Research Of Capacitive Humidity Sensor Based On Micro Control Unit

With the development of information technology, sensor technology gets moreand more attention. As a member of the family of sensors, humidity sensor is widelyused in the fields of military, meteorology, agriculture, industry, medical care,architecture etc. Recently, great progress has been achieved in this field at home andabroad. Humidity sensors are becoming intelligent, integrated, accurate and sensitive.In this background, this dissertation proposed a project that design a capacityhumidity sensor based on a micro control unit. The sensor owns the function ofnonlinear compensation, temperature compensation and is digital and intelligent. Themain content of this dissertation are as follow:First, I studied a humidity capacity HS1101LF made by Humirel corporation inFrance. I designed a linear voltage output humidity sensor based on it. The circuit ofthe sensor contained astable multivibrator circuit、filter circuit、comparison amplifiercircuit and so on. According to theoretical calculation and emulation and practicaldebug, I made the output voltage of the sensor change from0V to3.5V when therelative humidity changes from0%to100%.Then we tested the function of humidity sensor samples and attained the curve ofthe relation of humidity and voltage at10℃and25℃.Then we make a comparisonwith other humidity sensor products from both home and abroad, and I discoveredthat my sample was more sensitive and owned better degree of linearity, and theoutput voltage shared a bigger slope. However, I also met a problem that the curvelinearity and the output voltage of my sample changed with temperature.To solve the temperature drift and nonlinear problem I met above, thisdissertation proposed a design that using the processor stmf103c8t6to form a controlsystem. The control system contains a signal pickup module, a temperaturecompensation module, a nonlinear compensation module and a LCD display module.The system software designed with up-down procedure and mainly containedstmf103c8t6module and other function modules’programdesign.Finally, we combined the control system based on STM32and the linear voltageoutput humidity sensor together, do some test and validation. At last, we acquired thecurve about the relation of humidity and output voltage after compensation, and thecurve told that the control system based on stm32f103solved the temperature drift and nonlinear problem exactly and the aim of this dissertation was achievedsuccessfully.