The concentration of carbon dioxide in indoor air can affect people's health and comfort. When indoor air does not circulate, the concentration of carbon dioxide will rise, causing people to feel drowsy, headaches, lack of concentration and other symptoms. Therefore, real-time detection and regulation of indoor carbon dioxide concentration is an important measure to improve the quality of life and work efficiency. This article will introduce a carbon dioxide sensor based on photoacoustic sensing technology, which has the characteristics of small size, low cost, high accuracy, etc., and can meet the needs of various portable detection equipment.
Photoacoustic sensing technology is a technique that uses the interaction of light and sound waves to detect the concentration of gas. Its basic principle is: in a specially designed cavity, an infrared light source periodically emits infrared light of a certain wavelength range, which can be absorbed by the target gas molecules (such as carbon dioxide), causing the gas sample to heat up and cool down rapidly in the cavity. This temperature change leads to the pressure change of the gas, which in turn generates sound wave signals. By using a miniature microphone to receive these sound wave signals, and performing signal processing and analysis, the concentration value of the target gas can be obtained. Since different kinds of gas molecules have different absorption characteristics for different wavelengths of infrared light, it is possible to select the appropriate infrared light source and filter to achieve the detection of specific gas.
Compared with the common infrared absorption method (NDIR) based carbon dioxide sensors on the market, photoacoustic carbon dioxide sensors have the following advantages:
DFRobot offers a small-sized photoacoustic carbon dioxide sensor. Its measurement range is 400 - 5000 ppm, and the accuracy is ±(40 ppm + 5% MV). It has an I2C interface, which can be easily connected to microcontrollers such as Arduino.
To demonstrate how to use this sensor, we made a portable carbon dioxide concentration indicator keychain. It can display the current carbon dioxide concentration, so that we can go outdoors to breathe fresh air or open windows for ventilation in time.