In recent years, with the rapid development of automobile industry and the decline of people's living standards.
The number of cars in our country is increasing year by year. Meanwhile, car drivers in China and Africa.
The proportion of professional car drivers has also increased year by year. On roads, streets, parking lots,
When reversing in crowded and narrow places such as garages, drivers should not only look forward, but also look back.
A rear-end collision will happen if you are not careful. According to relevant survey statistics, 15% of cars.
The collision accident is caused by the poor rearview ability of the car when reversing. Therefore, increase
The rear-view ability of automobile can be realized by developing reversing radar to detect obstacles at the rear of automobile.
It is a research hotspot in recent years. The premise of safe obstacle avoidance is fast and accurate.
Accurately measure the distance between obstacles and cars. Therefore, a system based on single chip microcomputer is designed.
Heart, using ultrasonic to realize non-contact ranging of reversing radar system.
2 overall design and principle
Ultrasonic wave generally refers to mechanical wave with frequency above 20 kHz, which has penetrating power.
Strong sex, small attenuation and strong reflection ability [1]
. When working, the ultrasonic transmitter does not
Interrupt sends out a series of continuous pulses to provide a short pulse for the measurement logic circuit.
Finally, the signal processing device processes the received signal according to the time difference.
, automatically calculate the distance between the car and the obstacle. Brief principle of ultrasonic ranging
Simple, low cost, easy to make, but its transmission speed is greatly affected by the weather, can not
Accurate ranging; In addition, the ultrasonic energy decays in direct proportion to the square of the distance, because
Therefore, the farther the distance, the lower the sensitivity, so only the ultrasonic ranging method is applicable.
In a short distance. At present, the universal ultrasonic rangefinder at home and abroad is ideal.
The measuring distance is 4 ~ 5 m, so it is mostly used for close range such as automobile reversing radar.
Ranging.
The reversing radar system is controlled by a single chip microcomputer, as shown in figure 1. Use super
Acoustic wave realizes non-contact ranging, considering the influence of measuring environment temperature on ultrasonic velocity.
Influence, and through the method of temperature compensation to correct the speed. Use integrated number
The temperature measuring circuit composed of word sensor DS 18B20 can directly read the temperature.
Value, and then according to the temperature compensation to get the ultrasonic velocity at a certain temperature, by a single
The propagation time is obtained by counting the number of pulses, which is measured according to the principle of ultrasonic ranging.
Then the sounding frequency of the buzzer is controlled according to the displayed distance.
Figure 1 overall design block diagram
Design of reversing radar system based on ultrasonic ranging
Wang Hongyun
(Ordnance Engineering College, Shijiazhuang, Hebei 050003)
Abstract: This paper introduces a reversing radar system based on single chip microcomputer, which uses ultrasonic wave to realize non-contact ranging. The system mainly includes ultrasonic transmission contact and temperature control.
The characteristic of the temperature measuring circuit is that the digital sensor DS 18B20 is used to measure the temperature, and the sound speed is corrected by the correction formula between sound speed and temperature.
Yes, it improves the measurement accuracy of transit time, and then improves the accuracy of ranging. The distance suitable for measurement is below 5 m, which can meet the requirements of reversing safety.
Requirements.
Keywords: automobile; Ultrasonic wave; Reversing radar; Temperature compensation; single chip microcomputer
China Library Classification Number: TP368 Document Identification Number: A Document Number:1006-6977 (2008) 08-0070-03.
Design of Automobile Reversing Radar System Based on Ultrasonic Wave
distance measurement
Wang Hongyun
(Ordnance Engineering College, Shijiazhuang 050003, China)
This paper introduces an automobile reversing radar system based on single chip microcomputer. The system
Using ultrasonic wave to realize non-contact ranging. The system mainly includes transmitting and receiving.
And a temperature measuring circuit. Temperature measuring circuit using digital sensor DS 18B20
In view of. The accuracy of the distance is complete. The system is suitable for measuring distances below 5 meters.
Meet the safety requirements of reversing.
Keywords: automobile; Ultrasonic wave; Automobile reversing radar; Temperature compensation; Microprogramming controller
Date of receipt: May 2008-65438+June; Manuscript number: 200805048.
About the author: Wang Hongyun (1980-), female, born in Hengshui, Hebei, is a teacher. Research direction: measurement control.
Automatic control and instrument design of reversing radar system based on ultrasonic ranging
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2. 1 ultrasonic ranging principle
At present, the method of ultrasonic ranging [2]
There are phase detection method, acoustic amplitude method.
Value detection method and transit time detection method. The accuracy of phase detection is very high, but the detection
Limited scope; The detection of acoustic amplitude is easily influenced by reflected waves; Transmission time detection
The working mode is simple and intuitive, and it is easy for hardware control and software design and implementation. it
The principle is to detect the ultrasonic wave emitted from the emission sensor to the gas medium.
The time difference when the receiving sensor receives the ultrasonic wave, that is, the passing time t. Distance s=ct/2
(c is the speed of sound), and t can be realized by counting the number of pulses by a single chip microcomputer.
2.2 the relationship between temperature and sound speed
Because ultrasound is also a kind of sound wave, its sound speed V is related to temperature T .. Table.
1 lists the speed of sound at several different temperatures [2- 3]
. When in use, if the temperature is constant
Large, the visual speed of sound is basically unchanged; If the ranging accuracy is high, it should be passed.
The temperature compensation method is used for correction.
Generally, v=33 1+0.60T is used for temperature compensation to adapt to.
Working requirements at different temperatures. Table 2 shows the relationship between sound velocity and temperature after compensation.
Department. It can be seen that the sound velocity value is completely consistent below 0℃; Maximum error above 0℃
No more than 5%.
From the above analysis, it can be seen that the accuracy of temperature measurement not only directly affects the speed
Measurement accuracy also indirectly affects the distance measurement accuracy, so the temperature.
Measurement is very important.
3 Hardware circuit design
The reversing radar system is mainly composed of ultrasonic transmitting circuit and ultrasonic receiving circuit.
Road, temperature measuring circuit and display alarm circuit.
3. 1 Ultrasonic transmitting circuit
Under the control of single chip microcomputer, the pulse generator outputs ultrasonic waves. pulsation
The device consists of 555, and its wiring is shown in the figure.
2.7 stitches and 6 stitches and 2 stitches
The upper and lower parts of are r and c; Intermediate r sum
Parallel RP, RA=R 1+RA', RA=R2+
RB' and t 1 = 0.693 lak, T2=
0.693RBC, by adjusting RA and
RB resistor to realize output waveform.
Adjustable duty cycle. But, here
A square wave with a duty cycle of 50% is required because
This adjustable sliding rheostat makes T 1=T2, and the calculation formula of frequency is:
f= 1.443/( RA+RB) C ( 1)
Reasonable selection of R and C can make ultrasonic wave get 40 kHz output pulse. because
For ultrasonic transmission, there should be a distance. In order to facilitate the transmission of signals, generally
A modulation circuit should be added after the transmitting circuit.
3.2 Ultrasonic receiving circuit
Because ultrasonic ranging is only used in a short distance, the attenuation is relatively low when the distance is far away.
For severe cases, the reflected signal is relatively weak, so the receiving end should first
An amplifier circuit is provided, and then its output signal is decoded by a detector circuit.
Adjust, and finally compare and shape the detected output signals. Ultrasonic receiving circuit
The following aspects need to be considered:
(1) Environmental noise, interference, temperature and other influences.
Fig. 3 shows an enlarged circuit diagram. It selects a bootstrap combination circuit, which
This circuit improves the input impedance by reducing the current required by the input circuit, and its value is
Rin=R 1R2/(R 1- R2), which can be
Determine the sum of R 1 according to the preamble circuit.
R2, between it and the previous circuit stage.
Match. What is used in the circuit is
Inverse proportional amplifier circuit and amplifier
The benefit is relatively stable, usually K=-
R3/R 1 does not cause self-excitation, but it can
Reduce the influence of interference on the circuit
The ring. So R3 is a reasonable choice.
And the output voltage of R 1 can reach v level.
(2) Detection accuracy
The full-wave precision detection circuit as shown in Figure 4 is adopted in the design. To improve
The signal-to-noise ratio of the circuit will attenuate unnecessary frequency signals and increase harmonics at the input.
Get back on the road. Diodes VD 1 and VD2 have good high frequency performance ratio.
In 60 years, this detection method can make the sum of diode dead-time voltages nonlinear.
Great progress has been made.
(3) comparison shaping circuit
Fig. 5 shows a comparison shaping circuit. first
First, measure a distance equal to 5 m under static conditions.
The output voltage value of the detector (this voltage is the same as
The sample is obtained by amplification and detection circuit.
) and use this voltage value as a comparator.
The reference voltage uR of. Comparator selection
LM339 has a small offset voltage and a wide supply voltage range. The single supply voltage is
2 ~ 36 V, dual power supply voltage 1 ~ 18 V, compare the internal resistance of signal source.
Wide range of restrictions and so on. For LM339, when the voltage difference between the two inputs is large,
At 10 mV, its output can be guaranteed from one state (continue to page 73).
Fig. 5 comparison shaping circuit
Fig. 2 Pulse oscillation circuit with adjustable duty cycle
Fig. 3 Amplification circuit
Fig. 4 Precision full-wave detection circuit
-70- (continued from page 70)
Transition from the ground to another state. Therefore, LM339 is used for weak signal detection and so on.
This is an ideal occasion. Usually, the output waveform of the comparison circuit is on.
There are delays on both rising and falling edges, and an AND gate can be added after it to improve transmission.
The characteristics of. The output of the comparison shaping circuit is sent to the single chip microcomputer, and the pulses are counted to obtain
It's time to cross over. AT89C52 is selected as the single chip microcomputer.
3.3 Temperature measuring circuit
At present, most temperature measurement and control systems use temperature when detecting temperature.
The sensor converts the temperature into electric energy, which is amplified to an appropriate level by the signal amplification circuit.
Perimeter, and then converted into digital quantity by A/D converter. This circuit structure is very complicated.
Miscellaneous, complex debugging, accuracy is easily affected by component parameters. To do this, use one line.
The digital thermometer integrates the temperature sensor DS 18B20 and the single chip microcomputer.
High-precision digital temperature detection system. DS 18B20 Digital Temperature Sensor
Different from the traditional thermistor temperature sensor, it can directly read the measured temperature.
Value, and according to the actual requirements, 9 ~ 12 bits can be realized through simple programming.
Analog to digital conversion. Therefore, using DS 18B20 can make the system structure simpler, and at the same time, it can
The reliability is higher. Temperature measuring range
From -55~+ 125℃ to-10~+
The measurement error at 85℃ should not exceed.
0.5℃[4]
In the whole temperature measurement.
In the range of quantity, its measured value is 2℃
Accurate quantity, circuit connection as shown in the figure.
Six performances.
3.4 Display and alarm circuit
The display circuit adopts 4-bit * * * Yang.
LED digital tube, code segment by 74LS244
The drive circuit drives; The driving circuit includes
PNP transistor 8550 is driven. Figure 7
The alarm circuit is given. It uses transistors.
Drive.
4 conclusion
The reversing radar system uses ultrasonic wave to realize non-contact ranging; Adopt high
Precision temperature sensor realizes the temperature measurement and compensation of ultrasonic ranging system.
Compensation, that is, according to v=33 1+0.60T, the sound speed is compensated to improve the measurement accuracy.
Degree. It has the advantages of simple circuit design, low price and high measurement accuracy.
It has been mass-produced at present.
References:
[1] Feng Nuo. Handbook of ultrasound [M]. Nanjing: Nanjing University Press, 2002.
[2] Xiao Zhihong. Application of ultrasonic range finder in automobile safety system [J]. Zhejiang Province
Journal of Wanli University, 2007, (5): 43- 46.
Xu Guohua. Design and implementation of ultrasonic ranging system [J]. Application of electronic technology,
1995,( 12) :6- 7.
Tian, Qin, He Yongqiang. Temperature compensation based on ultrasonic ranging system.
Circuit design [J]. Microcomputer Information, 2007, (22): 307- 309.
Fig. 7 Alarm circuit
Figure 6 DS 18B20 Temperature Acquisition Circuit
Apply voltage for 30 minutes. Electrolytic capacitors should be stored in normal size.
In the case of anger.
7.8 solder
Improper welding temperature and time will lead to surface damage.
The rubber tube shrinks and breaks abnormally, and sometimes the guide pin will lead to high temperature.
And the terminal conducts heat to the inside of the element, which has adverse effects on the product.
The ring. So try to avoid too high a temperature and too long a time.
Solder.
Practical application of electrolytic capacitor in power supply circuit of refrigerator
Fig. 3 shows an application example of electrolytic capacitor in the power supply circuit of refrigerator. invest
The voltage is rectified by varistor protection circuit, transformer transformation and rectifier bridge circuit.
After that, the alternating current becomes pulsating 12 V DC, which is connected to the rectifier circuit.
The capacity of electrolytic capacitor e10/e102 is rectified by its charging and discharging characteristics.
The pulsating DC voltage becomes a relatively stable DC voltage. In practical application, in order to
When the power supply voltage of each part of the circuit is prevented from changing due to load change, the peak value is calculated.
Electrolytic capacitor value voltage and ripple current, choose two-stage filtering electrolytic capacitor.
The first stage is 2 200 μ f/35v; The second stage is 470 μ f/35 v. Due to the large capacity
Electrolytic capacitors generally have a certain inductance, which can not effectively filter out high frequency and pulse.
Therefore, the pulse jamming signal should be connected in parallel at its two ends, with a capacity of 0.1μ f.
C 102/C 103 capacitor is used to filter out high frequency and pulse interference.
9 conclusion
In order to better apply and improve the reliability of circuit design, this paper introduces
Relevant technical parameters and usage knowledge of aluminum electrolytic capacitor. At present, the new electrolysis
Capacitors develop rapidly, miniaturization, low impedance, chip and high speed.
Nature, wide temperature, high pressure, long life and environmental protection are developing in the direction of greening.
Exhibition, so the application prospect of aluminum electrolytic capacitor is broad.
References:
[1] Yu Anhong. A concise handbook of electronic components [M]. Shanghai: Shanghai Jiaotong University Press,
2005.
[2] Shen Renyuan, Wu Yong. A concise handbook of common electronic components [M]. Beijing: Machinist
Industry Press, 2004.
Shu Zhengguo. Selection of surface mount capacitors with high efficiency, high capacitance, low impedance and long life.
Type [J]. World Electronic Components, 2006( 1 1): 55- 57.
Fig. 3 Application of electrolytic capacitor in power supply circuit of refrigerator
Detailed technical description and application principle based on aluminum electrolytic capacitor
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