全自动冷饮机控制器外文资料翻译

淮 阴 工 学 院

毕业设计(论文)外文资料翻译

系 （院）： 专 业： 姓 名： 学 号：

电子与电气工程学院 测控技术与仪器

外文出处： Frontiers in Education Conference,1997.

(用外文写)

27th Annual Conference 1.外文资料翻译译文；2.外文原文。

附 件：

指导教师评语： 总体评价： 签名： 月 15 2014 年 3 日

注：请将该封面与附件装订成册。

附件1：外文资料翻译译文

基于单片机的温度控制：一个跨学科的本科工程设计项目

James S. McDonald

Department of Engineering Science

Trinity University San Antonio, TX 78212

摘要：本文描述了一个跨学科的设计项目，在作者的监督下，由四个工程科学系的大四学生为一组进行的。该项目的目的是开发一个充气室温度控制系统。该系统是允许在规定范围内输入所希望的腔室温度，并且显示出的实际的腔室温度阶跃响应的超调量小于1开尔文和稳态温度误差。这组学生开发的细节设计，基于摩托罗拉MC68HC05家庭单片机，进行了描述。结果表明，解决方案需要广泛的知识，分别来自多个工程学科包括电气、机械和控制系统工程。

1.引言

本文主题的设计项目源于一个真实的应用程序。显微镜载物片干燥器的原型已经开发在OmegaTM CN-390温度控制器，本项目的目标是建立一个自定义的温度控制系统来代替欧米茄系统，动机是专门为应用对象定制控制器以低得多的成本实现相同的功能，如欧米茄系统是以不必要的灵活来具备处理多种应用程序的能力。

幻灯片的烘干机样机的机械布局如图1所示，烘干机的主要元素是一个大型,绝缘,显微镜载玻片的充气室，每个样品用纸巾包裹石蜡，可以设置在球童。为了使石蜡保持适当的一致性，幻灯片室的温度必须维持在所需的温度常数。第二个室有电阻加热器和温度控制器，和一个风扇安装在干燥结束时使加热器的热量吹进幻灯片室。

这个设计项目是由四名学生在1996 - 97学年在作者的监督下作为一个部门的高级设计项目。本文的目的是描述和解决学生方案的一些细节问题，并讨论了由一个跨学科的这种类型的设计项目所提供的教育机会。学生自己的报告发表在1997届全国大学生研究上[1]。

第2节给出了问题的更详细的说明，包括性能指标，以及第3节描述了学生的设计。第4构成了大量的纸张，并讨论了在设计过程中的某些细节的几个方面而提供了独特的教学机会。最后，第5节提供了一些结论。

图1.幻灯机机械布局

2.问题陈述

该项目的基本思想是，取代使用定制设计的系统中的欧米加CN-390温度控制器的功能的有关部分。应用决定了温度设定通常保持很长一段时间不变，但它仍然重要的是阶跃变化被跟踪在一个―合理‖的方式。因此要求主要归结

●使室内温度设定点是进入 ●显示设定温度和实际温度

●跟踪设定点温度与可接受的上升时间，稳态误差和超调的阶跃变化 表1给出了规范的更精确的说法。

表1.温度控制器规格

虽然在表1中有一部分没有明确规范，很明显，客户想要的是数字显示设定值和实际温度，而温度设定点应该是数字(而不是，通过电位器模拟设置)。

3.系统设计

根据数字温度显示和定位点要求规定，基于单片机的设计可能是最合适的。图2显示了学生的设计框图。

图2.温度控制器的硬件原理框图

该微控制器，摩托罗拉MC68HC705B16（简称6805），是系统的心脏。它从一个简单的四键键盘接受输入，允许规范的设定点温度，并显示这两个设定点，使用两位数字的七段LED显示器的显示驱动控制，所有这些输入和输出是通过并行端口容纳6805。腔室的温度检测是通过预先校准热敏电阻和6805的模拟数字输入。最后，一个脉冲宽度调制（PWM）在6805输出用于驱动继电器的开关，线路功率电阻加热器的关闭。图3显示出了电子设备和其接口到6805的一个更详细的示意图。键盘，有四个键，连接到引脚Pa0-Pa3的端口，配置为输入。作为一个关键的功能模式开关。支持两种模式：设置模式和运行模式。在设置模式中两个其他键都用于指定设定点的温度：一种是增量和一个递减。第四个键是未使用的，目前。该LED显示器是由哈里斯半导体icm7212显示驱动器连接到引脚Pb0-Pb6的B口驱动，配置为输出。感温热敏电阻的驱动，通过电压分压器，针AN0（8个模拟输入中的一个）。最后，销PLMA（两个PWM输出中的一个）驱动加热器继电器。

图3.单片机控制板的原理图

6805软件实现了温度控制算法，保持温度显示器，并改变设定点响应键盘输入。因为写这篇文章的时候他是不完整的，所以，软件将不会在本文中详细讨论。特别是控制算法尚未确定，但是它可能是一个简单的比例控制器，肯定不会比一个PID更加复杂。有些控制设计问题将在第4节中讨论。

4.设计过程

虽然本质上该项目只是打造一个恒温器，但它提供了许多很好的教学机会。知识和经验的高级工程本科基础就足够让他或她解决各个方面问题的边缘。然而，在每一种情况下，实际的考虑使情况显著地复杂了。好在这些并发症并非不可克服，其结果是一个非常有益的设计经验。

本节的其余部分着眼于刚才所描述的问题的类型所体现出来的几个方面的学习机会，4.1节讨论了一些系统的热特性的简化数学模型，以及它如何能够容易地验证实验的特征。4.2节描述了现实的控制算法的设计如何才能到达使用控制设计的入门概念。4.3节指出这样一个简化的建模/控制设计过程中的一些重要的不足之处，以及他们如何可以通过模拟来克服。最后，4.4节给出了一些单片机设计的相关问题的出现和学习的机会，并提供了一个概述。

4.1数学模型

集成元件的热系统，在几乎任何介绍线性控制系统的资料上都有文字描述，

只是这种模式适用于载玻片干燥机的问题。

图4显示了载玻片干燥机的第二阶集总元件的热模型。状态变量是箱子和盒子本身的空气温度Ta。输出功率Q（t）和环境温度T∞。ma和mb是空气和盒子的质量，Ca和Cb是他们的比热容。μ1和μ2分别是从空气到盒子中和从盒子到外部世界的传热系数。

图4.集成原件的热模型

我们不难发现，图4对应的状态方程

以拉普拉斯变换（1）和（2）并解出TA（S），这是利益输出，给出如下的开环模型的热力系统：

其中，K是一个常数，Δ（s）是一个二阶多项式。K，τz，和Δ（s）的系数是出现在（1）和（2）中。

当然，在各种参数（1）和（2）是完全未知的，但它并不难证明，不论其价值，Δ（S）有两个实零点。因此，利益主体的传递函数可以写成

此外，开环的零极点图如图5

图5.Gaq(s)的零极点图

获得一个完整的热模型，然后，降低识别常数K和(3)中的三个未知的时间常数。四个未知参数是相当多的，但是简单的实验表明，1/τp1≤1/τz，1/τ2，这样τz，τp2≈0是很好的近似值。因此，开环系统本质上是一阶，因此可以写成

简单的开环阶跃响应实验表明，对于宽范围的初始温度和热输入，K≈0.14°/ W和τ≈295s。

4.2控制系统的设计

采用一阶模型（4）的开环传递函数Gaq（S）和假定的加热器的输出功率Q（t）是线性控制的是有可能的，图6表示的是闭环系统。

图6.闭环系统的简化框图

鉴于这种简单的情况，介绍线性控制设计工具，根据表1中的规定，如根轨迹法可以应用到一个符合要求的C（S）的阶跃响应上升时间，稳态误差和超调量，其结果，当然是一个能满足所有规格的具有足够的增益的比例控制器。超调量是不可能增加收益，降低稳态和上升时间。

不幸的是，足够的增益，以满足规范可能需要的热量比加热器本身能够产生的更多，在本系统的情况下，其结果确实是，上升时间规范不能得到满足。这是非常清楚的展示学生如何充分利用这样一个简单的模型，仔细确定整体性能的局限性。

4.3仿真模型

总的性能和它的局限性可以使用图6所示的简化模型来确定，但也有一些的闭环系统，其性能上的影响不是那么简单地建模。其中最主要的是

●在模拟到数字的转换所测量的温度和量化误差 ●使用PWM方式来控制加热器。

这两者都是非线性的，时变的影响，并研究它们的唯一可行的方法是（当然还是实验）通过模拟。

图7示出闭环系统，该系统具有以下仿真框图。A/D转换器量化和饱和度都使用标准的Simulink量化和饱和度块建模。模拟PWM比较复杂，需要一个自定义的S函数来表示它。

图7.闭环系统的仿真框图

该仿真模型已被证明对衡量不同PWM的基本参数的影响特别有用，因此选择这个仿真丝适当的。

PWM往往难以让学生掌握，仿真模型允许其操作和效果，这是相当发人深省的探索。

4.4单片机

简单的闭环控制，键盘读取，并显示控制是一些单片机的经典应用，而这个项目采用了三个。因此，它是一个很好的单片机综合运用。

另外，由于该项目是产生一个实际的包装原型，它不会简单的使用一个评估电路板与I/O引脚跳线到目标系统。相反，有必要制定一个完整的嵌入式应用程序。这需要广泛提供一个典型的微控制器系列的选择范围和学习使用一个相当复杂的开发环境，最后，一个自定义的印刷电路板上的微控制器和外围设备仍需设计和制作。

微控制器的选择

鉴于现有的专业知识，摩托罗拉线微控制器被选定为这个项目的微控制器。不过，这并不是狭隘的选择。一个相当严格的研究系统要求指定哪些微控制，大

量的变异，这对学生来说是困难的，如：他们普遍缺乏必要的经验和直觉，以及通过制造商的选择指南锲而不舍地探索。

这个问题的部分原因是在选择各种外设接口的方法（如，应该使用什么样的显示器驱动程序？）。摩托罗拉相关应用的研究笔记[2，3，4]被证明非常有助于了解可用哪些基本方法，单片机/外围组合应予以考虑。

该68HC705B16最终选择了现有的A/D输入、PWM输出，以及24个数字I/O线。回想起来，这可能是多余的，因为只有一个A/D通道，一个PWM通道，11个I/O引脚是真正需要的（见图3）。这一决定是犯错在安全方面，因为具体到所选择的部分是一个完整的开发体系是必要的，和项目预算不允许第二个这样的系统被购买应该第一个被证明是不够的。

单片机应用开发

外设硬件，开发微控制器的电路试验板软件，以及最后的调试和定制印刷电路板的测试微控制器和外围设备都需要某种形式的开发环境。

一个开发环境的选择，这样的微控制器本身就是令人困惑的，需要一些教师的专业知识。摩托罗拉是三级的开发环境，包括从简单的评估板（约100美元）到全面的实时仿真器（目前是7500美元）。MMEVS被选为这个项目，其中包括

●平台板(它支持所有6805家庭零部件) ●一个模拟器模块（特定的主要部分）， ●电缆线和目标适配器（特定包装）。

总体而言，该系统成本约900美元，在提供电路的仿真能力上具有一定的局限性。它还配备了简单但足够快速的软件开发环境[5]。

学生发现学习使用这种类型的系统具有挑战性，但他们利用简单的评估板获得的经验大大超过了现实世界中单片机应用的经验

印刷电路板

一个简单的印刷电路板的布局（但绝对不是小事）提供了一种实用的学习机会，最终的电路板布局，封装轮廓，如图8所示。该电路的相对简单性使得手动布局和布线实用。事实上，它可能做出来的效果比自动布局更好，它很好地暴露了学生在印刷和设计电路板布局的问题。所使用的排版软件是非常好的封装PCB2，板制作内部员工给予了电子技术帮助。

图8. 微控制器的印刷电路板布局

5.结论

本文的目的是要描述一个跨学科本科工程设计项目：基于单片机的温度控制系统，具有数字设定点输入和设定点实际温度显示。对这样的系统的的设计问题进行了说明，这些问题的解决通常需要超出基本课程所获得的知识，但实际上可以提高本科学生素质，尤其是教师的建议和监督很重要。

该问题的理想功能，从教学的角度来看，包括简单使用一个微控制器与外围设备，有机会有效地应用物理系统和闭环控制设计的入门级建模，并且需要相对简单的实验（用于模型验证）和模拟（详细性能预测）。一些相关技术方面的问题也是可取的，包括实际使用电阻加热器和温度传感器（分别需要的PWM和校准技术知识），微控制器的选择和使用的开发系统，以及印刷电路设计。

致谢

笔者要感谢辛勤工作，无私奉献，并通过参与这个项目显示能力的学生：马克朗斯多夫，马特拉尔，帕姆说，和戴维舒克曼。这是他们的项目，成功是属于他们的。

参考文献

[1] M. Langsdorf, M. Rall, D. Schuchmann, and P. Rinehart,―Temperature control of a microscope slide dryer,‖ in 1997 National Conference on Undergraduate Research, (Austin, TX), April 1997. Poster presentation.

[2] Motorola, Inc., Phoenix, AZ,Temperature Measurement and Display Using the MC68HC05B4 and the MC14489,1990. Motorola Semiconductor Application Note AN431.

[3] Motorola, Inc., Phoenix, AZ, HC05 MCU LED Drive Techniques Using the MC68HC705J1A, 1995. Motorola Semiconductor Application Note AN1238.

[4] Motorola, Inc., Phoenix, AZ,HC05 MCU Keypad Decoding Techniques Using the MC68HC705J1A, 1995. Motorola Semiconductor Application Note AN1239.

[5] Motorola, Inc., Phoenix, AZ, RAPID Integrated Development Environment User’s Manual, 1993. (RAPID was developed by P & E Microcomputer Systems, Inc.).

附件2：外文原文（复印件）

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, ● displaying both set-point and actual temperatures

●tracking step changes in set-point temperature with acceptable rise time, steady-state error, and overshoot.

Table 1 gives a more precise statement of specifications.

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 set point entry alone are enough to dictate that a microcontroller based design is likely the most appropriate. Figure 2 shows a block diagram of the students’ design.

The microcontroller, a Motorola MC68HC705B16 (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, real world 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 Mathematical Model

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 the box and Tb of the box itself. The inputs to the system are the power output q(t) of the heater and the ambient temperature T∞. ma and mb are the masses of the air and the box, respectively, and Ca and Cb their specific heats.μ1 and μ2 are heat transfer coefficients from the air to the box and from the box to the external world, respectively.

It’s not hard to show that the (linearized) state equations corresponding to Figure 4 are

Taking Laplace transforms of (1) and (2) and solving for Ta(s), which is the output of interest, gives the following open-loop model of the thermal system:

Where K is a constant and ?(s) is a second-order polynomial. K, τz, and the coefficients of ?(s) are functions of the various parameters appearing in (1) and (2).

Of course the various parameters in (1) and (2) are completely unknown, but it’s not hard to show that, regardless of their values,?(s) has two real zeros. Therefore the main transfer function of interest (which is the one from Q(s),since we’ll assume constant ambient temperature) can be written

Moreover, it’s not too hard to show that 1/τp1<1/τz<1/τp2, i.e., that the zero lies between the two poles. Both of these are excellent exercises for the student, and the result is the open-loop pole-zero diagram of Figure 5.

Obtaining a complete thermal model, then, is reduced to identifying the constant K and the three unknown time constants in (3). Four unknown parameters is quite a few, but simple experiments show that 1/τp1≤1/τz,1/τ 2 so that τz,τp2≈0 are good approximations. Thus the open-loop system is essentially first-order and can therefore be written

Gaq(s)=

(4)

(where the subscriptp1 has been dropped).

Simple open-loop step response experiments show that, for a wide range of initial temperatures and heat inputs, K≈0.14°/ W and τ ≈295s.1

4.2 Control System Design

Using the first-order model of (4) for the open-loop transfer function Gaq(s) and assuming for the moment that linear control of the heater power output q(t)is possible, the block diagram of Figure 6 represents the closed-loop system. Td(s) is the desired, or set-point, temperature, C(s) is the compensator transfer function, and Q(s) is the heater output in watts.

Of course the system is not actually linear, so the apparent parameter values vary with initial conditions and input magnitude. The effect on closed loop performance is not too serious, but it gives the student a good idea of what nonlinearity means and how feedback tends to mitigate its effects.

1

Given this simple situation, introductory linear control design tools such as the root locus method can be used to arrive at a C(s) which meets the step response requirements on rise time, steady-state error, and overshoot specified in Table 1. The upshot, of course, is that a proportional controller with sufficient gain can meet all specifications. Overshoot is impossible, and increasing gains decreases both steady-state error and rise time.

Unfortunately, sufficient gain to meet the specifications may require larger heat

outputs than the heater is capable of producing. This was indeed the case for this system, and the result is that the rise time specification cannot be met. It is quite revealing to the student how useful such an oversimplified model, carefully arrived at, can be in determining overall performance limitations.

4.3 Simulation Model

Gross performance and its limitations can be determined using the simplified model of Figure 6, but there are a number of other aspects of the closed-loop system whose effects on performance are not so simply modeled. Chief among these are

● quantization error in analog-to-digital conversion of the measured temperature and ● the use of PWM to control the heater.

Both of these are nonlinear and time-varying effects, and the only practical way to study them is through simulation (or experiment, of course).

Figure 7 shows a SimulinkTM block diagram of the closed-loop system which incorporates these effects. A/D converter quantization and saturation are modeled using standard Simulink quantizer and saturation blocks. Modeling PWM is more complicated and requires a custom S-function to represent it.

This simulation model has proven particularly useful in gauging the effects of varying the basic PWM parameters and hence selecting them appropriately. (I.e., the longer the period, the larger the temperature error PWM introduces. On the other hand, a long period is desirable to avoid excessive relay ―chatter,‖ among other things.) PWM is often difficult for students to grasp, and the simulation model allows an exploration of its operation and effects which is quite revealing.

4.4 The Microcontroller

Simple closed-loop control, keypad reading, and display control are some of the classic applications of microcontrollers, and this project incorporates all three. It is therefore an excellent all-around exercise in microcontroller applications.

In addition, because the project is to produce an actual packaged prototype, it won’t do to use a simple evaluation board with the I/O pins jumpered to the target system. Instead, it’s necessary to develop a complete embedded application. This entails the choice of an appropriate part from the broad range offered in a typical microcontroller family and learning to use a fairly sophisticated development environment. Finally, a custom printed-circuit board for the microcontroller and peripherals must be designed and fabricated.

Microcontroller Selection.

In view of existing local expertise, the Motorola line of microcontrollers was chosen for this project. Still, this does not narrow the choice down much. A fairly disciplined study of system requirements is necessary to specify which microcontroller, out of scores of variants, is required for the job. This is difficult for students, as they generally lack the experience and intuition needed as well as the perseverance to wade through manufacturers’ selection guides.

Part of the problem is in choosing methods for interfacing the various peripherals (e.g., what kind of display driver should be used?). A study of relevant Motorola application notes [2, 3, 4] proved very helpful in understanding what basic approaches are available, and what microcontroller/peripheral combinations should be considered.

The MC68HC705B16 was finally chosen on the basis of its available A/D inputs and PWM outputs as well as 24 digital I/O lines. In retrospect this is probably overkill, as only one A/D channel, one PWM channel, and 11 I/O pins are actually required (see Figure 3). The decision was made to err on the safe side because a complete development system specific to the chosen part was necessary, and the project budget did not permit a second such system to be purchased should the first prove in adequate.

Microcontroller Application Development.

Bread boarding of the peripheral hardware, development of microcontroller software, and final debugging and testing of a custom printed-circuit board for the microcontroller and peripherals all require a development environment of some kind.

The choice of a development environment, like that of the microcontroller itself, can be bewildering and requires some faculty expertise. Motorola makes three grades of development environment ranging from simple evaluation boards (at around $100) to full-blown real-time in-circuit emulators (at more like $7500). The middle option was chosen for this project: the MMEVS, which consists of ● a platform board(which supports all 6805-family parts), ● an emulator module(specific to B-series parts), and ● a cable and target head adapter(package-specific).

Overall, the system costs about $900 and provides, with some limitations, in-circuit emulation capability. It also comes with the simple but sufficient software development environment RAPID [5].

Students find learning to use this type of system challenging, but the experience they gain in real-world microcontroller application development greatly exceeds the typical first-course experience using simple evaluation boards.

Printed-Circuit Board.

The layout of a simple (though definitely not trivial) printed-circuit board is another practical learning opportunity presented by this project. The final board layout, with package outlines, is shown (at 50% of actual size) in Figure 8. The relative simplicity of the circuit makes manual placement and routing practical—in fact, it likely gives better results than automatic in an application like this—and the student is therefore exposed to fundamental issues of printed-circuit layout and basic design

rules. The layout software used was the very nice package pcb,2 and the board was fabricated in-house with the aid of our staff electronics technician.

5 Conclusion

The aim of this paper has been to describe an interdisciplinary, undergraduate engineering design project: a microcontroller-based temperature control system with digital set-point entry and set-point/actual temperature display. A particular design of such a system has been described, and a number of design issues which arise—from a variety of engineering disciplines—have been discussed. Resolution of these issues generally requires knowledge beyond that acquired in introductory courses, but realistically accessible to advance undergraduate students, especially with the advice and supervision of faculty.

Desirable features of the problem, from a pedagogical viewpoint, include the use of a microcontroller with simple peripherals, the opportunity to usefully apply introductory level modeling of physical systems and design of closed-loop controls, and the need for relatively simple experimentation (for model validation) and simulation (for detailed performance prediction). Also desirable are some of the technology related aspects of the problem including practical use of resistive heaters and temperature sensors (requiring knowledge of PWM and calibration techniques, respectively), microcontroller selection and use of development systems, and printed circuit design.

pcb is freely distributable software for UNIX/X11. It is written by Thomas Nau, Assistant Director of Computing at Universitat Ulm, Germany. He can be contacted at URL mailto:Thomas.Nau@rz.uni-ulm.de,the software is available at ftp://ftp.uni-ulm.de/pub/pcb, and an email list can be subscribed to at mail to: pcb @majordomo.uni-ulm.de

2

Acknowledgements

The author would like to acknowledge the hard work, dedication, and ability shown by the students involved in this project: Mark Langsdorf, Matt Rall, Pam Rinehart, and David Schuchmann. It is their project, and credit for its success belongs to them.

References

[1] M. Langsdorf, M. Rall, D. Schuchmann, and P. Rinehart,“Temperature

control of a microscope slide dryer,‖ in 1997 National Conference on Undergraduate Research, (Austin, TX), April 1997. Poster presentation.

[2] Motorola, Inc., Phoenix, AZ, Temperature Measurement and Display Using

the MC68HC05B4 and the MC14489,1990. Motorola Semiconductor Application Note AN431.

[3] Motorola, Inc., Phoenix, AZ, HC05 MCU LED Drive Techniques Using the

MC68HC705J1A, 1995. Motorola Semiconductor Application Note AN1238. [4] Motorola, Inc., Phoenix, AZ,HC05 MCU Keypad Decoding Techniques

Using the MC68HC705J1A, 1995. Motorola Semiconductor Application Note AN1239.

[5] Motorola, Inc., Phoenix, AZ, RAPID Integrated Development Environment

User’s Manual, 1993. (RAPID was developed by P & E Microcomputer Systems, Inc.).

[1] M. Langsdorf, M. Rall, D. Schuchmann, and P. Rinehart,“Temperature

control of a microscope slide dryer,‖ in 1997 National Conference on Undergraduate Research, (Austin, TX), April 1997. Poster presentation.

[2] Motorola, Inc., Phoenix, AZ, Temperature Measurement and Display Using

the MC68HC05B4 and the MC14489,1990. Motorola Semiconductor Application Note AN431.

[3] Motorola, Inc., Phoenix, AZ, HC05 MCU LED Drive Techniques Using the

MC68HC705J1A, 1995. Motorola Semiconductor Application Note AN1238. [4] Motorola, Inc., Phoenix, AZ,HC05 MCU Keypad Decoding Techniques

Using the MC68HC705J1A, 1995. Motorola Semiconductor Application Note AN1239.

[5] Motorola, Inc., Phoenix, AZ, RAPID Integrated Development Environment

User’s Manual, 1993. (RAPID was developed by P & E Microcomputer Systems, Inc.).

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