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2018 IEEE 3rd Advanced Information Technology, Electronic and Automation Control Conference(IAEAC 2018) Design of distance measuring and reversing system SUN Zhi1，YANG Yi1，WANG ZHI-sheng* 1.Research Institute of Photonics, Dalian Polytechnic University 313989901@qq.com, 329112607@qq.com, 23439176@qq.com Abstract—The main work of this paper is to design and enhancement of the ultrasonic wave frequency, the wavelength implement a set of ultrasonic ranging system which uses of the ultrasonic wave will also become longer. when the STC89C51 single chip microcomputer as the main control chip, frequency of the ultrasonic wave reaches a certain level, it will uses ultrasonic ranging sensor HC - SR04 as the ranging method, lead to the inability to pass through weak gas. However, if and uses DS18B20 temperature sensor to correct the sound the frequency of ultrasonic wave is too low, it will cause the speed in the current measuring environment, displays and ultrasonic wave to decay directly to a very weak frequency alarms the ranging result with LCD12864 liquid crystal display band, which will adversely affect the measurement accuracy. and buzzer, and supports the function of modifying the alarm distance. B. Ultrasonic sensor — Ultrasonic sensors are sensors that generate ultrasonic Keywords single-chip; alarm; sensing; microcomputer waves themselves and receive echoes. The principle of I. INTRODUCTION ultrasonic wave generation by ultrasonic sensors is to convert electrical energy into mechanical energy, and the principle of Due to the problem of driver's vision, there are often receiving echo signals is to convert mechanical energy into scraping accidents with pedestrians and obstacles in the electrical energy[1]. process of backing up and parking, causing danger. In essence, the reversing radar system is a kind of safety C. Working principle of piezoelectricultrasonic sensor assistance system aimed at the parking process of a vehicle. the system alerts and alerts the driver about the surrounding The piezoelectric ultrasonic sensor is manufactured by using environment during the parking process through intuitive the piezoelectric effect principle, and its internal structure digital, graphical display and different sound changes. It can diagram is shown in Fig.1. significantly improve the phenomenon that the driver often visits left and right in order to obtain a better parking field of Fig. 1. Schematic diagram of regional division vision during the parking process. at the same time, it can also effectively avoid the blind angle of vision and poor vision that the driver often encounters during the parking process, thus improving the safety during the whole parking process of the vehicle. II. DESIGN OF RANGING SYSTEM A. Acoustic wave properties Ultrasonic wave is an acoustic wave with a frequency of more than 20,000 Hz. it has strong directionality, slow energy attenuation, long distance in the medium, fast, convenient, easy to control and non-contact characteristics. The speed of sound wave propagation in different media is quite different. the main application scene of the ultrasonic A pair of piezoelectric bimorphs and conical vibrators technology-based ranging system design is air. together form a piezoelectric ultrasonic sensor. the working principle of the emission end is the reverse piezoelectric effect Acoustic wave propagation rate in air is related to the generated at both sides of the piezoelectric crystal. in other pressure p and temperature t of the current air medium. Due to words, a driving pulse voltage signal is applied to both ends of absorption, diffusion and other reasons, the energy contained the piezoelectric crystal, and the piezoelectric crystal vibrates in the sound wave will continuously decay during the with it, causing air to vibrate, thus achieving the effect of transmission process. However, the attenuation of sound sounding. When the frequency of the trigger signal is equal to wave in the transmission process will directly affect the signal the resonance frequency of the piezoelectric crystal, the strength that can be received by the ranging system, thus vibration of the piezoelectric crystal plate reaches the affecting the measurement accuracy. The higher the maximum value, and at the same time, it will drive the conical frequency of the ultrasonic wave, the smaller the relative vibrator to vibrate and send out ultrasonic waves[2]. weakening degree of the ultrasonic wave. with the 978-1-5386-4509-3/18/$31.00 ©2018 IEEE 2222
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This type of piezoelectric ultrasonic sensor works exactly Fig. 2. Dip - 40 package pin diagram opposite to the transmitting end at the receiving end and uses the forward piezoelectric effect of piezoelectric crystals. When there is no applied working voltage at both ends of the ceramic crystal plate, the conical vibrator receives the echo signal sent back by the transmitting end, which will vibrate the conical vibrator of the sensor at the receiving end, thus driving the piezoelectric crystal plate to vibrate. due to the positive piezoelectric effect, mechanical energy is converted into electrical energy, which will generate a high frequency voltage signal consistent with the acoustic wave frequency[3]. D. Characteristics of piezoelectric ultrasonic sensor The piezoelectric ultrasonic sensor has a wide voltage working range and can work normally in a wide voltage 90C516RD microchip processor has rich on-chip resources, working environment of 5 V to 3.3 V. Wherein, when the including 4k flash memory, 512 bytes of ram memory, 2k ee ultrasonic sensor works with 5 V as the working voltage, the rom and on-chip watchdog circuit. Mcu itself allows wide working current is 2.8 mA; When 3.3 V is used as the working voltage operation, effectively improving the anti-interference voltage, the working current is 2.2 mA. Due to the different ability to power supply jitter. With ESD protection, it can operating voltages, the performance indexes of ultrasonic resist static electricity and can work reliably between - 40 ℃ sensors will be different. and 85 ℃. The MCU chip has 216 - bit hardware timers, 4k on-chip program flash memory ( erasable up to more than The piezoelectric ultrasonic sensor uses TTL level rules to 100,000 times ), an optional external crystal clock, and support operate, and the ultrasonic wave emitted is selected as 840 bit operations sufficient to meet the requirements of the KHZ pulse square waves to detect the occurrence of acoustic ranging system for the MCU master control chip. waves. The distance is calculated and measured by an echo level proportional to the distance. During the design process of the ranging system, this MCU master control chip that is often contacted and used in daily E. Framework design of ranging system study was selected. one reason is that it is easy to design and The ranging system uses STC90C 516 RC single chip debug due to its more understanding and usage. Secondly, computer produced by hongjing single chip computer because the MCU is a very classic model, the relevant company as MCU master control chip. Select LCD screen information and experience are relatively comprehensive, and with Chinese character library (model 12864); Hcsr 04 was the function meets the design requirements of the ranging selected as the probe of piezoelectric ultrasonic sensor. Use an system. Therefore, this chip was chosen as the main control independent patch switch as a setting key; The DS18B20 MCU of the whole ranging system. temperature sensor is used to add a temperature compensation module to the ranging system. An active buzzer buzzer is used B. Ultrasonic sensorHC-SR04 piezoelectric ultrasonic to drive the buzzer through a triode, and a sound alarm module sensor is introduced into the ranging system[4] [5]. HC-SR04,as a classical piezoelectric ultrasonic sensor, has been favored by users in both industrial design and university III. ALARM SYSTEM HARDWARE SELECTION electronic competitions. In the medium and short distance ultrasonic ranging, it is very satisfactory in terms of A. MCU Master control chip measurement range and measurement accuracy. Mcu is called micro controller unit in English, i.e. a monolithic microcomputer. this distance measurement design HC - SR04 piezoelectric ultrasonic sensor has a non-contact uses 90c516 rd ( compatible with 89 series ) MCU, which is measuring distance ranging from 2 cm to 400 cm, which can produced by macro chip microcomputer company and is reach a precision level of 3 mm. The two ultrasonic commonly used in teaching, as the MCU master control chip transducers serve as the transmitting end and the receiving end of the distance measurement system. The package model is of HC - SR04 respectively. together with the control circuit, dip-40, and its package pins are shown in the Fig.2. they form the entire piezoelectric ultrasonic sensor. HC - SR04 piezoelectric ultrasonic sensor physical diagram, as shown in the Fig.3. 2223
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Fig. 3. HC-SR04 piezoelectric ultrasonic sensor DS18B20 is a single bus integrated sensor that requires very strict timing,so the timing should be mastered accurately. During initialization, the MCU main control chip first pulls down the level of dq port, then DS18B20 will have a waiting time of 15 - 60μs,after which the MCU main control chip will query dq port. It will receive a 60 - 240μ s presence pulse to complete the initialization of DS18B20. HC - SR04 piezoelectric ultrasonic sensor has a wide voltage range of 3.3v - 5v, with four pins connected to external DS18B20 has very strict requirements on timing and requires a circuits, VCC ( working power supply ), gnd ( ground ), trig subtle level. this requires precise calculation and compilation ( control terminal ) and echo ( receiving terminal ). of the delay function of the single chip microcomputer. the single chip microcomputer with different working clocks The completion of an ultrasonic distance detection can be needs to modify the delay function. the clock cycle of the divided into approximately four steps: Firstly, MCU main MCU main control chip selected in the ranging system is 12 control chip sends at least 10μs high TTL level signal to trig MHz. port. it is recommended to use 40 - 50μs for better effect. Then, the HC - SR04 piezoelectric ultrasonic sensor will IV. HARDWARE CIRCUIT DESIGN OF ALARM SYSTEM automatically send eight 40khz square wave signals to drive A. Schematic diagram of system hardware the ultrasonic transducer to send test ultrasonic waves. Secondly, waiting for the echo signal to be sent out from the The ranging system first purchased the required sensors and echo port, and the duration of high level is the total time from display screen. first, the development board was used to test sending out to returning the measurement signal; Finally, the each module. on the premise of confirming the correctness, the distance is calculated by the obtained time, and the distance system was rebuilt and designed. finally, the hardware circuit information is obtained. was drawn and made. C. DS18B20 temperature sensor The system hardware includes MCU master control chip minimum system, LCD display module, buzzer active buzzer DS18B20 is a temperature sensor which is widely used, sound alarm module, HC-SR04 piezoelectric ultrasonic highly accurate and highly favored by users. Its control circuit, ranging module, D18B20 temperature compensation module, sensing element, conversion circuit, etc. are all integrated in a and USB power supply module. In the working process, triode - shaped package of a Xiao Xiao. No additional MCU master control chip will carry out corresponding auxiliary circuit needs to be connected. only a pull-up resistor operations on each module according to the software settings with a resistance value of 4.7k needs to be connected to the dq to complete the measurement and display of distance. port. DS18B20 pin appearance, as shown in the Fig.4. Schematic diagram of system hardware design, as shown in Fig. 4. 7 DS18B20 appearance pin diagram the figure.5. Fig. 5. Schematic diagram of system hardware design The temperature sensor has a single bus interface mode, and communication with the MCU master control chip can be completed only through a separate dq pin. the MCU master control chip can complete data transmission (including precision setting, busy finding, conversion starting, result finding, etc.) only by operating on the dq pin.Its temperature measurement range is between - 55 ℃ and + 125 ℃. The MCU main control chip mainly operates DS18B20 in three parts, namely initialization, reading and writing. 2224
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B. Mcu master control chip minimum system module D. Temperature compensation module In the design of the ranging system, the 90C 51RD single When ultrasonic technology is used as a measuring method, chip microcomputer produced by hongjing company was the biggest influence on the measuring accuracy in the testing selected as the MCU master control chip of the entire ranging environment is the influence of temperature on the current system. Its minimum working system includes three parts: one sound speed. In order to improve the accuracy and reliability is the external clock circuit. in this design, 12m crystal of the ranging system, ds18B20 temperature sensor was oscillator tube is selected as the main clock circuit of MCU introduced into the system to build the temperature main control chip, and a 3 pin socket is used as the connection measurement compensation circuit. socket of crystal oscillator, which can be replaced twice as required. The connection between DS18B20 sensor and MCU master control chip is its unique single bus mode. it only needs to The second is the reset circuit. the usual reset circuit has two occupy a gpio port of MCU master control chip to complete all ways: software and hardware reset. in the design of the ranging communication with the sensor. Therefore, the p37 port of system, the external hardware circuit is connected to the rst the MCU main control chip and the dq port of the sensor are port of the MCU main control chip. connected as communication ports. Thirdly, because there is no pull-up resistor in the poport By checking the ds18B20 working manual and operating of the 90C51RD single chip microcomputer and it is an notes, it can be seen that a pull-up resistor with a resistance open-drain output, and in the ranging system, the p0port value of 4.7k needs to be pulled up at the dq port. Therefore, should be used as a data port for MCU master control chip and the hardware schematic diagram of the temperature peripheral circuit communication, so it needs to pull up a 10k compensation module is shown in the figure444. resistor to make the poport work as a gpio port.Mcu master control chip minimum system, as shown in the Fig.6. Fig. 8. Hardware schematic diagram of temperature compensation module Fig. 6. Principle diagram of minimum system hardware for MCU master control chip E. BUZZER Alarm module Active buzzer is selected in the ranging system to provide sound prompting and danger distance warning functions for the ranging system. The interior of the active buzzer is provided with an oscillation circuit, and when the MCU main control chip outputs high and low levels, the conduction and C. HC - SR04 piezoelectric ultrasonic distance measuring cutoff of the active buzzer can be completed.It is difficult to module reach the rated working current of the active buzzer. In order The piezoelectric ultrasonic distance measuring module and to protect the buzzer module, a diode for preventing peak MCU master control chip are connected with two ports, current voltage is connected in parallel at both ends of the namely, the p10 port of MCU and the trig ( control pin ) port buzzer to protect the buzzer. Hardware circuit diagram of of HC - SR04 respectively, and the p11 port is connected with buzzer alarm module, as shown in the figure.9. the echo ( reception pin ) port of HC - SR04. The principle is shown in the Fig.7. Fig. 9. Hardware schematic diagram of buzzer module Fig. 7. Figure HC - SR04 module hardware schematic diagram 2225
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F. Set key module Fig. 11. Pcb file diagram In the function planning of the ranging system, the function of setting and modifying the alarm prompt distance has been added. Therefore, three independent keys are adopted, namely, the setting key, + key, and - key, which are used to set and modify the warning distance. One end of the three independent keyboards is respectively connected with p22, p21 and P20 of the MCU main control chip, and a resistor with a resistance value of 10k is respectively pulled to finish the design of the key module. Set the hardware schematic diagram of the key module, as shown in the Fig.10. Fig. 10. Hardware schematic diagram of key module design G. USB Power supply module During the hardware selection process of the ranging system, 5v power supply voltage is used as the working voltage of each module and MCU master control chip. And the working voltage of USB is just 5v, so the power supply module of the ranging system chooses to use USB for 5v power supply. Hardware schematic diagram of USB power supply module. H. Design and manufacture of PCB board Firstly, the schematic diagram is designed, all electronic Resistance, switches and capacitors are all packaged in a devices are connected to the corresponding network, the more beautiful and exquisite patch. In order to make the wiring package is selected, and the update is linked to the PCB file. reasonable, the in-line resistor is selected for the package of Carry out component layout and pin wiring according to the resistors, which is beneficial to the conversion of double-sided design requirements, and carry out electrical rule detection. If wiring and can effectively use the double-sided wiring to make the design requirements are met, the PCB file can be sent to the circuit more reasonable and beautiful. the plate making factory to make the PCB board. The PCB file of the ranging system and the 3d model previewed by altium R EFERENCE design are shown in the figure11. [1] Chunguang Piao，Jin Oh，Kim. Vibration characteristics of an ultrasonic For the selection of each component package, LCD 12864 transducer of two piezoelectric discs[J]. Ultrasonics, 2017, 74(1): 72-80. has chosen to use a 20 pin socket to match with the l - shaped [2] Chen, Y. Focused intravascular ultrasonic probe using dimpled transducer elements[J]. Ultrasonics, 2015, (56): 227-231. pin soldered on LCD 12864 so that the LCD is displayed [3] Mathieson Andrew，Wallace Robert，Cleary Rebecca. Ultrasonic perpendicular to the layout. Needles for Bone Biopsy.[J]. IEEE Transactions on Ultrasonics Ferroelectrics & Frequency Control, 2017, 64(2): 433-440. [4] Holmes Caroline. Advanced post-processing for scanned ultrasonic arrays: application to defect detection and classification in non-destructive evaluation[J]. Ultrasonics, 2008, 48(6): 636-642. [5] Linton, Joan, Pong. The Acoustic World of Early Modern England (Book Review)[J]. Shakespeare Studies, 2000, 28(1): 356-356. 2226
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