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Arduino-PowerOutageDetector

Simple Arduino project to detect power outages. Following the KISS principle, the Arduino is limited to:

  • Detect changes on power supply status
  • Notify status using Serial
  • Turn ON/OFF two ON/OFF status LEDs

Schematic

Requirements

  • Arduino, any basic model is enough, but Serial is required (internal Serial<->USB converter recommended). Built on Arduino Nano compatible board with ATMega168P MCU.
  • PC817C Optocoupler.
  • 5V AC-DC adapter.
  • A device to read the Serial output of the Arduino and perform the required actions on power ON or OFF (e.g. send a message to a MQTT topic, turn ON/OFF a computer...).
  • (optional) 1x or 2x LED, 1 switch

How does it work?

The Arduino should be connected through USB to a computer or low power device (e.g. a router, a RPi) that can read the Serial output from the Arduino. This computer/device is supposed to be connected to a UPS or battery, so when there is a power outage, the Arduino and device can know that it happened and do whatever is supposed to do.

Outside of the UPS, a 5V AC-DC adapter feeds the Optocoupler (so the Arduino -UPS powered- circuit is isolated from the output circuit).

When there is a power outage (a.k.a. the 5V AC-DC adapter is OFF) the optocoupler turns off, so the Control Pin of the Arduino detects this change on the power status.

Pinout & Components

  • Control Pin (2): optocoupler 5V output (HIGH when power is ON, LOW when power is OFF)
  • ON LED (3): optional LED, turns ON when the power is ON, turns OFF when the power is OFF
  • OFF LED (4): optional LED, turns ON when the power is OFF, turns OFF when the power is ON
  • Maintenance Mode Switch: optional switch that can be activated to disable the power outage detection when the 5V adapter will be disconnected temporary due to some maintenance.
  • Resistor values can be changed, but keep in mind maximum current ratings. Optocoupler is limited to 50mA on both input and output.

Versions

  • PowerOutageDetector_Simple: Simple/classic Arduino version with a constantly running loop
  • PowerOutageDetector_Interrupt_Sleep: version that uses LowPower library to turn OFF the Arduino after detecting a change on the power status and sending it through Serial, using External Pin Interrupts. The Arduino will wake up after detecting another change.

Monitor script

Shell script that listen to a single Serial port and send each new received line through MQTT. Designed to be used on OpenWRT without Bash available.

Due to a bug on PowerOutageDetector_Interrupt_Sleep version, sometimes a certain status can be sent over Serial multiple times. To keep the Arduino sketch as simple as possible, a verification for repeated lines is performed on this script, instead on the microcontroller.