Final project for graduation in electrical engineering, with emphasis in electronics, describing in detail the development of a gas detector equipment based on infrared radiation absorption. Knowing the optical absorption bands of the carbon dioxide, a system capable of measuring the concentration of the passing gas was developed, based on the comparison between a reference and a measured signals, according to Beer-Lambert s Law. Optically, the system is composed of an LED type emitter, a photoresistor type detector and special mirrors and lenses for the infrared. The LED s emission wavelength is the same as one of the carbon dioxide s absorption band. The system s calibration allows the measurement of the gas in a wide range of concentrations through the variation of the optical path length.