| Monitoring soil moisture content at different depths efficiently and rapidly and grasping soil moisture change trend at real time is of great significance to study the water demand of crops and to realize the intelligent irrigation of farmland.It is also an important basis for the realization of agricultural information and intelligence in the Internet of things environment.In order to realize the measurement of soil moisture content in di?fferent depths and meet the needs of the Internet of water acquisition nodes in modern intelligent irrigation on the soil vertical profile,in this paper,a portable soil profile moisture sensor is developed.The performance of the sensor was tested by experiments,and it was proved that it could meet the requirement of actual soil moisture monitoring and it can be applied to the intelligent irrigation of the Internet of things.The following is the main work of this paper:(1)In order to avoid the problem that probe type structure of the traditional soil moisture sensor is used for direct contact with the soil,causing corrosion which can affect the accuracy of measurement and to solve the problem that the length of the probe is not enough and it is difficult to monitor the soil water content in a simple and fast way,In this paper,a non contact measurement structure is designed,which is based on the ring metal electrode.Through the simulation software of high frequency structure HFSS,the different sizes of the electrode and the electrode spacing are simulated.Based on the analysis of the simulation results,the probe structure combination with the best sensing range is determined.(2)By using the high frequency LC parallel resonant circuit composed of a voltage controlled oscillator and an annular electrode,the acquisition circuit of the sensor measurement node is designed.The volumetric moisture content of the measured soil was measured by the measured output frequency;The measuring terminal control circuit is designed,which can be used to control and measure the different soil depth sensor using time sharing control method.The control circuit uses AVR microcontroller as the microprocessor,and the function of measuring the output frequency and temperature of the circuit is realized on the hardware;At the same time,the handheld terminal control system is designed,which can be used for making wired or wireless communication with the measuring terminal control circuit.It has a simple human-computer interaction function,and set aside the Internet of things acquisition node interface.(3)On the basis of the hardware circuit,the Arduino language(C language)is used to design the embedded part of the sensor software.I designed and implemented the software function,including the sensor measurement terminal control,frequency measurement,temperature measurement,soil moisture conversion algorithm,wired communications,wireless communications,and hand side button display program,etc.Through the joint debugging of hardware and software,the sensor can meet the actual measurement requirements.(4)Based on the test and verification of soil moisture samples with different volume,the soil volumetric moisture content model was built:Ov = 0.8644 x NV2-0.0888 x NV-0.0035,R2 = 0.9963;Through the three functional tests,the sensor is designed and tested.The results show that there is a good consistency between the different acquisition nodes(The absolute range of relative error is 0.00?1.17%),and the sensor measurement results have good reproducibility(The absolute range of relative error is 0.00?1.49%)and stability(The maximum relative error is 2.12%);It has good adaptability to different kinds of soil(correlation coefficient R2 = 0.9644,RMSE=0.0423);The results of measurements with commercially available sensors are small(RMSE=0.0205). |
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