Midi Key in... The parts are: U1: A PIC16F84, the famous single-chip controller by Microchip, which is the core of this device; U2: A 74LS138, which is a 3-to-8 decoder, used to scan the keyboard dynamically; Q1, C2, C3: A 4 MHz quartz resonator, and 2 capacitors needed for the PIC's internal clock. C2/C3 : 27p R1, R2: 2 resistors to pull up specific IC pins (on U1 and U2) to Vcc (which is +5v supplied from pin 1 of the soundcard's DB-15 gameport); R1: 3300ohm R2: 1800ohm R3: 270 ohm A protective resistor; D1...: Generic Si diodes to prevent short-circuiting of 74LS138 outputs, and false keycrossing events, by simultaneously pressing a group of keys upon the piano keyboard;