Pi Super-UPS

Hardware

TODO: Explain design goals

TODO: Explain features

The KiCad design files are in the hardware subdirectory. They are still untested and no suitability for any purpose is claimed.

Firmware

The hardware needs some ATTiny13a code to correctly control the wakeup pin (GPIO3) state. This is still to be written!

Service software

Introduction

pi-super-ups is a simple power monitor for Raspberry Pi. It monitors a defined GPIO pin on the Raspberry Pi. If the pin goes high for ten seconds, a shutdown is triggered. Using GPIO 3 is highly recommended because that allows for automatic restarting when power is restored (pulling GPIO 3 low powers on the device if it is powered off).

The main use case for the script is to have the board powered via a couple of super-capacitors. In the case power for the board is disconnected, the supercaps are able to supply sufficient power that the device is able to shut itself down in a controlled fashion.

A sample circuit fulfilling the purpose is presented in the circuit subdirectory.

Installation

The monitor script can be installed by issueing the following command in the src subdirectory:

sudo python3 setup.py install

At this point, you should already be able to run the script. However, since calling poweroff requires elevated privileges, it is done using sudo. Give your preferred user permissions to call poweroff without a password by running sudo visudo and adding the following line:

pi ALL = NOPASSWD: /sbin/poweroff

Finally, to run the script automatically as a service, copy sk_power_monitor.service to /etc/systemd/system.

Usage

To configure the monitor behavior, directly edit the script file.