The hottest remote device of video monitoring syst

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Remote equipment of PSTN based video monitoring system

the remote video monitoring system based on PSTN introduced here is mainly composed of the following three parts: the first is the video monitoring center with computer as the core, the second is the remote equipment of video monitoring far away from the center, and the third is the public equipment used to connect the center and remote monitoring points. As shown in Figure 1

among them, the monitoring center is mainly composed of computer, video card, modem and monitor (display)

the computer is the core component of the monitoring center, which completes the startup, operation and control of the monitoring system, that is, decode the received video code stream and send it to display, process the user's operation commands, and store or playback the monitored images. The rate of modem is 33.6kb/s, which is used to complete the information transmission between the control center and the remote equipment. The main function of the video card is to decode the monitored video, and encode and send the video information of the center to the far end when necessary. The function of monitor or computer display is to display the image of the monitored scene

this article will focus on the implementation of remote devices

2 composition of remote equipment

remote monitoring equipment is a kind of equipment independent of computer, which is composed of four main parts, as shown in Figure 2

the video and audio codec board is mainly used for video compression and coding of the captured video; Modem is used for communication of ordinary lines; Camera and PTZ equipment are used to capture and monitor the current 6 maximum tensile experimental space (mm) 600 fields; The four picture processor is used to segment or select the pictures taken by cameras distributed in different places

3 function of remote device

3.1 video and audio codec board based on TM1300

this system uses TM1300 DSP chip of Philips company as the main processor, and the system block diagram is shown in Figure 3

to explain the working process of the video and audio codeboard, we can make a simple analogy between the functions of each unit in Figure 3 and the corresponding parts in the computer. EEPROM in the figure is similar to BIOS in PC,

flash memory is similar to hard disk in PC, SDRAM is similar to memory in PC, and V.34 modem is similar to modem in PC

the working process is briefly described as follows: after powering up the monitoring terminal, the CPU of the terminal first reads some important information about the system startup from the EEPROM, such as the clock frequency of the CPU and the size of the peripheral SDRAM. Then, the CPU reads the startup program into SDR mortar am from EEPROM, and then the startup program reads the main program in flashmemory into SDRAM and starts execution. After the data input from the video port and audio port is compressed and encoded by the main program, the code stream is sent to PSTN through V.34 modem and transmitted to the monitoring center

3.2 four picture processing and pan tilt control

the system realizes 4-channel real-time video input through the four picture processor at the remote end, and then the center selects any one or four channels to synthesize a picture transmission. The monitored scene can be transmitted by video in QCIF (176144) or CIF (352288) format, and the on-site sound can be transmitted to the center if necessary

the system can also control the selection, opening, closing, zooming in and pushing away of the remote camera and its lens through the PSTN network. If PTZ and PTZ controller are installed under the camera, the shooting angle of the camera can be controlled by the center. The rotation and zoom of the camera are driven by the mechanical device of the PTZ, and the mechanical movement of the PTZ is driven by the PTZ controller. The PTZ controller can receive the control code sent by the center to complete the corresponding action

3.3 after nearly one year of research and development and countless experiments, the transmission of control signals

as a monitoring system, the transmission of data streams is asymmetric, mainly the video data streams from the remote end to the center. In order to control the remote end, the monitoring center only needs to upload a small amount of control information, and these uplink control information needs to be transmitted in a special logical channel. When the code stream reaches the far end through PSTN, TM1300 solves the logic dedicated for control from the code stream, and the measure of extending longmang Baili upstream is not only the control code in this channel, which is output by the IIC interface of TM1300, and then sent to the PTZ controller. After decoding, PTZ and four picture splitter can be controlled

3.4 modem interface

to realize remote communication, the remote equipment must have a good communication interface. The TM1300 of the remote device provides a synchronous serial communication interface (SSI), which can design various communication interfaces by adding different communication front-end chips, such as PSTN interface, ISDN interface, etc. The remote equipment of the system is connected with the modem through a UART module, as shown in Figure 4

the interface module includes three parts: TM1300 synchronous serial communication port SSI, universal modem, UART (universal asynchronous transceiver). During normal operation, the SSI transceiver clock of TM1300 is provided by UART board. The data to be sent by TM1300 is sent to the UART board for caching, and then sent to the modem. Similarly, UART caches the received data from the modem first, and then sends it to the SSI port of TM1300

4 conclusion

because PSTN is the most extensive and economical public communication at present, the remote video monitoring system based on this network has a wide application prospect. Users only need to have monitoring center software, video card and remote monitoring equipment to build a low-cost remote monitoring system. This system allows the center to connect with a remote end through dialing instead of using a special line connection. Therefore, the system can be used for the monitoring of some industrial production or commercial sites, and can quickly and timely respond to various situations. The system can also be used for safety monitoring in unattended areas, as well as remote monitoring of important traffic intersections and key protected areas

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