“A Raspberry Pi does not have an On/Off switch and there is no easy way to shutdown the Pi while keeping the filesystem intact. This Intelligent Power Switch brings a clever solution to this problem: Power-On the Pi by pressing a pushbutton and also properly power-off the Pi with another press on the same button.The intelligence is provided by a program running in an AVR MCU ATtiny44. This C-program implements a Finite State Machine in the MCU. A small Python script is running in the Pi itself. Just one GPIO-Pin is used for two-way communication between the Pi and the iSwitchPi board. The iSwitchPi board additionally provides a square wave output with variable frequeny that can be used to trigger interrupts on the Pi.”