毕业设计基于单片机倒车防撞报警系统设计

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1、 重庆科技学院高等教育自学考试本科毕业论文 毕业设计（论文）高等教育自学考试本科毕业论文基于AT89C51单片机倒车防撞报警系统设计考生姓名： 准考证号： 专业层次： 院 （系）： 指导教师： 职 称： 重庆科技学院二O一二年 8 月15 日摘 要随着社会经济的发展交通运输业日益兴旺，汽车数量在大幅攀升。交通拥挤情况也日趋严重，撞车事件屡屡发生，造成了不可避免的人身伤亡和经济损失，针对这种情况，设计一种响应快，可靠性高且较为经济的汽车防撞预警系统势在必行，超声波测距法是最常见的一种距离测距方法，本文介绍的就是利用超声波测距法设计的一种倒车防撞报警系统。论文的内容是基于AT89C51单片机结合于

2、一体，设计出一种基于AT89C51单片机的倒车防撞报警系统。该系统采用软、硬件结合的方法，具有模块话和多用化的特点。论文概述了超声波检测的发展及基本原理，阐述了超声波传感器的原理及特性。对于系统的一些主要参数进行了讨论，并且在介绍超声波测距系统功能的基础上，提出了系统的总体构成，通过多种发射接收电路设计方案比较，得出了最佳设计方案，并对系统各个设计单元的原理进行了介绍。对组成各系统电路的芯片进行了介绍，并阐述了它们的工作原理。论文介绍了系统的软件结构，通过编程来实现系统功能。最后，通过对系统的误差分析，给出了系统的改进方案。关键词：单片机 超声波 AT89C51AbstractWith the

3、 development of society and economy of transportation industry is booming, the number of cars in the sharp rise. Traffic congestion has become more and more serious, the crash occurred repeatedly, resulting from the inevitable casualty and economic loss, in view of this situation, design a kind of f

4、ast response, high reliability and more economy car collision avoidance warning system to be imperative, ultrasonic ranging method is the most common type of distance measuring method, this paper describes the use of ultrasonic locating design a back-draft anti-collision alarm system.The content of

5、the thesis is based on the AT89C51 single-chip integration, design based on AT89C51 back-draft anti-collision alarm system. The system uses a combination of hardware and software, the method of module, and multi-use characteristics. This paper summarizes the development and basic principle of ultras

6、onic detection, introduces the principle and characteristics of ultrasonic sensor. Some of the main parameters for the system were discussed, and introducing ultrasonic ranging system functions basis, the overall composition of the system, through a variety of transmitting and receiving circuit desi

7、gn comparison, the best design scheme, and various system design unit this paper introduces the principle of. On the composition of the system circuit chip are introduced, and elaborated the principles of their work. This paper introduces the software structure of system, programmed to realize the f

8、unction of the system. Finally, through the analysis of system error, an improved scheme is presented.Key words: single chip ultrasonic AT89C51目 录1超声检测发展综述12 超声波介绍22.1 超声波传感器及其测距原理22.2 什么是超声波22.3 压电式超声波传感器简介22.4 频率特性42.5 指向特性53 单片机倒车防撞报警系统各组成单元方案设计63.1 发射接收电路方案设计63.2 系统显示电路设计73.3 系统报警电路设计73.4 单片机复位电

9、路83.5 时钟电路93.6 稳压电源94 系统硬件及软件实现104.1 单片机的选择104.2 AT89C51的主要性能参数104.3 AT89C51的结构104.4 CX20106芯片介绍114.5 系统软件结构124.6 硬件连接方法124.7超声波发射程序124.8 超声波接收及显示程序134.9 1602显示初始化写指令写数据程序144.10 蜂鸣报警程序18结束语18谢词19参考文献201超声检测发展综述随着改革开放，我国经济的高速发展。汽车拥有量在最近是一二十年里大幅增加，造成道路拥堵，交通事故频发，给人们的生命和财产安全带来了巨大损失。安全驾驶也以此成为大家关注的焦点，其中汽车

10、防撞系统CSA(Collision Avoidance System) 的设计和需要显得非常重要和迫切。此倒车防撞报警系统主要是利用超声波的特点和优势，将超声波测距的原理和AT89C51单片机结合于一体，设计出一种基于单片机的倒车防撞报警系统。该系统采用软、硬件结合的方法，具有模块化和多用化的特点。2 超声波介绍2.1 超声波传感器及其测距原理超声波是指频率高于20Hz的机械波。为了以超声波作为检测手段，必须产生超声波和接收超声波。完成这种功能的装置就是超声波传感器，习惯上称谓超声波换能器或超声波探头。超声波传感器有发送器和接收器，但一个超声波传感器也可具有发送和接收声波的双重作用。超声波传感

11、器是利用压电效应的原理将电能和超声波相互转化，即在发射超声波的时候，将电能转换，发射超声波；而在收到回波的时候，则将超声振动转换成信号。超声波测距的原理一般采用渡越时间法TOF（time of flight）2。首先测出超声波从发射遇到障碍物返回所经历的时间，再乘以超声波的速度就得到二倍的生源与障碍物之间的距离，即S=VT2.2什么是超声波人们能听到声音是由于物体振动产生的，它的频率在20Hz20KHz范围内，而超声波是指频率高于20KHz的机械波。超声波是一种在弹性介质中的机械振荡，有两种形式：横向振荡（横波）及纵和振荡（纵波）。在工业中应用主要采用纵向振荡。超声波可以在气体、液体及固体中传

12、播，其传播速度不同。另外，它也有折射和反射现象，并且在传播过程中有衰减。在空气中传播超声波，其频率较低，一般为几十KHz，而在固体、液体中则频率可用得较高。在空气中衰减较快，而在固体及液体中传播，衰减较小，传播较远。为了以超声波作为检测手段，必须产生超声波和接收超声波。完成这种功能的装置就是超声波传感器，习惯上称为超声波换能器或超声波探头。超声波传感器有发送器和接收器，但一个超声波传感器也可具有发送和接收声波的双重作用。常用的超声波传感器可以分为二大类，一是用电气方式产生超声波，如压电式、磁致伸缩式超声波发生器；二是用机械方式产生超声波，有加尔统笛、夜哨和气流旋笛等。下面我们主要介绍压电式超声

13、波传感器。2.3压电式超声波传感器简介压电式超声波传感器是利用压电效应的原理将电能和超声波相互转化，即在发射超声波的时候，将电能转换，发射超声波；而在收到回波的时候，则将超声振动转换成电信号。超声波发生器内部结构有两个压电晶片和一个共振板。当它的两极外加脉冲信号，其频率等于压电晶片的固有振荡频率时，压电晶片将会发生共振，并带动共振板振动，便产生超声波（图2.1）。图2.1超声波发生器反之，如果两电极间未外加电压，当共振板接收到超声波时，将压迫压电晶片作振动，将机械能转化为电信号，这时他就成为超声波接收器了，如图2.2图2.2超声波接收器2.4 频率特性图2.3超声波传感器的升压能级和灵敏度图2

14、.3是超声波发射传感器的升压能级和灵敏度。其中，40KHz处为超声发射传感器的中心频率，在40KHz处，超声发射传感器所产生的超声机械波最强，也就是说在40KHz处所产生的超声声压能级最高。而在40KHz两侧，声压能级迅速衰减。因此，超声波发射传感器一定要使用非常接近中心频率40KHz的交流电压来激励。另外，超声波接收传感器的频率特性与发射传感器的频率特性类似。曲线在40KHz处曲线最尖锐，输出电信号的幅度最大，即在40KHz处接收灵敏度最高。因此，超声波接收传感器具有很好的频率选择特性。超声接收传感器的频率特性曲线和输出端外接电阻R也有很大关系，如果R很大，频率特性是尖锐共振的，并且在这个共

15、振频率上林敏度很高。如果R较小，频率特性变得光滑而具有较宽的宽带，同时灵敏度也随之降低。并且最大灵敏度向稍低的频率移动。因此，超声接收传感器应与输入阻抗高的前置放大器配合使用，才能有较高得接收灵敏度。考虑到实际工程测量要求，可以选用超声波频率f=40kHz,波长=0.85cm。2.5指向特性实际的超声波传感器中的压电晶片是一个小圆片，可以把表面上每个点看成一个振荡源，辐射出一个半球而波（子波），这些波没有指向性。但离开超声传感器得空间某一点的声压是这些波叠加的结果（衍射），却有一指向性。图2.4是电路中选用的发射传感器的指向图。图2.4超声波传感器指向特性及结构超声传感器的指向图由一个主瓣和几

16、个副瓣构成，其物理意义是0度时电压最大，角度逐渐增大时，声压减小。超声传感器的指向角一般为40到80度，课题要求发射传感器的指向角度为60度。3 单片机倒车防撞报警系统各组成单元方案设计3.1 发射接收电路方案设计3.2 系统显示电路设计3.3 系统报警电路设计3.4 单片机复位电路3.5 时钟电路3.6 稳压电源4 系统硬件及软件实现4.1 单片机的选择本系统中所用到的主要芯片有单片机 AT89C51、CC4069、CX20106。以下就部分芯片的功能与结构做简单的介绍。AT89C51是美国ATMEL公司所生产低电压，高性能8位单片机，内含4K bytes的反复擦写的只读程序存储器（PERO

17、NM）和128bytes的随机存取数据存储器（RAM），器件采用ATMEL公司的高密度、非易失性存储技术生产，兼容标准MCS-51指令系统，片内置通用8位中央处理器（CPU）和Flash存储单元，功能强大，性价比高，可灵活应用于各种控制领域。4.2 AT89C51的主要性能参数与MCS-51产品指令系统完全兼容4K字节可重擦写Flash闪速存储器1000次擦写周期全静态操作：0Hz24MHz三级加密程序存储器1288字节内部RAM32个可编程I/O口线2个16位定时/计数器6个中断源可编程串行UART通道低功耗空闲和掉电模式4.3 AT89C51的结构AT89C51的结构如图3.3所示图3.3

18、 AT89C51的结构框图4.4 CX20106芯片介绍使用CX20106A集成电路对接收探头受到的信号进行放大、滤镜。其总放大增益80db。以下是CX2016A的引脚注释。1脚：超声信号输入端，该脚的输入阻抗约为40K。2脚：该脚与地之间连接RC串联网络，它们是负反馈串联网络的一个组成部分，改变它们的数值能改变前置放大器的增益和频率特性。增大电阻R1或减小C1，将使反馈量增大。但C1的改变会影响到频率特性，一般在实际使用中不必改动，推荐选用参数为R1=4.7,C1=1f。3.脚：该脚与地之间连接检波电容，电容量大为平均值检波，瞬间相应灵敏度低；若容量小，则为峰值检波，瞬间相应灵敏度高，但检波

19、输出脉冲宽度变动大，易造成误动作，推荐参数为3.3f。4脚：接地端。5脚;该脚与电源间接入一个电阻，用以设置带通滤波器的中心频率f0，阻值越大，中心频率越低。例如，取R=200k时，f042kHz，若取R=220K，则中心频率f038kHz。6脚：该脚与地之间接一个积分电容，标准值为330Ph，如果该电容取得太大，会使探测距离变短。7脚：遥控命令输出端，它是集电极开路输出方式，因此该引脚必须接上一个上拉电阻到电源端，推荐阻值为22K，没有接受信号是该端输出高电平，有信号时则产生下降。8脚：电源正极，4.55v4.5 系统软件结构4.6硬件连接方法首先把模块的OUT脚（2脚）接入单片机的中断引脚

20、，并且中断是下降沿有效的；40KHz脚（3脚）接入单片机的任意IO口（使用软件延时产生40KHz方波时）或者接入单片机的PWM输出口（使用单片机的PWM功能产生40KHz方波时）。4.7 超声波发射程序Void send()csb_in=1；for(i=0;i1;i+)_nop_();_nop_();_nop_();_nop_();_nop_();csb_in=0;_nop_();_nop_();_nop_();_nop_();_nop_();_nop_();_nop_();_nop_();_nop_();4.8 超声波接收及显示程序Void duqu() Uchar num;num0=num

21、1=num2=num3=num4=0;csb_out=1;for(num=0;num10;num+)send();TR0=1If(csb_out=0) TR0=0; time=(TH0*256+TL0)/2; Long=0.344*time;Distance=Long;P1=distance;Num4=distance/10000;Num3=distance%10000/1000;Num2=distance%1000/100;Num1=distance%100/10;Num0=distance%10;write_com(080+040+010);write_date(030num4);dela

22、y(10);write_date(030num3);delay(10);write_date(030num2);delay(10);write_date(030num1);delay(10);write_date(030num0);delay(10);/ delay(1000);TH0=000;TL0=000;4.9 1602显示初始化写指令写数据程序/*检查LCD忙状态Lcd_busy为1时，忙，等待。Lcd_busy为0时，闲，可写指令与数据。/bit lcd_busy()bit result;lcdrs=0;lcdrw=1;lcden=1;_nop_();_nop_();_nop_();

23、_nop_();result=(bit)(P0&080);lcden=0;return result;/*/* 1602液晶写指令函数 */* */*/void write_com(uchar com) white(lcd_busy(): lcdrs=0; /选择写指令模式 lcdrw=0; /设置1602液晶为写模式 Icden=0; /使能端置低电平 P0=com； /将要写的命令字送到数据总线上_nop_(); /稍作延时是为了数据稳定_nop_();_nop_();_nop_();Icden=1 /给使能端一个高脉冲，初始化已将能使端至低_nop_(); /稍作延时_nop_();_n

24、op_();_nop_();Icden=0； /将使能端置0为了完成高脉冲/*/1602液晶写数据函数/*/Void write_date() While(Icd_busy90);Icdrs=1 ; /选择读指令模式Icden=0; /设置1602液晶为写模式Icden=0; /使能端置低电平P0=date; /将要写的命令字送到数据总线上_nop_(); /稍作延时是为了是数据稳定_nop_();_nop_();_nop_();Icden=1; /给使能端一个高脉冲，初始化中已将使能端至低_nop_();_nop_();_nop_(); /稍作延时_nop_();Icden=0 /将使能端至

25、0是为了完成高脉冲/*/* */* 1062液晶显示函数 */* */*/Void icd_display() Uchar a,b,c,d; For(a=0;a16;a+) Write_date(table0a); /显示table0 Delay(200); Write_com(080+040); /第二行首地址For(b=0;b12;b+) Write_date(table1b)； /显示table1 Delay(200);Write_com(001); /清屏Write_com（080）； For(c=0;c16;c+) Write_date(table2c); /第二次写入显示table

26、2 Delay(200)Write_com(080+040);For(b=0;b12;b+) Write_date(table3d); /显示table3 Delay(200);TR0=1; /开定时器0TR1=1;/*初始化函数/*/Void init() Delay(15); Write_com(001); /清除LED的显示内容 Write_com(038)； /16*2显示，5*7点阵，8位数据 Delay（5） Write_com(038)； Delay（5） Write_com(038)； /设置162显示，57点阵，8位数据口 Delay（5） Write_com(00c); /

27、设置开显示，不显示光标 Delay（5） Write_com(006)； /设置写入一个字符后指针自动加一 Delay（5）；Write_com（080）； /第一行数据首地址TMOD=011TH0=000TL0=000TH1=(65536-50000)/256;/设定初值TL1=(65536-50000)%256;EA=1; /开总中断/ ET0=1; /开定时器0中断 ET1=1;/*设定显示位置/*/Void icd_pos(uchar pos) Write_com(pos|080); /数据指针=80+地址变量4.10 蜂鸣报警程序Void baojing() While(1) Bee

28、p=1; Delay(100); Beep=0; Delay(200) Led=1; Delay(300); 结束语本文所设计的基于AT89C51单片机倒车防撞报警系统是保障汽车倒车安全的辅助系统，通过超声波探头发出超声波，使用高速单片机测量车与障碍物之间的往返时间然后再计算车与障碍物之间的距离，并加入了软件补偿，提高了距离计算的精度，然后显示在1602液晶上。当在探测范围内有障碍物时，发光二极管以一定的频率闪烁，闪烁的频率以距离定，距离越近频率越高，同时蜂鸣器提示报警，距离越近蜂鸣器的报警时间间隔越短，当距离小于最小安全距离时，蜂鸣器不间断报警。谢词 衷心感谢我的指导老师。本文工作从选题一直

29、到撰写的每一个阶段都是在我的指导老师悉心教导下完成的。我们曾同探讨问题就各种出现的新情况提出自己的见解和积极的解决办法，她清晰敏捷的思路严谨的工作态度和丰富的实际经验给我留下深刻的印象使我受益非浅。指导老师以其严谨求实的治学态度、高度的敬业精神、兢兢业业、孜孜以求的工作作风和大胆创新的进取精神对我产生了重要影响。同时，在此次毕业论文过程中我也学到了许多关于模拟电子方面的知识，实验技能有了很大的提高。在本文完成之际本人对我的指导老师表示深深的敬意和诚挚的感谢。 感谢院系领导和我的师长们耐心指点和思想上给我的启发，感谢网站提供有关资料和所有与我交流探讨的同学和朋友。另外，我还要特别感谢学长和学姐以

30、及一起做毕业论文的同学们对我的无私的帮助和论文的写作的指导，使我得以顺利完成论文，在此我也衷心感谢他。 最后，再次对关心、帮助我的老师和同学表示衷心得感谢。参考文献1. 童诗白、华成英. 模拟电子技术基础M，第三版，北京：高等教育出版，20012. 阎石. 数字电子技术基础M，第四版，北京：高等教育出版社，19983. 马忠梅、籍顺信. 单片机的C语言应用程序设计M，第三版，北京：北京航天航空大学出版社，20034. 曾光奇. 工程测试技术基础M,武汉：华中科技大学出版社，20025. 罗四维. 传感器应用电路详解M，北京：电子工业出版社，19936. 滕志军. 基于超声波检测的倒车雷达设计，

31、20067. 胡建恺. 超声检测原理和方法M，合肥;中国科学技术大学出版社，19938. 刘凤然. 基于单片机的超声波测距系统J.信号与处理.20019. 荀殿栋. 数字电路设计实用手册.北京：电子工业出版社， 2003 年g an employment tribunal claiEmployment tribunals sort out disagreements between employers and employees.You may need to make a claim to an employment tribunal if: you dont agree with the

32、disciplinary action your employer has taken against you your employer dismisses you and you think that you have been dismissed unfairly.For more information about dismissal and unfair dismissal, seeDismissal.You can make a claim to an employment tribunal, even if you haventappealedagainst the discip

33、linary action your employer has taken against you. However, if you win your case, the tribunal may reduce any compensation awarded to you as a result of your failure to appeal.Remember that in most cases you must make an application to an employment tribunal within three months of the date when the

34、event you are complaining about happened. If your application is received after this time limit, the tribunal will not usually accept i.If you are worried about how the time limits apply to you, take advice from one of the organisations listed underFurther help.Employment tribunals are less formal t

35、han some other courts, but it is still a legal process and you will need to give evidence under an oath or affirmation.Most people find making a claim to an employment tribunal challenging. If you are thinking about making a claim to an employment tribunal, you should get help straight away from one

36、 of the organisations listed underFurther help.If you are being represented by a solicitor at the tribunal, they may ask you to sign an agreement where you pay their fee out of your compensation if you win the case. This is known as adamages-based agreement. In England and Wales, your solicitor cant

37、 charge you more than 35% of your compensation if you win the case.If you are thinking about signing up for a damages-based agreement, you should make sure youre clear about the terms of the agreement. It might be best to get advice from an experienced adviser, for example, at a Citizens Advice Bure

38、au. To find your nearest CAB, including those that give advice by e-mail, click onnearest CAB.For more information about making a claim to an employment tribunal, seeEmployment tribunals.The (lack of) air up there Watch mCayman Islands-based Webb, the head of Fifas anti-racism taskforce, is in Londo

39、n for the Football Associations 150th anniversary celebrations and will attend Citys Premier League match at Chelsea on Sunday.I am going to be at the match tomorrow and I have asked to meet Yaya Toure, he told BBC Sport.For me its about how he felt and I would like to speak to him first to find out

40、 what his experience was.Uefa hasopened disciplinary proceedings against CSKAfor the racist behaviour of their fans duringCitys 2-1 win.Michel Platini, president of European footballs governing body, has also ordered an immediate investigation into the referees actions.CSKA said they were surprised

41、and disappointed by Toures complaint. In a statement the Russian side added: We found no racist insults from fans of CSKA.Age has reached the end of the beginning of a word. May be guilty in his seems to passing a lot of different life became the appearance of the same day; May be back in the past,

42、to oneself the paranoid weird belief disillusionment, these days, my mind has been very messy, in my mind constantly. Always feel oneself should go to do something, or write something. Twenty years of life trajectory deeply shallow, suddenly feel something, do it.一字开头的年龄已经到了尾声。或许是愧疚于自己似乎把转瞬即逝的很多个不同的

43、日子过成了同一天的样子；或许是追溯过去，对自己那些近乎偏执的怪异信念的醒悟，这些天以来，思绪一直很凌乱，在脑海中不断纠缠。总觉得自己自己似乎应该去做点什么，或者写点什么。二十年的人生轨迹深深浅浅，突然就感觉到有些事情，非做不可了。The end of our life, and can meet many things really do?而穷尽我们的一生，又能遇到多少事情是真正地非做不可？During my childhood, think lucky money and new clothes are necessary for New Year, but as the advance o

44、f the age, will be more and more found that those things are optional; Junior high school, thought to have a crush on just means that the real growth, but over the past three years later, his writing of alumni in peace, suddenly found that isnt really grow up, it seems is not so important; Then in h

45、igh school, think dont want to give vent to out your inner voice can be in the high school children of the feelings in a period, but was eventually infarction when graduation party in the throat, later again stood on the pitch he has sweat profusely, looked at his thrown a basketball hoops, suddenly

46、 found himself has already cant remember his appearance.童年时，觉得压岁钱和新衣服是过年必备，但是随着年龄的推进，会越来越发现，那些东西根本就可有可无；初中时，以为要有一场暗恋才意味着真正的成长，但三年过去后，自己心平气和的写同学录的时候，突然就发现是不是真正的成长了，好像并没有那么重要了；然后到了高中，觉得非要吐露出自己的心声才能为高中生涯里的懵懂情愫划上一个句点，但毕业晚会的时候最终还是被梗塞在了咽喉，后来再次站在他曾经挥汗如雨的球场，看着他投过篮球的球框时，突然间发现自己已经想不起他的容颜。Originally, this worl

47、d, can produce a chemical reaction to an event, in addition to resolutely, have to do, and time.原来，这个世界上，对某个事件能产生化学反应的，除了非做不可的坚决，还有，时间。A persons time, your ideas are always special to clear. Want, want, line is clear, as if nothing could shake his. Also once seemed to be determined to do something,

48、but more often is he backed out at last. Dislike his cowardice, finally found that there are a lot of love, there are a lot of miss, like shadow really have been doomed. Those who do, just green years oneself give oneself an arm injection, or is a self-righteous spiritual.一个人的时候，自己的想法总是特别地清晰。想要的，不想要

49、的，界限明确，好像没有什么可以撼动自己。也曾经好像已经下定了决心去做某件事，但更多的时候是最后又打起了退堂鼓。嫌恶过自己的怯懦，最终却发现有很多缘分，有很多错过，好像冥冥之中真的已经注定。那些曾经所谓的非做不可，只是青葱年华里自己给自己注射的一支强心剂，或者说，是自以为是的精神寄托罢了。At the moment, the sky is dark, the air is fresh factor after just rained. Suddenly thought of blue plaid shirt; Those were broken into various shapes of st

50、ationery; From the corner at the beginning of deep friendship; Have declared the end of the encounter that havent start planning. Those years, those days of do, finally, like youth, will end in our life.此刻，天空是阴暗的，空气里有着刚下过雨之后的清新因子。突然想到那件蓝格子衬衫；那些被折成各种各样形状的信纸；那段从街角深巷伊始的友谊；还有那场还没有开始就宣告了终结的邂逅计划那些年那些天的非做不

51、可，终于和青春一样，都将在我们的人生中谢幕。Baumgartner the disappointing news: Mission aborted. r plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will m

52、ove through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratos

53、phere. As he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.The supersonic descent could happen as early as Sunda.The weatheThe balloon will slowly drift to the edge of space at 120,000 feet ( Then, I would assume, he will slowly step out onto something resemblin

54、g an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.

55、Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.I

56、f he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything