Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:3023709.

Here is my 'final' version of my homebrew hydrometer. As the specific gravity of your homebrew changes, so does the angle at which the hydrometer floats. You can then use Matlab to solve a non-linear regression to create the parameters to convert the angle to specific gravity.

BOM:

ADXL345 accelerometer: https://www.amazon.com/gp/B0151FIBZO HUZZAH ESP8266: https://www.amazon.com/dp/B0131V0WYI 18650 battery holder: https://www.mouser.com/ProductDetail/534-1043 PETG 5L preform: https://www.ebay.com/itm/5-pcs-XXL-set-of-BIG-PET-Micro-Geocaching-container-geocache-preform-Soda-bottle/132379354252

The source code for the hydrometer can be found here:

https://github.com/bdtower8/Hydrometer