| Wireless sensor networks are generated because of the expanding scope of application fields of wireless data transmission network. Especially in recent years the emergence of embedded wireless sensor network is quietly changing with every aspect of our work and life.The issue include the hardware design, software design, communication protocols, and other aspects. And I designed two practical, low-cost data acquisition node design based on wireless sensor network. In embedded wireless sensor networks, data acquisition nodes'mobility is weak,distribution environment is very poor, density is large(from tens to thousands of nodes). And in most cases, nodes are running on battery power, so power consumption is core issue in wireless sensor network's node hardware and software design.Node is the core of wireless sensor networks, nodes do not only cost lowly but also work as long as possible. Each node in the network is the terminal node and a router node, both can receive the data and forward data. IEEE802.15.4/ZigBee agreement meets these requirements, is optimized for embedded communication protocol for wireless sensor networks. According to the above requirements, the design present the solutions of wireless sensor network node and a number of solutions to further study issues.First, the hardware designData acquisition node hardware consists of three parts .Sensor part is mainly responsible for the collection of information and collection of signals into digital signals and transmitted to the micro-controller, for processing by the microcontroller. Here, I use the most commonly used sensors - temperature sensors DS18B20 and temperature and humidity sensor DHT11, two sensors are unique single interface mode, the microprocessor in connection with the sensor can be requires only one line of microprocessor and sensors can achieve two-way communication, to get quick and easy system integration. To facilitate debugging and taking into account the scalability of sensor, the sensor plates separate and connect with the core node board through the serial port.In the MSP430 + CC2420 program, the main controller is a TI company's 16-bit low-power microprocessor MSP430F149, realize the control and computing nodes, compared to other 16-bit micro-controller, it has more available resources and very low power consumption. RF module for sending data is, the physical realization of wireless communications. Wireless transceiver used low-power wireless RF transceiver chip CC2420 which meet the 2.4GHz IEEE802.15.4/ZigBee criteria. Communications between RF chip and micro-controller is using the JTAG interface to download the program. For the program of CC2430-chip integrated system, the biggest advantage is that CC2430 chip integrates enhanced 51 microprocessors, which nodes are smaller, cheaper. This program also uses JTAG interface to download the program.Second, software designIn software design, in order to limite time available of the subject, ensure the reliability and simplify software development,and to reducice software development time, in the MSP430 + CC2420 program I use embedded real-time operating system TinyOs, which is specifically developed for wireless sensor networks. Program in the CC2430, selected TI's free protocol stack Zstack protocol stack. The software's main function is to collect data and transfer through wireless between nodes.Third, system testThe entire system, including hardware testing, software testing and overall system testing. Hardware testing, including the board of the welding test, Weld sometimes happens, that can not be seen by naked eyes, when necessary according to test procedures to test in the end is the problem of the microprocessor chip or the RF problems, and then small light control will have a significant role, according to the color of light flash situations where problems can be resolved in accordance with the situation. As the chip packaging is different, microprocessor Weld is rarely, usually the number of radio frequency chips has more problems. Decomposition of software testing would be carried out separately debug unit. Serial interface part, wireless send data and wireless receiver data; further test the overall software,are from the collection of data to another node which receives these data, through the serial port debugging assistant this part of the testing process. Finally, the system performance parameters test include node distance test and node bandwidth test. After complete testing and debugging process, the collection data node based on WSN complete the pre-data collection requirements, the system fully functional work and stability, the parameters are up to standard.Fourth, SummaryThis article is devided six chapters to tell design process of collection data node based on wireless sensor network. The first chapter is introduction, which described in wireless sensor networks, research background and a brief description of the purpose; and the design of the research topic, the characteristics of the data acquisition nodes and applications are introduced. The second chapter discuss hardware design of data acquisition node. First introduces the data collection node's common schematic diagram, and then instruct specific design of the hardware-specific solutions, respectively MSP430 + CC2420 program and on chip integrated system CC2430 program. And the design of wireless sensor and communication interface design separately extracted description, communication interface design, including SPI serial communication bus, RS-232 serial interface, DMA controller. The third chapter discuss software solutions design of the data acquisition node. Software platform include IAR Embedded Workbench and Eclipse-based TinyOs operating system , software design for data acquisition node on the application layer, data link layer and physical layer for specific applications were introduced. Chapter four gives several examples about software design based on the ZigBee protocol, including Zstack protocol, MAC interface, and temperature control software design example. Chapter five give a specific test data of hardware test of the data acquisition node, including the node distance test and node bandwidth test. Chapter six is conclusion, a summary of the design. it present the design of wireless sensor networks research also not comprehensive enough and need for more in-depth study of local ideas. |
