Design of digital video monitoring system based on ARM

The proxy server is usually a PC. On the one hand, it runs the TCP/IP protocol to realize the Internet access function, and on the other hand, it is connected to the embedded system through a simple bus structure (RS232, RS485, etc.). As shown in Figure 1, only a part of the code that communicates with the proxy server is needed in the system. Its advantage is that it can easily solve the problem of equipment accessing the Internet, and the development difficulty is low; the disadvantage is that the access cost is relatively high, which is not conducive to large-scale promotion. This solution is more suitable for the Internet access needs of large or expensive industrial equipment, but not suitable for low-priced equipment.

(2) Implementing Internet access by directly implementing TCP/IP protocol on embedded processors. This solution does not use an operating system, which greatly saves resources. However, it places high demands on processor performance, increases development difficulty, and is also difficult to implement technically. See Figure 2.

(3) Use a network monitoring system based on ARM Linux

This solution is similar to the second solution, but it only uses the embedded ARM Linux operating system and runs the TCP/IP protocol on the operating system. Currently, most embedded operating systems have a TCP/IP protocol stack, which reduces the difficulty of development and is more flexible to implement. Since the operation of the embedded operating system requires considerable processor resources and memory space, it also has high requirements for hardware configuration. The third solution can save development time and shorten the development cycle. The monitoring system generally also needs to configure an industrial computer or a high-performance microcomputer as a server at the control site to store intermediate data, process events with high real-time requirements, and respond to monitoring requests from the monitoring terminal.

2 Monitoring System Hardware Design

The network monitoring system based on ARM embedded system adopts TCP/IP network protocol standard, the system networking is simple, the data transmission volume is large, the speed is fast, and the whole system structure is simple. It is small in size and low in price. The remote computer can detect the equipment through the WEB browser without additional programs, and the application program is easy to develop and realize the complete sharing of information. In this system, ARM is responsible for program control and network communication, and the image and video acquisition module is responsible for data acquisition and processing. When the data or command data is transmitted, the ARM system processes the command and transmits the command data or displays it on the LCD. At the same time, the system is responsible for uploading the processing results through the network interface. After the system receives the data command, it drives the D/A output or processes the data according to the A/D input after algorithm processing, and then transmits the result to ARM. The system has the following basic functions: data acquisition, data analysis and processing, program control, and network transmission. [page]

2.1 ARM Video Surveillance Platform

The development platform of the video surveillance application system is shown in Figure 3. The system expansion slot and device expansion slot of ARM are used to add interfaces such as Ethernet interface, data storage interface and PCMCIA to the ARM system, or for other function development boards, which expand the CMOS image acquisition function and VGA display function for the ARM system.

Among them, the VGA interface realizes 4096-color display through a resistor network. The registers related to SRAM access are: SDRAM control register, read address low 16 bits, read address high 16 bits, read data register, write address low 16 bits, write address high 16 bits, write data register; the registers related to CMOS image acquisition are CMOS acquisition control register and CMOS acquisition status register; the register related to VGA display is VGA display control register. It has the following characteristics:

(1) Good real-time performance, which can meet the real-time requirements of data collection and data processing.

(2) High cost performance: the system cost should be as low as possible while meeting the requirements.

(3) Good controllability, capable of long-distance control and data transmission.

2.2 Data Acquisition Module

The video source signal comes from a highly integrated CMOS digital image sensor module MB86S20, which is a product of Fujitsu. MB86S02 not only integrates CMOS image sensor array, automatic gain signal amplifier, analog-to-digital converter, but also includes color signal processing and micro lens, including all front-end processing of image acquisition, and can directly output digital signals. The system block diagram of the module is shown in Figure 4.

MB86S02 is a sensor based on CMOS technology and uses active pixels. It has the following differences compared to traditional CCD sensors.

(1) Imaging process

CCD and CMOS use the same photosensitive material, so the basic principle of generating electrons after being exposed to light is the same, but the reading process is different: CCD transfers in frames or lines with the cooperation of synchronization signals and clock signals. The entire circuit is very complex and the readout rate is slow; CMOS reads signals in a manner similar to DRAM, with a simple circuit and a high readout rate. [page]