Hi! This is ATOMIC, a 6-pad MIDI drum controller made with Arduino made for music production and fun!
The button allows you to change the notes of the pads which is defined in the codes as modes A (Pattern) and B (Fill mode). The idea behind this is that you first record the basic pattern in you DAW and then you add extra sounds like toms or plates. Two LEDs indicates which mode are you using, and there´s a connection for a hi-hat pedal.