| Wireless sensor network (WSN) is combined by wireless network and sensors. Wireless sensor networks, plastic electronics and bionics in human organs are together known as three the world's major high-tech in the future. There is a definition of WSN. It is a network of RF transceivers, sensors, machine controllers, microcontrollers and user interface devices with at least two nodes communicating by means of wireless transmissions. It can be set everywhere randomly to detect or percept the environment information by the way of multi-hop routing. Received data pack would be transmitted to the data processing center. WSN has changed the interaction of people and nature by combined the information world and the real world logically. As can be seen, data collection played a crucial role in WSN. This paper takes this as an opportunity to design and implement a handheld PDA system which is convenient and easy to operate. The system can be used in environment detection for data collection. Data packs can be transmitted to the data server or other sensors at real time. Work efficiency of staffs would be improved greatly. For example, working in wine temperature detection or meter reading in the three meters, wireless handheld PDA collects the data which is sent by nodes in WSN and stores them into its cache. It is located in the data layer of the system."Node - node relay - wireless handheld PDA / base station - the server"is the process of data collection of the entire system. It communicates with server by relevant applications. Data applied to the upper call can be analyzed and processed by server.The hardware platform of the handheld PDA system was built by S3C2410 processor based on ARM9 architecture and CC2420 RF module produced by Chipcon AS Company. S3C2410 processor is produced by Samsung Company. It's based on the ARM processor core ARM920T. S3C2410 processor running at up to 203MHz, the size of the core board is only about the 2 / 3 of the size of the business card. It has high reliability and rich peripheral interfaces. The operating speed and size are on the demand of the system meanwhile. Therefore S3C2410 is taken as the processor. CC2420 is introduced by Chipcon as the first RF transceiver based on zigbee protocol. It needs only a very small number of external components to ensure the effectiveness and reliability of short-distance communication with stable performance and low power consumption. CC2420 is chosen as RF module for wireless communication because its data transfer rate is up to 250kbps and it can achieve point to point network as quickly as possible.Embedded software platform is built by Linux operating system, because it has the following advantages: the cost-free license, a high degree of stability, transplanted easily, powerful networking features, good development tools, and comprehensive technical support, also the trend of open source and the company needs to enrich the product line. It includes: bootstrap loader, including the code in the firmware and bootloader; core, embedded cores on customized specific board, as well as controlling kernel boot parameters; file system, including the root file system and the file system set up in the Flash memory devices. It provides a variety of configuration files of the management system and the environment where system implements user applications; user applications, users'specific applications procedures. The first step to build software platform is to set up cross compile environment. It has follows aspects: installing the cross compiler tools toolchain, transplanting bootloader, burning Linux kernel image, updating the root file system. Vivi is taken as the system bootloader. Its function is copying the kernel from flash memory to RAM, implementing the kernel, initializing the hardware and providing the function of writing into flash memory which means it can firm process and providing the interface to send commands to target board or notify the user of the state of target board. Final step is to start the NFS service for updating the file system, YAFFS can be used as a file system because when the YAFFS read and write file system, the preservation of the files and settings will not be lost after power down.After built hardware and software platform, in order to make CC2420 work, it should develop SPI and CC2420 driver under linux 2.4 kernel. SPI bus developed by Motorola is full duplex synchronous serial bus, which has a master device and one or more slave devices. The master device starts synchronous communication with slave devices in order to exchange the data. S3C2410 is designed to communicate with CC2420 through SPI bus. According to user's manual, some registers will be configured to make SPI bus initialize. A function is used to release SPI bus. Another function is defined in order to transfer data on SPI bus. After these works, SPI driver is completed. Before CC2420 is developed, it should understand how CC2420 works. There is a work flow of CC2420. Character device drivers follow the same development steps: First of all, device initialized, including device registering with kernel and registers mapping to memory address. Then file_operations structure should be completed, includes opening CC2420, sending data, receiving data and releasing CC2420. Finally it unregistered device with kernel for the sake of releasing resource. After related drivers compiled, it can load or unload diver module of device. Some applications related to the system can be programmed after device driver works correctly. So far there are two basic functions programmed. One of them is serial communication; the other is multi-thread client/server service. RS232 interface is used as S3C2410 serial port. Main steps of serial communication are: opening serial port, setting serial port, mainly valued the members of termios structure, waiting to select, reading or writing serial port and closing serial port. Head file pthread.h is included to program multi-thread client/server service. The application adopts TCP protocol which is based on connection-oriented services by the way of three times handshake. Using the design of data communication protocols, wireless handheld PDA data collection system can analyze different types of data packets, so that some operations such as collecting informations btween nodes, controlling nodes or time synchronization in WSN can be realized.A framework of a handheld PDA system for wireless data collection now is completed. With the improvement of functions in the future as well as the continue development of GUI programming, a large number of the system used to collect data in WSN can be seen in order to improve the accuracy and efficiency of work, meanwhile it can enrich the function of WSN to realize the relevant node mobile work. With the upgrading of hardware, as well as the improvement of network data transfer speed, wireless sensor networks have a very wide range of applications, not only in industry, agriculture, military, environmental, medical and other traditional areas of great value, but also in emerging areas, such as home life, health, transportation and other fields which will be shown its superiority in the future. It dares to foresee the future, wireless sensor networks will be ubiquitous and fully integrated into our lives. Such as micro-sensor network will be eventually possible with daily necessities such as home appliances connected to the Internet to achieve long-range tracking. Wireless sensor networks will be set everywhere in the future, and they could be used on aspects which are related to daily life and human society in all areas of production activity. |
PDF Full Text Request