This is the "boi" part of the BeerBoi. This will get filled with a weighty material, I used BB's, but sand or lead shot would work fine. I generally ferment in buckets, so the size of the boi isn't a concern, but if you ferment in carboys or some container with a small mouth, you might want a smaller container. Regardless of your choice of containers, the boi should have a specific gravity of about 2.0, so 200 gm in a 100 ml container is just right. You could go with a 50 ml container with 100 gm, for example.
The specific ones that I bought are no longer available for some reason, but this link will take you to an Amazon page showing lots of similar choices, some are cheaper than what I paid. I actually started this project with an ESP-01, but found its limited pins a pain, so I upgraded to the ESP-12's. Easy to program, easy to solder, lots of pins available, and still pretty cheap.
There are several choices for this, but I chose the 1KG model because it's accurate to 0.1 gram, which has right accuracy for this project.
There are several choices for the display, I'm using the 128 x 32 pixel version as all it needs to show is the specific gravity, so just 4 numbers and a decimal point. The 128 x 64 pixel version is quite popular and can be used in place of this one.
