Code and full details can be found on github:

https://github.com/MakeOrBreakSociety/ESP32-air-quality-monitor

This is a simple air quality monitor that I built with simple and cheap parts

This was all built with the Waveshare ESP32-S3-Zero as a backbone. But any similar ESP32 with the same footprint, power\ground pin location, and analog on pin 6 will work!

The arduino code was written completely by me at first but was well over 700 lines of code. With the assistance of an LLM we compressed the code down to just over 300 lines. For the most part the arduino code is for testing and proof of concept the YAML is the code intended to be used. Instructions for the YAML are here https://github.com/MakeOrBreakSociety/ESP32-air-quality-monitor/tree/main#esphome-yaml-instructions.

3D Printable case for the PCB can be found here: https://www.printables.com/model/1749242-air-quality-monitor-case

What it does it do currently?

Arduino:

Using the MQ135 and DHT-22 Modules the ESP creates an internal webpage that tracks Temperature, Humidity, and Air Quality. It then charts it on a 60 min and 24 hour graph. It also saves the charts, so they survive a restart. However, it does not track time so if it is down for 20 min that gap does not show up it just continues where it left off.

ESPHome:

Fully intrigrates with Home Assistant and tracks Temperature, Humidity, and Air Quality giving you the ablility to run automations against the data it provides

The PCB design is funtcional but there is a change that needs to be made in the YAML's math depending on if you are using PCB or breadboard. Please see the ESPHome/Home Assistant section for instructions

📸 Features

✅ ESP32‑S3 web server (no external services required)

✅ Live sensor readings

✅ Air quality classification (Great → Warning)

✅ Interactive graphs:

Last 60 minutes

Last 24 hours

✅ Data persistence (survives reboot/power outage)

✅ Optional hostname (.local)

✅ Fully self-contained solution

🧰 Hardware Required

ESP32‑S3‑Zero (Waveshare or similar) - $8.29 CAD - www.aliexpress.com/item/1005009800317016.html

MQ‑135 Air Quality Sensor Module (4‑pin) - $1.39 CAD - www.aliexpress.com/item/1005007710261547.html

DHT22 / AM2302 Temperature & Humidity Sensor (3‑pin module) - $2.89 CAD - www.aliexpress.com/item/1005007188394422.html

10k resistor - Large pack $5.49 CAD - www.aliexpress.com/item/1005011772534173.html

20k resistor - Included in above pack

(Optional) 0.1µF/100nF ceramic capacitor - $4.41 CAD https://www.aliexpress.com/item/1005003979789534.html

Breadboard or PCB