2 Membrane 4x4 matrix keypad
2 Membrane 3x4 matrix keypad
http://www.parallax.com/sites/default/files/downloads/27899-4x4-Matrix-Membrane-Keypad-v1.2.pdf
http://www.vanallesenmeer.nl/4x4-Membrane-matrix-keypad
http://www.kiwi-electronics.nl/prototyping/sensoren/3x4-flexibel-matrix-keypad