Volatile Organic Compound Detector for Indoor Air Quality Measurement

Application circuit measures indoor air quality by using a metal-oxide sensor to detect gases composed of volatile organic compounds. The sensor is composed of a heating resistor and a sensing resistor. When the sense resistor is heated, its value changes as a function of the concentrations of different gases. The circuit uses a 12-bit, current output digital-to-analog converter (DAC) for precision control of the heater current, and the flexible software allows the heater to operate in one of the following four modes: constant current, constant voltage, constant resistance, and constant temperature. The circuit is able measure a wide range of sense resistance values by using a software-selectable, five range resistor divider. The board also includes a temperature and humidity sensor that is used for compensating the gas concentration value