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Drip Irrigation Control System Based on Pulse Width Modulation (PWM)

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Author
Tutor: WangXiao
School: Nanjing Agricultural College
Course: Detection Technology and Automation
Keywords: drip irrigation,PWM control,wireless sensor network,Water-saving irrigation,Soil
CLC: S152.7
Type: Master's thesis
Year:  2011
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Abstract:
The level of automatic control water-saving irrigation technology is a status of benchmarking to measure a country¡¯s agricultural modernization development. At present, the methods of hand and experience are used for drip irrigation, which seriously affect the level of automation of irrigation and water-saving efficiency. As to this condition, according to the laws of soil moisture movement after drip and the effects of drip irrigation frequency on the soil moisture distribution, a real-time irrigation control system based on PWM (pulse width modulation) is proposed in this paper.The system consists of the following several parts:Collecting information transmission module composed of wireless sensor network, the PC superior central monitoring module and pulse width modulation PWM control module. based on temperature and humidity acquisition module and DA300 expansion module (soil humidity acquisition module)terminal of Wireless sensor network gathers environmental data in real time which are transmitted to the PC monitor center through Wireless sensor network. After comprehensive analysis of PC monitor center, the comprehensive data on soil moisture are sent to gateway by 232 communication ports, which sends the analysed data to each terminal (CC2430) using wireless sensor network, and then the suited PWM waveforms outputted by PWM Control module, are sent to the radiotube actuator by drive circuit.According to humidity, temperature, light and soil humidity in the crop area, the system can make comprehensive processing and judgment. After the synthesized data converted to digital value by the A/D conversion are dived into microcontroller. The system makes reasonable PWM control decisions according to deviation size by comparing the actual value with the given value. PWM waves generated by MCU are controlled by PWM control technology based on the output of soil humidity deviation and change trends. The drip irrigation frequency based on soil moisture is obtained through the changes of PWM duty ratio. In order to understand the relationship between soil moisture and drip irrigation frequency, the soil water movement laws are studied under the condition of drip. The results show that when the laid location of soil moisture sensor is 5cm away from the emitter horizontally and 10cm vertically, soil moisture changes can be well monitored.Field experiments show that the system is stable, reliable, and can monitor field environmental information and soil moisture in real time. In addition, precise irrigation can be realized combining with PWM irrigation control model and automatic agricultural water-saving irrigation is also achieved.
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