毕业设计——基于单片机的高精度超声波测距系统的设计.doc
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1、华北科技学院毕业设计(论文)目录设计总说明IIntroductionIII绪论111系统设计背景112国内外研究现状2超声波测距原理和方案4.超声波测距的基本理论4.超声波简介4.超声波与传播介质的关系4.超声波换能器简介6.超声波测距系统总体设计6硬件设计9.硬件的选型9.主控单片机的选型9.超声波传感器的选型10.温度传感器的选型12.模块电路的设计13.电源电路的设计14.发射电路的设计15.接收电路的设计16.回波接收及滤波放大电路16.时间增益补偿()电路17.双比较器整形电路19.温度补偿电路的设计20.显示电路的设计21.通讯电路的设计24软件设计28.主程序28.初始化子程序2
2、9.温度测量子程序30.距离计算子程序33.显示子程序34.时间增益补偿程序35.通讯电路子程序36.时间峰值检测36结论38参考文献41附录基于单片机的高精度超声波测距系统原理图42致谢431设计总说明目前,超声波测距技术已经广泛的应用于各领域,由于其具有非接触式测量的特点,在工业领域液位、井深、管道长度以及建筑物测量、倒车雷达、智能机器人的控制系统中都发挥了重要的作用。但以我们当前的技术水平来说,对超声波测距技术的应用是有限的,未来的发展方向应该是朝着高精度、低盲区、拓展功能更丰富以及成本价格更低的方向发展。和普通超声波测距系统不同,高精度超声波测距系统要求的盲区更小、精度更高。为了达到该
3、标准,设计系统需包含温度补偿电路,双比较器整形电路和时间增益补偿电路等信号调理电路。最后,还需加入一些必须的外围电路如显示电路,用于显示测量结果,还必须含有通讯接口,方便与上位机进行通讯且可将测量结果进行上传。另外,该系统进行软件化峰值检测,使电路更加简化,充分利用了软件资源。通过对系统的需求分析,硬件电路的设计方案最终得以确定,主要由AT89C52单片机作为主控芯片。为了达到高精度的要求,首先我们需要了解造成测量精度不高的原因,首先,声波在空气中的传递速度会随着温度而发生有规律的变化。用平均速度计算出的距离和实际距离可能会有一定的误差。其次,由于超声波属于波的一种,因此具有波的衍射特性。这会
4、使得超声波没有经过反射,即不是由于碰到物体而返回的波,而是直接收到发射端由于衍射现象而改变了传播方向的那部分超声波。这就是会导致一个测量盲区,在测量近距离时产生错误读取而造成测量失败。因此,只要加入温度补偿电路,由一个温度传感器先测量环境温度,以实际温度带入计算,就能有效避免第一类误差的产生;其次,加入双比较器整形电路,就能有效避免第二类误差的产生。本系统由AT89C52单片机控制时间长短的计数以及控制超声波信号的发射、接收。整个电路采用模块化设计思想,主要包含显示电路、超声波发射电路、超声波接收电路、温度补偿电路等。显示电路主要采用LED数码管组成,采用动态显示的方式。即所有数码管的段选线并
5、联在一起,通过控制位选信号来控制数码管的点亮。用于超声波信号发射的发射电路,主要由非门和超声波探头组成。还有用于超声波接收的接收电路,对回波进行滤波放大,整形,最后送入单片机。其他电路还包括用于测量环境温度的测温电路,主要由一个集成芯片直接读取环境温度,送入单片机中,再通过查询事先做好的温度表,通过这个表即可得到当前测量环境中的实际声速,代入公式计算距离。程序设计主要包括:主要程序、温度补偿程序、发射子程序、接收子程序等组成。主要程序在系统启动时会进行初始化,接着马上开始测量温度,获取温度值并进行查表后同时启动发射电路且开始计时,等待回波信号,并进行处理,软件滤波开始工作,对峰值点进行查找并计
6、算出距离。测温子程序主要是根据温度与速度表进行查表的方式来获取当前声速,代入公式进行计算。具体实现的流程包括复位程序、发送匹配ROM命令、温度转换命令等。测量距离子程序的实现即是时间的测量,这也是该系统的核心部分。对定时器初始化处理后,计时便开始。综上,超声波探头的信号经过AT89C52单片机的分析和一系列处理,最后实现本高精度超声波测距系统的完整功能,也验证了该系统的设计满足实际需求,该课题的研究也具有一定价值。值得注意的是,为了降低该系统的测量的盲区,采用了双比较器整形电路来处理不同的距离的信号(分为3cm-50cm的近距离部分和50cm-400cm的远距离部分),使得精度进一步提高。本系
7、统的设计精度较高,可以用于汽车的倒车雷达,也可以用于智能机器人的距离识别系统或者其他距离3cm-500cm之内,精度1cm的系统。关键词:单片机;高精度;超声波;测距IntroductionAt present, ultrasonic ranging technology has been widely applied in various fields, because of its non-contact measurement, in industrial field level, well depth, pipeline length and the measurement of bu
8、ildings, reversing radar, intelligent robot control system play an important role. But in our current level of technology, the application of ultrasonic ranging technology is limited, the future direction of development should be towards high precision, low area, develop the function more abundant a
9、nd lower cost price direction.And ordinary ultrasonic ranging system is different, high-precision ultrasonic ranging system requirements of the blind area is smaller, higher accuracy. In order to achieve the standard, the design system contains the temperature compensation circuit, the Dual Comparat
10、or plastic circuit and the time gain compensation circuit and other signal conditioning circuits. Finally, it is necessary to add some necessary peripheral circuits such as display circuit, used to display the measurement results must also contain communication interface, convenient and PC communica
11、tion and can be used to upload the measurement results. In addition, the system of the peak detection software, make the circuit more simplified, fully utilize the software resources.Through the analysis of the system needs, the hardware circuit design scheme is finally determined, and the main cont
12、rol chip is the main chip of AT89C52.In order to achieve the high accuracy, we need to understand the cause of the low accuracy of the measurement. Firstly, the transmission speed of the acoustic wave in the air will change with the temperature. The distance and the actual distance calculated by the
13、 average velocity may have some error.The second is because the ultrasonic belongs to one kind of wave, so the diffraction characteristic of wave is of the wave. This will make the ultrasonic wave not reflected, that is not due to the wave of the object returned, but directly received the emitter du
14、e to diffraction phenomenon and changed the direction of the transmission of that part of the ultrasonic. This is the result of a blind measurement of the blind, in the measurement of the error caused by the error read while the measurement failed. Therefore, as long as adding temperature compensati
15、on circuit, by a temperature sensor to measure temperature, the actual temperature into the calculation, can effectively avoid the error of the first kind; Secondly, adding dual comparator circuit, can effectively avoid the second type of error. The system is controlled by the AT89C52 microcontrolle
16、r count as well as the transmitter and receiver of ultrasonic wave. The whole circuit uses the idea of modular design, including the display circuit, ultrasonic circuit, ultrasonic receiving circuit, temperature compensation circuit, etc. The display circuit is mainly composed of LED digital tube, a
17、nd the dynamic display is adopted. That is, all the digital control of the section of the line in parallel, through the control of the selected signal to control the light of the digital tube. Secondly, transmit circuit for ultrasonic signal which is transmitted by the main gate, and the ultrasonic
18、probe. There are also used for ultrasonic receiving circuit, the echo filtering amplification, shaping, and finally into the microcontroller. Other circuit also includes a temperature measurement circuit for measuring the temperature of the environment, mainly by a chip directly read environmental t
19、emperature, into the microcontroller, then through query well in advance of the thermometer, current measurement environment in the actual sound velocity through this table can be, substituted into the formula for calculating the distance.The program design mainly includes: the main program, the tem
20、perature compensation procedure, the launch subroutine, the receiving subroutine and so on. Main program at system boot time will be initialized, then immediately began to temperature measurement, to obtain the temperature value and look-up table and start transmitting circuit and the beginning of t
21、ime, waiting for the echo signal, and processing and filtering software began to work the peak search and calculate the distance. Temperature measurement child program is mainly according to the temperature and speed table look-up table to obtain the current velocity and substituted into the formula
22、 were calculated. The process of the realization includes the reset procedure, the sending matched ROM commands, the temperature conversion command, etc. The realization of the measurement distance subroutine is the measurement of time, which is the core of the system. After the timer initialization
23、, the time will start. In summary, ultrasonic probe signal through AT89C52 analysis and a series of processing and finally realize the full functionality of the high precision ultrasonic ranging system, also shows that the design of the system to meet the actual demand, this topic research has a cer
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