"Old" PS/2 -version of X-arcade.
D9-connector -> Arduino 5 -> 3 (clk) 6 -> 4 (data) 1 -> Vcc (5V) 2 -> Vcc (PS/2-mode) 9 -> Vcc (5V) Shield -> GND
Library: PS2KeyRaw
Arduino Pro Micro (select Arduino Leonardo from Arduino IDE).
PS/2 keyboard not needed.