CorO₂Sens

Build a simple device that warns if CO₂ concentration in a room becomes a risk for COVID-19 aerosol infections.

• Measures CO₂ concentration in room air.
• Controls an RGB LED (green, yellow, red, like a traffic light).
• A buzzer can be connected that alarms if levels are critical.
• Also opens a WiFi portal which shows current readings and a graph (not connected to the internet).
• Can be built for ~ $60 / 50€ (parts cost).

This project was heavily inspired by ideas from Umwelt-Campus Birkenfeld.

You can also find a good overview of the topic by Rainer Winkler here: Recommendations for use of CO2 sensors to control room air quality during the COVID-19 pandemic.

Sensors

• The sensor used here is the Sensirion SCD30 (around $50 / 40€) which is optionally augmented by a BME280 pressure sensor to improve accuracy.
• Look here if you want to use MH-Z19B sensors.

Threshold values

LED color	CO₂ concentration
Green ("all good")	< 800 ppm
Yellow ("open windows")	800 – 1000 ppm
Red ("leave room")	> 1000 ppm

Based on a Recommendation from the REHVA (Federation of European Heating, Ventilation and Air Conditioning associations, rehva.eu) for preventing COVID-19 aerosol spread, especially in schools.

Web server

You can read current levels and a simple graph for the last hour by connecting to the WiFi coro2sens that is created. Most devices will open a captive portal, immediately showing the data. You can also open http://10.0.0.1/ in a browser.

You need

1. Any ESP32 or ESP8266 board (like a WEMOS D32 (about $18 / 15€) or WEMOS LOLIN D1 Mini (about $7 / 6€)).
   ESP32 has bluetooth, for future expansion.
2. Sensirion SCD30 I²C carbon dioxide sensor module (mouser, digikey) (around $50 / 40€).
3. 1 NeoPixel compatible RGB LED (WS2812B, like the V2 Flora RGB Smart NeoPixel LED, you can also remove one from a larger strip which might be cheaper).
4. A 3V piezo buzzer or a small speaker.
5. Optional: Bosch BME280 I²C sensor module (like the GY-BME280 board), for air pressure compensation, improves accuracy (less than $5 / 4€).
6. A nice case :) Make shure the sensor has enough air flow.

Wiring

ESP8266 pin	ESP32 pin	goes to
3V3	3V3	SCD30 VIN, BME280 VIN
5V	5V	LED +5V
GND	GND	SCD30 GND, BME280 GND, LED GND, Buzzer (-)
SCL / D1	SCL / GPIO 22	SCD30 SCL, BME280 SCL
SDA / D2	SDA / GPIO 21	SCD30 SDA, BME280 SDA
GPIO 0 / D3	GPIO 16	LED DIN
GPIO 14 / D5	GPIO 19	Buzzer (+)

Flashing the ESP using PlatfomIO

• Simply open the project, select your env (esp12e for ESP8266 / esp32dev for ESP32) and run / upload.
• Or via command line:
  • pio run -t -e esp12e upload for ESP8266.
  • pio run -t -e esp32dev upload for ESP32.
• Libraries will be installed automatically.

Flash using the Arduino IDE

• Install the latest Arduino IDE.
• Download the latest code and unzip it somewhere.
• Open coro2sense.ino in the coro2sens sub folder in your Arduino IDE.
• Install (or update) your board platform:
  (Tools –> Board –> Board Manager...)
  • Install esp8266 or esp32.
• Install (or update) the following libraries using the built-in library manager:
  (Tools –> Library Manager...)
  • For ESP8266:
    • SparkFun BME280
    • FastLED
  • For ESP32:
    • SparkFun SCD30 Arduino Library
    • SparkFun BME280
    • FastLED
• Install the following external libraries:
  (download .zip file, then import it via Sketch –> Include Library –> Add .ZIP Library...)
  • For ESP8266:
    • paulvha/scd30 (.zip)
    • me-no-dev/ESPAsyncTCP (.zip)
    • me-no-dev/ESPAsyncWebServer (.zip)
  • For ESP32:
    • lbernstone/Tone32 (.zip)
    • me-no-dev/AsyncTCP (.zip)
    • me-no-dev/ESPAsyncWebServer (.zip)
• Run & upload :)

Please let me know of any issues you might encounter (open a GitHub issue or write me on twitter.com/kmetz or k@kjpm.de). Also, I'd be for hire for customizations.