My Purchases (Don't have to match):
Nano V3: https://www.amazon.com/gp/product/B00SGMEH7G/ref=ppx_yo_dt_b_asin_title_o00__o00_s00?ie=UTF8&psc=1
Bi-Directional Logic Level Converter: https://www.amazon.com/gp/product/B00NAY3J7O/ref=ppx_yo_dt_b_asin_title_o00__o00_s01?ie=UTF8&psc=1
GCC Extender: https://www.amazon.com/gp/product/B00E1LX3CQ/ref=ppx_yo_dt_b_asin_title_o00__o00_s01?ie=UTF8&psc=1
Junction Boxes (Case): https://www.amazon.com/gp/product/B07HMPWNLM/ref=ppx_yo_dt_b_asin_title_o00__o00_s00?ie=UTF8&psc=1
Follow the Making the Module Reference under 'Refrences'. Use the wire diagram below instead of the one in the guide. This is a modified version of the diagram within the guide.
Adapter Wiring Diagram (The logic-level converter diagram isn't correct in the bottom-left, the one above it is)
Don't assume that your GCC extension wires match OEM! Guide is in the doc. I personally recommend the potentiometer method without plugging into the console.
Wire color diagram for extension cable - will likely vary
Inside of the finished product
Finished product
Just open the .ino file in the Arduino IDE and upload via serial. This file will also work for an in-controller design. Instructions for use are at the top of the .ino file. Modifications to original inputs are also listed throughout the file.
The arduino should work natively with a wii or gamecube. In order to get it working on pc with a Mayflash adapter you will likely need to download the firmware below and have the device in Wii U mode. I recommend using native input for dolphin (Guide: https://dolphin-emu.org/docs/guides/how-use-official-gc-controller-adapter-wii-u/#Using_Zadig). The arduino must be powered through either the grey rumble cord, an alternative 5V power source, or the serial bus (micro USB). www.mayflash.com/File.asp?Id=106
At the bottom of the file you will find a time delay debugger. You can un-comment this if you have a different processor then modify standardTime at the top of the file until your character/cursor no longer runs right on its own in game. If your character/cursor does not run right, decrease the value. Otherwise, increase the value. The goal is usually to have standardTime be as low as possible while still being an integer.
None of these links below are mine. These are the bases that I used in order to build the adapter.
Code Base (v3): https://github.com/OtaK/GCCArduino
Making the Module: https://docs.google.com/document/d/1KZrORDtJBuovVAHRZjteRitBKkwibZOc7VW0PdGedEk/edit
Mayflash Firmware: NicoHood/Nintendo#11