Portable infrared carbon dioxide detector for monitoring vehicular emissions

This paper describes the design of a portable carbon dioxide detector from low cost hardware and software components. The carbon dioxide molecules absorb light at a specific wavelength of 4.26 μm in the mid-infrared radiation. High concentrations of carbon dioxide molecules absorb more IR light than low concentrations. The design of the system includes a monochromatic infrared source, located in the source housing, and is activated by a constant voltage source obtained from the Switching Regulator Assembly. The infrared energy entering the sample chamber is absorbed at the wavelength specified as a result of the concentration of carbon dioxide being measured. The reflector assembly at the rear of the sample chamber returns the energy onto the IR detector. The detector signal is amplified by a low noise pre-amplifier and directed to the microprocessor. The signal goes into the processor through an ADC circuit. The amplitude of the digital signal is then threshold detected at a predetermined value to detect the amount of carbon dioxide.