倒计时器.doc

倒计时器.doc数字电子技术论文
题目: 倒计时器
系别: 机电工程系
专业: 机械设计制造及其自动化
学生姓名:
学号:
指导教师:宾恩钧廖晓梅

题目类型: 理论研究实验研究工程设计工程技术研究软件开发
2010年 0 7月 0 9 日
摘要
倒计时器作为一种电子产品,早已广泛应用于各种智力和知识竞赛场合,是竞赛问答中一种常用的必备装置,加强准确性,公平性。在交通灯方面也有很广泛的运用,为城市交通提高安全性。
数字电路构成的倒计时器在实际运用中有其诸多优点便于使用,数字电路构成的倒计时器有性价比高,运用灵活,稳定性高等诸多特点。
本次实训的内容是完成一个两位的倒计时器,设计的要求是要实现随意时间的倒计时,实现可调而且要实现暂停恢复等功能。倒计时系统主要由5个子系统构成,555组成的脉冲发生器;74LS192减计数器;74LS48七段驿马器;LED显示器;控制器。
经测试该套系统基本能实现预期功能,能达到显示功能,计时功能等。
关键词:74LS192;555;74LS48;CD4071
Abstract
The training content pleted a two counter-down and design is to realize the requirement at the time, adjustable and realize the countdown to suspend recovery etc. Function. Using digital circuit system to realize the function. The GongFen circuit design for the second pulse generator and counter, decoding display circuit and control circuit and other four modules. In pulse generator part before we use posed by the schmidt circuit 555 T1 = (R1 + R2) Cln2, T2 = R2Cln2 calculate formula 1 second pulse of resistance, we use the part in the counter 74LS192 chip is reduced by counting functions JieWei the output of the chip 192 low level for the number of changes to achieve high level changes to achieve any automatic offset, and using the high level of output bytes changes occur as ten pulse of realizing the countdown. In decoding show circuit we use is 74LS48 74LS192 will generate digital signal decoding into can make LED display code that can be realized. Control circuit consists of four 2 CD4071 input or door, and 10 JieWei by bits of low level of output terminals to control automatically buy. The whole circuit is the fourth part posed of us to achieve desired results, the design requirements.
Key words:74LS192 ;555;74LS48;CD4071
目录
引言……………………………………………………………………………………………………………………1
1 电路的设计………………………………………………………………………………………………….2
2 555定时器………………………………………………………………2
555定时器工作原理…………………………………………………………………3
555定时器与施密特触发电路………………………………………………………3
……………………………………………………………………4
3 74LS192计数器………