Portable on-site law enforcement recorder based on SPCA1527A

Abstract: According to the needs of law enforcement agencies for on-site law enforcement process records, a portable on-site law enforcement recorder was designed based on SPCA1527A main control chip. It has functions such as video recording, recording, photographing, storage, etc. It can record on-site law enforcement in real time and provide real and powerful on-site evidence.
Keywords: live recorder: law enforcement; SPCA1527A; video capture: audio capture

0 Introduction In modern society, the creation of urban civilization and the development of a harmonious society are inseparable from the inspections of various sectors of society by law enforcement agencies such as public security, industry and commerce, and urban management. However, disputes and conflicts in law enforcement have occurred from time to time, affecting law enforcement. The image of the department is also not conducive to creating a harmonious law enforcement environment. The on-site law enforcement recorder designed in this paper is a professional video recording device for law enforcement. It can record the law enforcement personnel's on-site law enforcement in real time, comprehensively and accurately, thus effectively avoiding malicious complaints, reducing rash lawsuits, and investigating violent resistance. The criminal liability of legal acts provides valid evidence and is applicable to various law enforcement departments such as public security, traffic police, urban management, judicial, procuratorial, fire, industrial and commercial, electric power, water, tobacco, and disaster relief.
The on-site law enforcement recorder designed in this paper adopts an adjustable shoulder-mounted integrated portable structure. The host and camera are integrated and designed to be worn on the shoulder or chest to rotate and adjust the camera 180 degrees. After completing the system setup in advance, the on-site law enforcement situation can be recorded with one-click operation, which does not increase the burden on law enforcement personnel or other work of law enforcement personnel. This recorder is suitable for professional law enforcement as well as for popular use as an audiovisual recording device.

1 The overall design system of the system adopts Lingjia SPCA1527A main control chip, which is a professional camera (recording) image and camera chip. It can provide high-quality audio and video (recording) system and PMP multimedia playback. Its resolution, The frame rate and other parameters are superior to other non-professional chips. The main control frequency is up to 800MHz. It is embedded in the Linux 2.6.31-6 operating system. The system runs fast and has reliable performance. It meets the digital law enforcement, digital photography and digital recording of the on-site law enforcement recorder. Basic requirements for functions such as.

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The industrial grade OV7725 enclosed integrated camera module can be used in various external environments such as high temperature, low temperature, dry and humid; the internal dual-channel CMOS image sensor filter is used to meet the needs of clear shooting during day and night. .
The dynamic random access memory (SDRAM) uses the Samsung 64MB K4S641632K chip, which can be synchronized with the CPU clock, can perform dynamic data storage, and randomly read the specified address data.

2 main functions and features of the system
2.1 Video Capture The system can record audio and video simultaneously, or record or record separately. Video recording can be selected in multiple modes, and different resolutions and frame rates can be selected according to requirements. The available modes are: 1) HD 720p mode, 1280 720, 30 frames/sec; 2) VGA mode, 640 480, 60 frames/sec; 3) D1 mode 720 480, 30 frames/sec. The video uses standard H. 264 encoding, video file output format is AVI, MOV, ASF, MP4, WMV and other formats, the default is AVI format, can be directly output to any NTSC, PAL system display device, with a dedicated USB cable to store video to the PC. The video collection process can be performed by means of segmented recording, timed recording, and cyclic recording. When taking photos alone, the photo resolution can reach 5 million pixels. Low illumination at less than 0.11x allows for imaging with infrared LEDs.
2.2 Audio Acquisition The audio signal is input from the microphone and is used for audio acquisition via an external amplifier and a mono PMW digital-to-analog converter. The audio codec is encoded by adaptive differential pulse code modulation (ADPCM) with sampling frequencies of 8 kHz, 11 kHz, 16 kHz, 22 kHz, 32 kHz, 44 kHz, and 48 kHz. The system hardware has an AV/IN port, through which the input signals of any audio and video equipment (CMOS/CCD camera, DVD, TV, etc.) of NTSC and PAL can be connected and recorded, and the sound can be applied to the above equipment. Output.

3 hardware design
3.1 Audio Video Recording Function Implementation The Lingjia SPCA1527 is a low-cost system-on-chip with a complete digital camera system. In the video, it embeds Sunplus' high-quality image processing tools, with high-speed JPEG decoding and a wide range of peripheral interfaces, enabling low-cost DSC (Dynamic Stability Control). Lingjia SPCA1527 supports a variety of popular CCDs, and supports RGB and YCbCr formats in color processing.
The system uses CMOS image sensor OV7725 for video acquisition, which can directly convert optical signals into analog current signals. The current signals are amplified and analog-digital converted to realize image acquisition, storage, transmission, processing and reproduction. OV7725 has the advantages of small size, low power consumption, impact resistance and vibration. It has stable overall performance, high sensitivity, low noise, large dynamic range and fast response, self-scanning function, small image distortion and no residual image. The OV7725 supports multiple output modes, mainly in RGB565/555/444, GRB422 and YCbCr422 formats. The digital video signal collected by the OV7725 is transmitted to the SPCA1527 master chip. The wiring diagram of the OV7725 and the main control chip is shown in Figure 2 and Figure 3.

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3.2 Memory The memory K4S641632K chip is directly connected to the SPCA1527A. The circuit schematics are shown in Figure 2 and Figure 4, respectively.

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4 software design The software is based on Linux 2.6.31-6 embedded system, using C++ language, the program flow chart shown in Figure 5.
The program flow is as follows: Open the system handheld device, the system performs self-test first, and then initializes, the process is set to 2s. If the system button is not operated, ie the video/record button or camera button is not pressed, the system automatically enters the main menu. The operator can select functions through the main menu, such as video playback, photo browsing, deleting files, camera or camera mode selection, function settings, and so on. After booting, you can also enter the camera mode by pressing the corresponding function button, such as the camera button. The photo file is directly saved into the inserted SD or MMC card. When the card is full, the system automatically stops shooting.

5 Conclusion The on-site law enforcement recorder designed in this paper can meet the basic needs of law enforcement agencies for audiovisual records during on-site law enforcement, and can effectively cooperate with relevant departments to enforce law enforcement and reduce law enforcement disputes. In order to make the system more suitable for practical use, the juice is drawn in the next development process, and the following functions are improved: adding a Bluetooth module to realize the wireless intercom function; adding a wireless transceiver module to realize wireless Internet access, emergency call, remote monitoring, etc. . This paper has certain reference value for the development of other civil audio and video recorders, such as car audio and video recorders.

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