陕西理工学院毕业设计
6 结论与展望
在经过了多次验证与调试后，本设计完成。
本系统以单片机为核心部件，利用软件编程，最终实现了设计要求。虽然系统还存在一些不足，比如温湿度测量不够精确，特别是湿度，波动误差较大。尝试了各种改进方法。仍然不太理想，不过能反映出设计的目的和要求，与预期的结果相差不多。
经过近两个月的奋斗，从确定题目，到后来查找资料，理论学习，实验编程调试，这一切都使我的理论知识和动手能力有了很大的提高。了解了单片机的硬件结构和软件编程方法，对单片机的工作方式有了很大的认知。同时，对一些外围设备比如传感器、显示屏、键盘、蜂鸣器、继电器等有了一定的了解。学会了对一项工程应该如何设计：首先，要分析需要设计的系统要实现什么功能，需要什么器件；然后，针对设计购买相应的硬件，选用硬件时不仅要选用经济的，更重要的是如何能更精确更方便的完成系统的要求；再次，对各个硬件的驱动软件实现要弄清楚，如何更好的实现各个硬件的协调，更好的通过主控制器件实现硬件的功能。最后，通过各种测试与调试，让设计更好的完成系统要求。
但由于水平有限，本次设计中也存在一定的不足。例如对湿度的控制方面，由于温度时刻都在发生着变化，而湿度的变化又大体上取决于温度。因而对于湿度的控制有点困难。同时由于湿度变化波动比较大，造成报警频繁，为湿度限值的设定也带来了不小的麻烦。
粮仓温湿度控制已经成为了21世纪热门研究话题之一。而智能化的控制温湿度已经发展成为一种必然。随着世界经济的发展，人们生活水平的提高以及社会的进步。我们不可能一直墨守陈规，不能在恪守以前利用人力资源来控制温湿度的方法。不仅浪费大量的人力资源、财力资源，并且控制系统也相对单一化。而采用自动控制的办法，既节省了人力资源，更体现了与时俱进的思想。世界在进步，而这种进步就该体现在各个方面。
第 17 页 共 39 页
陕西理工学院毕业设计
致 谢
毕业在即，为期两个多月的毕业设计过程中，我收获了许多，感悟了许多。
首先我非常感谢院领导对我们毕业生在毕业设计过程中的支持与帮助。其次我要特别感谢帅老师，不管在选题阶段，还是在设计阶段，在制作阶段，他都给予我很多的指导与帮助，老师既要忙于教学，而且科研任务重大，但仍然抽出时间，定期召集我们组的同学给与指导、督促，找到大家存在的问题并加以解决。帅老师给我们提供了丰富的学习资源和良好的学习环境，为我们的毕业设计带来了很大方便。在我完成毕业设计的过程中提供了很多指导性的意见，使我能明确完成自己的设计。帅老师为人严谨，对待问题要求严格，但也正是这样，才使我们这些毕业生有对待毕设的态度有了很大的转变。在此，我衷心感谢帅老师给予我的帮助和教育。最后我要感谢我的同学们，在编写和调试过程遇到困难时，正是由于同学们的帮助我才能顺利的克服困难，我毕业设计的完成离不开同学们的帮助，在此，我真诚地感谢他们。
总之，无论是从同学、老师还是到学校。本次毕业设计过程中我受到了很大的帮助和启发。没有你们，我的毕业设计就坚持不下来。感谢你们，有了你们，我受益匪浅。
第 18 页 共 39 页
陕西理工学院毕业设计
参考文献
[1] 陈明荧.8051单片机课程设计实训教材[M]. 北京：清华大学出版社，2003． [2] 徐新艳.单片机原理、应用与实践[M]. 北京：高等教育出版社，2005．
[3] 吴金戌，沈庆阳，郭庭吉.8051单片机实践与应用[M]. 北京：清华大学出版社，2002.. [4] 张毅刚.MCS-51单片机应用设计[M]. 哈尔滨工业大学出版社，2004 [5] 冯博琴.微型计算机原理与接口技术[M]. 北京：清华大学出版社，2004. [6] 张毅刚.MCS-51单片机应用设计[M]. 哈尔滨工业大学出版社，2004.
[7] 张淑清，姜万录等.单片微型计算机接口技术及应用[M]. 国防工业出版社，2003. [8] 吴金戌，沈庆阳，郭庭吉.8051单片机实践与应用[M]. 北京：清华大学出版社，2001. [9] 冯博琴.微型计算机原理与接口技术[M]. 清华大学出版社，2004..
[10] 王振红，李洋，郝承祥.ISD4004语音芯片的工作原理及其在智能控制系统中的应用[J]. 电子器件2002,25(1). [11] 王千.实用电子电路大全[M]. 电子工业出版社，2001
[12] 赵亮,侯国锐.单片机C语言编程与实例[M]. 北京:人民邮电出版社,2003.
[13] R.L.Geiger，P.E.Allen，N.R.Strader.VLSI.Design Techniques for Analog And Digitial Ciruits,McGraw-Hill Inc.1990. [14] ANALOG DEVICES.The technology of AT89C51[EB/OL].White Paper,Spe.28.2000.
[15] V.K. Gryzhov, V.G.Korol’kov,E.V.Gryzhov, A.D.Akshinsky.Flexible Converter of Analog Signal into Discrete Digital
One with the Example of Double Integration Voltmeter [J].Automation and Remote Control,2014,75(4).
第 19 页 共 39 页
陕西理工学院毕业设计
附录 A 英文文献
Temperature Control Using a Microcontroller:
An Interdisciplinary Undergraduate Engineering Design Project
James S. McDonald
Department of Engineering Science
Trinity University San Antonio, TX 78212
Abstract
This paper describes an interdisciplinary design project which was done under the author’s supervision by a group of four senior students in the Department of Engineering Science at Trinity University. The objective of the project was to develop a temperature control system for an air-filled chamber. The system was to allow entry of a desired chamber temperature in a prescribed range and to exhibit overshoot and steady-state temperature error of less than 1 degree Kelvin in the actual chamber temperature step response. The details of the design developed by this group of students, based on a Motorola MC68HC05 family microcontroller, are described. The pedagogical value of the problem is also discussed through a description of some of the key steps in the design process. It is shown that the solution requires broad knowledge drawn from several engineering disciplines including electrical, mechanical, and control systems engineering.
1 Introduction
The design project which is the subject of this paper originated from a real-world application. A prototype of a microscope slide dryer had been developed around an OmegaTM model CN-390
temperature controller, and the objective was to develop a custom temperature control system to replace the Omega system. The motivation was that a custom controller targeted specifically for the application should be able to achieve the same functionality at a much lower cost, as the Omega system is unnecessarily versatile and equipped to handle a wide variety of applications.
The mechanical layout of the slide dryer prototype is shown in Figure 1. The main element of the
dryer is a large, insulated, air-filled chamber in which microscope slides, each with a tissue sample encased in paraffin, can be set on caddies. In order that the paraffin maintain the proper consistency, the temperature in the slide chamber must be maintained at a desired (constant) temperature. A second chamber (the electronics enclosure) houses a resistive heater and the temperature controller, and a fan mounted on the end of the dryer blows air across the heater, carrying heat into the slide chamber. This design project was carried out during academic year 1996–97 by four students under the author’s
supervision as a Senior Design project in the Department of Engineering Science at Trinity University. The purpose of this paper is to describe the problem and the students’ solution in some detail, and to discuss some of the pedagogical opportunities offered by an interdisciplinary design project of this type. The students’ own report was presented at the 1997 National Conference on Undergraduate Research [1]. Section 2 gives a more detailed statement of the problem, including performance specifications, and
Section 3 describes the students’ design. Section 4 makes up the bulk of the paper, and discusses in some detail several aspects of the design process which offer unique pedagogical opportunities. Finally, Section 5 offers some conclusions.
2 Problem Statement
The basic idea of the project is to replace the relevant parts of the functionality of an Omega CN-390 temperature controller using a custom-designed system. The application dictates that temperature settings are usually kept constant for long periods of time, but it’s nonetheless important that step changes be tracked in a ―reasonable‖ manner. Thus the main requirements boil down to
·allowing a chamber temperature set-point to be entered,
第 20 页 共 39 页
陕西理工学院毕业设计
·displaying both set-point and actual temperatures, and ·tracking step changes in set-point temperature with acceptable rise time, steady-state error, and overshoot. Although not explicitly a part of the specifications in Table 1, it was clear that the customer desired digital displays of set-point and actual temperatures, and that set-point temperature entry should be digital as well (as opposed to, say, through a potentiometer setting).
3 System Design
The requirements for digital temperature displays and setpoint entry alone are enough to dictate that a microcontrollerbased design is likely the most appropriate. Figure 2 shows a block diagram of the students’ design.
The microcontroller, a MotorolaMC68HC705B16 (6805 for short), is the heart of the system. It
accepts inputs from a simple four-key keypad which allow specification of the set-point temperature, and it displays both set-point and measured chamber temperatures using two-digit seven-segment LED displays controlled by a display driver. All these inputs and outputs are accommodated by parallel ports on the 6805. Chamber temperature is sensed using a pre-calibrated thermistor and input via one of the 6805’s
analog-to-digital inputs. Finally, a pulse-width modulation (PWM) output on the 6805 is used to drive a relay which switches line power to the resistive heater off and on.
Figure 3 shows a more detailed schematic of the electronics and their interfacing to the 6805. The keypad, a Storm 3K041103, has four keys which are interfaced to pins PA0{ PA3 of Port A, configured as inputs. One key functions as a mode switch. Two modes are supported: set mode and run mode. In set mode two of the other keys are used to specify the set-point temperature: one increments it and one
decrements. The fourth key is unused at present. The LED displays are driven by a Harris Semiconductor ICM7212 display driver interfaced to pins PB0{PB6 of Port B, configured as outputs. The
temperature-sensing thermistor drives, through a voltage divider, pin AN0 (one of eight analog inputs). Finally, pin PLMA (one of two PWM outputs) drives the heater relay.
Software on the 6805 implements the temperature control algorithm, maintains the temperature displays, and alters the set-point in response to keypad inputs. Because it is not complete at this writing, software will not be discussed in detail in this paper. The control algorithm in particular has not been
determined, but it is likely to be a simple proportional controller and certainly not more complex than a PID. Some control design issues will be discussed in Section 4, however.
4 The Design Process
Although essentially the project is just to build a thermostat, it presents many nice pedagogical
opportunities. The knowledge and experience base of a senior engineering undergraduate are just enough to bring him or her to the brink of a solution to various aspects of the problem. Yet, in each case, realworld considerations complicate the situation significantly.
Fortunately these complications are not insurmountable, and the result is a very beneficial design experience. The remainder of this section looks at a few aspects of the problem which present the type of learning opportunity just described. Section 4.1 discusses some of the features of a simplified mathematical model of the thermal properties of the system and how it can be easily validated experimentally. Section 4.2 describes how realistic control algorithm designs can be arrived at using introductory concepts in control design. Section 4.3 points out some important deficiencies of such a simplified modeling/control design process and how they can be overcome through simulation. Finally, Section 4.4 gives an overview of some of the microcontroller-related design issues which arise and learning opportunities offered. 4.1 MathematicalModel
Lumped-element thermal systems are described in almost any introductory linear control systems text, and just this sort of model is applicable to the slide dryer problem. Figure 4 shows a second-order
lumped-element thermal model of the slide dryer. The state variables are the temperatures Ta of the air in
第 21 页 共 39 页