I've figured out the setting! After scouring the manual, I found a way to turn the DIN MIDI Out port on and off. I'm not quite sure yet how it works as a USB-MIDI and DIN-MIDI device, but we're making progress.

For those interested, refer to pages 32-34 of the manual:
https://media.americanmusical.com/ItemF … manual.pdf

Thats good news and good luck figuring out the Axiom. There must be a small setting you're missing.

After some more testing, I found that the issue I was having was indeed with my keyboard. After trying another keyboard, I got mGB mode to work. The last thing to test with these is a PS2 Keyboard (whenever I get one). I'll be sure to update when I get that tested out!

I'm trying to use mGB mode, and I think I'm connected all properly.
Axiom (MIDI Out) -> AB (MIDI In) -> mGB (tested on GBA & DMG via CGB 001 and DMG-14 adapter respectively)

I didn't see the link to the code at first but that is the right one, yes.
The mode lights will display the mode and then are used to display activity on each respective channel.
Which Mode are you using? Try sending MIDI data on Just Channel 1 for starters.
This question may seem silly but has to be answered. Is your midi cable connected between Axiom's MIDI OUT and Arduino's MIDI IN?

I'm using this fork of the code, linked on the product page:
https://github.com/catskull/Arduinoboy

And the Axiom 25 is a controller by M-Audio. It has function keys that allow you to choose between "global channels" 1-16, which I assuming are the correct midi channels.

The 'mode' led's on the board do not stay lit (i'm not sure if they are supposed to) and the 'status' led does not go on at all.

Can you link us to the exact code you uploaded to it?
Also, I'm not familiar with your MIDI controller. How d you confirm the channel it is controlling?

I'm also having issues with my Catskull arduinoboy shields but I'm not sure whether or not to tag onto this post or make a new one. I'm using this version of the shield:
https://catskullelectronics.com/product … eq=uniform

I've downloaded the proper PS2 library, and the code goes up fine, but I'm getting no response when I attempt to use an axiom 25 to control the mGB function on the PS2 and non-PS2 versions

Definitely! I'm gonna try all the modes and functions and give an update!

I looked at Catskull's eagle files on github and the opto is indeed backwards. I suspect you originally thought I meant diode, but you soldered that correctly. Let's hope the opto is not damaged, but its likely fine.

Good. Please give us an update with the full status of the project. Are there any more issues?

hmm alright I'll try that. but it has a stripe at one of the ends of it and it matches up with the printed marking on the pcb.
Edit: SOrry I confused the components, I'll try and update!

EDIT2: Thank you!!! That was the issue!
It's beyond me how I managed to mess that up though, cause I was sitting and carefully pairing up the components in the right direction/order before soldering!

Thank you very much for your help!

You can also test midi input with keyboard mode in LSDj (Using channel 16 and keyboard mode from arduinoboy) check the note values from arduinoboy repo.
If that fails I can upload you serial print gb rom that can print what gameboy receives (Unless you have GBDK installed and can build the rom yourself)

Is your optocoupler IC in backwards?

EDIT: Yeah, it looks like it is. The stripe on the IC indicates the side with pin 1. Pull the IC out and rotate it 180 degrees.

Thank you for helping out,
I must admit that I'm quite overwhelmed by it all, especially after my extensive troubleshooting.

Unfortunately it doesn't seem to receive midi notes via the midi in port cause the status led doesn't blink when in mGB mode. Tried sending notes to it with both my Arturia Keystep and my soundcard but I get complete silence from mGB

This problem seems to go down to this commit:
https://github.com/catskull/Arduinoboy/ … d560e23821
I cannot see this commit in official Arduinoboy repo.
Maybe catskull could shed some light in here, is this cherry picked from somewhere else or was it just removed from master?