The Design of Wireless Sensor Network System Based on ZigBee Technology for Greenhouse

Wireless sensor network is a new research field. It can be used in some special situation for signal collection, processing and transmitting. Zigbee is a new Wireless sensor network technology characteristic of less distance and low speed. It is a new wireless network protocol stack of IEEE 802.15.4. Lately traditional system to collects parameters for Greenhouse is widely used in agriculture. The traditional system adopts wired way wiring, which makes the system complex and expensive. Generally modern Greenhouse has hundreds of square meters and they may plant variety of plants depending on different seasons. So we need to adjust the sensors which collect parameters for Greenhouse to a better place to work more efficient. Adopting wireless way wiring is convenient and economical. This paper developed a wireless sensor network system based on ZigBee technology for greenhouse. It offers flexibility and mobility to save cost and energy spent on wiring. The framework hardware and software structure, related programming are also discussed in this paper. Comparing the system which uses ZigBee technology with traditional wired network system for greenhouse, it has advantage of low cost low power and wider coverage. Additionally it complies with IEEE802.15.4 protocol, which makes it convenient to communicate with other products that comply with the protocol too. 1. Brief Introduction to ZigBee Technology ZigBee is a new technology now being deployed for wireless sensor networks. A sensor network is an infrastructure comprised of sensing, computing and communications elements that allows the administrator to instrument, observe and react to events and phenomena in a specified environment. Typical applications include, but are not limited to, data collection, monitoring, surveillance and medical telemetry. The administrator typically is a civil, government, commercial or industrial entity. The mainly advantages of ZigBee technology lies in the following aspects: (a) Reliable and self configuration. (b)Supports large number of nodes. (c)Easy to deploy. (d)Very long battery life. (e)Secure. (f)Low cost. (g)Can be used globally. 2. Wireless Sensor Network System for Greenhouse 2.1. System Framework for greenhouse Every greenhouse in this system comprises a gateway and some wireless nodes. Gateways and nodes are all embedded with a CC2420 RF transceiver (ZigBee compliant) produced by Chipcon company. Institute of Physics Publishing Journal of Physics: Conference Series 48 (2006) 1195–1199 doi:10.1088/1742-6596/48/1/223 International Symposium on Instrumentation Science and Technology 1195 © 2006 IOP Publishing Ltd Data can be transmitted by transceiver between gateways and nodes, and finally the data from all greenhouses are collected to be transmitted to a server. The sketch of the system is shown in Figure 1. The framework and functions of the system lies in the following: Functions of gateway: (1) Communicating with the server via Ethernet; (2) Communicating with nodes by RF transceiver. Framework and functions of wireless nodes: (1) Atmega128L MCU and TinyOS operating system; (2) Temperature, humidity and light intensity collection periodically; (3) Transmitting collected data to gateway by using CC2420. Figure 1. the Framework of Wireless Sensor Network for Greenhouse. Figure 2. Typical Framework of Wireless Sensor Network. 2.2. The Framework of Wireless Sensor Network The Framework of Wireless Sensor Network is shown in Figure 2. Each node can sense, compute and communicate each other. They can either receive message or transmits message, and can transmit messages to a gateway via self-configuration and multi-hop routing. The gateway can use many ways to communicate with remote network, such as Internet, satellite and mobile communication network (in this system we use Ethernet). More than one gateway may be used for large-scale application. Because of its limited communication areas the node must use multi-hop routing to access the nodes out of communication areas. 3. Hardware of Wireless Node The wireless sensor network nodes use battery power and their power capabilities are limited due to its small size of node. The transmission rate of the network is low and it needs enough power to work steadily for a long time. Therefore low-power design is significant. The system adopts MICAz mote module produced by Crossbow Technology and its sketch of hardware is shown in Figure 3. MICAZ is embedded with a ZigBee compliant RF transceiver and it works between 2.4 and 2.4835 GHz, a globally compatible ISM band. Its DDSS radio offers both high speed (250 kbps) and hardware security (AES-128). The MICAz 51-pin expansion connector supports Analog Inputs, Digital I/O, I2C, SPI and UART interfaces. These interfaces make it easy to connect to a wide variety of external peripherals, including a variety of sensor, data acquisition boards and gateway. 3.1. Microcontroller We adopt Atmega128L, a High-performance, and Low-power AVR 8-bit Microcontroller as our processor. The ATmega128 provides the following features: 32 general purpose working registers connected to ALU directly, On-chip 2-cycle Multiplier, 128K bytes of In-System Programmable Flash 1196