with 320x256. Component video has no such limit, and can easily support HD resolutions all the way up to 1920x1080, just like RGB can (typically in the form of VGA).

[rkauer]

As MagerValp wrote, YUV will not be better than the original RGB because the circuit will make a conversion.

Conversions from one output type to another will always make a loss in the image quality. So, beside the fact the YUV is superior to S-video (but not to original RGB), and the alarming fact that almost all TV and monitors from nowadays simply doesn't have Svideo any more, it's time to have other ways to connect our favourite computer to those.

Oh, and our good old CRT monitors will not last forever, either.

[orange]

upconversion can make video look better. however its probably not worth the effort with analog signal and would add some lag.

[AmmoJammo]

Originally Posted by narmi

A520? That would be freaking huge . This is the board layout I finished yesterday.



It's about 2x2" in size. I'm still waiting for parts so that I can test it before posting the schematic.

old thread, but your opamp appears to be backwards, and you've used a 25 pin connector instead of 23 pin

did you ever end up finishing this?

[kipper2k]

Originally Posted by AmmoJammo

old thread, but your opamp appears to be backwards, and you've used a 25 pin connector instead of 23 pin

did you ever end up finishing this?

I don't think Narmi was been online for a long time now. (2 Aug 2010)

[AmmoJammo]

Originally Posted by kipper2k

I don't think Narmi was been online for a long time now. (2 Aug 2010)

yeah, I noticed that after posting

[kipper2k]

Originally Posted by AmmoJammo

yeah, I noticed that after posting

I do have a working component video schematic that i created, i won't sell it at the moment as it seems to be very picky on the TV/Monitor it is feeding. When it does work, it works great, when it doesn't there is no picture.

It uses a pair of LT6550 chips and produces a very nice picture. The Component schematic is actually in the datasheet for them. I have the schematic built onto my Svideo boards, but just don't populate that part of the board when i sell it

[AmmoJammo]

this I assume?

http://circuits.linear.com/images/ci..._circuit_1.jpg

[kipper2k]

Originally Posted by AmmoJammo

this I assume?

http://circuits.linear.com/images/ci..._circuit_1.jpg

Yup, and i also tied it in to the Svideo and composite video schematic too, so it does all in one.

[AmmoJammo]

what issues does it have on some TVs?

[kipper2k]

Originally Posted by AmmoJammo

what issues does it have on some TVs?

sync on green, some TV's do not use it, so therefore this board won't work on them. I do have a Sharp multi region TV that it works on fine in Pal/NTSC but i also have a Sony Bravia that won't work. My big LG works great too. This is why i am hesitant to sell it as a component video adapter, too many possible issues

[AmmoJammo]

you mean "Y"?

why wouldn't the ypbpr input have the sync signal on the "Y" input? if it's not there, where is it?

[AmmoJammo]

I've soldered one of these up as per the schematic, but the opamp I had isn't suitable... makes a picture, but it's horrible...

So, I've got some LT1254 on order, which are the same pin configuration, suitable for video, and will accept the +-12volts from the amigas video port

I might update this when they arrive...

I'd like to build one circuit into my Sega Megadrive/Genesis, probably the "prototype" board I've just finished... and try to stuff one into a D23 back shell for the amiga

[AmmoJammo]

Incase you're wondering what the silver box is....



9 - 18volts goes in one end... regulated +-12volts comes out the other

As the Sega only has +10volts DC, it's perfect!

Before I cut, drill, or modify anything, I'm going to wait for the correct opamps to arrive... I connected the circuit to the sega, and once again, got a picture, but with rather odd colours...

[lesta_smsc]

Think the colours can be improved by changing the resistors... Not sure if it is worth putting 'pot' resistors that you can 'tweak' to give best colour/contrast?

[AmmoJammo]

Originally Posted by lesta_smsc

Think the colours can be improved by changing the resistors... Not sure if it is worth putting 'pot' resistors that you can 'tweak' to give best colour/contrast?

the opamp I was testing with doesn't have the bandwidth needed to display the image properly, once the suitable opamps arrive, I'll see what the colours are like then

[Stedy]

Originally Posted by kipper2k

sync on green, some TV's do not use it, so therefore this board won't work on them. I do have a Sharp multi region TV that it works on fine in Pal/NTSC but i also have a Sony Bravia that won't work. My big LG works great too. This is why i am hesitant to sell it as a component video adapter, too many possible issues

The issue some TVs have is with the sync signal being the wrong type. YPbPr video should have a Tri-level sync signal, the Amiga outputs a normal bi-level sync. Some TVs will cope fine, others will not, it all depends on the analog front end of the TV.

With some creative circuitry you could create a tri-level sync from the Amiga, that should help.

Ian