Intelligent monitoring signal acquisition and processing module design

With the improvement of broadband wired and wireless network infrastructure and the increasing demand in the global security market, the application of video surveillance is showing explosive growth. The development trend of video surveillance systems is very obvious. After experiencing digitalization and networking, the next important trend is intelligence, namely the application of intelligent monitoring and video analysis technologies.

This article presents a circuit design scheme for smart video surveillance devices that are used in classrooms. The terminal controller of this device mainly realizes two functions. One is to control the integrated camera and the PTZ according to the instructions of the main controller, and the second is to collect the voice signals of the current classroom and process and upload them.

Camera and PTZ control circuit and implementation: Receive control commands of the RS485 control bus via the MAX485 and control the action of the relay group according to the instructions to achieve the top, bottom, left, and right rotations of the PTZ motor, and the zoom, zoom, and zoom of the iris motor. Bright/dark regulation. With the chip MC145027 to complete the decoding of the single-chip microcomputer instruction, the microcontroller sends the address command to the terminal controller, and the terminal controller sends the data command. Only when the address command that the one-chip computer sends and MC145027 sets up the same address, MC145027 receives the data instruction of the one-chip computer, namely control the order. This enables addressable individual control of each terminal.

Matrix Switcher Circuit

This system is designed to monitor audio and video with a capacity of 32 channels. To simplify the design, and to facilitate debugging, installation, and upgrade, the 32-channel audio and video are not processed on a PCB board, but are divided into 4 daughter boards, each of which is Board at the N8 audio and video, 8-channel audio and video channels to achieve 8 election 1 output function, that is, 4 sub-panels form a matrix switcher, at the same time achieve 32 election 4 output function. The circuit diagram of each daughter board is shown in Figure 1.

Figure 1 Matrix Switcher Daughter Board Schematic

In Figure 1, J1...J8 are relay coils. The double-knife, double-throw relay J4078 enables simultaneous switching of audio and video. J11 and J12 are jumper sockets. The jumper sets the address for the daughter board. When the set slave board address is the same as the master controller's daughter board selection address (A0, A1, A2), 4099 of the child board is in working condition. At this time, the channel selection command (cmd0, cmd1, cmd2) of the main controller is used to make any one of the J1...J8 relays complete the switching action, so as to achieve the simultaneous gating of a certain road audio and video.

Voice signal acquisition and processing circuit

Because it is necessary to collect speech signals at various positions in the classroom (generally in the range of 20 to 50 m2), it is obviously not possible to use an ordinary microphone amplification circuit. The system uses a logarithmic amplifier circuit to amplify the voice, and relatively clearly collects voice signals at various positions within a range of 50m2. The logarithmic amplifier circuit designed is shown in Figure 2. IC2 is an operational amplifier. The system uses LM358 to achieve two-stage operation amplification.

Figure 2 MIC logarithmic schematic

Editor's Statement

The use of sensing technology and electronic technology system design ideas is simple, low cost, convenient and practical. It has played a very important role in improving student self-consciousness, monitoring the operation of autonomous learning equipment and software platforms, preventing unnecessary losses caused by human damage, and improving the stability and reliability of equipment operations.