Arduino-Based Power Failure Alert System

arduinoPowerFailBox

When the power went out at his parents’ shop and ruined the contents of their fridge, [Lauters Mehdi] got to work building a custom power failure alert system to prevent future disasters. Although some commercial products address this problem, [Lauters] decided that he could build his own for the same cost while integrating a specific alert feature: one that fires off an SMS to predefined contacts upon mains power failure.

The first step was to enable communication between an Arduino Micro and a Nokia cell phone. His Nokia 3310 uses FBus protocol, but [Lauters] couldn’t find an Arduino library to make the job easier. Instead, he prototyped basic communication by running an Arduino Uno as a simple serial repeater to issue commands from the computer directly to the phone, and eventually worked out how to send an SMS from the ‘duino. [Lauters] then took the phone apart and tapped into the power button to control on/off states. He also disconnected the phone’s battery and plugged it into an attached PCB. The system operates off mains power but swaps to a 1000mAH 9V backup battery during a power outage, logging the time and sending out the SMS alerts. A second message informs the contacts when power has been restored.

Head over to [Lauters's] project blog for schematics and photos, then see his GitHub for the source code. If you want to see other SMS hacking projects, check out the similar build that keeps a remote-location cabin warm, or the portable power strip activated by SMS.

Discussing Pulse-Width Modulation

[Michael Kleinigger] posted a lengthy discussion on Pulse-Width Modulation that goes beyond the traditional beginner tutorial. He starts a bit of background info on PWM and a tip about using a camera to judge frequency and duty cycle of LEDs. From there it’s down the rabbit hole with some testing of power-loss versus frequency.

When you change from frequencies of 50 Hz to 1 MHz how does the parasitic power loss from switching affect the overall efficiency of the circuit? It turns out there’s a rather large amount of loss at the highest level, around 1.5 mW. The greatest balance of low power loss and elimination of flicker seems to be right in the 300-500 Hz range.

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