When using cc commands does anything on mGB change? ...is your volume turned up...?
Make sure you check the link cable lines to the GB

Depending on the mode of the arduinoboy. if its in any mode other than midi out from lsdj or mGB mode, they should blink to midi sync. in mGB mode each led represents a midi channel (1-4)

I do have the leds connected, They do blink when i sent data..
My guess is they should be blinking if they recieve data as well?

Anyway, they don't

Oh you might also want to check your cable wiring on the gameboy port, since I'm guessing you dont have leds to indicate midi is actually working. You could also use the arduino serial monitor to see if its getting data (it would print garbage of course)

Yeah, i'm gonna try getting another 6n138. And see if I can use it with something else, like a drum machine, if I find one

Midi-out was the main reason I built it, but it still would be nice if in worked

Yeah I don't know. if you tried flipping the wires on the midi jack, tried flipping / disabling the diode, then its either the code that is running, the midi cable or host midi device, or the 6n138.

I've used plenty of the pro minis for various projects so I know its not that, if it is indeed the 16mhz/5v version.

Where is the dot on the 6N138? Do you have it upside down? That looks so awesome by the way

neat looking GB indeed!

Ah no, I had to remove the speakers... pretty much everything inside... to fit in the arduino. So it's just a shell at the moment.

Besides, they are just a bit louder than the normal speaker, (and stereo) but the sound is not that great actually...

Are those speakers loud enough for basic monitoring onstage?

Thanks, I was quite pleased with that solution myself

This is how the total set looks like, I like the colours, blue and neon green go together nicely
I added an extra 1/8 inch connector on the bottom for headphones, and the arduino is connected to the gameboy via an USB connector that i wired to the external connectors.
I just made a gap where the pro-sound goes in

That is a mighty clever thing to build an arduinoboy into!

I tried taking a picture, but i only have a phone cam at the moment, as it is blurry as hell, i added some pointers

with added lines:

Hope that helps in any way

Send a picture of what you're done so we can take a look at it

It's  the 5volt version.