Abstract: Sensor network is a new research field of computer science and technology. The sensor network formed by integrating sensors, MEMS and network technology is a new information acquisition and processing technology. In recent years, research on sensor network management, query and data distribution has been considerably developed. However, if the sensor network is to be put into use, it cannot be completely isolated. It needs to access the external network through the gateway device, such as the Internet, local area network or intranet, to provide remote access and monitoring of the wireless sensor network.
1. Overall system design
With the rapid development and maturity of communication technology, embedded computing technology and sensor technology, miniature sensors with sensing, computing and communication capabilities are beginning to emerge. The sensor network is formed wirelessly by a large number of low-cost sensor nodes of this type. Sensor network integrates sensor technology, embedded computing technology, distributed information processing technology and wireless communication technology. It is one of the emerging frontier research hotspots with high degree of interdisciplinary research. It has remote monitoring, real-time monitoring, and can be used in harsh or special Environmental work.
1.1 system hardware platform design
The system hardware platform design mainly includes the choice of microprocessor and the choice of peripherals. This paper selects ARM processor as the core device, and the peripheral devices include SDRAM, FLASH, serial port and Ethernet interface. The embedded gateway device consists of a core board and a backplane. The core board integrates AtmelAT91RM9200 processor, 64MSDRAM and 16M FLASHoAT91ARM9200 microprocessor chip is an industrial grade 200MIPSARM920T core with 16K bytes of instructions and 16K bytes of data cache processing. Device.
The following peripheral interfaces are provided on the gateway device backplane: two RS-232 serial ports and one lOM/100M adaptive Ethernet interface. The choice of peripheral hardware interface will determine how the entire system accesses the network. At present, the most common access method with low performance and high performance is to adopt the most mature Ethernet interface, which can meet the requirements of LAN access and most broadband network access. Therefore, the sensor network gateway device designed by Muwen accesses the Internet through the Ethernet interface, enabling remote users to manage the data of the wireless sensor network.
1.2 software platform design
The software platform design mainly involves two major aspects: one is the software part related to hardware: the second is the application software part. Hardware-related software includes ARM-based Linux kernel porting, bootloader migration, and more. The application software mainly includes two parts: one is WebServe: and TCP/IP protocol stack; the other is sensor data acquisition, fusion and storage, etc. This part includes remote management module, query instruction analysis processing module, data storage module, data. Analysis and fusion module and data acquisition module.
2, hardware circuit design
The system hardware platform is designed into two parts, one is the core board part, integrated with AtmelAT91RM9200 processor, 64MSDRAM and 16M FLASH memory: Second, the bottom plate part, consisting of two four-wire RS-232 serial ports and one 10M/100M adaptive Ethernet interface and other components.
2.1 SDRAM memory
SDRAM (SynchronousDynamicRAM) synchronous dynamic memory, using SDRAM small but can improve system performance, can also simplify the design and provide high-speed data transmission. Functionally, it is similar to conventional DRAM, but it also requires a clock to refresh. When the system is running, all programs and data interact with the CPU and peripherals in RAM (mainly in SDRAM), so the speed of SDRAM has a crucial impact on the speed of the entire system.
This article uses two Hynix HY57V281620BTSDRAM chips, 16MX 16-bit data width, a total of 64MSDRAM. The AT91RM9200 has a built-in SDRAM controller (SDRAMC) with SDRAM control interface, which provides great convenience for simplifying circuit design. The circuit is shown in Figure 1.
Figure 1 SDRAM memory circuit 2. 2RS232 serial communication port RS-232 is currently the most widely used serial interface in PC and communication industry. RS-232 is defined as a single-ended standard that increases communication distance in low-rate serial communications. RS-232 adopts a small balanced transmission method called so-called single-ended communication. The serial signal output by the AT91RM9200 is TTL level and must be level-converted to meet EIA/TIA-232 levels. The circuit design is shown in Figure 3.
2.3 100M Ethernet
The AT91RM9200 integrates the Ethernet controller EMAC (EthernetMAC) to make this chip more widely used. From the hardware point of view, the Ethernet interface circuit is mainly composed of two parts: the MAC controller and the physical layer interface. In this design, LXT972 is used as the physical layer interface of Ethernet. The LXT972 is a low-power, high-performance chip that supports lOM and 100M Ethernet transmissions, which encode and decode input and output data. Since the EMACs of the LXT972 and AT91RM9200 support the MII interface function, they can be connected according to the definition of the signal. The transmitting and receiving ends of the signal are connected to the transmission medium through the network isolation transformer and the RJ45 interface. The Emac block diagram is shown in Figure 4.
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