Abstract: The anti-collision system for automobiles has been designed and developed. Based on the principle of ultrasonic waves, the anti-collision system measures the time difference by transmitting and receiving ultrasonic signals, and then converts the distance into a distance by the control system to judge the processing. The system uses a generator circuit, a transducer, and a linear power amplifier. In addition, the system has taken three anti-interference measures. Due to the implementation of anti-interference measures, the system can have a small steady-state error in the industrial field, effectively preventing the occurrence of collision accidents. This article refers to the address: http:// 1.3 Working principle The anti-collision device uses sound waves as the detection wave and ultrasonic waves as the mechanical wave, and its frequency is 20 kHz to 20 MHz. As the frequency increases, the detection distance decreases, the frequency of use is between 15 and 40 kHz, and the detection distance is 0.5 to 3.0 m, which consists of a transmitter, a receiver, a controller, and a reflector. The transmitter, receiver and controller are mounted on the collision avoidance body (referring to the car panel that is controlled by the product to achieve the collision avoidance function). The transmitter emits a detection wave, which is reflected by the reflecting surface to the receiver. After the judgment process, the transmitting controller performs the prescribed function. To obtain a reflected sound wave emitted from the microcontroller based on AT89C52 crane collision avoidance system uses a dedicated chip and transmitted to the measurement ultrasonic reflected back to the desired time t, the S = vt (v = 314 m / s, temperature compensation is added is calculated) The distance of the face. This distance is displayed in the cab of the car at any time. The software can set several levels of prompts and alarms. When the distance between the barriers is less than the safety distance, the sound and light alarm device installed in the cab emits an acousto-optic signal to inform the driver to operate with caution. Thereby effectively preventing collision accidents and ensuring the safety of people and equipment. This program divides the working process into eight states: preparation state (t0~t1), transmitting ultrasonic waves (t1~t2), not receiving signal time (t2~t3), waiting for sound wave reflection time (t3~t4), measuring reflection The number (t4 to t5), regardless of the number of reflected waves, intermittent (t5 to t6), the number of re-measured waves (t6 to t7), and intermittent time (t7 to t0). In order to measure the ultrasonic transmission and reception time difference t, convert it into distance s and judge whether to alarm, two functions are used in the program:
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Key words: single chip microcomputer; ultrasonic ranging; automobile anti-collision radar; software system
0 Introduction The core component of the car crash alarm is the car collision avoidance radar. The anti-collision radar (commonly known as the electronic eye) can realize the anti-collision alarm function. There is mainly an invisible ruler for ultrasonic waves, which measures the distance of the nearest obstacle and informs the owner. The principle of ultrasonic ranging is simple: it transmits ultrasonic waves and receives reflected echoes. The time difference t is obtained by the single-chip counter, and the distance is calculated by the formula S=Ct/2 (S is the distance between the vehicle and the obstacle; C is the sound wave in the medium The propagation velocity in the middle, C=331.4 (1+θ/273); θ is Celsius. The ultrasonic ranging system described in this paper has 4 ultrasonic transducers (commonly known as probes), which are arranged in the front left of the car. The front right, rear left, and rear right positions can detect the distance between the obstacles in the forward and reverse directions, and display the distance and the azimuth through the display unit built in the rear view mirror to emit a certain sound, and alarm and anti-collision.
1 overall program design crane anti-collision alarm
1.1 Main design indicators of anti-collision alarm device (1) Alarm distance: 5~30 m, continuously adjustable according to the specific needs of users;
(2) According to the user's needs, the bins are selected: 0.6 m, 1.0 m, 1.5 m, 1.8 m, 2.4 m;
(3) Power supply: car battery 12 V;
(4) Ambient temperature: -20 ~ +70 ° C;
(5) Alarm size: 155 mm × 155 mm × 63 mm, weight: 3.5 kg.
1.2 System overall scheme The automobile anti-collision alarm device adopts the microcomputer system composed of AT89C52 single-chip microcomputer as the core to control the instrument. Its hardware system is shown in Figure 1. 
2 Hardware Design
2.1 the natural frequency of positive feedback generator circuits in the hardware circuit configuration, it is important to ensure consistent and stable natural frequency of the transmission frequency of the ultrasonic transducer, not time or due to temperature drift, but also conducive ultrasonic transducer The conversion of the energy emitted by the energy device. To achieve this, the natural frequency positive feedback generator circuit is one of the measures.
2.2 Transducer It is also beneficial to use only one transducer, because the reflected sound is the sound wave emitted by itself, the resonance frequency is the same, and the piezoelectric effect is the best. From the circuit structure, the transmitting and receiving switches enable two transducers to function as both transmitting and receiving.
2.3 Linear Circuits Linear circuits include preamplifier, noise filtering, linear amplification, and shaping circuits. The weak acoustic emission and reception signals are processed to match the subsequent circuits of the microcontroller section.
2.4 micro-processor (master on AT89C52)
Through software programming, it can control the normal operation of the system. The specific functions are as follows: acoustic emission control, alarm distance level selection, sound and light voice alarm, parking distance display, car and serial port interrupt transmission data.
2.5 Display section The display section consists of the AT89C52 and the LED digital tube. The signal transmitted from the main AT89C52 can be transmitted to the serial port of the AT89C52 located in the cab, and then the LED digital tube is illuminated.
The above circuit (except for the display part located in the cab) uses an integrated circuit chip to make it compact and reliable. The encoding and decoding of ultrasonic waves can completely overcome the interference of automotive light sources and natural light sources of various spectrums. Because the system with single-chip circuit structure must ensure anti-interference, in this instrument, the power supply circuit and the corresponding anti-interference circuit are indispensable, the software program should also be matched with the hardware, and solve the problem of anti-electromagnetic interference. Since the sound waves are used to measure distances, it is necessary to consider the acoustic environment in the field because they can also be received by the ultrasonic transducer. The natural frequencies of the ultrasonic transducers used to measure the distance are generally 15 to 40 kHz, and the noise frequency of the road surface is very rich, and the sound spectrum frequency in them has the same portion as the natural frequency of the transducer used. Then interfere with the echo measurement. Therefore, it is necessary to solve this problem on the hardware circuit, and at the same time, there must be an anti-interference part in the preparation of the software program. The alarm distance level is selected so that the user can select according to the user's own wishes without modifying the program.
3 Software Design In order to achieve the main functions of the aforementioned instruments, the program is implemented one by one using the functional modules of C51. The program is divided into the main program (chret.c) and three other module files, namely display. c, eraseint. A51,transplant. c.
3.1 Main program The main program block diagram is shown in Figure 2. 
One is void t0Interrupt(void)interTupt:1 using 1, which is the t0 timing interrupt function, which handles the eight states divided by the working process through the switch statement.
The other is the function void intInterrupt(void)interrupt2 using 2, which processes the reflected input signal, which occurs in the t3~r4 phase, mainly by the external interrupt of int1 to derive the time distanceIn-time, and starts the T1 counter, which is used to calculate The number of reflected waves.
Through the above two functions, you can get t, then convert it to s and judge whether the alarm will be solved. Chret. The function of c is: 
The main program has taken three measures against interference (to prevent false alarms):
(1) The state of t4 to t5, which sets a window for the reflected wave, and does not count for waves higher than 33.3 Hz or less than 11.1 Hz;
(2) t6 ~ t7 state, is judged by measuring 10 ms: if the interference at this time can be measured; if the normal reflection, this time should be less than the fundamental wave sensing;
(3) Judging the alarm twice (1.3 s will be automatically cleared once).
3.2 serial communication module - transplant. c
Mainly the chDis in the program of the main AT89C52 is accurately transmitted to the display part (located in the cab), and a communication protocol is designed to ensure that the garbled code is not received, that is, a header data is added in front of the data of chDis, and a test data is added later. , so that the display part is only received when the Head appears, and the test is displayed correctly. Since the timing of the program is fixed when t is measured, on the basis of serial communication, only the interrupt mode can be used, and the query mode cannot be used, otherwise the phenomenon of "dead" will occur.
For display. c, eraseint. A51 These two modules can be called in the main program, with a single function: one for displaying data and one for executing itre instructions.
4 Conclusion The anti-collision device designed in this paper adopts microcomputer technology and special chip design. It has the characteristics of simple structure and miniaturization. It is very suitable for measurement and control system. In software design, it highlights the flexibility of the module and the C51 language is simple. , greatly simplifies the workload of writing programs. Compared with the existing automobile bumper on the market, the system has compact structure, low cost, good reliability and strong communication capability, and can effectively avoid the occurrence of automobile collision accidents, and has certain market value.
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