基于单片机的汽车倒车防撞系统的设计与制作毕业设计开题报告(编辑修改稿)

基于单片机的汽车倒车防撞系统的设计与制作毕业设计开题报告(编辑修改稿)内容摘要：

BB A, 3CH MOV 30H, A SETB EX0 ； 开外部中断 0 POP ACC POP PSW RETI 对于一个平坦的目标，距离测量包括两个阶段 :粗糙的测量和精细测量。 第一步：脉冲的传送产生一种简单的超声波。 第二步：根据公式改变回波放大器的获得量直到回拨被检测到。 第三步：检测两种回波的振幅与过零时间。 第四步：设置 回波放大器的所得来规格输出，假定是 3伏。 通过脉冲的周期设置下一个脉冲。 根据第二部的数据设定时间窗。 第五步：发射两串脉冲产生干扰波。 测量过零时间与回波的振幅。 如果逆向发生在回波中，决定要不通过在低气压插入振幅。 第六步：通过公式计算距离 y。 四、超声波测距系统的软件设计 软件分为两部分，主程序和中断服务程序，如图 3（ a）（ b） (c) 所示。 主程序完成初始化工作、各路超声波发射和接收顺序的控制。 定时中断服务子程序完成三方向超声波的轮流发射，外部中断服务子程序主要完成时间值的读取、距离计算、结果的输出等工作。 系统初始化后就启动定时器 T1 从 0开始计数，此时主程序进入等待，当到达定时时间时 T1 溢出进入 T1 中断服务子程序；在 T1 中断服务子程序中将启动一次新的超声波发射，此时将在 引脚上开始产生 40KHz 的方波，同时开启定时器 T0计时，为了避免直射波的绕射，需要延迟 1ms 后再开 INT0 中断允许； INT0 中断允许打开后，若此时出现低电平则代表收到回波信号，将提出中断请求进入 INT0 中断服务子程序，在 INT0 中断服务子程序中将停止定时器 T0计时，读取定时器 T0 时间值到相应的存储区，同时设置接收成功标志；主程序一旦 检测到接收成功标志，将调用测温子程序，采集超声波测距时的环境温度，并换算出准确的声速，存储到 RAM 存储单元中；单片机再调用距离计算子程序进行计算，计算出传感器到目标物体之间的距离；此后主程序调用显示子程序进行显示；当一次发射、接收、显示的过程完成后，系统将延迟 100ms 重新让 T1置初值，再次启动 T1 以溢出，进入下一次测距。 如果由于障碍物过远，超出量程，以致在 T0溢出时尚未接收到回波，则显示 “ERROR” 重新回到主流程进入新一轮测试。 五、结论 对所要求测量范围 30cm~200cm 内的平面物体做了多次测量发现 ，其最大误差为，且重复性好。 可见基于单片机设计的超声波测距系统具有硬件结构简单、工作可靠、测量误差小等特点。 因此，它不仅可用于移动机器人，还可用在其它检测系统中。 思考：至于为什么接收不用晶体管做放大电路呢，因为放大倍数搞不好， CX20206 集成放大电路，还带自动电平增益控制，放大倍数为 76dB，中心频率是 38k 到 40k，刚好是超声波传感器的谐振频率。 附件 2：外文原文 （复印件） Ultrasonic distance meter Document Type and Number:United States Patent 5442592 Abstract:An ultrasonic distance meter cancels out the effects of temperature and humidity variations by including a measuring unit and a reference unit. In each of the units, a repetitive series of pulses is generated, each having a repetition rate directly related to the respective distance between an electroacoustic transmitter and an electroacoustic receiver. The pulse trains are provided to respective counters, and the ratio of the counter outputs is utilized to determine the distance being measured. Publication Date:08/15/1995 Primary Examiner:Lobo, Ian J. OF THE INVENTION This invention relates to apparatus for the measurement of distance and, more particularly, to such apparatus which transmits ultrasonic waves between two points. Precision machine tools must be calibrated. In the past, this has been acplished utilizing mechanical devices such as calipers, micrometers, and the like. However, the use of such devices does not readily lend itself to automation techniques. It is known that the distance between two points can be determined by measuring the propagation time of a wave travelling between those two points. One such type of wave is an ultrasonic, or acoustic, wave. When an ultrasonic wave travels between two points, the distance between the two points can be measured by multiplying the transit time of the wave by the wave velocity in the medium separating the two points. It is therefore an object of the present invention to provide apparatus utilizing ultrasonic waves to accurately measure the distance between two points. When the medium between the two points whose spacing is being measured is air, the sound velocity is dependent upon the temperature and humidity of the air. It is therefore a further object of the,present invention to provide apparatus of the type described which is independent of temperature and humidity variations. OF THE INVENTION The foregoing and additional objects are attained in accordance with the principles of this invention by providing distance measuring apparatus which includes a reference unit and a measuring unit. The reference and measuring units are the same and each includes an electroacoustic transmitter and an electroacoustic receiver. The spacing between the transmitter and the receiver of the reference unit is a fixed reference distance, whereas the spacing between the transmitter and receiver of the measuring unit is the distance to be measured. In each of the units, the transmitter and receiver are coupled by a feedback loop which causes the transmitter to generate an acoustic pulse which is received by the receiver and converted into an electrical pulse which is then fed back to the transmitter, so that a repetitive series of pulses results. The repetition rate of the pulses is inversely related to the distance between the transmitter and the receiver. In each of the units, the pulses are provided to a counter. Since the reference distance is known, the ratio of the counter outputs is utilized to determine the desired distance to be measured. Since both counts are identically influenced by temperature and humidity variations, by taking the ratio of the counts, the resultant measurement bees insensitive to such variations. DESCRIPTION of ultrasonic distance measurement 1, the principle of piezoelectric ultrasonic generator Piezoelectric ultrasonic generator is the use of piezoelectric crystal resonators to work. Ultrasonic generator, the internal structure as shown in Figure 1, it has two piezoelectric chip and a resonance。