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.

When the Arduino code sees the button getting pressed, it brings the corresponding LED pin high and starts a fade out timer using the SoftPWM library by [Brett Hagman].

I made this Arduino 8 bit binary led counter as a solution for one member from Arduino forum. He asked if somebody can make a project that displays a decimal number in 8 bit binary format using 8 leds ...