0 Introduction With the rapid development of the automotive market and the increasing awareness of security, people are increasingly demanding automotive safety technology, while existing automotive lighting systems are less visible in snowy nights, snowy days or fog. The shortcomings of short distance and poor effect have become one of the safety hazards of driving cars. What is more serious is that when driving at night, the driver is usually disturbed by the lights of the other vehicle, which is prone to car accidents. The night vision system can help the driver navigate in the dark, allowing the driver to see the driving environment in both light and dark conditions. Therefore, the development of a vehicle infrared night vision system with simple structure, stable performance, good reliability and strong applicability has important market application prospects.
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1 System overall design 1) System principle According to different working principles, infrared night vision system is divided into passive infrared night vision system and active infrared night vision system. The active infrared night vision system actively illuminates the target by using the infrared light source carried by the infrared light source, and receives the infrared radiation reflected by the target from the objective lens of the optical system, and forms an infrared image of the target radiation on the photocathode surface of the infrared image tube. The image tube performs spectral conversion and brightness enhancement on the infrared image of the target, and finally displays the visible image of the target on the fluorescent screen, and the human eye can observe the enhanced target image through the eyepiece. Considering the durability of use, economic rationality, versatility of the device, etc., active infrared night vision systems are mostly selected as in-vehicle systems.
According to the functional objectives and design requirements, the system is mainly composed of infrared illumination lamps, CCD cameras, video processing systems and on-board displays.
2) Hardware design (1) Camera selection Camera is also called camera or CCD. It can convert light into electric charge and store and transfer electric charge. It can also take out the stored charge and change the voltage. It is an ideal imaging element. The working principle is as follows: the light reflected by the camera is transmitted to the lens, and is focused by the lens onto the CCD chip. The CCD accumulates the corresponding electric charge according to the intensity of the light, and periodically discharges to generate an electrical signal representing a picture. Filtering and amplifying processing, outputting a standard composite video signal through the output terminal of the camera. Here, the WAT-902H2 camera is selected as the camera. It has the advantages of good camera effect, easy maintenance and economical benefits.
(2) Design of infrared illumination part The far infrared laser is selected as the light emitter. It is a laser emitter with good monochromaticity, concentrated beam, small volume, long life and high electro-optical conversion efficiency. It consists of a fiber-coupled semiconductor laser, a driver circuit, a temperature control circuit, and a beam shaping lens. The core part is the drive circuit design. DD312 is selected as the driver chip. It is a single-channel constant current driver chip designed for high-power LED. It is a current-absorbing architecture that can provide up to 1A constant current output and supports enable switch function. The command signal is applied to the enable terminal of the DD 312 through an optocoupler to control the switching of the laser. The drive circuit is shown in Figure 1.
(3) Design of power module The display, MCU, MAX487 communication chip, CCD camera, and laser transmitter drive circuit all require power supply. Among them, the single chip microcomputer and DD312 driver chip require relatively stable power supply voltage, small ripple and small electromagnetic interference. The LM2576 module is used to provide regulated power to the microcontroller and the DD312 driver chip (Figure 2). The MAX4877 has a relatively high operating voltage and a wide range, and is powered by the NW1-05S05S power conversion module.
(4) Control system design PIC16F877A and PIC16F876A are used as the control chip of the system. The whole control system is also a small transmission system. The PIC16F877A MCU is the initial end of the transmission system, responsible for data acquisition and "memory" buttons; the Max487 chip is a communication chip responsible for receiving and transmitting signals. The PIC 16F876A microcontroller acts as the receiving end of the drive system and controls the rotation of the motor.
1 The beginning of this part of the core is the PIC16F877A microcontroller. It is an 8-bit single-chip microcomputer produced by Microchip Corporation of the United States. It has a unique RISC structure, a data bus and a Harvard bus structure separated by an instruction bus. It connects each terminal device, responds to the query command sent by the master controller, and returns the status information of the device under test to the master controller. The I/O port of the MCU is connected to the terminal of the device under test to obtain the required status information. The circuit is divided into three parts: data acquisition circuit (Figure 3), LED display circuit, and button circuit.
The external temperature sensor of the 2 pin of the single-chip microcomputer transmits the real-time temperature change signal of the system to the single-chip microcomputer; the external display LED display circuit of 3~7 feet, when the pin low-level signal is turned on, the corresponding LED becomes bright; 8 and 9 feet external laser drive circuit The laser state is detected; the 19-pin external semiconductor cooler collects information and determines whether to trigger the operation of the semiconductor refrigerator; 22, 25, 26 feet connect the communication circuit, and transmit signals to the main control chip; 27 to 40 feet are the PTZ And the lens button detection signal, when the operator presses the button on the panel, the single chip receives the button signal through these ports, and sends the information to the main control chip through the communication circuit, and the main control chip receives the signal, analyzes, controls, and executes The corresponding command.
2 Communication circuit The communication circuit is connected to the initial end and the receiving end of the transmission system. The main function is to realize the receiving and transmitting of signals. Using the Max487 chip, it is a low-power half-duplex transceiver for communication with an integrated driver and receiver. The initial end first encodes the signal, the receiving end decodes the signal, and in order to eliminate the interference, the optocoupler is used to isolate the circuit. See Figure 4.
The 3 terminal control chip uses the PIC 16F876A microcontroller. The RA0-RA5, RC0, and RC1 pins are respectively eight signal input ports for detecting the PTZ on-position, down-position, left-to-position, right-to-position, upper reset, lower reset, left reset, and right reset; RB0-RB7 are control lenses. The focal length, magnification, and eight ports of the pan/tilt are rotated up and down, and the external relay circuit controls the motor to rotate. As shown in Figure 5.
3) Software design The whole system software is divided into PIC 16F876A terminal and PIC16F877A terminal. In addition to the software of the communication interface part, the host computer software also includes a user interface, data processing, and the like. The slave software includes data acquisition and the MAX487 communication program. The flow of the slave communication interface software is shown in Figure 6.
2 Experimental results Figure 7 shows the pictures taken on the highway. Where a is the picture when the night vision system is not used, and b is the picture when the night vision system is used. The experimental results prove that this system enables the driver to accurately identify the road ahead and reduce traffic accidents in the dark.
3 Conclusion This article uses PIC microcontroller to design a complete set of infrared night vision system, which has the advantages of simple structure and high reliability. It is especially suitable for long-distance driving, which can effectively reduce traffic accidents and has very good social benefits.
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