CorO₂Display

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

Forked from CorO₂Sens by Kaspar Metz.

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).
Displays current CO₂, temperature and pressure values on a small display (optional)
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

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.
Sensirion SCD30 I²C carbon dioxide sensor module (mouser, digikey) (around $50 / 40€).
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).
A 3V piezo buzzer or a small speaker.
Optional: Bosch BME280 I²C sensor module (like the GY-BME280 board), for air pressure compensation, improves accuracy (less than $5 / 4€).
Optional: SSD1306 128x64 pixel OLED (Tested only on ESP32)
A nice case :) Make shure the sensor has enough air flow.

Wiring

ESP8266 pin	ESP32 pin	goes to
3V3	3V3	SCD30 VIN, BME280 VIN, SSD1306 VIN
5V	5V	LED +5V
GND	GND	SCD30 GND, BME280 GND, LED GND, SSD1306 GND, Buzzer (-)
SCL / D1	SCL / GPIO 22	SCD30 SCL, BME280 SCL, SSD1306 SCL
SDA / D2	SDA / GPIO 21	SCD30 SDA, BME280 SDA, SSD1306 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
  - adafruit/Adafruit SSD1306
    - adafruit/Adafruit GFX Library
    - adafruit/Adafruit BusIO
- For ESP32:
  - SparkFun SCD30 Arduino Library
  - SparkFun BME280
  - FastLED
  - adafruit/Adafruit SSD1306
    - adafruit/Adafruit GFX Library
    - adafruit/Adafruit BusIO
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:
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).