Development Of Solar-powered Soil Moisture Monitor

As we all know China shows a shortage in water, its per capita water is low, the same time, our country is a large agricultural country, the use of agricultural water accounted for70percent of the total water consumption, irrigation water accounted for90%of agricultural water. So the state has to strongly advocate the reasonable irrigation and precision irrigation. This will not only help us to save the water resources, but also can increase crop’s yield and quality, and improve the ecological environment. To save water resources, the most important thing is the real-time monitoring of soil moisture status. Developing an energy efficient, low carbon, environmental protection, high sensitivity, stable performance and wide applicability soil moisture monitor is the basic and technical assurance for reasonable irrigation and precision irrigation. The main work of this thesis as follows:(1)By consulting a large number of literatures, compare and analyze the disadvantages of soil moisture monitor home and abroad, use the high frequency electric field theory to produce a soil moisture sensor. Study on the optimum frequency of the soil moisture sensor, finally choose the50MHz high frequency as the signal source of the monitoring system. The source operating voltage is5V.(2) Designed and developed the signal acquisition, modulating and display circuit. The measured soil moisture data is displayed by LCD and stored by the system.(3) Use the yellow and purple soil of Chongqing district to calibrate the system respectively. With the different content of soil moisture, there is a linear relationship between the voltage the system measured and the water content. By MATLAB, fit out the maths model of yellow and purple soil moisture. Bring the model in the MPLAB, and programme into single-chip microcomputer. The system can be used to monitor the change of the yellow and purple soil moisture content.(4) The system power is supplied by solar battery indirectly. The solar battery management circuit is used to charge the lithium battery, using efficient step-up or step-down module to meet the system’s requirement of5V stable DC voltage. The system can realize the lithium battery voltage monitoring, when lithium battery voltage value falls below the threshold, switching to the other one for power supply, and charge the battery, so as to ensure the full utilization of the solar energy.(5)By using the monitor, study on the measurement error, stability and reliability of the system. The experimental results show that the maximum relative error of the yellow soil moisture measurements is9.8%. and the purple one’s is9.7%. The test data shows that the system is stable and reliable, it can meet the measurement requirements. The characteristics of the system are convenient, fast, easy to carry, low cost and low power consumption, it can achieve the design aim.