CorO₂Sens - MH-z19B variant

This is a fork of https://github.com/kmetz/coro2sens to enable usage of the other mentioned CO₂ sensor: MH-z19b.
I used this board (relevant for the pins, always check your pins!): https://joy-it.net/de/products/SBC-NodeMCU-ESP32

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 (i didn't include one yet): 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 sure the sensor has enough air flow.

Wiring

ESP32 pin	goes to
5V	MH-z19b VIN, LED +
GND	MH-z19b GND, LED GND, Buzzer (-)
D26	MH-z19b Rx
D32	MH-z19b Tx
D23	LED DIN
D19	Buzzer (+, or "H")

Flashing the ESP using PlatfomIO

• Simply open the project, select your env (esp12e for ESP8266 / nodemcu-32s for ESP32) and run / upload.
• Or via command line:
  • pio run -t -e nodemcu-32s upload for ESP32.
• Libraries will be installed automatically.
• There is a small test suite to help with the wiring. Run it like this:
  • pio test The test contains automated parts that should fail if the dev-board itself or the co2 sensor would be miswired.
    For the LEDs and the buzzer, it will sparkle and play a few tones respectively.

Flash using the Arduino IDE

I didn't try that myseld, please see the original repo for further information