OpenCO2 Sensor is an open-source indoor air quality sensor made in Germany. Measurements are displayed via an 1.54" E-Ink display, RGB LED in traffic light colors, or Wi-Fi, e.g., to Home Assistant. The Arduino code for the ESP32-S2 and Sensirion SCD40 is available here on GitHub.

Especially in winter, when windows stay closed, reminders to ventilate regularly help health and comfort. Poor indoor air quality can lead to lower productivity and learning difficulties. This open-source project helps you keep an eye on this at all times using the E-Ink display and LED. Take the small sensor with you wherever you go to monitor air quality – the battery life is up to 11 weeks.

Based on the SCD40 from Sensirion, a completely new, miniaturized CO2 sensor with photoacoustic measurement principle. The integrated, industry-leading humidity and temperature sensor delivers high accuracy with low energy consumption.

• Automatic self-calibration ensures maximum long-term stability
• CO2 measuring range: 400 ppm – 40,000 ppm
• Accuracy:
  • CO2: ±(50 ppm + 5% of measured value)
  • Temperature: ±0.8 °C
  • Humidity: ±6%

1.54" in size with high resolution (200 x 200 pixels). Enables low power consumption and a wide viewing angle. Display refreshes every 5 seconds during normal operation; in battery mode it refreshes ~every 30 seconds.

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

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+)") }}
        unit_of_measurement: "ppm"
      - name: "Temperature"
        unique_id: "d611314f-9010-4d0d-aa3b-37c7f350c821"
        device_class: temperature
        value_template: >
            {{ value | regex_findall_index("(?:atmp.*})((?:\d|\.)+)") }}
        unit_of_measurement: "°C"
      - name: "Humidity"
        unique_id: "d611314f-9010-4d0d-aa3b-37c7f350c822"
        device_class: humidity
        value_template: >
            {{ value | regex_findall_index("(?:rhum.*})((?:\d|\.)+)") }}
        unit_of_measurement: "%"

Size: 4.9 x 3.8 x 2 cm

• 3D Model viewer
• 3D File FRONT
• 3D File BACK

Press the Menu button on the back. Long press (≥1 s) selects, short press cycles to the next item. Choose between:

• LED control color, brightness and when the LED should be enabled.
• Display can be inverted. Max battery charge percentage threshold. 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. Setup via connecting to the Network "OpenCO2 Sensor".
• Info shows MAC Address, serial numbers, uptime, version and battery details.
• Fun little easter eggs

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.

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

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.

1. Download FIRMWARE.BIN from the latest release
2. Plug a data USB-C Cable
3. Restart the OpenCO2 Sensor using the switch on the side
4. Copy FIRMWARE.BIN to the USB device

1. Download FIRMWARE.BIN from the latest release.
2. Enable Wi-Fi via the Menu button, in an area where no previously known network is active.
3. Make sure that power is connected.
4. Connect you PC/mobile to the WiFi network OpenCO2 Sensor and navigate to http://192.168.4.1
5. Under Update select the FIRMWARE.BIN file and click Update.
6. The Sensor will restart.

1. Copy the esp32-waveshare-epd folder to your Arduino/libraries/ directory
2. Install the ESP32 support for Arduino IDE
3. Choose ESP32S2 Dev Module under Tools -> Board -> esp32
4. Connect the Sensor via USB and flip the power switch to on while holding the button on the back
5. Choose the new COM Port in the Arduino IDE under Tools -> Port -> COMXX

• FastLED
• Sensirion Core
• Sensirion I2C SCD4x Arduino Library
• WiFiManager