A multi-gas sensing system for air quality monitoring

It is widely known that the atmosphere has been highly polluted over the recent years, and thus more and more people start to take this subject seriously. The air pollutant are emitted from both man-made and natural sources, such as burning of fossil fuels in electricity generation, industrial process and solvent use, and windblown dust. Therefore, most of the existing air-quality monitoring products aim to detect harmful gases which are common seen pollution resources, such as carbon monoxide (CO), carbon dioxide (CO 2 ) and formaldehyde (CH 2 O) as well as a mixture of smoke and fog, i.e. smog (PM2.5). Most of the current affordable air monitor system can detect only one kind of gas. When multiple gases are of interest, users have to buy many products. In this paper, we propose a wireless multi-gas sensing system which is able to detect the concentration of three harmful compounds, i.e. CO, CO 2 and CH 2 O as well as PM2.5. A smartphone App is developed to show real-time data and alert users when the corresponding gas concentration is too high, so that users can take actions to eliminate those factors in time. The hardware sharing technique is utilized to maximize the hardware utilization and thus reduce the hardware cost. As far as power consumption is concerned, the energy-hungry Wi-Fi module will enter the deep sleep mode while the Bluetooth mode is selected. The power consumption saving report is given. In addition, the sensor calibration schemes for these four gas sensors are also presented in this paper.