This is my Wii U Gamepad.
I build with many breaks 9 month and finish last two days and works fine

Part list
-Raspberry Pi 3
-Wii U pad
-China 7 Inch Screen / 1024x600
-Adafruit FPC Stick - 20 Pin 0.5mm/1.0mm Pitch Adapter
-FPC FFC 0.5mm Pitch 14 Pin Flip Type Ribbon Flat Connector
-Teensy 2.0
-Mini PAM8403 two-channel Double Track Power Amplifier Module Volume Adjustment
-5 Pin 3.5mm Female Audio Stereo Jack Socket PCB Panel Mount
-2x DS Speaker
-RAVPower 13000mAh 4,5A Powerbank
-Many Cabels
Color
Front: is Tamyia TS46 Desert Color
Back: Matt Black
I can also use for PC / Display Gamepad

Many thanks goes to.....
banjokazooie’s for the Teensy Code
and
SpaceAgeWizard from another Forum for the technical overview
best regards from Germany

(sorry for my bad english)