two 12 button independent arduino-based sample players. samples are stored on an sd card and a loudspeaker is going to be put inside it. each button has a 12v lamp inside it, an MCP23016 extends the arduino’s I/O ports and 12 transistors turn the lamps on and off. all buttons are connected through a resistor ladder so that they only use up one pin. it’s monophonic, but several machines allows for polyphony.