Getting Started


The CO2-Ampel shows a color according to the carbon dioxide concentration and application.

Power is supplied via the USB-C connector with 5V (4.3-5.3V). On power-up the sensor needs approx. 30s until a valid value is displayed (standard measuring interval: 3s).

The brightness can be adjusted with the Switch button.

The light sensor is checked every hour and when it is dark, the brightness is reduced and the measuring interval is increased to 30s.

  • for covid prevention

    • up to 799 ppm -> green
    • 800 to 999 ppm -> yellow
    • 1000 to 1199 ppm -> red
    • 1200 to 1399 ppm -> red flashing
    • 1400 ppm and higher -> red flashing + buzzer
  • against tiredness

    • up to 999 ppm -> green
    • 1000 to 1199 ppm -> yellow
    • 1200 to 1399 ppm -> red
    • 1400 to 1599 ppm -> red flashing
    • 1600 ppm and higher -> red flashing + buzzer


Update Instructions

  • Connect the device to a computer via USB.
  • Press the reset button twice within 500ms.
  • A new USB mass storage device will appear. (On problems try another USB cable (no longer than 1m).)
  • Copy the new firmware file to this device/drive. On Linux/Mac the dd command can be used for the writing: dd if=APP.BIN of=/media/CO2AMPEL/APP.BIN conv=notrunc
  • The device will update itself and restart with the new firmware.


The SCD30 CO2 sensor is pre-calibrated by the manufacturer and according to our tests, it has an accuracy of +/-50ppm. Therefore we recommend a calibration after one year at the earliest.

A calibration can be done directly on the device if it is operated in fresh air (400ppm CO2).

  1. Operate the CO2 traffic light in fresh air for at least one minute (outdoors or at an open window, but protected from the wind).
  2. Start the test mode by holding down the Switch button on power-up.
  3. Test mode:
    1. Buzzer
    2. LEDs: red, green, blue
    3. Sensors: LED 1 = light, LED 2 = CO2 (200-1500ppm), LED 3 = temperature (5-35°C), LED 4 = humidity (20-80%)
  4. After the LED test (blue LEDs), short press the Switch button during the sensor test (buzzer sounds).
  5. The calibration is started after the sensor test (all LEDs green) and it takes at least 2 minutes. The LEDs show the current CO2 value: green up to 499ppm, yellow up to 599ppm, red from 600ppm
  6. After successful calibration, the LEDs light up blue and the buzzer sounds for a short time.