ESPHome Air Quality Monitor

This ESPHome configuration builds firmware for a DIY indoor air quality monitor. It monitors:

CO₂ concentration
PM2.5 and PM10 concentration
temperature, humidity and pressure

It optionally shows feedback for the current air quality with an RGB LED: green if the air quality is good, yellow if it's acceptable, and red if it's bad. An alternative is showing the sensor measurements on a display.

You can build an example implementation on a perfboard in a project box like this:

Requirements

ESP8266 or ESP32 board
Winsen MH-Z19B or Telaire T6615 CO₂ sensor
Nova Fitness SDS011 particulate matter (PM) sensor
Bosch BME280 breakout board (the 3.3 V version)
ESPHome

Optionally:

Common cathode RGB LED (or separate red, green and blue LEDs)
220 Ω resistor and two 47 Ω resistors

Connections

I have tested this code with:

the NodeMCU v2 ESP8266
the ESP32-DevKitC V4
the LilyGO TTGO T-Display ESP32 (using the built-in display instead of an RGB LED for feedback)

Here are the connections to the pins of these boards:

Component	NodeMCU ESP8266	ESP32-DevKitC V4	TTGO T-Display ESP32
BME280 SCL	D1	GPIO21	GPIO21
BME280 SDA	D2	GPIO22	GPIO22
MH-Z19B / T6615 TX	D4	GPIO35	GPIO39
MH-Z19B / T6615 RX	D5	GPIO32	GPIO32
SDS011 TX	D3	GPIO34	GPIO25
SDS011 RX	D6	GPIO33	GPIO33
LED red	D7	GPIO5	/
LED green	D8	GPIO17	/
LED blue	TX	GPIO16	/

Make sure to connect the power and ground connections too. The BME280 needs 3.3 V, the MH-Z19B, T6615 and SDS011 need 5 V.

The red component of the RGB LED needs a current-limiting resistor of 220 Ω, while the other two color components need a 47 Ω resistor.

Modularity

This is a modular ESPHome configuration split up in various YAML files that you can import as packages. You can find these in the directory common:

aqi.yaml: Computes the air quality index (AQI) value (good, acceptable, bad) based on the current CO₂ concentration and the 24-hour averages of the PM2.5 and PM10 concentrations. This value is published as a text sensor and shown as a color (green, yellow, red) on the RGB LED.
base.yaml: Sets up the basic ESPHome functionality for the board, including Wi-Fi, a captive portal, logger, Home Assistant API and OTA support. It also sets the threshold values for the CO₂, PM2.5 and PM10 concentrations, as well as the messages when the air quality is good, acceptable or bad.
bme280.yaml: Sets up the BME280 sensor for temperature, humidity and pressure and the I²C bus it uses.
display.yaml: Configures colors and fonts as well as graphs for the CO₂ and particulate matter concentrations.
mh-z19b.yaml: Sets up the MH-Z19B CO₂ sensor, a binary sensor that shows whether the sensor has been calibrated yet (and sets the LED to blue when it isn't) and a switch to calibrate the sensor.
no_feedback/aqi.yaml: Use this if you don't want to show AQI status.
no_feedback/calibration.yaml: Use this if you don't want to show calibration status.
rgb_led/aqi.yaml: Shows AQI status on the RGB LED.
rgb_led/calibration.yaml: Shows calibration status on the RGB LED.
rgb_led/esp32.yaml: Sets up the RGB LED on the ESP32 with its LEDC peripheral (a hardware PWM).
rgb_led/esp8266.yaml: Sets up the RGB LED on the ESP8266 with software PWM.
sds011.yaml: Sets up the SDS011 PM sensor.
secrets.yaml.example: Contains the secrets used in this ESPHome project. Copy this file to a file secrets.yaml in the common directory and enter your Wi-Fi, API and OTA credentials.
t6615.yaml: Sets up the T6615 CO₂ sensor, which doesn't need calibration.

Usage

To use this configuration, create a YAML file with:

substitutions for all pin numbers used by the components, your device's name, platform and board and parameters like update intervals.
packages that include the relevant YAML files in the common directory.

There are three example configurations in this repository:

esp8266_example.yaml for the NodeMCU v2 ESP8266
esp32_example.yaml for the ESP32-DevKitC V4
t-display_example.yaml for the TTGO T-Display ESP32

After this, flash the firmware to your device, e.g. with:

esphome run esp32_example.yaml

After you have added your device to Home Assistant's ESPHome integration, the air quality measurements are available in Home Assistant and you can start the calibration of the CO₂ sensor from within Home Assistant too (or with the top button on the TTGO T-Display ESP32).

If you successfully created a configuration for another ESP8266 or ESP32 board, please contribute this configuration with a pull request.

Customizations

Thanks to the modularity of the code, it shouldn't be that difficult to create a variant of this project with other sensors. Here are some suggestions:

Change the temperature, humidity and pressure sensor: This sensor is currently not referenced in the other YAML files, so you can just add a configuration file for another sensor, disable the package for the BME280 and add a package for the other sensor.
Change the CO₂ sensor: Make sure you give the CO₂ value of your sensor the ID co2_value and create a binary sensor for its calibration state with ID co2_calibrated.
Change the RGB LED: You can swap the classical RGB LED for another light, as long as it has the ID led_rgb and it's a light with platform rgb (with red, green and blue components).
Change the PM sensor: Make sure you give the PM2.5 and PM10 values of your sensor the IDs pm2_5_value and pm10_value.

With these changes, the rest of the code should still work.

If you successfully created a customization, please contribute this with a pull request, ideally with an example configuration.

More complex customizations could be supported in future versions of this project.

Learn more about ESPHome

If you want to learn more about ESPHome, read my book Getting Started with ESPHome: Develop your own custom home automation devices and the accompanying GitHub repository koenvervloesem/Getting-Started-with-ESPHome.

License

This project is provided by Koen Vervloesem as open source software with the MIT license. See the LICENSE file for more information.

The included Roboto font is licensed under the Apache License, Version 2.0.

The C++/runtime codebase of the ESPHome project (file extensions .c, .cpp, .h, .hpp, .tcc, .ino) are published under the GPLv3 license. The Python codebase and all other parts of the ESPHome codebase are published under the MIT license. See the ESPHome License for more information.

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