LabPi CO2 traffic light
Air quality is currently a particular focus in connection with the Covid-19 pandemic. Scientific studies show that the CO2 concentration indoors provides information about the microbial load. The CO2 concentration is therefore commonly used as an exposure marker in impact studies because it correlates strongly with the organic emissions released by people. A working group of the German Environment Agency currently recommends that a CO2 threshold of 1,000 ppm should not be exceeded. Especially in classrooms without permanently installed ventilation systems, and particularly during colder seasons, concentrations are often above this recommended limit.
A CO2 traffic light can indicate when ventilation is advisable or necessary in indoor spaces and can therefore help to reduce the risk of infection. Below, two such CO2 traffic lights are presented, both based on LabPi. This article also provides more detailed background information on the topic.
Full CO2 traffic light
The full LabPi system can be turned into a CO2 traffic light very quickly: the corresponding CO2 sensor is simply connected via USB-C and the matching measurement method is selected on the display. Additional sensors can be connected as well. The sensor works on the characteristic absorption of infrared radiation by carbon dioxide. In the measurement chamber, radiation from the light source passes through the gas and reaches a sensor. A filter ensures that only the wavelength of the measured gas reaches the detector. The gas concentration is then calculated from the light intensity.
Additional parameters can optionally be recorded at the same time using sensors for temperature, humidity or pressure.
Standalone CO2 traffic light
In addition to the full version, LabPi can also be used to create a reduced standalone variant that focuses on the essential functions for CO2 measurement: a mini computer (Raspberry Pi Zero W) with SD card, one sensor and a small OLED display. To start it up, the microSD card with the software is inserted into the Raspberry Pi. In the next step, the OLED display is connected to the GPIO pins using four jumper wires. After that, the CO2 sensor is connected to the GPIO pins marked in the figure, and finally the power supply is connected via the micro-USB port. Power can be provided by USB cable, power adapter or a standard power bank.
The software for controlling the sensor and reading out the values is available here as a free download. With this software, the standalone version can also display the current CO2 concentration as a traffic light.