aqi-monitor

This DIY air quality monitor will measure:

• temperature
• humidity
• pressure
• gas
• CO2
• number of particles
• ozone (expansion)
• earthquakes through an IMU (expansion)
• radioactivity (expansion)

There's an optional case and screen for both. The code is set up to allow you to only use a subset of sensors.

By default, results are uploaded periodically to Freedom Robotics for easy inspection and alerting.

BOM

If you want to encase the electronics, an STL file for 3D printing a case is in the design folder. Make sure you get the right case for either base or base+expansion set.

Base set

item	function	~price	notes
Adafruit FeatherS2 - ESP32-S2	microcontroller	$22	adafruit boards are often available on digikey and amazon if adafruit is sold out
Adafruit BME680	Temp/Humidity/Pressure/Gas	$19	incredibly sensitive pressure sensor, can possibly detect which floor of a building robot is on
Adafruit PMSA003I	PM1, PM2.5, PM10 particle sensor	$45	this messes up the I2C bus it is placed on, thankfully ESP32-S2 has 2 I2C buses so this can have its own bus
SeeedStudio SCD30	CO2/temp/humidity sensor	$60	NDIR CO2 sensor (much better than chemical); buy from Mouser for faster shipping to US destinations

For a total of ~$146 excluding screen and case.

The STL files for 3D printing the base case can be found in the design folder.

Expansion set

These are extra sensors you can purchase in addition to the base set.

item	function	~price	notes
Adafruit BNO085	IMU (Earthquake detection)	$20	this is a really good IMU
SeeedStudio Multichannel Gas Sensor v2	CO, VOC, alcohol, NO2	$35	buy from Mouser for faster shipping to US destinations
DFRobot I2C Ozone Sensor	ozone	$49	buy from Mouser for faster shipping to US destinations
Geiger Counter	Radioactivity	$45	ships from Russia; not yet tested; couldn't find a US-stocked I2C Geiger counter

Optional Screen

item	function	~price	notes
Monochrome 0.91" 128x32 I2C OLED Display	screen	$12.5	optional

Instructions

Wire the electronics

See pictures

Modify the parameters

1. Download the code and open wifi.json. Enter your Wifi name (SSID) and password. The microcontroller needs WiFi access to be able to upload the sensor data.
2. Create a new device on your FreedomRobotics account. When you get to the installation page, from the link that is shown, copy the account, device, token, and secret embedded in it into the credentials.json file. This lets the microcontroller send the sensor data to the Freedom API.
3. Open code.py and modify any of the parameters (LOAD_XXX) at the top to match your configuration.

Load on the code

Plug the microcontroller into your computer using a USB-C cable. It should appear in your file explorer. Copy and replace the files from the code folder including the files you modified into the CIRCUITPY folder.

Press reset. You should see data coming through in the Stream tab of FreedomRobotics.

Troubleshooting

From a terminal window, you can log into the Feather S2 microcontroller to read the logs using

sudo screen /dev/ttyACM0 115200

The actual device name might be different. This opens up a python terminal. You can re-run the code by typing import code.