Neo Geo compatibility for my portable arcade test rig

I figured I’d go over some mods done to make my arcade test rig Neo Geo compatible. The first thing to do was make a JAMMA fingerboard adapter. I have a 2-slot motherboard so it’s not the vanilla JAMMA pinout, but it’s pretty close. Take a look:

The main changes I made are these:

moved test button to the right location

moved service button to the right location

tied right and left speaker together through 1uF caps and connected them to speaker positive

tied case ground to speaker negative

wired select up and down to player 1 buttons E and F

wired coin 3 and 4 to player 2 buttons E and F

One quirk I found is that I couldn’t make the mono audio work well, perhaps it’s my amplifier behind a matching transformer, perhaps my board is messed up in that respect, that’s why I had to mix the stereo audio to get it to work. The last time I talked about this project I had also not used the buttons D, E, and F for either player. I have installed those wires now and built an adapter to make those work. I decided to keep the theme running with the genesis controllers, but now I’m using unmodified ones and an arduino to make them work.

I have an arduino pro mini (running off the same 5v power supply as the rest of the system) connected to two MCP23018 I/O expanders. Plenty of people use the MCP23017 for things, the 23018 just has open-drain outputs. That means that when the outputs are live they ground the pins instead of pulling them high, and when deactivated they float rather than pulling them low. This simulates button presses for a system that all the buttons have a common ground pin like the Neo Geo. The code just glues two libraries together, one for reading genesis controllers found here and one for talking to I/O expanders found here. I may re-shuffle the button positions to more closely simulate the button placement on a Neo Geo, but this is more meant as a general purpose expansion to allow for 6-button JAMMA games to be used in this tester, not just the Neo Geo.

Another new feature (along with my 3d-printed fan grills) is video out. Having the ability to throw this up on a bigger monitor is nice, so I added a tap for video out. I don’t know how having both monitors connected will affect the impedance of the video line, but it probably won’t be too bad.

One Response to “Neo Geo compatibility for my portable arcade test rig”

  1. Genesis controller to arcade game PCB | Evan's Techie-Blog Says:

    […] previously I added 6 button controller support to the arcade test rig with an arduino and some i2c IO […]

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