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Corona is over, but colds, seasonal flu, RS virus, and others keep sickness levels high. Infections in an aerosol-contaminated environment remain topical regardless of Corona. CO2 as a measure of the potential for infection via aerosols remains of interest. A very simple, yet accurate measurement system is presented.

Inspired by the post "DIY eCO₂ Telegram Bot" I would like to present an alternative solution that measures the CO2 concentration directly.
With suitable components, measuring devices for assessing air quality can already be created with little effort. I will show you here a very compact variant of a measuring device for the acquisition of temperature, relative humidity, and CO2 concentration of the ambient air for indoor use. The measuring device consists of a M5Stack AtomS3 Controller and a M5Stack CO2 Unit with temperature and humidity Sensor (SCD40)
Both components can form the compact assembly shown in the pictures. The sensor and the controller are connected by a short Grove cable. Power is supplied via a USB Type-C cable from a small plug-in power supply.
The SCD40 from Sensirion shows very good characteristics for the application considered here and with the M5Stack CO2 Unit this sensor is also very easy to handle. Any controller with an I2C interface can be used as a controller. I used the completely over-dimensioned AtomS3 (basis ESP32-S3) because of the suitable design and the integrated display.
The display shows CO2 concentration as well as temperature and relative humidity. The display background indicates the different CO2 concentration ranges by color (the range is added to the respective picture).
You will find the program on GitHub @  https://github.com/ckuehnel/Arduino2023/tree/main/M5Atom/M5AtomS3_SCD40_1.