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BrewPi: Raspberry Pi and Arduino Powered Fermentation Chamber
For the homebrew hardware nerds out there who also homebrew beer: "BrewPi is an open source fermentation controller that runs on an Arduino (for now) and a Raspberry Pi. It can control your beer temperature with 0.1 degree precision, log temperature data in nice graphs and is fully configurable from a web interface."
Source code. The article has lots of photos and screenshots. The project involves rewiring the compressor's electrical connection through a PID controller, and includes both a fancy OLED display on the fridge and support for logging statistics and control over the web. If you've ever had the joy of gradually crash-cooling a lager (not too fast, not too slow), the software includes settings to effect gradual temperatures changes in the fermenting wort. Certainly fancier than a Johnson controller and a probe attached to a fermenter with a strip of insulating tape.
I'd be interested in multiple control points... I've started to do pressurized fermentation once the gravity of the beer of approaches the final gravity. This carbonates the beer without a secondary fermentation, and reduces risk of introducing oxygen and contamination into the beer. If the system could electronically monitor specific gravity then seal the airlock, but blow off any excess over 10psi... would be awesome!
is what technology is for.
You reckon you can do temperature control in an uncontrolled environment with a handful of transistors? Keep in mind the external temperature is uncontrolled. The yeast itself generates heat within the ferment at varying (and often unpredictable) rates.
The simplest approach you can reasonable consider for the level of control they're looking for in their environment would be a PID controller, which if memory serves me correctly will have more than a handful of transistors in it. You're going to need a pretty decent PID to handle temperature profiling, which their solution
They're using cheap, off-the-shelf parts to solve their problem, which in turn allow them to put extra features in there like web control, and it's now much easier for anyone to do the same thing. The parts may not have existed in 1964, but you need to keep in mind The Doors aren't the only good thing to happen since then.
Why does it have to be a Raspberry? Why do you have to control it in C? Is it because people don't teach or know how to do it the old school way anymore? Is the effect somehow less if you DONT have a fancy OLED display?
Why? Because these methods are objectively better than the old way. And I say this as someone reasonably experienced in the old school way.
The controller is far more sophisticated than a simple PID loop, even if you ignore the ability to log the temperature history, store profiles, query the status remotely, etc.
The OLED display isn't necessary, but it's actually a helpful, useful feature to be able to display the status of the system clearly and unambiguously.
And good luck implementing this "the old school way" in the same period of time as someone using these tools could do it.
It doesn't have to be a Raspberry Pi or Arduino with a spiffy display, but there's no glory in doing things the hard way. There's educational value in it, and in knowing the basics, but a system that works doesn't benefit from having been hard to build.
I guess if you consider the problems you would have calibrating an analog version, along with the display interface, the digital stuff has become more practical than the old analog stuff we grew up with. Did you forget all those trimpots we always had to design in because we never knew the exact parameters of our parts?
Those old analog panel meters are now quite expensive. As well as being fragile, and never were much better than 2% accurate. The cheapest 3 1/2 digit display you get today blows them out of the water.
Personally, I enjoyed this article - as I build a lot of heat transfer controllers - and I find it very interesting what others are doing.... Not to say I would do it the same way, but others often find some way around a situation that has stymied me in the past.
I am very interested in when people start controlling compressor speed via variable-speed three-phase drives. Some washing machines already use these pancake-like motors to completely eliminate the transmission, controlling the motor speed and direction directly from a microcontroller so as to seamlessly shift the motor function between agitate and spin. I have been waiting with baited breath for a refrigeration compressor made in that manner so I can optimize the refrigeration process for whatever heat transfer I can get into the evaporator coil and out of the condenser coil. The only control point I now have is either flat all-or-nothing from the compressor and limited control of the thermal expansion valve. With finer control of heat exchanger temperatures, I can control not only air temp but also the humidity.
Articles like this constitute a design snippet to show a usable part of a larger system.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
That sounds a bit fishy. A Raspberry Pi can't keep up with switching a fridge on and off to keep temperature in a range? That beggars belief. I have an Apple II bit-banging a 1-Wire temperature sensor and clock and toggling a relay on and off for the same purpose. If a 1-MHz 6502 can run a fermentation fridge, I'd think a Raspberry Pi would be more than up to the task. I'm pretty sure there's a 1-Wire USB interface available that would let the RPi use the same sensor I'm using, with less overhead.
20 January 2017: the End of an Error.
The Arduino does the temperature control (as that's what microcontrollers are good for) and the Pi is there to add a nice display and web server (as that's what a mini SBC is good for), seems like using the right tools for the right jobs to me. If you don't want a fancy display you could just use the Arduino part and skip the Pi.