I only have a software background, so implementing a single sensor is like a mystery to me.
I have been researching ways to use a couple of different existing sensors that could be used to determine the abv.
-Take temperature readings
-Find a way to calculate a Density reading, mass of the solution,divided by the volume of solution
Calculate Mass Change
-A way to measure the CO2 coming out of the carboy using a blowoff tube, collect the expelled CO2 and use a pressure sensor to measure the amount given off
-Need a way to measure the mass of the trub
-Subtract the mass of the trub and the mass of CO2 from the original mass
Calculate Volume Change
-Using the mass of trub you should be able to do a couple of conversations to calculate the new volume of the system
-A SG reading is just the density of the beer divided by the density of a known solution (water) at that given temperature
-Another idea I had was to use a colorimeter which can be calibrated with the wort and water
-Measuring the absorbance of UV during the course of a fermentation and during a clearing period
-but you want to avoid UV radiation as to not skunk your beer, so..
I am also thinking of other ways, but I am trying to keep this cost effective. A single sensor would be preferred but if it could be done with a collection of sensors for a modest price I would be open for that as well
The ultimate goal here is to be able to monitor the ABV and temp during the course of a fermentation, and possibly send a text/email, or have a simple webpage that can give updates, and help monitor the fermentation.
And yes, I do know about the ferMonitor but that does not seem to be available currently