0 Preface This article refers to the address: http:// In recent years, the combination of embedded technology and Internet technology has made embedded technology occupy an increasingly important position in the fields of remote control, intelligent transportation, video conferencing, and security. With the improvement of people's living standards and the accumulation of personal wealth, cars have gradually become a common means of transportation for people to travel, and car stolen cases are also common. Therefore, how to ensure that individuals or collective cars become an urgent problem to be solved. This prompted us to develop a low-cost, more convenient video surveillance device - car security system to meet the needs of the car mass. 1 system hardware design The car security and defense system is mainly composed of video acquisition and processing module, 3G wireless network card, embedded Web Server, GSM module and client browser. The embedded Web Server consists of Samsung's ARM processor S3c2440 and a network chip. The camera first transmits the collected image data to the video processor, and is compressed and encoded by the video processor, and then transmitted to the ARM processor, and the ARM processor compares the frame data with the previous frame data, if the same, that is, If there is no moving object, the frame is discarded to save storage space; if not, it indicates that there is a moving object, the processor will store the frame data, and start the GSM module to send an alarm message. If the client wants to know the situation in the car in time, he can access the embedded web server through the browser to view the live video. The system hardware mainly includes Samsung's ARM processor S3c2440, 3G wireless network card, 16/32-bit ARM processor to implement MMU, AMBA BUS and Harvard cache architecture, with independent 16KB instruction cache and 16K B data cache. The network chip uses the more commonly used Cs8900. Two HY57 V561620 (32M) are used for SDRAM. NORFLASH uses AM29LV 160DB. NAND FLASH uses 32M K9F 1208 chip. The video processing part adopts the hardware H.264 codec, specifically adopts QL202B of Q pixel Company of the United States, which is a low-power real-time single-chip half-duplex H.264/AVC encoder. The system hardware structure is shown in Figure 1. Figure 1 system hardware block diagram 2 software design The software design of the system includes: transplantation of embedded Linux operating system, preparation of video capture program and dynamic detection program, implementation of embedded Web Server and writing and porting of related drivers. 2.1 Dynamic detection of video capture The principle of video acquisition and dynamic monitoring is shown in Figure 2. Set the period of the camera video capture loop to T. After the system is initialized, the obtained first frame image is saved as the background image. Next, one frame is acquired every time T, and the motion target detection is performed by the background subtraction method. The detection method is to extract a target from a video stream in real time, detect a point in the image sequence related to the moving three-dimensional object, and filter out information in the image that is not related to the moving object. The software was developed using QT/E's image processing library QImage process. First, two frames of image data are cyclically acquired, and after binarization processing, the luminances of the two images are extracted separately. After the background difference image is obtained, it is compared with the set brightness threshold, and the frame is discarded if the threshold is not exceeded. If the value is exceeded, an alarm is triggered, and the GSM module is started to send an alarm message, and the ARM processor is also informed, so that the ARM processor can perform subsequent work. Figure 2 video capture flow chart 2.2 Embedded Web Server Software Design The software design of embedded Web Server is divided into two parts: 　　 (1) Linux server boa configuration and porting; 　　 (2) Implementation of embedded CGI. The working flow chart of the embedded Web is shown in Figure 3. Figure 3 Embedded Web server work flow chart 1) Boa transplantation and configuration Boa is a single-tasking Http server with superior performance and speed. You can download the source code from the mainstream version of the boa distribution package at http:// and configure and port it. Since the configuration and porting method of Boa can be easily found on the Internet, it will not be described here. 2) Embedded CGI This design requires the Web to dynamically display and interactively operate. Traditional static web pages do not have such functionality. To solve this problem, CGI (Common Gateway Interface) can be introduced, which is a standard interface between the external application extension application and the , which can realize the interactive operation between the client and the server of the Web. CGI provides many features that are not possible with static HTML pages, such as search engines, remote monitoring, web-based database access, and more. It also has the advantages of fast running speed, support for multiple programming languages, and compatibility with the browser. The process of CGI implementing client-server interaction is shown in Figure 4. Figure 4 HTTP call CGI process diagram 3 Conclusion This system only needs to open any browser to input the IP number to log in to the embedded server to watch real-time or historical car conditions. Its video capture picture is shown in Figure 5. Figure 5 video capture The solution of the vehicle security system described in this paper has the advantage of being easy to place. Therefore, it has a very broad market prospect in the field of automobile installation, but there is a need for improvement, such as the limited capacity of stored video, because each machine There is a separate IP, which occupies more IP resources, and the video information is very large. The transmission rate of 3G wireless network card is limited, and there will be a delay of several seconds when transmitting. I believe that in the near future, with the technology of compression algorithm The development of 3G wireless network card transmission, the popularity of IPV6 protocol and other issues will be solved.
Birefringent Crystals include Calcite, alpha-BBO, undoped YVO4, quartz and MgF2 crystal, etc. Birefringent Crystals Birefringent Crystals,Birefringent Yttrium Vanadate Crystal,YVO4 Birefringent Crystal,Calcite Birefringent Crystal Coupletech Co., Ltd. , https://www.coupletech.com
Alpha-BBO is transparent in deep UV range, and YVO4 has the high transmittance in the middle IR range.
Alpha-BBO, Calcite and undoped YVO4 have the big birefringence, which are suitable for polarizing prisms. The birefringence of Quartz and MgF2 is relatively small, which makes them the best materials for wave plates.
For more information, please Don't hesitate to contact us.