Previously I have been measuring the ambient temperature of my apartment and the water temperature of my swamp cooler with the Raspberry Pi in combination with the DS18B20 temperature probes.
While this has been useful, it is not the best way to measure the temperature of the wort. The best way would involve sticking another DS18B20 probe into the wort while it ferments.
There are a few ways this could be achieved. If you are using a carboy, it is really easy: purchase a cap that comes with a built in thermowell. If you are using a bucket, as I am, then you could drill a hole, add a bung, and insert a thermowell into the bung. I however don't know how to accomplish that, so I did what I always do when I am lost: ASK MOM.
My mother used to make aquariums when she was my age and sell them on the market. In order to glue the glass together, she used silicone glue, which keeps everything air tight. She suggested I cut a hole into the top of the bucket and then use silicone glue to keep the DS18B20 probe permanently attached to the lid.
1) I used a nail and hammered a hole into the lid, opposite of the bung for the airlock. I placed the half of the lid on the counter, pressed my left arm's elbow on top, held the nail with my left hand and hammered with my right. This took more than a few minutes.
2) After making the hole, I got a smaller sized pen and started to wedge the hole open. My goal here was to make the hole just big enough so that the tip of the DS18B20 probe would enter. The smaller sized pen didn't make a big enough hole, but it opened it enough for a bigger sized pen to finish it off.
3) I tried to determine how far down I wanted the probe. I figured about halfway down would be best, and then I held it in position while I prepared for the silicone.
4) I purchased a brand of silicone glue that claimed to be water proof at Home Depot. There were several waterproof options available. The first one I looked at said "Not for Aquariums" on the back, so I found another bottle that didn't have that warning on it. I'm not sure if this was necessary, or if the silicone I bought was even good enough for aquariums, but I figured I might as well play it safe.
5) If you try this, make sure to push out the running liquid silicone on some paper towels before applying it to the lid. This was my first time working with silicone glue, so I just immediately began to apply it. It is not supposed to be a running liquid, but a very viscous, doughy consistency. My mistake caused the liquid silicone to run down the wire on the DS18B20 probe and harden up. I tried to get it off, but I'm sure that it is now coming into contact with my wort (Silicone beer, anyone?). I only put silicone on the top of the lid, because I figured that if I put it underneath, the taste of it could possibly get into my beer. This is a trade off as it would be more airtight if I did it underneath. I applied it and then stood there holding the probe for a good 3-5minutes before I relaxed. I waited until the next morning before brewing, as silicone takes some time to harden up fully.
6) Normally when I sanitize the lid I simply submerse it fully in the bucket full of star san. Even though the silicone glue claims to be waterproof, I figured I would carefully submerge each side of the lid and not allow any water to come into contact with the silicone on the top of the lid.
7) I connected the wires on the end of the probe to a breadboard connected to my Raspberry Pi, made some modifications to the python program I am using on the RPi, and it worked. However, I doubt it was perfectly air tight, as the bubbling seemed very diminished. However, the lid had been used on multiple occasions, and it could have just been a leaky lid.