A NDIR-based CO2 monitor system for wireless sensor networks

The ever-increasing application of wireless sensor networks in many different fields is causing a growing demand of low-cost energy-efficient sensors for monitoring physical variables such as temperature, pressure or gas concentration. This paper presents a conditioning system for low-cost non-dispersive infrared gas sensors used to measure the CO₂ concentration in an open air environment. It mainly consists of an amplification and filtering circuit that adapts the small and noisy signal provided by the sensor to a signal which can be easily read by a low-power microcontroller. The proposed interface presents a good tradeoff between energy consumption and accuracy, compatible with the energy requirements of wireless sensor network applications. Test performed connecting the system interface to a node sensor in a wireless sensor network using a simple communications protocol only causes a 5% reduction in the operating life of the node.