Quantity   Component name
1 × Arduino For interfacing with USB
1 × TLP521-4 optocoupler In order to isolate the arduino from the autoguide port
2 × RJ12 socket 1 if your mount already has an ST4 port
1 × RJ12 straight cable To connect the adapter and the mount
1 × A case for the adapter Excepted if you prefer to see the bare electronics :-)
4 × 100 ohm resistor To protect internal diodes of the optocoupler