So mh, build this for myself, thought i may as well share it here (there are probably already tons of mods like these...)
It's basically the PCB of a wiimote (with a cut off camera/dpad section) that is directly wired to the traces of the buttons on the NES controller.
In addition I added a thin LiPo battery at the back (stuck on with double sided tape, didn't fit in the case anymore...) and microusb charging circuit + battery protection.
Here is a short video of it in action (using an NES emulator on computer):
It's basically the PCB of a wiimote (with a cut off camera/dpad section) that is directly wired to the traces of the buttons on the NES controller.
In addition I added a thin LiPo battery at the back (stuck on with double sided tape, didn't fit in the case anymore...) and microusb charging circuit + battery protection.
Here is a short video of it in action (using an NES emulator on computer):
