Quantity   Component name
1 × Teensy 3.0 Really any Arduino board can be used as long as it has a UART and free pins to talk PS/2
1 × RS232 Level Shifter The DEC mouse port runs at RS232 voltages and isn't friendly with direct connection to most MCUs.
1 × mini-din 6 PS/2 jack Find one cheap or snag one off an old extender or broken motherboard.
1 × mini-din 7 STANDARD plug Be sure to get the correct one, there is also non-standard plug that shares pin and keyway positions with mini-din 4 - you DON'T want that kind.