How long can you keep an Arduino circuit running on three AA batteries? With careful design, [educ8s] built a temperature sensor that lasts well over a year on a single charge of three 2250 mAH rechargeable cells (or, at least, should last that long).

Like most long-life designs, this temperature sensor spends most of its time sleeping. The design uses a DS18B20 temperature sensor and a Nokia 5110 LCD display. It also uses a photoresistor to shut off the LCD display in the dark for further power savings.

During sleep, the device only draws 260 microamps with the display on and 70 microamps with the display off. Every two minutes, the processor wakes up and reads the temperature, drawing about 12 milliamps for a very short time.

Along with the code, [educ8s] has a spreadsheet that computes the battery life based on the different measured parameters and the battery vendor’s claimed self discharge rate.

Of course, with a bigger battery pack, you could get even more service from a charge. If you need a refresher on battery selection, we covered that not long ago. Or you can check out a ridiculously complete battery comparison site if you want to improve your battery selection.

The art of brewing beer is as old as civilization itself. Many people enjoy brewing their own beer at home. Numerous steps must be taken before you can take a swig, but fermentation is one of the most critical. [Martin Kennedy] took up the hobby with his friends, and wanted a convenient way to monitor the fermentation temperature remotely. He started working on the BrewMonitor, a cloud-based homebrewing controller powered by an Arduino clone.

His goal was to create something cheap, convenient, and easy to set up. Traditional fermentation monitoring equipment is very expensive. The typical open-source alternative will set you back 80 euros (roughly $101), using the Arduino-sensor with a Raspberry Pi gateway via the BrewPi webserver. [Martin] did not want to go through the hassle of viewing BrewPi remotely, since it requires a home network and all of the configuration that would entail. Instead, he coupled an Arduino clone with a DS18B20 temperature sensor while using an ESP8266 module for wireless communication, all for less than 18 euros ($23). This connects to a simple webpage based on Scotch.io with a PHP backend (Laravel with RESTful API), a MySQL database, and an AngularJS frontend to display the graph. Once the sensor is placed into the fermenter bucket’s thermowell, the temperature is transmitted once a minute to the REST API. You can see the temperature over time (in Celsius). The design files are available on GitHub.

[Martin] would like to expand the functionality of BrewMonitor, such as adding the ability to adjust the temperature remotely by controlling a heater or fridge, and lowering its cost by single boarding it. Since the information is stored on the cloud, upgrading the system is much easier than using a separate gateway device. He doesn’t rule out crowdfunding campaigns for the future. We would like to see this developed further, since different yeast species and beer styles require very stringent conditions, especially during the weeks-long fermentation process; a 5-degree Celsius difference can ruin an entire brew! Cloud-based temperature adjustment seems like the next big goal for BrewMonitor. DIY brewers salute you, [Martin]!

[via Dangerous Prototypes]