MH-Z19B infrared co2 sensor
We've connected a MH-Z19B co2 sensor to our MQTT network. This allows us to monitor the co2 concentration in our space.
The project itself is fairly simple: we just connected the serial port of the co2 sensor to an Arduino Ethernet and used the software-serial library to communicate with the sensor. The Arduino ethernet then uses the Adafruit MQTT library to send the values read from the sensor to the MQTT network.
Where to buy the sensor?
You can get the MH-Z19B sensor cheaply on Aliexpress.