Low Cost RGB Out for 800

[Cybernoid]

Does anyone know more about this modification? (see included zip).

 

It looks like it would be possible to drive an ST monitor with the right connection to the 13pin connector and with a simple sync separator circuit.

 

Also, what is the A103 chip on the 800 motherboard? Is this the GTIA? If so, does this mod just use one of the 4 luma outputs from the GTIA for each color component, one for Red, one fore Green, and one for Blue? This would be 3bit color.

 

rgb800.zip

[Rybags]

A301 is GTIA according to my schematic in the official printed Hardware Manual.

 

Looks like simple 3-bit colour from here too.

 

I wonder if it could be taken up a level - mix in the LUM outputs as well, although each component of R,G,B would receive the same dose.

[Curt Vendel]

There are a few RGB mods for the 800 out there, none are terribly good, I did one a long time ago with a TDA3330 which just never really as good as I wanted, but then I'm not good with analog circuits anyways....

 

Quite frankly, just spend the $50 and buy a composite to VGA adapter and use a VGA monitor, the image does look much crisper then on a standard composite monitor.

 

 

 

Curt

 

A301 is GTIA according to my schematic in the official printed Hardware Manual.

 

Looks like simple 3-bit colour from here too.

 

I wonder if it could be taken up a level - mix in the LUM outputs as well, although each component of R,G,B would receive the same dose.

Edited February 25, 2007 by Curt Vendel

[puppetmark]

Does anyone know more about this modification? (see included zip).

 

It looks like it would be possible to drive an ST monitor with the right connection to the 13pin connector and with a simple sync separator circuit.

 

Also, what is the A103 chip on the 800 motherboard? Is this the GTIA? If so, does this mod just use one of the 4 luma outputs from the GTIA for each color component, one for Red, one fore Green, and one for Blue? This would be 3bit color.

 

rgb800.zip

 

This is a very interesting idea. I once built a simple logic circuit to seperate the Atari composite synch, and tied the composite luma to the R G B inputs on a SC1224 monitor. It gives a very nice BW display. Very nice to data entry and Word Processing. It might be fun to play around with this 3 bit color idea. SC1224 monitors can still be found for a decent amount.

[Rybags]

I'm pretty sure I've seen DIY VGA convertor projects around before.

 

But, factor in the labour and chasing of parts and it might well be better to just spend $50 on something already available.

[Mathy]

Howdy folks

 

This looks like Bob Woolley's doing. Or was it Ben Poehland. It's been reprinted in Atari Classics. IIRC around the time (maybe even the same issue) as the Super Video upgrades.

 

Greetings

 

Mathy

[ShosMeister]

What about using the DIN-5 on the side? Could anything be connected using that? I thought it separated some of the video. Any capture cards that could handle that output?

[Rybags]

The Atari monitor plug is electrically compatible with composite (VCBS) and S-video systems. As such, that is fine with most capture cards although the non-interlaced display can cause trouble with some cards (esp. older ones).

 

The problem with standard chroma vs RGB is that RGB gives a seperate signal for the state of red, green and blue at a point in time.

 

Chroma follows the television standard of having the colour-space wheel where the signal just has to peak at the correct point in time for each pixel, so conversion back to RGB isn't straight-forward.

[ShosMeister]

Thanks! So if I understand correctly from discussions here and reading, the composite video out from the monitor plug is all of the video information and I can either use that or build a adapter to get the composite chroma and composite luma out of the monitor plug to an s-video connector and use that; correct?

 

So the next question is, which would result in the better quality picture? Obviously, RGB would be best, but, since there is no RGB out from the Atari, what's next best? Just the composite video or the chroma/luma?

[Rybags]

Chroma and luma are the best from a "stock machine". That equates to the same as an S-video outlet.

 

But also be aware that practically all 8-bit Ataris have pretty ordinary to bad video quality - although S-vid from the monitor port is a good deal better.

 

You might, however, find that your machine doesn't have the chroma line connected. That was the case with many XL and XE machines.

 

Adding it back in is pretty straightforward - just a resistor and short length of wire and some soldering.

 

Making an adaptor is fairly easy - you can take the audio output from the monitor jack too. Or you can just modify the Atari and add S-video and/or A/V jacks to the machine itself.

[ShosMeister]

Thanks! I think I'll first try for the DIN-5 to S-Video. I have a DIN-5 that already terminates in RCA connectors so I can make that work. This is what I have for the S-Video pinout:

 

Pin Name Description

1 GND Ground (Y)

2 GND Ground ©

3 Y Intensity (Luminance)

4 C Color (Chrominance)

 

So I should be able to use the ground from the DIN-5 (pin 2) for the S-Video 1 & 2? I think the best way to do this would be to make a small box that takes the input as an RCA-M (that way I could use a simple RCA patch cable from the DIN-5), connects the appropriate wires on the inside, and has an S-Video F for the output (again to be able to use a standard S-Video patch cable).

 

Thanks for the help!!!

[puppetmark]

Thanks! I think I'll first try for the DIN-5 to S-Video. I have a DIN-5 that already terminates in RCA connectors so I can make that work. This is what I have for the S-Video pinout:

 

Pin Name Description

1 GND Ground (Y)

2 GND Ground ©

3 Y Intensity (Luminance)

4 C Color (Chrominance)

 

So I should be able to use the ground from the DIN-5 (pin 2) for the S-Video 1 & 2? I think the best way to do this would be to make a small box that takes the input as an RCA-M (that way I could use a simple RCA patch cable from the DIN-5), connects the appropriate wires on the inside, and has an S-Video F for the output (again to be able to use a standard S-Video patch cable).

 

Thanks for the help!!!

 

to correctly convert composite video to rgb is a pretty major undertaking. It requires a lot of decoding. without a conversion box, Your best bet is s-video. Your pin out for s-video is correct. You can tie 1 and 2 to ground. Take a look at my XEGM video upgrade that includes instructions for adding a s-video jack to the back of the unit. It might have some info you are looking for. I just posted it here:

http://www.atariage.com/forums/index.php?showtopic=102734

Edited February 26, 2007 by puppetmark

[Cybernoid]

to correctly convert composite video to rgb is a pretty major undertaking. It requires a lot of decoding. without a conversion box, Your best bet is s-video. Your pin out for s-video is correct. You can tie 1 and 2 to ground. Take a look at my XEGM video upgrade that includes instructions for adding a s-video jack to the back of the unit. It might have some info you are looking for. I just posted it here:

http://www.atariage.com/forums/index.php?showtopic=102734

 

Yup, that is right. To correctly convert S-video to RGB with a homebrew circuit, would take some work (well, luma is not a problem, but demodulating the chroma is). The file I posted was a "low-cost" solution for back in the day. However, it only uses the upper 3 bits of the luma to drive R, G and B (one bit per color). So, if your program you are running sets the background to 0 and the foregroung to 0xe, then it would show up as white on black, but if the program uses 0 for the background and say 0x0a for the foreground, then this would look like purple on black.

 

You could however, build a circuit that would do 4-bit per pixel greyscal by connecting the 4 luma pins on the GTIA to each of the R, G and B 4 pins on this thing:

 

http://www.digilentinc.com/Products/Detail...;Nav2=Accessory

 

Then, you would need a VGA to 5-BNC (RGB+HV) to connect up to a flat panel that take RGB and external syncs or build the VGA to 13pin connector on the ST monitor or be lucking enough to have a multi-sync monitor that will work at 15hz or 30Hz. This would have limited uses.

 

However, all of this will not buy you much as the real low cost solution today would be to drive a scan converter with the Atari S-video output and connect to a VGA monitor. Ah, the advances in video over the last 20+ years and how cheaply companies can make this stuff now...

 

I use S-video output from all my Atari's and it looks great!

[ShosMeister]

Thanks! Nice work. If I'm going to do it, I may as well do it right, eh? Any information on putting an audio jack on it while we're at it?

[puppetmark]

Thanks! Nice work. If I'm going to do it, I may as well do it right, eh? Any information on putting an audio jack on it while we're at it?

 

which machine you you want to add an audio jack too? Are you looking for an RCA jack or a standard 1/8" audio jack? Either one would be fairly easy, I just need to have some more info.

Edited February 26, 2007 by puppetmark

[Rybags]

I did a 3.5 mm stereo jack on my 130XE but really an RCA jack would be better.

 

Just mount it and run the wires to the back of the board to the solder points for the relevant monitor plug outputs.

[ShosMeister]

which machine you you want to add an audio jack too? Are you looking for an RCA jack or a standard 1/8" audio jack? Either one would be fairly easy, I just need to have some more info.

 

It's looking like I have a hardware problem with my 800 so I'll probably use the 130XE.

[puppetmark]

which machine you you want to add an audio jack too? Are you looking for an RCA jack or a standard 1/8" audio jack? Either one would be fairly easy, I just need to have some more info.

 

It's looking like I have a hardware problem with my 800 so I'll probably use the 130XE.

 

The easiest way to do it is to get a panel mount rca jack and mount it on the back of the 130XE. The ground connection which is the outside metal part of the connector can be connected anywhere ground is located on the main board. The other connection on the RCA jack gets connected to pin3 of the monitor jack.

 

Monitor jack Pin Function:

1 Composite Luminance (not on North American 600XL's)

2 Ground

3 Audio Output

4 Composite Video

5 Composite Chroma (not on 800XL,1200XL; grounded on 600XL)

 

you can also pick up audio at the junction of R8 and R10. A continuity tester will help you make sure you have the right connection

Edited February 27, 2007 by puppetmark

[puppetmark]

Does anyone know more about this modification? (see included zip).

 

It looks like it would be possible to drive an ST monitor with the right connection to the 13pin connector and with a simple sync separator circuit.

 

Also, what is the A103 chip on the 800 motherboard? Is this the GTIA? If so, does this mod just use one of the 4 luma outputs from the GTIA for each color component, one for Red, one fore Green, and one for Blue? This would be 3bit color.

 

rgb800.zip

 

I took a closer look at this last night and from the Docs that I have, A103 is not GTIA but a CD4050. Its a non inverting hex buffer. It takes the 4 luma signals from the GTIA and multipexes them together with the composite sync signal to create the Luminance signal. So, this RGB circuit picks up the buffered siganls off the CD4050 instead of the GTIA which is actually a good idea. It protects the GTIA and increases the signal strength.

 

The idea is correct, 3 luma outputs are conected to R G B inputs to make 3 bit color. So, the color on the RGB monitor would change as the intensity of the color registers change. This won't be the same color you would see on a TV or composite / s-video monitor. Still it is an interesting idea and I will do some experimenting.

[mimo]

Anyone know where to get one cheap, in the uk i can only find them for £80-£90 !

 

 

 

Quite frankly, just spend the $50 and buy a composite to VGA adapter and use a VGA monitor, the image does look much crisper then on a standard composite monitor.

 

 

 

Curt

 

A301 is GTIA according to my schematic in the official printed Hardware Manual.

 

Looks like simple 3-bit colour from here too.

 

I wonder if it could be taken up a level - mix in the LUM outputs as well, although each component of R,G,B would receive the same dose.