Before some years I started beeing interested in smart home and especially in creating it by myself 
My first project was a tutorial to build a temperature sensor which sends the data to my raspberry gateway via 433MHz. As these tutorial were quite old I had to exchange some hard and software to make it work but it was a nice challenge. End of 2018 I then thought that it might be nice to enhance the sensor by measuring volatile organic compounds and CO2. Some could say that I could buy an existing sensor but you know, ... that wouldn't be fun 
Measuring volatile compounds
After some research I decided to choose CCS811 chip for measuring the total volatile organic compounds (tVOC) because it was quite cheap and it can operate on 2.7V+, which was necessary because my existing setup is supplied by 3 AAA batteries. The chip can also calculate the estimated co2 value (eCO2) based on the tVOC. So I bought a CJMCU-8118 breakout on Amazon for around 15€ but you can buy it cheaper on
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