Design of a vehicle-mounted infrared night vision device based on PIC microcontroller

0 Preface

　　With the rapid development of the automobile market and the increasing awareness of security, people have higher and higher requirements for automobile safety technology. However, the existing automobile lighting system has the disadvantages of short visibility and poor effect in low visibility conditions such as snowy nights, snowy days or heavy fog, which has become one of the safety hazards of automobile driving. What is more serious is that when driving at night, drivers are usually disturbed by the lights of other vehicles and have blind spots, which is prone to traffic accidents. The night vision system can help drivers navigate in the dark, allowing drivers to see the driving environment clearly in both light and dark conditions. Therefore, the development of an automobile infrared night vision system with simple structure, stable performance, good reliability and strong applicability has important market application prospects.

1 Overall system design

　　1) System Principle

　　According to different working principles, infrared night vision systems are divided into passive infrared night vision systems and active infrared night vision systems. The active infrared night vision system uses the infrared light source it carries to actively illuminate the target, and the objective lens of the optical system receives the infrared radiation reflected by the target, and forms an infrared image of the target radiation on the photocathode surface of the infrared image converter. The image converter performs spectral conversion and brightness enhancement on the infrared image of the target, and finally displays the visible light image of the target on the fluorescent screen. The human eye can observe the enhanced target image through the eyepiece. Considering the durability of use, economic rationality, versatility of devices, etc., most people choose active infrared night vision systems as vehicle-mounted systems.

　　According to the functional objectives and design requirements, this system is mainly composed of infrared irradiation lamps, CCD cameras, video processing systems and vehicle-mounted displays.

　　2) Hardware Design

　　(1) Camera selection

　　Camera, also known as camera head or CCD, can convert light into electric charge and store and transfer the electric charge. It can also take out the stored electric charge to change the voltage. It is an ideal camera element. Its working principle is: the light reflected by the camera body is transmitted to the lens, and then focused on the CCD chip through the lens. The CCD accumulates the corresponding electric charge according to the intensity of the light, and generates an electric signal representing each picture through periodic discharge. After filtering and amplification, a standard composite video signal is output 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.

      (2) Design of infrared irradiation part

　　A far-infrared laser is selected as the light emitter. It is a laser emitter with good monochromaticity, concentrated beam, small size, long life and high electro-optical conversion efficiency. It consists of a fiber-coupled semiconductor laser, a drive 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 LEDs. It has a current absorption architecture and can provide a maximum constant current output of 1A. It also supports the enable terminal switch function. The microcontroller command signal is added to the enable terminal of DD312 through an optical coupler to control the switch of the laser. The drive circuit is shown in Figure 1.

　　(3) Design of power module

　　The display, microcontroller, MAX487 communication chip, CCD camera, and laser transmitter driver circuit in the system all need power supply. The microcontroller and DD312 driver chip require a relatively stable power supply voltage, small ripple, and small electromagnetic interference. The LM2576 module is used to provide a regulated power supply for the microcontroller and DD312 driver chip (Figure 2). The MAX4877 chip has a relatively high operating voltage and a wide range, and the NW1-05S05S power conversion module is used to provide power for it.

　　(4) Control system design

　　The PIC16F877A and PIC16F876A microcontrollers are used as the control chips of the system. The entire control system is also a small transmission system. The PIC16F877A microcontroller is the initial end of the transmission system, responsible for data collection and "memory" buttons; the Max487 chip is a communication chip, responsible for receiving and transmitting signals. The PIC 16F876A microcontroller is the receiving end of the transmission system, controlling the rotation of the motor.

　　① Initial

　　The core of this part is the PIC16F877A microcontroller. It is an 8-bit microcontroller produced by Microchip Corporation of the United States. It has a unique RISC structure and a Harvard bus structure with separate data bus and instruction bus. It connects various terminal devices, responds to the query command sent by the host computer, and sends the status information of the device under test back to the host computer. The I/O port of the microcontroller 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 key circuit.

　　Pin 2 of the single-chip microcomputer is connected to an external temperature sensor to transmit the system's real-time temperature change signal to the single-chip microcomputer; pins 3 to 7 are connected to external LED display circuits, and when the low-level signal of the pin is turned on, the corresponding LED becomes brighter; pins 8 and 9 are connected to external laser drive circuits to detect the laser status; pin 19 is connected to an external semiconductor refrigerator to collect information and decide whether to trigger the semiconductor refrigerator to work; pins 22, 25, and 26 are connected to the communication circuit to transmit signals to the main control chip; pins 27 to 40 are pan-tilt and lens button detection signals. When the operator presses the buttons on the panel, the single-chip microcomputer receives the button signals through these ports, and sends these information to the main control chip through the communication circuit. After receiving the signals, the main control chip analyzes and controls and executes the corresponding commands.

　　②Communication circuit

　　The communication circuit connects the initial end and the receiving end of the transmission system. Its main function is to realize the reception and transmission of signals. The Max487 chip is used, which is a low-power half-duplex transceiver device for communication. It integrates a driver and a receiver. The initial end first encodes the signal, and the receiving end decodes the signal. At the same time, in order to eliminate interference, an optical coupler is used to isolate the circuit. See Figure 4.

　　③Terminal

　　The terminal control chip uses PIC 16F876A microcontroller. RA0-RA5, RC0, RC1 pins are eight signal input ports for detecting the upper position, lower position, left position, right position, upper reset, lower reset, left reset, and right reset of the pan/tilt. RB0-RB7 are eight ports for controlling the lens focus, zoom, and pan/tilt up, down, left, and right rotation. The external relay circuit controls the motor rotation. As shown in Figure 5.

　　3) Software Design

　　The entire system software is divided into the master PIC 16F876A side and the slave PIC16F877A side. In addition to the communication interface software, the master software also includes the user interface, data processing, etc. The slave software includes data acquisition and MAX487 communication programs. The slave communication interface software flow is shown in Figure 6.

2 Experimental Results

　　Figure 7 shows pictures taken on the highway. a is a picture without the night vision system, and b is a picture with the night vision system. The experimental results show that this system can enable drivers to accurately identify the road ahead in the dark and reduce traffic accidents.

3 Conclusion

　　This paper 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, can effectively reduce traffic accidents, and has very good social benefits.