Thanks to Peter Boxler for sending this in via our forums. And not only for sharing the project with us, but for providing the source code and EagleCAD files here on GitHub, as well as providing an extremely thorough PDF manual of sorts, available in both English and German to reach as many users as possible! It’s great to see how a simple one-time need grew into a prototype circuit on breadboard, and eventually multiple boards were fabricated for custom soft power control of the Pi for various project installations.
Native 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 allows just that: 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. In addition, a variable frequency square wave is available for externally interrupting the Pi.