【導讀】糧食儲存的一個重要問題。本設計采用STC89C52單片機最小系統(tǒng)對檢測、報警、顯示、調(diào)控等模塊進行多點控制，傳統(tǒng)的溫濕度控制利用溫度計、濕度表、濕度試紙等測試器材，通過人工進行檢測，對不符合溫濕度要求的庫房進。行通風、降溫、去濕等操作。這種方法費時費力，效率低，隨機性大，誤差大，不能及時的解決問題。過自動檢測、即時報警、自動調(diào)控等功能很好的解決了。并且，本設計不僅針對糧倉，對于大多譬如蔬菜大棚、花。圃、實驗室、醫(yī)院等需要溫濕度檢測控制的各個領(lǐng)域都是適用的。

　　

【正文】 e project was to develop a temperature control system for an airfilled chamber. The system was to allow entry of a desired chamber temperature in a prescribed range and to exhibit overshoot and steadystate 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 realworld application. A prototype of a microscope slide dryer had been developed around an OmegaTM model CN390 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, airfilled 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 CN390 temperature controller using a customdesigned system. The application dictates that temperature settings are usually kept constant for long periods of time, but it’s noheless important that step changes be tracked in a ―reasonable‖ manner. Thus the main requirements boil down to allowing a chamber temperature setpoint to be entered, 陜西理工學院畢業(yè)設計 第 21 頁 共 39 頁 displaying both setpoint and actual temperatures, and tracking step changes in setpoint temperature with acceptable rise time, steadystate error, and overshoot. Although not explicitly a part of the specifications in Table 1, it was clear that the customer desired digital displays of setpoint and actual temperatures, and that setpoint 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 fourkey keypad which allow specification of the setpoint temperature, and it displays both setpoint and measured chamber temperatures using twodigit sevensegment LED displays controlled by a display driver. All these inputs and outputs are acmodated by parallel ports on the 6805. Chamber temperature is sensed using a precalibrated thermistor and input via one of the 6805’s analogtodigital inputs. Finally, a pulsewidth 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 setpoint 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 temperaturesensing 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 setpoint in response to keypad inputs. Because it is not plete 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 controll