Research On STM32Humidity Sensing System Based On High Polymer Humidity Device

This thesis used the signal output circuit of high polymer humidity sensor as the core ofthe humidity sensing system. The author designed corresponding hardware circuit, softwareprogram, and PC interface.More and more fields need to measure and control the humidity, both in largeapplication of industrial production and small application of food storage. For example, theproduction shops of precision instruments need to detect the humidity accurately, or to causea decline in precision instruments. To prevent the paper from fading, and to reduce thewastage of the crops, libraries, archives, grain and other places also need to measure andcontrol the humidity.The humidity sensing system need to constantly improve, the most important reason isthat the humidity measurement is difficult. First, the humidity can be impacted by the changeof external environment factors instantly. Second, the methods of detecting humidity still canbe improved in many aspects. For instance, the method used to detect the humidity calledpsychrometer method use the different temperature of dry and wet balls to calculate thehumidity, that is hard to realize the electronic and the automation. Third, there is difficulty indemarcating the humidity. Another important reason is that as the concepts of "Internet ofThings" and "Smart Appliances" are deeply rooted in the hearts of the people, and theintelligent humidity sensing system has received more and more attention.This thesis selected humidity sensor based on high polymer named porous polytriphenylamine that loaded Fe(NO3)3as the humidity material. The LCR intelligent tester hasbeen used to test the characteristics of humidity sensor. The corresponding signal outputcircuit of the humidity sensor has been designed as the core of the humidity sensing system.First of all, in terms of hardware, this thesis improved the generation circuit of thesquare wave signal to design a signal output circuit of the high polymer humidity sensor. This circuit mainly includes two operational amplifiers, the role of one of the operationalamplifiers is the inverse hysteresis comparator, by adjusting the size of the feedbackresistance, which can guarantee the humidity sensor work under ac voltage. Anotheroperational amplifier is the role of voltage regulator. Humidity changes of the characteristicsof the signal can be converted into square wave signal to output, and by detecting thefrequency of square wave signal, the humidity can be calculated. The microcontroller of thissystem is produced by ST called STM32F103x as the main control chip of the wholehumidity sensing system, which is one of ARM chips with various interfaces with differentfunctions, they can equipped with LCD12864screen, level conversion chip(MAX232),DS18B20temperature sensor, the RS-232interface module and so on to meet therequirements of the humidity sensing system.Secondly in terms of software program, according to the design requirements, theauthor used C language to program in Keil u Vision4development environment. In order toachieve human-computer interaction, remote communication, to better meet the needs ofdifferent users, increasing the host computer program is written with LabVIEW2011software, which includes two kinds of mode, not only can realize a single measurement butalso can set the number of measurements to achieve multiple measurements. By thecomputer program, a computer can real timely and effectively to detect temperature andhumidity.After all the debugging, the humidity sensing system got the ideal experimental resultsof the measuring accuracy and stability.