The 4×4 is a home made midi controller unit. I developed it partly as a way to better understand some micro controller basic and partly cause I wanted to knobs for live performances. Originally there was going to be 64 knobs (one for each pad on the monome 40h) but I quickly found that not only were potentiometers too expensive for my taste that but also the arduino system I was using would be too heavily taxed by that much input.
The “brain” of the system is an arduino which is then linked into a multiplexing unit designed byme with much help from folks on the arduino forums. All input is converted into midi through a small max/msp patch I wrote based on Arduino2Max. My wife found the little brief case that I built it into.