Elco Jacobs uses an electronics board called the Arduino (above) and a tiny Raspberry Pi Linux computer to power his personal fermentation machine. The fermentor inside Elco Jacobs's BrewPi fridge. Those wires are connected to sensors that measures the temperature of the brew. The sensors are watertight, and so are the holes in the fermentor. The view on top of the BeerPi, where Jacobs can tap into the refrigerator's compressor and light bulb. "It’s a great fridge to hack, because all circuits are accessible from the top," says Jacobs. Jacobs rerouted the connections to the fridge compressor and light bulb through a pair of "relays" controlled by the Beer Pi Arduino. The compressor is used for cooling, and the light bulb can be used for heating. The two relays, just in front of the Arduino. Jacobs uses a USB hub (left) to power the Raspberry Pi (right) and the Arduino. The Pi controls the Arduino, but also serves up a web interfaces for his contraption. The BeerPi's 4- by 20-character OLED display. One of the 3-pin DIN connectors inside the fridge that connect the Arduino to the beer sensors. And here's the BeerPi's web interface. You can slowly increase or decrease the temperature inside the fridge. You can keep the temperature of the fridge constant. Or you can keep the temperature of the beer constant.

Beer is as old as civilization itself, but beer brewers are still finding new ways of improving the way the stuff is made. Case in point: BrewPi, a fermentation temperature control system powered by the tiny Rapsberry Pi computer that's taking the tech world by storm.

The project is just one example of how open source software and a new breed of ultra-cheap computer hardware make it that much easier for the people to build, well, whatever they want. The Raspberry Pi and other low-cost hardware platforms such as the Arduino microcontroller boards are a means of connecting all sorts of existing devices so that they can readily interact with each other. They let hobbyists and small companies build their own "internet of things."

BrewPi was created by Dutch electrical engineering student and home-brewer Elco Jacobs. Although he plans to sell kits for turning refrigerators into BrewPi systems, he has released the instructions and source code online for free and thinks the code might be useful even for non-brewers.

BrewPi is essentially a beefed-up refrigerator. An Arduino board gathers data from sensors, adjusts temperature controls on the refrigerator, and runs an OLED display. There's also a web-based interface for viewing and controlling temperatures. This runs on a web server loaded onto the RaspberryPi, which also runs Python scripts for communicating with the Arduino.

"To tie all these languages together took a lot of work," Jacobs says. "But it allows you to use the best tool for each job."

He thinks his code would be useful to anyone wanting to build a web interface for controlling an Arduino, or use an Arduino to filter sensor data or control an OLED display without replicating all his hard work.

Jacobs started brewing beer as a university student. "I found out that it cost about 60 euros to start brewing your own beer and thought: 'Well, that's something every guy should at least try once,'" he says. "I quickly found out that temperature is very important for brewing results: It determines the fermentation rate and which flavors are created."

Too much or too little heat could radically alter the taste of a beer. His favorite style of beer – hefeweizen – was particularly sensitive to temperature fluctuations. He started out trying to control temperatures by moving his brew buckets closer to or farther away from his radiator. But he found that without finer-tuned temperature controls he couldn't brew in the summer, and commercial temperature control systems were too expensive for him to afford or required a dedicated PC. He wanted something that he could set up on small, cheap hardware and then monitor from the web.

So Jacobs started building UberFridge, BrewPi's predecessor. The original version used an Arduino with the web server on a home network router running the open source firmware DD-WRT. Although studied C and C++ programming in school, he didn't have any web development experience and turned to StackOverflow and other websites for help.

When he published his plans and source code online the project attracted so much attention that he decided to turn it into a business. He says the router only had 16MB of RAM and wasn't very stable, so he replaced it with the Pi, even though his original design goal was to avoid needing a computer. But at least it's a cheap and small one.

"Nothing beats the Pi in bang for buck," he says. But the Pi still isn't stable enough to replace the Arduino, hence the need for both pieces of hardware. He thinks the next iteration will involve replacing the Arduino with something more powerful but just as cheap.

Jacobs says the whole thing can be built in a weekend. But in the long run, he says, he wants to make it easier by selling complete kits with boards, displays, and sensors — no soldering required. He says the kits will cost about $75, not including the Raspberry Pi and refrigerator (a Raspberry Pi sells for around $35).

He doesn't think open sourcing his plans will hurt business. "I think it's the only way it's viable," he says. He hopes other people will contribute to the project and make it better. "My market research also showed that most people want to use BrewPi because it is open source. Many brewers are engineers and want to be able to modify and add things."

Photos: Elco Jacobs

Update: This story has been updated to clarify the cost of the kits Jacobs plans to sell.