WiiTar Hero mod - Transform your old Wii guitar into a USB wired universal guitar

Transform your old Wii guitar into a USB wired universal guitar using a Pico Pi board (in this case a Xiao RP2040 smaller board, with USB C) and Santroller (https://santroller.tangentmc.net/)
I am using mine on these platforms without any issue :

• old 2013 MacBook Air / MacOSX with Clone Hero
• an android tablet with Clone Hero
• PS5 with RockBand 4
  (and Fortnite Festival with a small tweak, see bellow)

Usually modders using Santroller configurator are using a Pico Pi board; but it lacks USB-C (it's a micro USB board); that's the reason why I searched for a board with USB-C which was in fact smaller than the Pico Pi (the Xiao RP2040 has plenty enough pins for my need).

I used https://makerworld.com/en/models/26512 model as an inspiration for my mine. It was originally designed for Pico Pi and comes only with the nunchuck slot. In my case I needed a slot for the accelerometer too.

Software and wiring guide :
https://santroller.tangentmc.net/wiring_guides/wii.html

BOM :

• XIAO RP2040 : https://wiki.seeedstudio.com/XIAO-RP2040/ , but I guess any RP2040 Zero will do : https://www.waveshare.com/wiki/RP2040-Zero .
• Adafruit Wii nunchuck breakout board : https://www.adafruit.com/product/4836 (with QWIIC / Stemma QT connectors)
• (optional, used only for TILT feature) Adafruit LIS3DH accelerometer : https://www.adafruit.com/product/2809 (with QWIIC / Stemma QT connectors)
• some QWIIC / Stemma QT cables/connectors depending of your ability/willing to solder or not
• and/or some dupont jumper wire cables
• ... and obviously a Wii guitar : I used a Guitar Hero World Tour sunburst one (with curved back cover -- which was missing -- and used https://www.thingiverse.com/thing:5442324 cover as a replacement)
• a USB-C (to USB or USB-C) 3m cable (or maybe a 2m might be sufficient)

Of course, QWIIC/Stemma QT connectors are not mandatory; you could easily replace the accelerometer with a ADXL-345 or a LIS3DH part from AliExpress (not Adafruit) but it will need some changes in the box. Same thing for the Wii nunchuck adapter; some (cheaper) parts exist on AliExpress; but the box is not designed for them.
As a replacement for the XIAO RP2040 board I think you could even use an Adafruit QT Py board : https://www.adafruit.com/product/4900 that comes with QT Stemma connectors too. With that board you will need ZERO soldering. Once again : the box might need some changes too in that case.

The box has a little groove just above the cover in order to have two cables going out of it; I was using it as a simple switch to replace the use of a fret or a button to activate keyboard mode (which is needed for Fortnite Festival) as on PS5 it doesn't seem to work with the frets/buttons. But it has been fixed in the latest Santroller release so it is no longer needed. The groove still can be used to ease the lid opening though.