I was in need of a lot of buttons, and I found an YL-4 4x5 module. Unfortunatly, I wasn't able to find any information about it. The most i could find was this video here I was wondering if anybody ever worked with it and could help me out.
I believe this is a 4x4 matrix, with lines connected to pins L1 - L4, and rows connected to pins R1 - R4. You can use the Keypad library.
4 additional (red) keys, connected to pins S1 - S4 (not sure if they are pulled HIGH, or LOW, with these resistors R9 - R12)
8 LEDs connected to pins D1 - D8