Embedded systems are application-centric, based on computer technology, and can be tailored for software and hardware. They are suitable for application-specific computer systems that have strict requirements for functions such as reliability, cost, volume, and power consumption. It generally consists of hardware and software. Among them, hardware includes embedded microprocessors and peripheral devices; software includes embedded operating systems and specific application programs. Embedded technology can be widely used to control, monitor or manage other devices.
Measurement and control technology refers to the monitoring and control of a certain characteristic. Remote measurement and control refers to the management personnel connecting the equipment to be controlled through the computer network in different places, and inquiring, configuring and modifying the remote equipment through the local computer. Remote measurement and control technology can realize the seamless connection between office automation and industrial automation, and has become an emerging research hotspot. With the demand and development of the network, the B / S model has developed rapidly. Using this mode, the client only needs to install a Web browser to download the program from the Web server to the local simply to execute through the browser, thereby achieving remote measurement and control.
The rapid development of computer technology, communication technology and microelectronic technology has made a huge change in the field of measurement and control systems. Networking and informatization have become the development direction of measurement and control systems. Integrating sensor network technology, embedded technology and industrial measurement and control technology, building a Web-based remote measurement and control system can greatly improve the real-time, safety and maintainability of measurement and control products, and it is also more conducive to realization Centralized monitoring, unified scheduling and optimized management. This article introduces an embedded remote measurement and control system based on the Web method combined with various technologies, and successfully implements a smart home system using this solution.
1 Overall structure design of remote monitoring system
The basic architecture of the embedded remote measurement and control system based on Web is shown in Figure 1. The remote measurement and control system is mainly composed of three parts: an embedded measurement and control unit, a local server and a remote management host.
The embedded measurement and control unit at the bottom is mainly distributed on each measurement and control node. It is composed of a central processor, sensors, actuators, network interfaces, GPS modules, and GPRS modules. If the fixed value comparison exceeds the specified range, the alarm will be used to alarm, and each actuator will work to obtain the normal parameter range, and the test data will be transmitted to the local server through the customized protocol, so as to reach the remote manager for display. The GPS module can clearly locate the faulty equipment. The GPRS module as a wireless transceiver module can achieve high-quality data transmission when the wired network fails, providing a very practical and practical significance for applying the embedded system to the remote measurement and control system.
Located in the middle as a bridge is a local server, which mainly receives the monitoring parameters uploaded by each measurement and control unit and saves it in the database. It periodically queries and analyzes the status of the measurement and control unit. If it finds an error, it immediately informs the user by SMS. At the same time, the server also needs to regularly feed back the data in the database to the remote manager in time, so that the user can monitor the status of each measurement and control device in the first time, and realize the operation of the manager on each measurement and control unit.
The top layer is the remote manager, which can systematically analyze, query and manage each measurement and control unit, can receive various information uploaded by the measurement and control server, and can also issue commands to control and process the bottom unit, and can be based on The IP address directly controls a specific measurement and control unit and manages all devices in a unified manner. When the wired network fails, you can also perform wireless connection operations through GPRS, so that users can control it at any time.
The system collects the parameters of each node through the front-end sensor module and information receiving module, sends them to the embedded system for processing and storage, and regularly transmits the monitoring information to the measurement and control server, which is reflected on the management machine through the server, so as to realize the control of each measurement and control device. control. The remote measurement and control system realizes the connection of small devices to the Internet, and can timely monitor the operation of each device. For the monitoring system, the network monitoring method is flexible, the system construction and maintenance costs are relatively low, the amount of data that can be saved is larger, the data storage method is more, and the system integration is higher. Network-based remote monitoring breaks through the limitation of time and region. As long as there is a network in place, users can monitor at any time and without restrictions under the authorization of the user, and realize plug and play.
2 Research on key technologies
2.1 Embedded system design
The embedded measurement and control unit is equivalent to each node of the sensor network. It is mainly responsible for the collection of information, and converts other optical signals and chemical signals into electrical signals, and sends them to the microcontroller for processing. The measurement and control equipment is an intelligent detection and control system developed by embedded technology. It uses a central microprocessor as the core, and is equipped with SDRAM, NAND FLASH, network interface RJ-45, 4-wire touch screen interface, serial interface, LCD , USB port, SD card storage interface and A / D and D / A converter. Using UART1 and UART2 to convert TTL level to RS 232 level through SP3243ECA chip, GPS and GPRS communication can be realized. The hardware block diagram of the system is shown in Figure 2.
The software system mainly considers startup programs, various drivers, operating systems and applications. The Linux operating system is open source, can cut the kernel, and has been running stably and efficiently on various hardware platforms such as Motorola-la, NEC, ARM, etc. It has the advantages of powerful network functions and excellent file system support functions. Select the Linux operating system, and according to the specific application, after cutting and cross-compilation, an ARM executable file is formed, which is downloaded into FLASH through the serial port and the network port. The application programs of the measurement and control unit mainly include data acquisition module, LCD display module, keyboard control module, network service module, communication service module and control execution module. In order to build a better human-machine interface, the QT / Embedded graphical user interface support system was ported to Linux, and the corresponding graphical user interface was developed.
2.2 Web application technology
The system adopts the B / S mode. In order to be able to directly access the intelligent measurement and control unit through the browser from the measurement and control server or the measurement and control management machine, the intelligent measurement and control unit must have a Web server function. Under the embedded Linux platform, using .Boa as a Web server can make the system run stably and efficiently in the target system, and it is easy to use and maintain, and has high reliability. The embedded Web server Boa, like ordinary Web servers, can complete tasks such as receiving client requests, analyzing requests, responding to requests, and returning request results to clients. Unlike other traditional Web servers, Boa has high HTTP request processing speed and efficiency, and has high application value in embedded systems.
The transplantation of Boa program is mainly divided into the following steps:
(1) Download the Boa source code for the ARM-Linux system and unzip it;
(2) Generate and modify Makefile, modify CC = gcc to CC = / usr / local / arm / 2.95.3 / bin / arm-linux-gcc, modify CPP = gcc-E to CPP = / usr / local / arm / 2.95.3 / bin / arm-linux-gcc-E;
(3) Download the Boa server after configuring the Boa server. After downloading the compiled binary file into FLASH, the Web server has the Web server function.
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