The Arduino Yún – designed in collaboration with Dog Hunter – is based on Atmel’s popular ATMega32u4 microcontroller (MCU) and also features the Atheros AR9331, an SoC running Linino, a customized version of OpenWRT. The Yún is somewhat unique in the Arduino lineup, as it boasts a lightweight Linux distribution to complement the traditional microcontroller (MCU) interface.
Although the Atmel-powered Yún hit the streets just a few short months ago, the board has already been used in a wide variety of Maker projects that we’ve recently covered on Bits & Pieces, including an electricity monitor, mesh extender platform, Foursquare soap bubble machine and the Gmail (alert) lamp. And today we’ll be taking a closer look at how George Koulouris used the Atmel-powered Yún to regulate his water heater.
“I have two small problems in my house. An ever-increasing electricity consumption bill and a girlfriend [who] likes to take hot baths at unpredictable times during the day,” Koulouris wrote in a recent blog post re-published on the official Arduino site. “Until recently, we left our water heater switched on, 24/7. But then we took a look at our electricity counter readings. Needless to say, we switched it off immediately! An old water heater can indeed make the electricity counter wheel spin fast, very fast.”
As such, says Koulouris, he started switching it on and off whenever the two needed to take a bath. However, the duo weren’t always at home and the water took almost an hour to heat. Enter the SmartBoiler, a device housed in a small box and placed on top of the main electricity board.
“A mechanical arm extends out of the box. Its bottom end is clipped to the heater’s switch whereas its top end is attached to a motor in the SmartBoiler,” Koulouris explained. “The box contains a motor and an Arduino Yún. The latter checks, at regular time intervals, a .txt file on a web-server to see whether me (or my girlfriend!) have turned on the heater. If yes, it launches the motor and the switch is turned on.”
Although Koulouris originally created the SmartBoiler to regulate his water heater, he does note that the project can be used as a basis to control any mechanical switch.
“Simply dimension the box correctly and you can control everything via the Internet. Your lights, your main electricity switch… The possibilities are limitless!”
Interested in learning more? You can download the laser cutter files here, the code on Github and the dimensions of the mechanical parts on Thingiverse, while the user interface (UI) can be viewed here.
Atmel | Bits & Pieces 
