Measuring CO2 with ESP8266 and MicroPython

As I wrote in Monitoring Air Quality Open Data I wanted to build a small device for monitoring the air quality and noxious gases, and since lately I have been hacking with Python for the ESP, I wanted to do it with MicroPython.

Most of the experiments, libraries and calibration details related to the MQ135 are based on two main articles:

Note: R0 (RZERO) may have different values in different sensors, so in case you want to have your sensor calibrated more precisely it is recommended to follow the next steps:

In case you want to test the device yourself, you need to install MicroPython for the ESP8266 first.

Install ESPtool (the bootloader utility for ESP8266)

Erase the flash and deploy MicroPython firmware

Then, clone or download the MQ135 git repository

and then connect to the device with the serial communication program (e.g.: minicom) to see the output.

MicroPython could be configured to load a script after the device boot. If you want to load the code just after the boot, use:

The required hardware is just a breadboard, some wires and:

This is the final prototype, including the Wemos D1 mini and the MQ135 and DHT11 sensors.

Dweet allows to easily upload to the cloud the values you got from your sensors and Freeboard is used to visualize the data in a dashboard.

For uploading the data to Dweet is enough to define the URL with a unique name (line 21) for logging your data, and then use Python urequest to get the URL with the parameters (lines 41–45).

Once the device is uploading data to the cloud you could see in the next URL if the data is being recorded in Dweet.

Dweet and Freeboard are well integrated, so, to show the data in the dashboard it is enough to add dweet.io as datasource, then add new pane to your dashboard and a gauge or text widget with the variable you want in the value field. The result could be something similar to this:

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