Design of a vehicle-mounted infrared night vision device based on PIC microcontroller
With the rapid development of the automobile market and the increasing awareness of security, people have higher and higher requirements for automobile safety protection technology. Not far away, the disadvantage of poor effect becomes one of the safety hazards of automobile driving. What's more serious is that when driving at night, the driver will usually be disturbed by the lights of the other side's vehicle and appear in a blind spot, which is prone to traffic accidents. The night vision system can help the driver navigate in the dark, so that the driver can see the driving environment clearly in both light and dark situations. Therefore, the development of an automotive 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 imaging tube. The image-changing tube 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, and the human eye can observe the enhanced target image through the eyepiece. Considering the durability of use, the rationality of the economy, the versatility of the device, etc., most of them choose the active infrared night vision system as the vehicle-mounted system.
According to the functional objectives and design requirements, the system is mainly composed of infrared lighting, video processing system and vehicle display.
2) Hardware design
(1) Camera selection
Video camera is also called camera head or CCD. It can convert light into electric charges and store and transfer electric charges. It can also take out stored electric charges to change the voltage. It is an ideal imaging element. Its working principle is as follows: the light reflected by the camera object spreads to the lens, and then focuses on the CCD chip through the lens. The CCD accumulates the corresponding charge according to the intensity of the light, and after periodic discharge, it generates an electrical signal representing a picture. After filtering and amplification processing, a standard composite video signal is output through the output terminal of the camera. Here choose WAT-902H2 camera as the camera. It has the advantages of good camera effect, easy maintenance, and economic benefits.
(2) Design of infrared irradiation part
A far-infrared laser is selected as the light emitter. It is a laser transmitter 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 specially designed for high-power LEDs. The command signal is added to the enable end of DD312 through the optocoupler to control the switch of the laser.
(3) Design of power module
In the system, the display, microcontroller, MAX487 communication chip, CCD camera, and laser transmitter drive circuit all need 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 a regulated power supply for the microcontroller and the DD312 driver chip (Figure 2). The MAX4877 chip has a relatively high operating voltage and a relatively wide range, and the NW1-05S05S power conversion module is used to provide power for it.
(4) Design of control system
Two single-chip microcomputers, PIC16F877A and PIC16F876A, are used as the control chips of the system, and the entire control system is also a small transmission system. Among them, PIC16F877A single-chip microcomputer is used as the initial end of the transmission system, responsible for data acquisition and "memory" button; Max487 chip is a communication chip, responsible for receiving and transmitting signals. The PIC 16F876A single-chip microcomputer is used as the receiving end of the transmission system to control the rotation of the motor.
①Initial end
The core of this part is 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 Harvard bus structure in which the data bus and the instruction bus are separated. It connects each terminal device, responds to the query command sent by the main control computer, and returns the status information of the device under test to the main control computer. The I/O port of the one-chip computer is connected with the terminal of the equipment under test to obtain the required state information. The circuit is divided into three parts: data acquisition circuit (Figure 3), LED display circuit, and button circuit.
The 2 pins of the single chip microcomputer are externally connected with a temperature sensor, which transmits the real-time temperature change signal of the system to the single chip microcomputer; the 3~7 pins are externally connected with an LED display circuit, when the low level signal of the pin is connected, the corresponding LED lights up; the 8, 9 pins are externally connected with a laser drive circuit , to detect the status of the laser; 19 pins are connected to an external semiconductor cooler to collect information and decide whether to trigger the semiconductor cooler to work; 22, 25, and 26 pins are connected to the communication circuit to transmit signals to the main control chip; 27 to 40 pins are the pan/tilt And the lens key detection signal, when the operator presses the key on the panel, the single-chip microcomputer receives the key signal through these ports, and sends the information to the main control chip through the communication circuit, and the main control chip analyzes and controls after receiving the signal. corresponding command.
② Communication circuit
The communication circuit connects the initial end and the receiving end of the transmission system, and its main function is to realize signal reception and transmission. It adopts Max487 chip, which is a low-power half-duplex transceiver device for communication, and integrates a driver and receiver inside. The initial end encodes the signal first, and the receiving end decodes the signal. At the same time, in order to eliminate interference, the circuit is isolated by an optocoupler.
