introduction

At present, there are two new technologies for reversing: ultrasonic ranging and rear-view camera.

Reversing radar and rear-view camera have their own advantages and disadvantages. The former has the advantage of accurately judging the distance, but ultrasonic can not sense the ditches, cliffs, protruding steel bars and bamboo poles behind the vehicle, which is also a dead corner in reversing safety; The latter image is intuitive and real, but can not obtain the accurate distance. How to combine their advantages and eliminate their disadvantages is the key problem to be solved by the reversing multimedia visual ranging terminal.

The reversing multimedia visual ranging terminal uses the latest ultrasonic ranging technology, character generation and Superposition Technology and video display technology to realize the combination of reversing ranging and image monitoring functions. It is an electronic device for detecting the object distance behind the vehicle and monitoring the image behind the vehicle. It has three functions:

First function: ultrasonic ranging —- embedded ultrasonic ranging to make parking ranging accurate.

Second function: rear view camera system —- shoot the scene image behind the car, which is intuitive and free of dead corners.

The third function: On-board TV —- displays the image of the scenery behind the car and the distance between the obstacles behind the car, and can be connected to VCD \ DVD to watch TV programs and provide entertainment and leisure.

Hardware circuit design

The reversing multimedia visual ranging terminal consists of switching power supply, ultrasonic probe, ultrasonic ranging, OSD display controller, camera probe and on-board TV (see Figure 1). The OSD display controller consists of microprocessor w87e58, character superimposer uPD6453, clock chip DS12C887, keyboard, ultrasonic ranging interface circuit con4, character superimposition interface con2, RS-485 interface circuit Indicator lights D1 and D4, buzzer driving circuit S2, buzzer U5 driver and switching circuit. The clock chip is used to generate time signals and enter the CPU through the parallel bus; The ultrasonic ranging signal enters the CPU through the interface con4; The character superposition signal is output to the character superposition controller by the CPU, and the character superposition controller completes the superposition of time, distance information and video. The keyboard is used for time adjustment and function setting; Indicator lights D1 and D4 are used to indicate the working state; The buzzer circuit is used for alarm.

The design of reversing multimedia visual ranging display using microprocessor w87e58

The working principle of the reversing multimedia visual ranging terminal is: connect the ultrasonic signal installed from the rear bumper of the vehicle to the OSD display controller, and connect the camera probe signal in the video monitoring subsystem to the OSD display controller. Through the automatic switching circuit, character superimposer and microprocessor of the OSD display controller installed inside the vehicle, Connect the output of OSD display controller to the monitor, so as to realize the functions of automatic image switching, monitoring, ultrasonic reverse ranging, automatic alarm and so on. The OSD display superimposer uses the OSD special chip to realize character superposition: the input video signal is synchronously separated first, and the travel and field synchronization signals are separated as the OSD reference signal. Then, the OSD chip outputs the red primary color voltage VR, green primary color voltage VG and blue primary color voltage VB signals for coding, and the encoded video signal is synchronized with the input video signal. The two video signals are switched at high speed. The switched keying pulse is a signal, that is, as long as there is a character signal, it is switched to the video signal encoded by the character signal. As a result, the image of the input video signal is matted, and the matting part is replaced by the character signal.

Its advantage is that it can be installed on any kind of vehicle for reversing. When reversing, the driver can clearly see the scene behind the vehicle from the monitor without opening the door; CCD color or black-and-white wide-angle camera probe with an angle of 80 ° and a horizontal distance of 0.3 ~ 1.5m; The rear view is a positive image display, without distortion and geometric distortion; The working voltage is DC12V, which can be shared with automobile power supply.

System software design

The OSD display controller of reversing multimedia visual ranging terminal adopts microprocessor w87e58, and the software is programmed in C language. The flow direction of rear image and ranging data is shown in Figure 2.

Limited to space, the program code is not detailed here.

epilogue

The reverse ranging multimedia terminal has strong functions and accurate ranging. It has been successfully developed and applied in vehicles.

Responsible editor: GT

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