CO2 sensors are often used in building automation to monitor the quality of the air and to trigger measures to improve that quality. These devices have proved very useful during the recent covid-19 pandemic. They are usually powered using mains or batteries. However, there are use cases where energy autonomy is desired. In some cases, it is also advantageous to transmit the data to a central point, using an appropriate long-range protocol.
CO2 sensor using the NDIR method are among the best in terms of measurement quality and life span. However, that method requires more energy, which negatively impact energy consumption. LPWAN protocols also require more energy than short range wireless systems. All that make it difficult to design a good quality node that measures often and yet runs on harvested energy indoors.
We first analysed the energy requirements of different NDIR sensors that on the market in order to choose the most appropriate. We then used some power management techniques to optimise the power consumption of the node and to make it operate in an office environment using LoRa.
At 350 lux (artificial light) and using a solar cell of 8 cm2, sufficient energy is harvested to make measurements and transmit the data every minute, using the LoRa protocol with SF7.
We will present the challenges of the design, explain how those challenges were solved and show the results.