Yep, SNES controller would work, just wouldn’t clock out all of the extra buttons, without tweaking the code some more.
Tried taking a closer look at that photo, few things:
- doesn’t look like 5V is connected to the VCC pin of the Pro Micro (guessing that you have USB connected for power when testing?)
- can’t tell if the two orange leads going into Pro Micro pins 4 & 5 are going to the same pin?
- can’t tell if pull-up resistors on shift register pins 1 & 4 are plugged into pin 1 & 4?
- not sure it will change anything, but try grounding shift register pin 11 (schematics show it grounded):