OpenCO2 Sensor using ESP32 and SCD4x

OpenCO2 Sensor is an Arduino IDE compatible Repository for an E-Ink Indoor air quality Sensor using the ESP32, SCD4X and an RGB LED.

Buy it here on Tindie

Especially in winter, when windows are closed, a reminder to ventilate regularly is useful for health, comfort and well-being. Poor indoor air quality can lead to decreased productivity and learning disabilities. Therefore, I developed an Open-source ESP32 project that uses an E-Ink display and a LED to show the indoor CO2 content. Take the small Sensor anywhere you go to monitor the Air Quality, with Battery life of 11+ days.

CO2 Sensor

With the SCD40, Sensirion offers a completely new miniaturized CO2 sensor based on the photoacoustic sensor principle. The integrated, industry-leading humidity and temperature sensor offers high accuracy with low power consumption.

Automatic self-calibration ensures the highest long-term stability
CO2 output range: 400 ppm – 40'000 ppm
Accuracy:
- CO2 ±(50ppm + 5% of reading)
- Temperature ±0.8°C
- Humidity ±6%

Clear E-Ink display

1.54" in size with a very high resolution (200x200 Pixel). Enables low power consumption and wide viewing angle. Per partial refresh, readings are updated every five seconds (every 30 seconds in battery mode).

RGB LED

For displaying the air quality as a traffic light (green, yellow, red, magenta). Brightness and color are adjustable via software.

Home Assistant

Add this config to the configuration.yaml of your Home Assistant. Below Version 5.4 please change OpenCO2 to the IP address.

rest:
    scan_interval: 60
    resource: http://OpenCO2:9925/metrics
    method: GET
    sensor:
      - name: "CO2"
        device_class: carbon_dioxide
        unique_id: "d611314f-9010-4d0d-aa3b-37c7f350c82f"
        value_template: >
            {{ value | regex_findall_index("(?:rco2.*})(\d+)") }}
      - name: "Temperature"
        unique_id: "d611314f-9010-4d0d-aa3b-37c7f350c821"
        device_class: temperature
        value_template: >
            {{ value | regex_findall_index("(?:atmp.*})((?:\d|\.)+)") }}
      - name: "Humidity"
        unique_id: "d611314f-9010-4d0d-aa3b-37c7f350c822"
        device_class: humidity
        value_template: >
            {{ value | regex_findall_index("(?:rhum.*})((?:\d|\.)+)") }}

3D-printed housing

Size: 4.7 x 4.1 x 2.4 cm

LED control color, brightness and when the LED should be enabled
Display can be inverted. Also change the Temperature unit, language and font
Calibrate put the sensor outside for 3+ minutes (only run this, if calibration is needed)
History display up to 24h of CO2, temperature and humidity as a graph. Values can also be exported via QR codes containing 1h of CO2 measurements each.
Wi-Fi enable or disable wireless connections
Info shows MAC Address, serial numbers, uptime, version and battery details
Rainbow fun little easter egg

Wi-Fi

Enable Wi-Fi via the Menu button. When power is connected, an access point OpenCO2 Sensor is enabled. Connect to it and navigate to http://192.168.4.1 (it will open automatically on modern Smartphones). Insert your home Wi-Fi credentials under Configure WiFi. Choose your network name from the list in the top and insert the password. Click Save. The sensor will now be automatically connected. Navigate to openco2:9925 to see a graph of CO2, Temperature and Humidity measurements.

Machine-readable Measurements over WiFi

Connect the sensor to your Wi-Fi network and find out the IP of the sensor in your home network via the ui of your router or on the sensor itself via the button under Menu -> Info . curl [IP]:9925/metrics

Result:

# HELP rco2 CO2 value, in ppm
# TYPE rco2 gauge
rco2{id="Open CO2 Sensor",mac="7C:DF:A1:96:B9:72"}571
# HELP atmp Temperature, in degrees Celsius
# TYPE atmp gauge
atmp{id="Open CO2 Sensor",mac="7C:DF:A1:96:B9:72"}25.37
# HELP rhum Relative humidity, in percent
# TYPE rhum gauge
rhum{id="Open CO2 Sensor",mac="7C:DF:A1:96:B9:72"}55.15

AirGradient / Grafana

Use internet-pi to store the CO2 / Temperature / Humidity data on your Pi. First connect the OpenCO2 Sensor to your Wi-Fi network and follow the instructions https://www.youtube.com/watch?v=Cmr5VNALRAg Then download the https://raw.githubusercontent.com/davidkreidler/OpenCO2_Sensor/main/grafana_OpenCO2_Sensor.json and import it into Grafana.

Update via USB

Download FIRMWARE.BIN from the latest release
Plug a data USB-C cable into your PC and the Sensor
copy FIRMWARE.BIN to the USB device

OTA Update

Download FIRMWARE.BIN from the latest release. Enable Wi-Fi via the Menu button, in an area where no previously known network is active. Connect power. Then connect to OpenCO2 Sensor and navigate to http://192.168.4.1 . Under Update select the FIRMWARE.BIN file and click Update. The Sensor will restart.

Update via USB (from an old release)

Download all files from the latest release
Make sure, that the power switch is in the ON position (down)
Plug a data USB-C cable into your PC and the Sensor
Hold the Button on the backside of the CO2 Sensor near the USB-C port and shortly push simultaneously the reset ↪️ Button
In Device Manager under Ports (COM & LPT) find the COM number and modify it in update.bat
Run update.bat
Afterwards push the reset ↪️ Button

Installation inside the Arduino IDE

Copy the esp32-waveshare-epd Folder to your Arduino/libraries/
Install the ESP32 support for Arduino IDE
Choose ESP32S2 Dev Module under Tools -> Board -> esp32
Connect the Sensor as described in step "Update to the latest release" and choose the new Port under Tools -> Boards -> Port