| With the increase of the world population,the demand for agricultural water is increasing,and smart agriculture and precision agriculture have become the development trend of modern agriculture.In order to accurately and stably measure soil water content using frequency domain measurement technology,a high-frequency soil water content sensor is used in this thesis,combined with NB-loT wireless communication technology to design a high-precision,easy-to-operate,low-power,automatic soil moisture content measurement system.The main research contents are as follows:(1)A set of soil moisture content measurement system based on high frequency oscillation method is proposed,including system external structure,hardware design scheme and software design scheme.By establishing a sensor probe model,the principle of high-frequency oscillation soil water content measurement is theoretically analyzed,which provides a theoretical basis for the development of sensor.(2)The system hardware scheme designed the soil water content sensor circuit and the NB-loT wireless communication circuit.The high frequency oscillating circuit with operating frequency of 75-100 MHz is designed to solve the problem of converting soil moisture content into oscillating signal frequency.Improve sensor sensitivity by analyzing and optimizing PCB layout,design a high-performance low-pass filter network,designed and implemented by adding advanced phase compensation method.Minimize overall system sleep power by controlling power supply to circuits such as sensor and memory chip.(3)The system software solution uses a modular approach to software design.Keil uVision5 is used as a development tool to design and implement the components of the system software.Improve the anti-interference ability of the whole system by using the watchdog interrupt reset function during software operation.(4)Consistent analysis of sensor measurements to verify sensor performance.The test results show,to verify sensor performance,repeat the test to verify that the sensor is very consistent.According to the calibration experiment,the calibration equation of sandy loam is obtained.Comparing the measurement results of the sensor and the drying method,the measurement accuracy of the sensor satisfies the soil moisture content accuracy requirements of the Ministry of Water Resources.Test the key indicators of the measurement system,and the test results meet the expected design requirements,which largely meet the actual engineering requirements. |
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