Hardware Design And Firmware Development Of Humidity Sensor Measure System Based On DSP Technology

Humidity is a physics quantity that is often encountered in our daily life. The humidity measurement is accomplished by the humidity sensor. In our country, there is a very high demand for humidity sensor in every field. But the low efficiency of the measurement restricts the further growth of the production. Therefore, how to solve the problem of automatic batch measuring becomes the chief factor that restricts the improvement of production efficiency. The paper introduced the measurement theory of capacitive humidity sensor complex number voltage and establishes humidity sensor complex number voltage measure mathematics model based on DSP technology which is used in circuit design to simple the circuit and reduce the error segment. All of these were provided a theory to realization high precision and high speed measurement. The paper designs humidity sensor measure system which uses TMS320LF2407A as the main control device to realize hardware circuit design; using high speed SPI interface D/A chip MAX5722 bring sine wave; uses USB interface chip PDIUSBD12 for high speed bus communication and uses digital electronic switch CD4051 for multi-route channels selection design. They are improved agility, adaptability and expansibility of the system. The system accomplishes the measurement of capacitance(C) and quality factor(Q) of the 32-route capacitive humidity sensor with high speed and high accuracy. In the measurement of 30~100pF capacitance, the quote error is 0.2%. The accomplishment of this system not only solves the problem of high error and low speed in the process of producing humidity sensor but also provides reference of method and system frame for designing similar measure system.