毕业设计是每一个大学生都必须完成的作业，它是检验学生对专业知识掌握的程度，更重要的是检验学生能否灵活运用所学的知识来创造、设计，和解决所遇到的难题。简单地说，毕业设计就是用来全面检测学生综合素质的一种途径。
正因为如此，选好毕业设计的课题，就相当重要了。经过慎重的考虑后，我决定选择超声波测距和倒计时器的设计。以此来给自己更多的实践动手能力，同时增强对硬件知识的了解、掌握。

一、 前言························································2
二、超声波的设计················································3
1、系统方框图················································3
2、总思路····················································3
3、总原理····················································3
4、方案的选择与确定以及对设计过程中出现的问题的分析··········3
4.1四脉冲震荡电路的选择与确定···························4
4.2放大电路的选择与确定·································5
4.3计数、锁存、显示电路的选择与确定·····················12
4.3.1计数部分的选择与确定·····························12
4.3.2 锁存部分的选择与确定·····························13
4.3.3译码部分的选择与确定·····························13
4.3.4我们使用非门和锁存器的原因：·······················13
4.3.5测量的原理·······································14
4.4、RS双稳电路的作用···································14
5、电路的调试···············································15
6、电路中存在的干扰·········································16
7、总电路图·················································16
8、发射和接收电路的PCB图··································17　　
9、对完整的电路不足之处的分析·······························17

1、《现代电工电子测量技术》 主编：何 超2、《传感器原理及应用》 主编：王化祥 张淑英3、《传感器及其应用技术》 主编：林友德 郭亨礼4、《现代传感技术》 主编：魏永广 刘存5、《传感及其遥控遥测技术应用》 主编：丁镇生