Design of regulation system of light environment in greenhouse based on wireless sensor network

Abstract: In China, the monitoring methods and regulation systems of precision agriculture have some deficiencies, especially in light environment regulation. Recently, light environment regulation has become a significant research focus in the precision agriculture development of our country. Important factors in light environment regulation consist of expandability, energy consumption, deployment and maintenance, and dynamic regulation of light illumination, which directly affects crop production, quality, and efficiency. First, studies on the biological mechanisms of photosynthesis have provided a theoretical basis for accurate and quantitative regulating of the light of crops. Secondly, with the rapid development of semiconductor and opto-electronics technology, specific-band, single-wavelength and narrow-band light emitting diodes have been produced. And wireless sensor network technology has been applied to more and more fields, such as environmental monitoring and controlling. Based on the above analysis, using a wireless sensor network, an intelligent light environment regulation system was designed, which was described from the overall architecture, hardware, software features, and experimental verification. The system adopted a tree topology and took CC2530 as the core processor, which could realize a self-organized network and information transmission by ZigBee. It was comprised of three kinds of nodes: the central control node, environmental monitoring node, and light regulation node. The environmental monitoring node adapted a 6450 vantage pro-solar radiation sensor and a DS18B20 temperature sensor to gather internal environment information in a greenhouse. Using the proportional relationship of a solar elevation angle and a red-blue light, the current photo flux density (PFD) of the red-blue light was calculated, which was combined with the temperature information in the greenhouse and was transmitted to the central control node periodically. At the same time, the monitoring node realized routing forward as the ZigBee routing node. The light regulation node, as a ZigBee leaf node, received regulating control parameters of the red-blue light. Through controlling the light emitting diodes output intensity by pulse width modulation (PWM), the light regulation node implemented real-time, wireless, and quantitative supplemental light control. The central control node, as the ZigBee root node, had functions of network coordination and intelligent controlling. According to the monitoring information and threshold value of temperature and photo flux density of the red-blue light, the supplement light value of crops were calculated, and then was converted to a PWM control signal which was transmitted to the light regulation nodes. Based on the characteristics of the actual system and light requirements of crop growth, the actual deployment scheme of the regulation system was optimized, which could effectively improve the utilization rate of light intensity. From October 2012, the system has been deployed in the modern agriculture exhibition area of Wuquan in Yangling. Compared to the results tested by spectrometer, the relative error of PFD values of red-blue light monitored was within 6%. Field test results showed less than 3% relative tolerance in outputting light value. Experiments proved the system could realize real-time, on-demand, quantitative regulated under the condition of temperature constraint and dynamically adjusted energy output under the condition of meeting the demand of crops. So it has the advantages of highly reliable, easy to expand, low-power.