Development of seismic intensity meter based on IPv6 and ARM9

Using low-power miniature capacitive tri-axial accelerometer as the sensing component, an ARM9-based embedded system with customized Linux as the master control system, and wireless communication technology that complies with the 802.11b standard as the network access method of the instrument, we have developed an SI-2 type seismic intensity meter based on wireless IPv6, which realizes the network and digital observation of earthquake intensity and solves the problem of lack of instruments for directly measuring earthquake intensity in my country.

introduction

当前国内外已建设的城市地震灾害速报系统一般以地震烈度计观测系统为主体。日本东京煤气公司在1994年就完成了由331台谱烈度计、20台液化传感器和5台强震仪构成的地震监测与震害快速评估系统(SIGNAL)。阪神地震取得显著的减灾效益后，东京煤气公司于1997年～2007年的十年间布设了3 800个新型地震谱烈度计。

At present, the earthquake intensity measured by instruments in my country is calculated by converting the observation data of strong motion instruments. However, the structure of strong motion instruments is relatively complex, the manufacturing cost is very high, and it is not convenient to deploy them on a large scale. It is also unrealistic to use a large number of foreign earthquake intensity measuring instruments. Therefore, it is necessary to independently develop earthquake intensity sensors suitable for my country.

In recent years, the research and application of sensor networks have become a hot topic. Professional sensor components are also developing towards miniaturization and high precision. The development of sensors has shown a new trend of intelligence and networking rather than the traditional simple detection function. Network sensors are based on embedded microprocessors and integrate sensors, signal processors and network interfaces. Due to the introduction of microprocessors, embedded technology and integration technology, the size of sensors is reduced, the anti-interference performance and reliability are improved, and the real-time and reliability of the control system are improved; the application of network interface technology provides great convenience for the expansion of the system, and has the advantages of easy remote operation, simple maintenance, and real-time monitoring. Therefore, embedded systems and network technologies have been widely used in the field of earthquake observation.

In view of this, the newly developed SI-2 seismic intensity meter is not just a simple seismic intensity detection instrument, but a highly integrated networked sensor, which integrates seismic intensity sensing devices, acquisition modules, embedded processors and memories, communication devices, embedded software systems, etc. It has functions such as data acquisition, data storage, data communication, and positioning, and can be wirelessly connected to the IPv6 network. The IPv6-based seismic sensor demonstration network built using the SI-2 seismic intensity meter has broad application prospects in earthquake monitoring and early warning, earthquake emergency rapid response, and earthquake disaster reduction.

1 System Architecture

The software and hardware resources of the IPv6-based SI-2 seismic intensity meter are composed of acceleration sensors, data acquisition modules (A/D), power supplies, embedded systems (CPU), wireless network cards that comply with the 802.11b standard, GPS, built-in measurement and control software, and other modules. The operating system that comes with the existing embedded systems on the market is generally the Linux 2.4 kernel. In order to support IPv6, the kernel of the operating system must be recompiled and upgraded to the 2.6 version kernel. Figure 1 shows the overall architecture of the SI-2 seismic intensity meter.

2 Selection of main components

2.1 Sensing components

The MMA7260Q low-power miniature capacitive triaxial acceleration sensor produced by Freescale of the United States is selected. The sensor itself has the characteristics of signal conditioning, first-order low-pass aluminum foil and temperature compensation, high sensitivity, low noise, low power consumption, linear output, self-test, etc. The measurement range is +/-2 g, and the measurement accuracy is 0.2μg.

2.2 Data Acquisition A/D

Earthquake intensity is obtained by measuring acceleration. According to the China Earthquake Intensity Scale, the maximum earthquake intensity of 2 g corresponds to an acceleration of about 200 cm/s2. Using 10-bit A/D for sampling, the acceleration resolution is 0.04 g, and the corresponding intensity resolution is 0.024 degrees, which is much higher than the accuracy that people can accept.

2.3 Embedded Systems

The embedded system uses Samsung's S3C2410X based on ARM microprocessor. S3C2410X adopts 6-layer board design, uses ARM920T core, and has full-performance MMU (memory processing unit) inside. It has excellent characteristics such as high performance, low power consumption, rich interfaces and small size. 64 MB SDRAM, 64 MB NAND FLASH, 1 MB BOOT FLASH, RJ 45 network card, USB Host, standard serial port, SD card socket, etc. are integrated on the smallest possible board. Embedded wireless LAN equipment can be integrated to realize data collection and wireless transmission.

2.4 Positioning module

The selected GPS module has the following receiving characteristics: 16 channels, L1, C/A code; built-in ceramic antenna; start-up time: cold start 45 s, warm start 38 s, hot start 2-8 s; accuracy <2.5 m CEP; recapture <1 s, 1PPS; refresh rate: 4 Hz; built-in LNA; speed <4 g.

2.5 Communication components

Taking into account the actual needs of earthquake observation in the seismic industry, a wireless network card that complies with IEEE802.11b and a wireless AP with a communication distance of 1.2km are used to form a communication link as the wireless communication unit of the SI-2 type seismic intensity meter.

2.6 Power Module

A rechargeable lithium battery pack is used as the power supply for long-term repeated use. The battery pack capacity is 60 Ah.

3 System Function Implementation

3.1 IPv6-based SI-2 seismic intensity sensor

The operating system that comes with the ARM embedded system is generally based on the Linux 2.4 kernel. To support IPv6, the kernel of the operating system must be recompiled and upgraded to the 2.6 kernel. However, recompiling the Linux 2.6 kernel is a relatively complicated process. The specific steps are as follows:

3.1.1 Establishing a cross-compilation environment

To develop kernel porting on a RedHat9 host, you first need to build a cross-compilation environment. Since the 2.6 kernel uses some new features and instructions, a newer tool set is needed. Use binutils-2.15, gcc-3.4.2, glibc-2.2.5, linux-2.6.8, glibc-linuxthreads-2.2.5 to build a cross-compilation tool chain. After building it, add the tool chain path to the system path MYMPATH.

3.1.2 Kernel modification

The Linux 2.6.11.7 kernel has added support for the S3C2410 chip, and no patch files are needed. Modify the cross-compile options ARCH=arm, CROSS COMPILE=arm—linux-1 in the Makefile in the kernel source code. For hardware configuration, you need to add the FLASH partition information s3c nand info in arch/arm/mach—s3c2410/devs.c or smdk2410.c. Then add .dev={.platform data=&s3c nand info} in s3c device nand, and add &s3c device nand in the initdata section in arch/arm/mach—s3c2410/mach—smdk2410.c, so that the kernel can initialize the NAND FLASH information when it starts.

3.1.3 Kernel compilation and loading

Since the 2.6 kernel will be initially configured according to the local system configuration, you can import the default S3C2410 configuration file of the kernel source code to facilitate loading the basic kernel configuration, and then select the required options. For the MTD configuration, select to support the MTD device driver and NAND FLASH driver; select to support various file systems (DEVFS, TMPFS, CRAMFS, YAFFS, EXT2, NFS) and network devices and protocols to be used. This sensor system is loaded with the network chip CS8900 and USB support; in the H.264 multimedia system, it is also necessary to load the Frame buffer to support the LCD display function. After compiling the kernel source code using the cross-compilation tool, a kernel image named zImage will be generated under arch/arm/1boot/. Use the download command in the command prompt mode of the Boot loader to complete the kernel loading into the storage device FLASH of the development board.

3.1.4 File System Customization

Linux uses the file system to organize files and devices in the system and provide a unified interface for devices and user programs. Linux supports multiple file systems. This system uses the read-only root file system in CRAMFS format, and uses the read-write YAFFS file system format for the USER area in FLASH, which is convenient for adding your own applications.

3.2 Main hardware device drivers of seismic intensity meter

3.2.1 Network device driver

The system uses the CS8900A 10 Mb/s network chip, which uses the nGCS3 and IRQ_EINT9 of S3C2410. Modify linux/arch/arm/mach-s3c2410/irq.c accordingly, and add {SMDK2410_ETH_IO, S3C2410_CS2, SZ_1M, MT_DEVICE} to smdk2410_iodesc[] in roach-smdk24.10.c. Add the chip drivers drivers/net/arm/cs8900.h and cs8900.c to the kernel source code, configure the Makefile and Kcon-fig files of the network device driver, and add the configuration options of CS8900A, so that the network device driver can be loaded when the kernel is compiled.

3.2.2 Wireless network card driver

Download the driver of rt2x00 in IPv4 environment from the Internet, and transform the program to IPv6, modify the driver, and add the driver to the kernel of the system when the system is recompiled. Pack the driver of the wireless network card as a module into the operating system to avoid reinstalling the wireless network card driver every time the system loses power.

3.3 Software design of seismic intensity meter terminal

The communication transmission software is mainly responsible for completing the IPv6 data communication between the sensor and the business service system. The software functions are as follows: