Hi
I did the automatic shutdown in a different, more universal way.
If got myself a smarthome power switch, a 'FRITZ!DECT 200'.
This switch cam be turned on or off by my AVM FritzBox. It can also be configured to turn off the power when the the connected device uses little or no power for a certain time.
I use it the following way: When about ready to print, I use my computer to turn on the power to my printer and start preheating the bed and extruder.
When the printing is done and the drawn power drops below 50W for more than 30min the power to the printer will automatically be turned off. The power and the time before shutdown can be adjusted.