(Sorry to do this in english, but m skills in German is to low.)
I have worked a bit more on my fermentation Logger/controller, measuring "Temperature and Sound detection of CO2 bubbles" for NodeMCU (ESP8266). The software give an indicative SG estrimate based on S-airlock is used with a precise amount of water (4 ml)!
What I meassure is the Sound Blops pr. Min (SBM) comming when CO2 is released by a Sound detction module. If we look at the chemistry behind the metabolisms of fermentation of sugar by yeast cells, we see one part Alcohol generate two part CO2. Hence, CO2 is a direct measument of the alcohol production. The key issue is to measument this gas accuarate and precise. Hence, the need of sealed airtight tanks.
C6H12O6 ====> 2(CH3CH2OH) + 2(CO2) (+Energy)
Sugar ====> Alcohol + Carbon dioxide gas (+Energy)
Hence, by knowing the SBM and brew sieze (L) and other involving constants like pessure (p) and temperature (t) we can plot a curve of SBM/pt/L vs. the reduction in Gravity and generate a model or polynomial for the alcohol production based on our initial measument of Sound Blops pr. Min (SBM), se below graph.
This software give an indicative SG with an offset of +/- 2 SG untis if used in a airtight tank and an S-shaped airlock with 4 ml water in it!
Resume, of the Data behind there currently give an indicative SG by an error of +/- 2:
So, if a keen eye on placement/alingment of sound probe in airlock, 4ml water amount in s-arilock and a slow/controlled fermentation in a airtight fermenter and the use of the same calibrated sensor, it is possible to use CO2 as a SG measument though a 2nd degree poly.
You might have to re-calculate you own polynomial based on your sound sensor and its calibration. Hence, make 2-3 brews and take hydrometer measuments over the time compared to SBM/pt/L and update your polynomial. The same is likley needed if you change sound sensor.
All used data can be seen here: https://1drv.ms/x/s!An5QQQ1io7W7icIIREC ... Q?e=b4ph5j
Reason and what we will see
Knowing the yeast activity though CO2 bubble measurements over time including the start of decline, we can better foresee when the SG is close to FG, and better make decision on dry-hopping, temperature changes, etc.!
Brooklyn Lager Clone:
"Yoga Pils":
A more full description (diagram/equipment) and the code + dependicies can be seen at:
https://github.com/kbaggen/Cheapfathers-Bubble-Logger
/Best Regards Klaus