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Homebrew (hardware and beer) Kegerator Thermostat

Homebrew (hardware and beer) Kegerator Thermostat

Here’s a picture of a project I recently completed: a thermostat for controlling the temperature in a homebrew kegerator. I am using a small chest freezer which can hold two cornelius kegs and associated CO2 tank. I could have spent the $ to just buy a nice digital one (from my favorite homebrew supply shop, Chicago Brew Werks), but I had some parts on hand and picked up a few parts from Adafruit and pieced it all together for much less. The main switch is a 25A solid state relay which is controlled by a spare ColorNode board I had laying around (eventually I’ll use the transceiver to let me monitor/control the temperature wirelessly). The design uses the Maxim 1-Wire DS18B20 for temperature measurement (accurate to ~0.5°F with ~0.1° resolution), white I2C seven-segment display, round tactile buttons for adjusting temperature settings (high/low turn on/off points) and enabling the temperature control, and cable glands to hold the input/output power cords securely in place (not necessarily for water proofing).  The electronics are powered from the AC line input using a miniature AC/DC converter which supplies 5V @ 1W. The temperature sensor is attached via some speaker wire and encapsulated in Sugru on one end and the other end terminates at a 1/8″ stereo plug. The enclosure is a Radio Shack plastic project box into which I cut holes for the display, buttons, ON LED, power cables, and temperature probe jack. The display and buttons (and a bunch of wires) are soldered to a protoboard and mounted via standoffs to the box lid. The height of the buttons and the display almost matched up perfectly to each other when mounted on the board. I made sure to isolate the AC line wiring from the DC control wiring to make sure it would be safe to use. Overall it turned out really well and I’m looking forward to having cold homebrew on tap! For a summary and more info on the design, see the parts list and specs below. The firmware can be found on GitHub.

Item Manufacturer Part Number Price
SSR Opto 22 120D25 $30.00
PCB DigitalMisery ColorNode V1.1 $4.00
Components See CN BOM See CN BOM $6.00
AC/DC Recom Power RAC01-05SC $12.50
Temp Sensor Maxim DS18B20 $4.00
Display Adafruit 1002 $11.00
Buttons Adafruit 1009 $6.00
Hardware Ace Hardware Nuts, screws $2.00
Cable Glands Adafruit 761 $4.00
Cords CNC Tech 800-0.75-44L-BL-00200 $9.00
1/8″ Plug Radio Shack 274-284 $4.50
1/8″ Jack Radio Shack 274-249 $3.50
Wire Radio Shack Speaker wire $1.00
Box Radio Shack 270-1803 $5.50
Proto Board Sparkfun PRT-08815 $4.50
 Parts Total $107.50
Specifications
Temperature Accuracy ~ 0.5°F
Temperature Resolution 0.1°F
Temperature Range -67°F to +257°F
Temperature Regulation High/Low Temp Points
Temperature Update Rate Once per second
Solid-State Relay Rating 25A
SSR Motor Rating 1/3 HP (248W)
My Kegerator (small Jewel freezer, fits 2 kegs)
Volume 5.3 ft^3
Compressor Current 1.5A
Compressor Power 180W / 1/4 HP

So if you hadn’t heard, there was a Kickstarter project called HexBright. Check it out or see the main website for more info. I pre-ordered one because I thought the idea of a super bright flashlight built on open-source hardware was too good to pass up. Well it came this week and it lives up to my expectations.  I’ve included some pictures below and also check out my GitHub repository where I’m keeping my software modifications.