The next review is about a home-built Co2 meter, which is built on the concept of NDIR. NDIR stands for non-dispersive infrared sensor which is a simple spectroscopic device often used as gas detector. It is called non-dispersive because wavelength which passes through the sampling chamber is not pre-filtered instead a filter is used before the detector. We already have NDIR based gas-modules which are a common type, small size sensor, using non-dispersive infrared (NDIR) principle to detect the existence of CO2 in the air, with good selectivity, non-oxygen dependent and long life.
The sensor used is a MH-Z14 IR module which outputs a PWM wave based on the level of gas detected. It has a sensitivity of 0 to 2000ppm Co2. For those who are interested in the project an inbuilt library has been provided for the AVR Mega controller whose main job is to read PWM and with the help of some mathematical operation, that are not too hard to derive, the level of Co2 is displayed. A rather simple project but it can act as a base who are needs level of Co2 in their projects.