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1、A wireless solution for greenhouse monitoring and control systembased on ZigBee technology*ZHANG Qian, YANG Xiang-long, ZHOU Yi-ming, WANG Li-ren, GUO Xi-shanAbstract: With the rapid development of wireless technologies, it is possible for Chinese greenhouses to be equipped with wireless sensor netw
2、orks due to their low-cost, simplicity and mobility. In the current study, we compared the advantages of ZigBee with other two similar wireless networking protocols, Wi-Fi and Bluetooth, and proposed a wireless solution for greenhouse monitoring and control system based on ZigBee technology. As an e
3、xplorative application of ZigBee technology in Chinese greenhouse, it may promote Chinese protected agriculture.Key words: Greenhouse, Monitoring and control, Wireless, ZigBee, IEEE802.15.4, JN5121INTRODUCTIONWireless technologies have been rapidly developed during recent years. Starting from milita
4、ry and industrial controls, it is now being widely applied inenvironmental monitoring and agriculture. Its advantages include the liability, simplicity, and low cost in both installation and maintenance. In greenhouse control applications, Serodio et al.(1998; 2001) developed and tested a similarly
5、distributed data acquisition and control system for managing a set ofgreenhouses. Inside each greenhouse, a WLAN network with a radio frequency of 433.92 MHz was used to link a sensor network to a local controller. Morais et al.(1996) implemented a wireless data acquisition network to collect outdoo
6、r and indoor climate data of greenhouses in Portugal. Mizunuma et al.(2003) deployed a WLAN in a farm field and greenhouse to monitor plant growth and implemented remote control for the production system. Mancuso and Bustaffa (2006) worked at a short-term deployment of a wireless sensors network in
7、a tomato greenhouse in the south of Italy.In China, Liu and Ying (2003) reported a greenhouse monitoring and control system using the Bluetooth technology. The system collected environmental data from a sensor network in a greenhouse and transmitted them to a central control system. Qiao et al.(2005
8、) introduced systematic frames of wirelesssensor networks and expatiated their agricultural applications such as monitoring greenhouse, irrigation, precision farming and so on. Luo et al.(2006) designed wireless sensors for greenhouse monitoring. The wireless communication was based on nRF401 wirele
9、ss module, working at 433 MHz ISM frequency. Wu et al.(2006) reported the design and implementation of Greenhouse Wireless Data Acquisition System based on CC2420, as a low-cost transceiver designed specifically for low-power, low-voltage RF applications at the 2.4 GHz unlicensed ISM band. Li et al.
10、(2007) reviewed cable and wireless communications used in agriculture, and compared their advanadvantages and disadvantages Wireless sensor technology, however, is still at its early development phase in China, and its applications in Chinese greenhouses remain few. In the current study, we compare
11、the advantages of ZigBee with two similar wireless communications, Wi-Fi and Bluetooth, and propose a wireless solution forgreenhouse monitoring and control system based on ZigBee technologyCOMPARISON OF ZIGBEE, WI-FI, AND BLUETOOTHPROTOCOLSWi-Fi, Bluetooth and ZigBee work at similar RF frequencies,
12、 and their applications sometimes overlap (Seager, 2006). In the current study, we chose the following five main factors of greenhouse networks to compare: cost, data rate, number of nodes, current consumption and battery life(1) Cost. ZigBee chip is US$ 1 or less, the lowest; Wi-Fi and Bluetooth ch
13、ips are $ 4 and $ 3, respectively. The overall system cost can be significantly reduced by the employment of ZigBee chip.(2) Data rate. ZigBee is 250 kbps, while Wi-Fi and Bluetooth are 54 Mbps and 12 Mbps, respectively. Despite the lowest data rate, ZigBee is sufficient for a greenhouse. Generally,
14、 data traffic in a greenhouse is lowusually small messages such as the change of temperature or a command from the controller to an actuator. And also, low data rate helps to prolong the battery life.(3) Number of nodes. The capacity of network is determined by the number of nodes, and ZigBee has up
15、 to 254 nodes, the largest among the three. It meets the application demand of more and more sensors and actuators in a greenhouse.(4) Current consumption. ZigBee has the lowest current consumption, 30 mA, while Wi-Fi, 350 mA, and Bluetooth, 65170 mA. It also greatly helps to prolong the battery lif
16、e.(5) Battery life. ZigBee chip has the longest battery life, a few months or even years.As a whole, ZigBee technology offers long battery life, small size, high reliability, automatic or semi-automatic installation, and, particularly, a lowsystem cost. Therefore, it is a better choice for greenhous
17、e monitoring and control than other wireless protocolsOUR WIRELESS SOLUTION FOR GREENHOUSEOverview of the solutionAs shown in Fig.1, wireless sensors, such as temperature sensor, humidity sensor, light sensor and so on (integrated with PIC 16F877 and ZigBee module), collect the environmental informa
18、tion and transmit it to hand-held controller (HHC) (integrated with ARM MCU and ZigBee module). In HHC, thedata is stored and displayed on the LCD. After the data being dealt through control algorithm, the HHC sends control commands to the actuators (also integrated with PIC 16F877 and ZigBee module
19、). The actuators accomplish the actual control task. All the wireless nodes are based on ZigBee module.We designed the nodes based on JN5121 module produced by Jennic Company (Jennic Ltd., 2006a).The JN5121 is the first in a series of low-power,low-cost IEEE802.15.4 compliant wireless microcontrolle
20、rs, combining an on-chip 32-bit RISC (Reduced Instruction Set Computing) core, a fully compliant 2.4 GHz IEEE802.15.4 transceiver, 64 kB ROM and 96 kB RAM. The high level of integration helps to reduce the overall system cost. The JN5121 connects upper controller and sensors/actuators through SPI (S
21、erial Peripheral Interface) or parallelNetwork establishmentSinem Coleri Ergen (2004) summarized three types of topologies of ZigBee: star topology, peer-topeer topology and cluster tree topology. In the star topology, the communication is established between devices and a single central controller,
22、 called the PAN (Personal Area Network) coordinator. The PAN coordinator may be mains powered, while the devices are most likely battery-powered. Each star network chooses a PAN identifier, which is not currently used by any other network within the radio sphere of influence.This allows each star ne
23、twork to operate independently. In our project, we established the network according to the star topology. As shown in Fig.2, once the HHC (FFD, Full Function Device) is activated forthe first time, it establishes its own network and becomes the PAN coordinator. Then it initializes the hardware, sta
24、ck and application variables, choosing an unused PAN identifier of zero, and broadcasting beacon frames to sensors and actuators (RFD, Reduced Function Device). Sensors and actuators receiving a beacon frame may request to join the network. The HHC will add them as a child device in its neighbor list and return a response. The sensors and actuators will add the HHC as its parent in their neighbor list and return an acknowledgement. The HHC monitors all network nodes in real-time, maintaining the network information database PIB