This electronic analogue of the push–button switcher allows a short press on one of the control buttons S1–S3 to turn on the selected load Rload1-Rload 3, simultaneously disabling other loads. Unlike ...

He decided instead to use an Arduino to monitor the 3.3V power rail on the Pi. When the Pi is shut down in software, the Arduino can sense that the Pi isn’t on any more and disconnect the power.