With all of the cool features on the Raspberry Pi, it is somewhat notable that it lacks a power button. In a simple setup, the only way to cut power to the tiny computer is to physically remove the power cord. [Dalton63841] found that this was below his wifeís tolerance level for electronics, and built a simple remote control for his Raspberry Pi.
[Dalton63841] started this project by trying to use the UART TX pin, but this turned out to be a dead-end. 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 isnít on any more and disconnect the power. The remote control is used to turn the Pi on. The Arduino reads the IR code from a remote and simply powers up the Pi. This is a very simple and elegant solution that requires absolutely no software to be installed on the Raspberry Pi.
We know that this isnít the most technically complex project weíve ever featured, but it is a good beginner project for anyone just getting started with a Pi, Arduino, or using IR. Plus, this could be the perfect thing to pair up with abattery-backup Raspberry Pi shutdown device that allows it to power itself down in a controlled way when a power outage is sensed.

http://hackaday.com/2015/07/18/ardui...-raspberry-pi/