A new ranging principle is adopted, combined with a single-chip microcomputer, to establish an infrared ranging system. The car infrared anti-collision system designed and developed according to this system has automatic detection and tracking display of the distance between the car and obstacles; when the set safety limit distance is reached, it can sound an alarm; if combined with an automatic braking device, it also has automatic braking Deceleration function. And the system has low cost, high accuracy, and has a broad market.
1 Introduction
With the economic development, the transportation industry is increasingly prosperous, but due to the difficulty of keeping up with road conditions and traffic management hardware, coupled with subjective principles such as driving overtaking, small deviations in driving, and incorrect estimation of the distance, collisions of traffic accidents occur frequently. occur. The fundamental measure to solve this problem is to install a device that can automatically track and measure distances and brake automatically within a dangerous distance.
Due to the development of electronic technology, there have been laser ranging, microwave radar ranging, ultrasonic ranging and infrared ranging. Among them, laser ranging is to detect the distance between the two vehicles by the laser beam reflected by the mirror (the rear of the car) irradiated by the laser beam on the front car. Due to bad weather, intense vibration of the car, abrasion of the mirror surface, pollution and other factors, the detection distance of the reflected laser beam at a certain power is reduced by 1/2 to 1/3 than the maximum distance that can be detected, and the loss is great , Affecting the accuracy of detection; microwave radar ranging technology for military and certain industrial development equipment and oscillators and other circuit parts are expensive, and now almost have not developed the civilian market; ultrasonic ranging has been studied by people at home and abroad Due to the high price of special components, it is difficult to promote; infrared as a special light wave, has the basic physical transmission characteristics of light waves-reflection, refraction, scattering, etc., and because its technical difficulty is relatively small, the composition of the measurement The distance system has low cost and excellent performance, which is convenient for civilian promotion.
The basic principles of ranging used in current ranging systems are all based on measuring the time difference, and the methods of measuring time mainly include "pulse mode" and "frequency modulation 2 continuous wave mode". Both measurement methods are implemented by analog circuits. Due to the influence of device delay, the measurement accuracy is greatly reduced. This article uses the "count" method, through the single-chip processing, so that the measurement accuracy has been greatly improved.
Therefore, the infrared distance measurement system studied in this paper has a lower cost and a smaller body size, and the use of a new distance measurement principle combined with the processing of single-chip technology has greatly improved the measurement accuracy; at the same time, this distance measurement system is applied to Car anti-collision system, and carried out anti-collision test. The test results show that the distance that this system can detect is greater than 40m, and the analysis and judgment of the danger is fast and the accuracy is high.
2 The basic principle of infrared distance measurement and the establishment of its system
2.1 Basic principles
The infrared transmitter continuously emits infrared rays with a frequency of 40 kHz, and is reflected by an obstacle. The infrared receiver receives the reflected wave signal and converts it into an electrical signal. By measuring the time difference t between the transmitted wave and the received reflected wave, the distance s can be obtained:
In the formula, c is the speed of light, generally 3 & TImes; 108m / s.
This article adopts the "counting" method to measure through the processing of the single-chip microcomputer. The basic principle is: the infrared transmitter is always in the state of emitting infrared light. When the infrared receiver receives the infrared light reflected back by the obstacle for the first time, the single-chip microcomputer processes When a counting start signal is issued, the counter of the single-chip microcomputer starts to count at a certain frequency; when the infrared receiver receives the reflected infrared light for the second time, the single-chip microcomputer gives a stop counting pulse through the circuit processing, and the counter stops counting. Through programming, the single-chip microcomputer automatically processes and multiplies the period T of the pulse by the number of pulses n to obtain the time difference t between emitting infrared rays and receiving infrared rays, namely:
Substitute (2) into (1) and measure the distance.
2.2 System establishment
According to the above ranging principle, the basic block diagram of the system is designed as shown in Figure 1.
Figure 1 Basic block diagram of infrared distance measuring system
The infrared transmitting circuit emits infrared rays with a frequency of 40 kHz. When infrared rays encounter diffuse obstacles and the infrared receiving circuit receives the reflected infrared rays for the first time, it sends a signal pulse to the microcontroller, starts the counter in the microcontroller, and sets the counter to enter the count. Status; when the receiving circuit receives the infrared light of the reflector for the second time, a signal pulse is processed by the single-chip microcomputer to stop the counter from counting, the data is latched, and then processed by the single-chip microcomputer, and the measured distance is displayed on the display.
3 Application of infrared distance measurement in automobile anti-collision system
3.1 Basic characteristics
The car infrared anti-collision system studied in this paper absorbs some of the characteristics of various rangefinders at home and abroad, and is designed based on the development direction of China's automotive electronics industry and existing electronic technology. It has the following characteristics:
1) The car can automatically track and display the distance of obstacles while traveling;
2) The workshop distance on expressways with large traffic volume is generally 30-50m. The device sets the limit safety distance to 30m. When the detected vehicle spacing is 30m, a warning sound is issued to remind the driver to pay attention to the brake;
3) When the detected vehicle spacing is 20m, an automatic brake signal is given; if an automatic brake device is installed, the automatic brake decelerates.
3.2 Automobile infrared anti-collision system
The circuit block diagram of the automobile infrared anti-collision system is shown in Figure 2.
Fig. 2 Circuit block diagram of automobile infrared anti-collision system
This system is composed of six parts: transmitting part, receiving part, single chip computer, decoding display circuit, alarm part and automatic brake deceleration device.
Transmitting part: It is composed of a 40kHz oscillator, a constant current transmitting path and a transmitting probe. The oscillator generates a narrow pulse with a very small duty cycle. A constant current source is used to provide a current of about 20mA, which reduces power consumption and improves Transmitting power, the infrared rays are finally focused by the transmitting probe and emitted with a scattering angle less than 2 °.
Receiving part: It is composed of infrared receiving head, first-stage amplifier circuit, second-stage amplifier circuit, shaping, AGC control gain and other circuits. After receiving the signal, the infrared receiver head is amplified by the first-stage and second-stage amplifier circuits, and then by Shimi The special trigger circuit is shaped and sent to the single-chip microcomputer for processing. Among them AGC controls the gain of the receiving circuit to ensure a constant amplitude output.
Single-chip computer: It is composed of clock oscillator and single-chip computer. After programming, the single-chip computer automatically counts, calculates time t and measured distance s, and continuously outputs the measured distance to the display device. At the same time, when the workshop distance is 30m, an alarm signal and vehicle spacing At 20m, an automatic brake deceleration signal is generated.
Decoding display circuit: It is composed of a decoding circuit and a display. The distance signal output by the single-chip microcomputer is decoded by the decoder and displayed through the display.
The distance between the car and the obstacle can be displayed dynamically.
Alarm part: composed of trigger, drive circuit and small horn. When the vehicle spacing is 30m, the single-chip microcomputer gives a signal to the trigger to set the trigger to generate a set of pulses. Through the drive circuit, the small horn emits an alarm sound. When it is greater than 30m, the trigger resets and stops generating pulses.
Automatic brake deceleration device: It is composed of switch K and automatic brake deceleration device. When the driver deems it necessary to use automatic brake deceleration device, switch K is closed. When the distance between cars is less than 20m, the single-chip microcomputer provides a signal to activate the automatic brake deceleration device to prevent collision.
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