I found a dented 5.2 cu ft Arctic King at HD. They gave me $50.00 off, so I figured why not? I set up a Raspberry Pi with a DS18B20 waterproof temperature probe and an Adafruit FeatherWing (ADA3191) hooked into a power strip to control the freezer, a small fan to circulate air, and an always-on heating pad. I wrote a simple shell script to read the probe and control the FeatherWing. It keeps the temp within about 0.6 C right now, but I'm pretty sure I can dial it in even closer. I've had it running for about 24 hours now, and my logs report excellent consistency in the temp readings and power switching.
Right now, the temp probe measures ambient air temp inside the freezer, but my next step is to set up a second probe inside the fermenter. These probes are completely watertight, and the only surfaces in contact with the brew will be either the soft plastic shell or the stainless steel probe body, so I don't think there will be any problems.
In the pics, you can see the Pi with the FeatherWing on one mini breadboard, and the temp probe wiring on a second breadboard. You can also see the inside of the freezer. Note that the heating pad doesn't actually touch the bucket, I just didn't get a great angle when I took the picture. The fan keeps air moving inside the box, nothing special. The black cord is the temp probe. The probe body is hanging from the cord, not touching any surface.
Right now, the temp probe measures ambient air temp inside the freezer, but my next step is to set up a second probe inside the fermenter. These probes are completely watertight, and the only surfaces in contact with the brew will be either the soft plastic shell or the stainless steel probe body, so I don't think there will be any problems.
In the pics, you can see the Pi with the FeatherWing on one mini breadboard, and the temp probe wiring on a second breadboard. You can also see the inside of the freezer. Note that the heating pad doesn't actually touch the bucket, I just didn't get a great angle when I took the picture. The fan keeps air moving inside the box, nothing special. The black cord is the temp probe. The probe body is hanging from the cord, not touching any surface.
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