1
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
锛?/p>
This
paper
describes
an
interdisciplinary
design
project
which
was
done
under
the
author鈥檚 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
鈥?7 by four students under the author鈥檚 supervision as a Senior Design project in the
Department of Engineering Science at Trinity University. The purpose of this paper is