DIY: Temperature Monitoring and Regulation for HomeBrew

Beer brewing is a fun hobby, whether you wanna just brew something easy from a kit, or take the time to fine-tune your preferred style. With every batch, there are always two things that weigh heavy on a brewer’s mind: risk of contamination or, depending on where you live, extreme temperatures. I live in an area where the temperature often dips below 60° F during the winter, which is too cold for the yeast to thrive. Using a space heater wastes a ton of energy, and I’ll still have to turn it off manually. I decided to tackle this problem.

At the very least, I knew I would need a heating belt, a temperature sensor, and an AC power source that can be activated/deactivated. Generally speaking, heating belts don’t come with any sort of feedback control, and an off-the-shelf regulator costs far more than I’m willing to pay. After a bit of research, I decided that I needed the following:

  1. 1 x Arduino micro-controller
  2. 1 x DS18B20 waterproof temperature sensor
  3. 1 x character LCD
  4. 1 x 10 kΩ trimmer, to adjust the LCD contrast
  5. 2 x 330 Ω, 1/4 W resistor
  6. 1 x 100 Ω, 1W resistor
  7. 1 x IR sensor
  8. 1 x 2N6344G TRIAC
  9. 1 x MOC3023 optoisolator
  10. 1 x 2N2222 NPN
  11. 1 x DIP IC socket
  12. 1 x 250 VAC, 0.5 A, 1.25″ x 0.25″ fuse
  13. 1 x  fuse holder for 1.25″ x 0.25″ fuse
  14. 1 x Brew Belt
  15. some wires

I started off the project by doing a bit of programming on the Arduino to display the temperature read by the sensor on the LCD, and the IR sensor to trigger the LCD backlight (via the Arduino). Once that all worked, I was left with a dilemma: I could use either an electromechanical relay or a solid state relay, like a TRIAC. Since I had no experience in using one, I went with the TRIAC.

For those of you unfamiliar with TRIACs (triode for AC), here’s a little background info: they are 3-pin transistors. When a current is injected into the gate terminal, it allows for current to pass through the other two terminals, just like it would for a BJT. The great thing about TRAICs is that they can conduct both ways, making this a great switch for AC applications. If you open a light dimmer-switch, you’re likely to find a TRIAC inside. For safety’s sake, TRIACs should be driven by optocouplers (a.k.a. optoisolators), which in turn are driven by a controlling signal. TRIAC/isolator combinations are, in my opinion, better than electromechanical relays because they are cheaper and require less space. The optocoupler’s datasheet provides example circuit diagrams for different kinds of loads. I picked the one for resistive loads and tested it. After testing, the circuit was soldered onto a PCB. As you can see, the IC socket is soldered-on, and the isolator simply inserted. That way, if it stops working, it will be easier to pinpoint the problem.


An extension cord was stripped on the female side and the leads soldered as shown in my schematic, then thrown into an outlet box. Finally, I threw together everything as shown in the schematic:


Update: I soldered the stuff seen in the video onto a protoshield, and added a few things.


Final thoughts:

  • I’ve tested this circuit with a couple different “sensitive gate” TRIACs, and a normal (sometimes advertised as a “snubberless”) one, and they all work similarly in my experience. There are texts out there saying to avoid the sensitive gate TRIACs because of their tendency to turn-on as soon as AC voltage is applied to M1 and M2. Personally, I’ve not had that experience. But it’s better to be safe than sorry.
  • The datasheet of the 2N3364 seems to infer that the TRIAC cannot be turned-on in Quadrant IV; in other words, it would be on for only half a cycle. Testing proved this to be untrue. Maybe I read it wrong.
  • Don’t wrap the heating belt around a glass carboy. I’ve been told that the belts cause the glass to crack. Use a bucket instead.
  • That enclosure is ugly as sin. I sure would like a 3D printer…

After my tests are all said and done, it’ll be time to start brewing. How can one better kick-off the summer than with homemade Stout and Honey Wheat?

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