What's new
By:

Supergun DB15 controller to Megadrive adapter (not MD>Neo but Neo>MD)?

GeorgeSpinner said:
What are we looking at here? You are making your own converter? I feel like a post before this one is missing.
Click to expand...

I'm building some off a PCB design I found online. Can't find any pre-built anywhere, so going to see if I can use my hot air station without major injury or property damage.

This PCB, with the listed surface mount 10kOhm resistors, 100nF capacitor and a 74157 compatible multiplexor. This is designed to allow the use of Neo Geo or similar DB15 controllers on a MegaDrive/Genesis. No idea how well this design works, not been able to find a lot of information on it. It does have a MS/MD mode change jumper, so fingers crossed it supports six buttons (thinking it does not based on the design, we can see here that pins 2, 3 & 4 from the DB15 side are not connected). But I'll find out!
51469211d617e2c378b4df1e608b4e7b.png

536c5d21cc07b71b45d21f86516182dc.png
 
Last edited:
Definitely the ones I'm building will be three button only, the 74157 simply can not handle the input/output for six. Pity. But looking into it more, the six button controllers are dependent on a custom SOP-24 chip, the SEGA 315-5638-01. I do not know of any clone chips out there, so would have to find old stock or salvage them from a six button controller. May be able to reverse engineer it and "emulate" via a micro controller (Arduino or similar) but not sure.

1582677611.jpeg
 
I think I have two of those chips from 6 button controllers somewhere. I’m away this week, and living in NZ means shipping times could be long, but if you want them you’re welcome to them.
 
OK.... so built the first one, and it's not fully functional. Not registering 'A' button input. Full disclosure, I put on the 74157 backwards and then had to remove and reapply. So it's much less clean than I would like. Going to try to diagnose the failure, but I may need to make another one and see if it behaves any different.

IMG_0943.jpg
 
Looks great!

BTW- I invested in some gender changers to test the NEOGEO2GEN functionality of the PCBs I mentioned and, as you said, they didn't work.

I just wanted to confirm that they worked or didn't because I wouldn't want anyone that comes across this thread to waste money.
 
So, checking the expected output.
genesis_joystick.gif

In my last test it seemed that everything worked except Button A. Since it shares a bit with Button B, which worked and shares a state with other buttons that work (low 0v) I'm not sure. Will put it under an inspection microscope later I can find a short.

So, no short. But clearly pins not making proper contact. This is a side effect of trying to flip and reattach the chip.
Quick Camera Image 2021-08-14 at 4.00.02 PM.png

Quick Camera Image 2021-08-14 at 4.02.55 PM.png
 
Reflowed the solder under the lifted pins and it looks like it's working. It has a bit of a flaw, in that pressing C Button combined with any other does weird things. I think this is because C puts one of the 74157 pins to a high state, which then causes issues with other button combos. But it's not too bad. Was able to quickly fire up Strider on my MegaDrive model 2 on my Vewlix.

So in conclusion, far from perfect. But this is a workable solution for most MegaDrive/Genesis games. Six buttons would be nice, and I may look into that at a later date. But for now I think I'll make a couple more of these (not today, this took a lot of effort) and call this a wrap. Not sure off hand how much they cost me to make, but if anyone wants one let me know and I'll put one aside when I get around to making more (which honestly may not be any time soon, working next weekend etc).

Edit: Looking into it more, the 'C button issue' may not be a real problem. If I use a different testing cart it doesn't show anything out of the expected inputs. Need to find a game that uses three buttons to tell for sure.

IMG_0944.jpg

IMG_0946.jpg
 
Last edited:
Damn, sucks it doesn't work out perfectly. Thanks for doing the science on this one!

Hopefully someone out there makes a decent MD2NEO adapter down the line...
 
djsheep said:
Damn, sucks it doesn't work out perfectly. Thanks for doing the science on this one!

Hopefully someone out there makes a decent MD2NEO adapter down the line...
Click to expand...
Well as I said in my edit, it may be that the testing software/rom I'm using is having issues more than the adapter is. I tried a different rom and it seemed to respond exactly as expected with no issues. But anytime you multiplex you're going to get weird results. If you looks at the DIN9 pinout picture above, both button A and B are on the same pin with both a high and a low voltage. So it's kind of up to the software to figure out what happens when you press both. The testing tool I posted a screen shot of before is intended for six button, which has an even more complex schema, so it may just not work reliably for three button.

I'll play around with it some. But in my brief testing of a hand full of games it's working well as a three button adapter.
 
Tested for awhile using different games, including SF2 (which only gives access to punches since it's limited to three button). Everything works well, no issues.

Looking at building a proper six button adapter, I see a couple options out there.
A) Try to build my own. This is problematic as the information I'm seeing about the Sega 315-5638-01 is sparse. For example, in the diagram I posted earlier I can see the -||- symbols that indicate a VCC source. But not the polarity or the voltage.
B) What I've seen others do, is take a dremel to a six button controller board and cut out the relevant parts.

What may do is a middle ground. Test an actual controller to see what the voltage etc is and then desolder the chip to use in my own circuit. I'd hate to hack up a good controller for this, so will have to keep my eyes out for a beaten up one.
 
So got ahold of a genuine Sega 6 button (all the ones I had were clones like Hyperkin which use an epoxy glob-top chip). Looks like a really simple circuit. They really streamlined things with these custom SEGA 315-5638-01 chips. Plan is to lift it out and put it on the pictured breakout board so I can prototype a converter on a breadboard. Chip matches the SOP24 1.27mm standard. Frankly, the circuit is so simple I may be able to just wire it onto the breakout board. It's just a couple resistors and capacitors.
IMG_0953.jpg


1582677611-jpeg.jpg
 
You must log in or register to reply here.
Back
Top