Looks awesome....trying to figure out the wiring...the tablet usb is running to a power controller then to the battery and then to the usb sound card - the usb sound output is going to the gamevice original headphone port? How did you wire the buttons???
The tablet usb is a USB-C OTG connector, which is connected directly to an unpowered usb hub. The usb hub is on the right side of the controller together with the sound card and external usb port. The sound card is wired to the original 3.5mm port on the gamevice controller.
On the left side, most of the endpoints can be found of the buttons, so I went and put a teensy 3.2 (running on arduino) in remaining space on the left side of the controller. The teensyduino is in Joystick HID mode, so I managed to make it a full game controller, which is recognized by windows as a generic game controller.
The only remaining problem was connecting the usb hub from the right side over to the left side. There was a flat cable running through the rubber, but all the lines were already occupied by the buttons. I finally decided to lead some wires trough the very tight space where the flat cable is.
Then the last challenge was recognizing the buttons on the teensy, because most of them appeared to be pressure sensitive analog buttons. I had to use all the analog ports on my teensy to get all the buttons to work. I had a few code wise problems, because one of the buttons' analog reading wasn't accurate, but luckily solved it on the software side.
Fun fact: Getting the wires trough the tight rubber space was actually the hardest problem to solve, because I didn't want to damage it. I solved it by taping a fish wire to a metal pin, stuck the pin through the tight space. Then I untaped it, knotted the fish wire to 4 tiny wires and pulled it back.