Archive of Wii Rock Band 1 Guitar and Wii/PS3 Rock Band 3 Keyboard to act as RB1 Guitar for use with Rock Band 4 on PS4 (using Arduino Uno).
This project was between 2011 and 2021, there are much better methods available elsewhere since then.
The work of Dean Camera (LUFA 100807) and Darran Hunt (joystick HID firmware) were the base of this project.
More details can be found at: https://jasonharley2o.com/projects/rb/rb4arduino/