The schematic shows, in fact, the gameboy-end side of the cable.

Since it's my little monster, I may scream: IT LIIIIVES !!!! GWAHAHA!

Thank you very much, shizcake!

if i remember correctly, the piece of link cable that is shown represents a cable that is cut up and soldered to the arduino.
When you check the link cable with a multimeter, you'll find out that there are two leads that are crossed over in the cable, so the pinout is different when you use a link port and plug a cable into it.
I think it's the bottom left and the top middle ones, but i'm not sure. Try to swap these two.
i can check if you need.

My circuit is a little bit like Frankenstein's monster because I wanted to test everything before thinking about how to put everything inside a box, so I hope the annotations are helpful. There are no short circuits or loose connections. I tried to change the sides of the pins of the MIDI ports - I have no clue which way they have to go (the schematic is not very good at describing the MIDI pins).

Overview:

I guess you can't see very much here, but I uploaded it just for a overview of that beauty.

GB cable:

This is a part of the four-player-link-adapter thing. It was too hard to desolder it so I destroyed the PCB. The pins on the top layer are those of the flat side, the pins on the bottom are those of the shaped side of the plug.

Midi-In:

Midi-Out:

The 2K Ohm resistor that goes to the GND pin of the MIDI-Out is the pulldown resistor of the button. The 220 Ohm resistor goes to +5V.

Maybe post a picture of your circuit, I know the arduinoboy page has a mistake/is confusing about the pinout on the midi outand has some cables swapped, which led to problems with the scienceguy run... not sure if that was ever fixed.

I wanted to try out the MIDI-out function of LSDJ 4.7.3 (arduinoboy version) and built an Arduinoboy (using an Arduino Uno SMD Edition) so that I can hook it up to a SammichSID and a Korg Electribe.
The probem is: I don't get any MIDI signals.
I have checked the pinouts of the MIDI socket and the GB cable and LSDJ is playing some notes with Q commands.
Do you have an idea what I could possibly have done wrong? Or some common mistakes that I may have overseen?
As I don't need the MIDI-in I left that whole part away from the build (i.e. pins RX and 4 are not used) - could that be a problem?

Thank you very much.
Fabian

//edit:
I added the MIDI-in so that I can look if I can connect via MAX. The Midi-in seems to work (as the status LED is flashing when I try to connect). But for whatever reason there is still nothing coming from the Midi-out