introduction
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 realize 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
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