SEGA Genesis Portable Project

[+selgus]

As I am finishing up an ATARI 8-bit Portable project, which has been in development for a long time, I started doing some initial work on an SEGA Genesis Portable system.

 

It is based on the SEGA Genesis Model 2, VA1 schematics and uses harvested chips and components from a real Genesis. It has a built-in LCD display (same as I'm using on the ATARI) and a similar LiPo powering/charging USB-C setup.

 

I have started laying out the PCB and have created devices for all the custom SEGA ICs/components. The schematic is about 95% wired, with just some passives still needed to be added to the board..

 

I am taking a few liberties with my design, like not implementing mono audio, the edge connector or the SEGA CD/32X audio mixing. It takes standard SEGA cartridges inserted into the top and will have stereo speakers, along with a built-in stereo amp.

 

As you can see from the PCB, I am using the Genesis controller as the basis for the shape of the portable, with a built-in joypad (I think I am going to do a 6-button controller for the built-in) along with a second db-9 controller port.

 

I started mocking up the enclosure so I can get some of the proportions right..

 

More to come...

 

[Steven Pendleton]

Why use a Genesis 2? The YM3438 busy behaviour thing will ruin the music in Hellfire unless you use the Retro-Bit version.

[+selgus]

8 hours ago, Steven Pendleton said:

Why use a Genesis 2? The YM3438 busy behaviour thing will ruin the music in Hellfire unless you use the Retro-Bit version.

It's what I have experience with and have donor motherboards to harvest chips from. I also was a SEGA Genesis developer many years ago and this was the version I had been using.

[+selgus]

Making more progress laying out the PCB.. Modified my design to use the SONY CXA1145 RGB encoder, instead of the SAMSUNG KA2195D that is on my VA1 motherboards, since the LCD will be using strictly a composite signal. Finished the stereo amp, but still have a few passives still to add to the schematic..

 

[M-S]

That's quite interesting, but why use composite? Also, you are using later chips and the design of the PCB looks quite different, so why not use an ASIC clone chip?

[+selgus]

3 hours ago, M-S said:

That's quite interesting, but why use composite?

That is what these 5" LCD displays take as input. The controller boards don't take any other connection types. The PCB design is my own and the point of this project is to use the real custom SEGA chips.

[+selgus]

After no luck trying to locate 33pF bussed capacitor arrays, small enough to use in my portable, I designed this little PCB (12mm x 7mm) that takes SMD isolated capacitor arrays and lets me tap into the data bus..

 

[+selgus]

I've completed laying out the motherboard and am more than half-way through routing all the traces. Some are tricky with all these dense pins on the ICs and having a much smaller motherboard than the model 2 Genesis..

 

 

I also finished the 6-button controller PCBs, that hold a directional joystick and the 6-buttons, the custom SEGA IC that controls all the multiplex logic (I am assuming it is some sort of micro-controller) and connections to the MODE, START and motherboard..

 

[Yurkie]

On 10/13/2022 at 11:37 PM, selgus said:

As I am finishing up an ATARI 8-bit Portable project, which has been in development for a long time, I started doing some initial work on an SEGA Genesis Portable system.

 

It is based on the SEGA Genesis Model 2, VA1 schematics and uses harvested chips and components from a real Genesis. It has a built-in LCD display (same as I'm using on the ATARI) and a similar LiPo powering/charging USB-C setup.

 

I have started laying out the PCB and have created devices for all the custom SEGA ICs/components. The schematic is about 95% wired, with just some passives still needed to be added to the board..

 

I am taking a few liberties with my design, like not implementing mono audio, the edge connector or the SEGA CD/32X audio mixing. It takes standard SEGA cartridges inserted into the top and will have stereo speakers, along with a built-in stereo amp.

 

As you can see from the PCB, I am using the Genesis controller as the basis for the shape of the portable, with a built-in joypad (I think I am going to do a 6-button controller for the built-in) along with a second db-9 controller port.

 

I started mocking up the enclosure so I can get some of the proportions right..

 

More to come...

 

I'd be very interested in owning one of these. Do you plan a video out to connect to a TV? Is the case going to be 3D printed or do you have a plan for injection molding?

[+selgus]

6 hours ago, Yurkie said:

I'd be very interested in owning one of these. Do you plan a video out to connect to a TV? Is the case going to be 3D printed or do you have a plan for injection molding?

I wasn't planning on a video out port on the portable, as this is meant to be used not tethered to anything.. though wouldn't be hard to add a composite out.

 

I have been doing 3D printing with commercial high-end multi-jet fusion printer, with my ATARI portable, and will be doing the same for this project.

[M-S]

Its impressive how you are developing this so fast. Are you going to make this available with pre-built units or a DIY kit?

[Tanooki]

Probably would be more budget busting but if it had like mini hdmi to hdmi with a proper quality output for a modern TV that would be fantastic.  Either way hadn't posted yet but been watching this and it's looking good.  Makes me want one, and I have a composite modded Nomad as it is.

[+selgus]

Down to the last 59 traces to route, so making progress. I don't know about it developing fast, as I do it at night, since I have a day-job (I work at EA SPORTS).

 

I don't believe this would make a good DIY kit, as you need to solder some very fine pitch pqfp smt devices.. and to get these parts, I am harvesting them from SEGA consoles. To be honest, I haven't really thought about the step past getting one to operate the way that I planned. Though I am designing this so that I can build multiple units. Basically I want one, so I am designing and building this portable.. others might like one too, I don't know.

 

Already got back my directional-pad and 6-button PCBs, so will assemble one of them this weekend.

[Yurkie]

22 hours ago, selgus said:

 Basically I want one, so I am designing and building this portable.. others might like one too, I don't know.

 

I absolutely want one. Paypal is ready when you are sir.

[+selgus]

Board is now completed and validated. Next step is to fix all the part names and value location and make a few PCBs and start the testing..

 

 

[+selgus]

Now have my PCBs so I can start assembling one..

 

[M-S]

Do you have any portable consoles that you can use to do a size comparison?

[Tanooki]

16 hours ago, M-S said:

Do you have any portable consoles that you can use to do a size comparison?

or you know, you could look at the size of a genesis and megadrive cart and just eyeball it out from there to figure out things.  The board is going to be smaller than the larger shell around it built with smooth curving lines for comfort, and it will have to be fairly thick to house the screen, pcb, buttons/pads, and the cart in the slot too without being too flimsy and easily cracked.  I doubt it'll be quite as thick as the Supaboy S, but closer to that than a standard genesis controller.

[+selgus]

Sorry, missed the question.. the above post is correct, it is slightly larger than a standard Genesis controller.. but will be the 6-button configuration with a MODE button, too. I actually used the scaled dimensions of the standard controller to design the PCB, and that in turn, to design the enclosure. The goal is to feel comfortable in the hand, but be self-contained.

 

[DeathAdderSF]

On 10/13/2022 at 8:42 PM, Steven Pendleton said:

Why use a Genesis 2? The YM3438 busy behaviour thing will ruin the music in Hellfire

 

Not necessarily.

[+selgus]

While working with my rev1 PCBs and checking the cartridge cut-out, I miscalculated the depth of the cartridge, as it wasn't large enough to allow the cartridge to fit properly.

 

Not sure how that happened, so I took out my EA SPORTS Genesis cartridge, measured the dimensions and then needed to re-layout the board (since the needed to remove parts of the PCB that had components and traces going through them..

 

 

Once I completed the modifications and layout, I started having new PCBs manufactured.

 

Then while working on the enclosure and having to change the dimensions of the cartridge opening on that too, I measured a SEGA cartridge and discovered that they are larger than EA's. Ugh.

 

So another round of re-layout needed to be done and yet another revisions of the PCB..

 

This one should allow all cartridges to inserted.

[+selgus]

Here are the 3 early revisions of the board, from the wrong cartridge opening size, the EA SPORTS cartridge size, then the standard SEGA cartridge size.. on the right are the final boards, with a few fixes found during testing..

 

[+selgus]

Been busy with life, but started assembling one of the boards.. just need to solder all the harvested ICs from the standard SEGA Genesis to complete the motherboard..