Abstract: Wireless sensor networks [1], which integrate multiple disciplines such as sensor technology, embedded computing technology, distributed information processing technology and communication technology, have attracted great attention. They have wide applications in fields such as national defense, environmental science and smart homes. Since they usually operate in environments that are inaccessible or difficult for humans to access, and energy cannot be replaced, the design of reasonable network nodes has become a key issue for wireless sensor networks. This paper proposes a design scheme for ZigBee wireless sensor network nodes based on the RF chip CC2430 and a microprocessor. The composition and working principle of the system are discussed, and the hardware circuit and software design of the system are explained. Keywords: Wireless sensor network, ZigBee technology, CC2430 [b][align=center]The design of Zigbee sensor wireless network node based on RF CC2430 Liu Yaju, Cai Zhenjiang, Zhang Li, Li Dongming, zhaoqiuxia[/align][/b] Abstract: Wireless sensor network are integration of sensor techniques, nested computation techniques, distributed computation techniques and wireless communication techniques and so on, is an interesting field, and gains more and more attentions. The wide application prospects make it develop rapidly in some fields such as military, environment science, smart home and so on. As it running at a remote area where people can't or can't conveniently reach and might being impossible in substitution of power resources, the wireless sensor network has a key problem on designing a rational network node. The design of ZigBee wireless solution is presented mainly adopting RF chip CC2430 with MCU. The system's structure and working principle, and hardware circuits and software designing are given too. keyword: Wireless sensor network, ZigBee technology, RF CC2430 I. Introduction ZigBee[2] is a wireless technology based on the IEEE 802.15.4 specification. It has many advantages such as security and application layer interfaces created on the 802.15.4 specification, operation in the unlicensed 2.4GHz band, ultra-low battery life calculated in years, highly scalable network and star network topology (each master device can support more than 40,000 nodes), and has great development potential in the fields of national defense, industrial control, and consumer electronics[3]. The RF CC2430 chip[4] is supported by a powerful integrated development environment, and the interactive debugging of internal circuits is supported by the IAR industry standard of IDE, which has been highly recognized by embedded systems. It combines Chipcon's advanced global ZigBee protocol stack, toolkit and reference design to demonstrate leading ZigBee solutions. Its products are widely used in the fields of automobiles, industrial control systems and wireless sensor networks, and are also suitable for other devices in the 2.4GHz frequency other than ZigBee. II. Hardware Design 1. Internal Structure of the Chip Wireless Transceiver Module The internal structure of the CC2430 chip is shown in Figure 1. After the radio frequency signal received by the antenna is processed by low noise amplifier and I/Q downconversion, the intermediate frequency signal is only 2MHz. This mixed I/Q signal is filtered, amplified, AD converted, automatic gain control, digital demodulation and despreading, and finally the correct data of transmission is recovered. [align=center] Figure 1 Internal structure of CC2430 chip[/align] The transmitter part is based on direct upconversion. The data to be transmitted is first sent into a 128-byte transmit buffer. The header frame and start frame are automatically generated by hardware. According to the TEEE 802.15.4 standard, every 4 bits of the data stream to be transmitted are spread by a 32-chip spread spectrum sequence and sent to the DA converter. Then, the radio frequency signal after low-pass filtering and upconversion is finally modulated to 2.4GHz and amplified before being transmitted through the transmitting antenna. 2. System hardware design Sensor nodes are generally composed of modules such as data acquisition unit, data processing unit, data transmission unit and power management unit[5]. The node hardware structure is shown in Figure 2. The ATmega128 microprocessor communicates with the CC2430 RF transceiver chip via the SPI bus and some discrete control signals. [align=center]Figure 2: Block diagram of sensor network node composition[/align] The peripheral circuit of the CC2430 is shown in Figure 3. The CC2430 internally uses a 1.8V operating voltage, suitable for battery-powered devices, while the external digital I/O interface uses 3.3V, maintaining compatibility with 3.3V logic devices. It integrates an on-chip self-regulator that converts 3.3V to 1.8V. This means that devices with only a 3.3V power supply do not require additional voltage conversion circuitry to operate normally. [align=center]Figure 3: Peripheral circuit of CC2430 chip[/align] The CC2430 transmits and receives RF signals differentially. Its optimal differential load is [value missing], and the impedance matching circuit should be adjusted according to this value. If a single-ended antenna is used, a balanced/unbalanced impedance conversion circuit (BALLUN) is required to achieve optimal transmission and reception. The CC2430 requires a 16MHz reference clock for transmitting and receiving 250kbps data. This reference clock can be from an external clock source or generated by an internal crystal oscillator. If an external clock is used, it is directly introduced from the XOSC16-Q1 pin, and the XOSC16-Q2 is left floating; if an internal crystal oscillator is used, the crystal is connected between the XOSC16-Q1 and XOSC16_Q2 pins. The CC2430 requires the accuracy of the clock source to be within 100%. III. Software Design According to the hardware circuit design, the basic idea of ​​system software programming [6] is: first initialize the SPI port and CC2430 control port; enable the SPI port, UART port and ADC; initialize the CC2430 chip; after turning on the receiver, the task program can be run to receive or send data. The flowcharts of the sending and receiving programs are shown in Figure 4 and Figure 5. [align=center] Figure 4 Flowchart of the sending program Figure 5 Flowchart of the receiving program[/align] The wireless communication protocol is an important issue in the software because it is directly related to the performance of the node. Therefore, at the link layer, a simplified CSMA/CA protocol was designed, that is, any node must listen for a random period of time before sending, and only send data when it is confirmed that no other node is transmitting data. The sender and receiver exchange data through a three-way handshake. When the system is idle, the listening function is turned off to minimize power consumption. Of course, this protocol has problems such as hidden nodes and power loss during listening, but it is still very effective within a certain number of nodes. At the network layer protocol, a simplified IPv6 routing protocol[7] was adopted. The reason for adopting IPv6 is to take into account its huge address space, neighbor discovery function, good security and other excellent characteristics. IV. Conclusion The Smart RF CC2430 is a highly integrated commercial radio frequency transceiver device that conforms to ZigBee technology. Its MAC layer and PHY layer protocols conform to the 802.15.4 specification and operate in the unlicensed 2.4GHz band. Wireless sensor network nodes developed using this chip have low cost and low power consumption and are suitable for long-term battery power supply. It features hardware encryption, security and reliability, flexible networking, and strong resilience, providing an ideal solution for the widespread application of wireless sensor networks. References [1] Chen Shuai, Zhong Xianxin, Liu Jixue, et al. New progress and application of wireless sensor networks [J]. Piezoelectrics and Acousto-optics, 2006, 28 (3): 297-299 [2] Jon Adams. Designing with 802.15.4 and ZigBee. www.zigbee.org, 2004 [3] Yuan Yi, Su Honggen. Research on wireless network application based on ZigBee technology [J]. Computer Applications and Software, 2004, 21 (6): 89-91 [4] SmartRF CC2430 Peliminary (rev.1.O1). 2005 [5] HILL J, HORTON M, KLING R, et al. The platforms enabling wireless sensor networks [J]. Communications of the ACM, 2004, 47 (6): 41-46 [6] Li Li. An Implementation of a Bluetooth Wireless Sensor Network [J]. Microcomputer Information, 2006, 22(7): 59-62 [7] Hou Huifeng, Liu Xiangwen, Yu Hongyi, et al. Research on Interconnection Methods of Wireless Sensor Networks and IPv6 Networks [J]. Telecommunications Science, 2006(6): 59-62