Worklog [2025 Contest Entry] StellaNova - Hand Wired Atari 2600 Portable

Y2K

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It's that time of the year again! No procrastination allowed this time!

With the current uhh, political situation in the US, a couple of us folks in the Discord were cracking jokes about having to go back to hand wired projects for the summer contest because custom PCBs are too expensive to import from the usual places right now.
Well, I decided to take those jokes way out of context and actually do a hand wired project for my entry, and what better system to do that with than the good ol' Atari 2600!

If any of you are familiar with Ben Heck (which, if you've been a part of this community for as long as a lot of us have, you should know who I'm talking about), you may be familiar with his Ben Heck Show episode on a hand wired Atari 2600 motherboard, which he eventually turned into a full portable in another episode. I think he did a fantastic job on this, but it's been almost 10 years since those two videos came out, and a lot has changed in the portablizing scene. While I totally could make a full custom PCB for this project and make it highly integrated with all the latest bells and whistles, but what's the fun in that? Let's go old school, with some modern twists to improve the overall usability and user experience!

After running a poll on the Discord, I decided on the name StellaNova (Stella being the Atari 2600 VCS codename, also means star in Latin, Nova meaning the birth of a new star. Get it? I thought it was cute at least...).

Feature set is as follows:
  • Hand wired Atari 2600 motherboard featuring chips pulled from an Atari 2600 Junior console. No emulation here!
  • 1x 4000mAh 18650 battery - I have yet to do battery life calculations, but even this should yield significant battery life
  • USB-C PD charging (5V3A) with an off the shelf BQ25606 based battery charger module
  • 3.5in Screen - ideally the 3.5in 640x480 IPS (1)
  • Highest quality video output possible w/o FPGA based mods using a custom S-Video circuit (2)
  • Shank's Lumadoub for upscaling the 240p S-Video(3) output to 480p VGA
  • Ideally, the final build will not be much bigger than a cartridge itself

(1). I will settle for the original G-Boy's Tianma 3.5in 240p screen if the S-Video circuit and Lumadoub doesn't end up working out. The composite video output is not great, but it's good enough.
(2). I found this circuit online and I have absolutely no idea if it will work, but it seems promising. I've seen others implement it on custom PCBs, but I haven't seen anyone attempt a hand wired version yet.
(3). I may still use Lumadoub if the S-Video circuit doesn't work, since it can do composite input as well.

There's a lot of "ifs" hinging on me achieving the vision I have for this project, but I think I have a good set of backup plans in case things don't work out the way I hope. I'm taking things one step at a time, and trying to pace myself so I don't burn out at the beginning, which I think was the big issue I was having with previous years.

As for current progress, I started working on this project in the beginning of May, and first started by recreating the Atari 2600 cartridge in CAD as closely as I can to help model out a well functioning cartridge slot. I already released the model to the Model Repository, and so far it's proven very useful. I already pretty much have the shape of slot nailed, and after 1 or 2 test prints, cartridges insert and remove very smoothly.

1747359786634.png


A big requirement I had when it came to the cartridge slot is that I wanted the cartridge to slot in from the top and be nearly flush with the unit, and I also wanted the label to be fully visible. I think this design nails these goals perfectly!

During this I was also trying to come up with a good solution for video output, as 240p video is a bit tricky to deal with using the screens that are most popular currently with the community. Most screens these days straight up won't accept anything less than 480p VGA video, and for a long time there wasn't really a good, low power & low latency way of upscaling 240p/480i content to be viewable on these displays. Enter Shank's LumaDoub project - an open source, low power, and lag free analog video encoder/decoder/line doubler. It can accept a variety of analog video standards in, and output a variety of analog video standards out. It's absolutely perfect for this project, with one issue: it's not released yet.

According to Shank, LumaDoub is feature complete, but just needs code cleanup & some spit shine before it's ready for prime time. Unfortunately, this would mean that I'm unable to use it for this contest until it gets released according to contest rules. However, Shank graciously decided to provide enough information on the Discord for anyone to be able to implement a basic version of LumaDoub on their own before release! The actual hardware design was pretty simple, it just requires a very specific i2c initialization routine, which he graciously shared with the class, enough to get CVBS/S-Video to 480p VGA up and running! Armed with the knowledge to perform great acts of sorcery, I set off to design the schematic, and came up with something that I'm pretty pleased with!

1747361890122.png


I also got started on the board routing, but haven't finished yet. My plans are to order this from Aisler using their 0.8mm ENIG service, which right now has a coupon for $20 off, so the boards are basically free at the price I was quoted!

1747361955057.png


Finally, once I got some of the necessary parts in from Amazon, I got started soldering the Atari board. I went with a chip layout very similar to Ben's original design, but I'll be doing all the routing my own way to try and keep things as clean as possible. So far I finished the whole data bus, and started laying out some of the basic passives. I still have quite a bit of work to do on this!

1747362036171.png


And that's all for now! I hope you all enjoyed the first post on this journey to greatness! I'm very much looking forward to continue working on this in the coming months! Stay tuned!
 
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However, Shank graciously decided to provide enough information on the Discord for anyone to be able to implement a basic version of LumaDoub on their own before release! The actual hardware design was pretty simple, it just requires a very specific i2c initialization routine, which he graciously shared with the class, enough to get CVBS/S-Video to 480p VGA up and running!

Lumadoub's core circuit is based on the ADV728A Eval board. The schematic can be found on Analog Devices page here.

Startup Sequence can be found in the datasheet here.

Example scripts to get the ADV7280A (and ADV7391) running in this configuration and others can be found in a .txt file here.

Additional parameters can be adjusted via i2c. Info on that is in the programming guide here.

Additionally, turning on fast lock can fix stability with 240p. And finally, resetting bits 3 and 4 of ADV7280A VPP map register 0x5A will disable the field blending, making it perform simple line doubling. Shoutouts to Mike Chi of RetroTink for sharing that info

This is basically all the info one would need to make this video circuit.
 
This thoroughly tickles my tism
 
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Who said PCBs were better than hand wiring? This is some clean wiring ya got goin' on here. Looking great! Can't wait to see where this project goes!
 
Hey!
you mentioned a circuit you found online in your first post (1) & (2). I assume it's about S-Video output for the Atari 2600. Could you share, which one it is or where you found it?

Thanks!

Any progress otherwise on the project?
 
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Hey!
you mentioned a circuit you found online in your first post (1) & (2). I assume it's about S-Video output for the Atari 2600. Could you share, which one it is or where you found it?

Thanks!

Any progress otherwise on the project?

Hi!
At the time, I was considering using/reverse engineering the CleanComp mod but I decided against it due to its complexity & use of components that would be very difficult to implement on perfboard. Recently a new CVBS/S-Video mod came out called the Tiara that's nothing more than a couple of BJTs, a bunch of passives, and a quad line driver (much simpler!). When I come back to this project, I'll probably reverse engineer and implement that instead, as that should be a lot more perfboard friendly. Alternatively I could just buy the existing mod board and mount it underneath the TIA as intended, but that presents wiring challenges for the rest of the board.

Currently I have a lot of changes going on in my life that require my near-full attention, so I don't have time to do this project at the moment, but I will certainly come back to it at some point in the future.
 
Hi!
Ah, okay - I thought you meant an S-Video circuit separately from the CleanComp. Just as you said, something with fewer and simpler components.
I was just checking the prices of the ADV7280A and ADV7391, but I could only find them for around €15 each.
I’ve also seen the TIARA last week and took a close look at the PCB photo. Unfortunately, I’m not skilled enough in electronics to reverse-engineer it just from the picture. You can make out the resistor values & the IC, but that’s about it.
I'd be happy if there is the schematic of the TIARA or a good alternative available freely.

Thanks for answering so quickly! :)
 
Hi!
Ah, okay - I thought you meant an S-Video circuit separately from the CleanComp. Just as you said, something with fewer and simpler components.
I was just checking the prices of the ADV7280A and ADV7391, but I could only find them for around €15 each.
I’ve also seen the TIARA last week and took a close look at the PCB photo. Unfortunately, I’m not skilled enough in electronics to reverse-engineer it just from the picture. You can make out the resistor values & the IC, but that’s about it.
I'd be happy if there is the schematic of the TIARA or a good alternative available freely.

Thanks for answering so quickly! :)

I think I have a rough understanding of how a S-Video circuit would be implemented, and it's pretty simple:

The TIA outputs 5 separate signals that ultimately define the video signal. You have 3 bits of luminance information (7 brightness levels), your Chroma sub carrier signal (nearly the same as your S-Video Chroma, just needs some work done to bring it up to spec), and a TTL CSYNC signal.

For Luminance, you can achieve your analog Luma + sync output by running everything through a simple resistor ladder DAC. The output of that can then be fed through a two transistor amplifier to bring everything up to "75ohm" voltage levels that a TV would expect.

Chroma is even easier, you "just" need to feed the Chroma output from the TIA into a similar two transistor amplifier like you did with Luma.

I did find a circuit online detailing this exact setup but I haven't tested it. Let me know if you give it a shot and have any luck!
 

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  • Atari 2600 Junior S-Video SCHEMATIC.GIF
    Atari 2600 Junior S-Video SCHEMATIC.GIF
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Thank you!
I'll have a look and see if I can make something out of it!
I'll let you know!
 
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