Salt Lake City, Utah
June 23, 2018
June 23, 2018
July 27, 2018
Experimentation and Laboratory-Oriented Studies
By its very nature, electrical engineering is largely an abstract discipline. While we can easily see the effects of an electrical process, i.e., a light comes on, or a motor turns, the underlying principles of the process are frequently only understood via mathematical expressions. This may lead to incomplete student comprehension or a level of discomfort with the material. Many undergraduate courses such as Circuits or Electronics include a laboratory component that attempts to alleviate this condition and frequently simple concepts such as Ohm's law, power consumption, or basic filters, are adequately exemplified. However other concepts such as phasors, superposition, fixed current sources, and controlled current sources are not covered in a laboratory context due to a lack of laboratory equipment that can adequately expose the underlying concepts. In this paper, we will present several simple printed circuit modules that will snap onto a typical solderless breadboard and allow students to perform experiments in these topics. We will offer typical laboratory assignments that might be used with each, and example test questions that might be included in exams or quizzes. An experiment that is seldom seen in introductory laboratory coursework is the direct phasor addition of several sinusoidal voltage sources. Traditionally this would require multiple synchronized signal generators, an expensive proposition. Our design exploits the use of cascaded all-pass filters, accepting one sinusoidal input and producing two equally spaced phase-shifted outputs. The original input is passed through as an output as well, thus deriving a total of three signals from a single source. The input frequency determines the amount of phase shift, but the output amplitudes are all constant at the same level as the input level. The circuit derives its power from the distribution rails on a typical solderless breadboard and includes a BNC connector for the signal generator input. Experiments that may be performed with this device include passive phasor voltage summation using resistive networks, superposition and phase measurements from multiple sources, operational amplifier voltage summers, and even low voltage 3-phase measurements. A second concept that is seen as an abstraction by most students is the fixed current source. Frequently it is presented as a part of homework problems, especially in the early stages of a linear circuits course as students are learning fundamental circuit laws. However, students never to get to experience its operation in a laboratory. Our current source is a true two-terminal device powered by a 9-volt battery and snaps into a solderless breadboard and is switchable between 10 or 20 mA. Experimentally, it may be employed to illustrate Norton and Thevenin equivalent circuits as well as fundamental concepts of mixed source superposition for D.C. circuits. A third concept that is only taught through lecture and homework is the voltage controlled current source. While this idea is vital to the understanding of MOSFET or BJT circuit models, it is never seen in a "pure" form; its operation is frequently obscured by the small-signal linearizations that are performed in transistor experiments and the operation of the underlying circuit model may easily be lost on the students. Our device snaps onto a solderless breadboard and derives its power from the voltage distribution rails. It allows experiments to be performed in which the central element of the exercise is a true voltage controlled voltage source. Examples include double loop calculations with a shared impedance between one of the voltage input nodes and the current output node. This may be expanded upon to allow students at the introductory levels to build, as a laboratory experiment, the small-signal model of a single stage transistor amplifier without having seen a "real" transistor, easing the pathway to understanding this crucial concept in later courses.
Powell, H. C. (2018, June), BYOE: Circuit Modules for Visualizing Abstract Concepts in Introductory Electrical Engineering Courses Paper presented at 2018 ASEE Annual Conference & Exposition , Salt Lake City, Utah. https://peer.asee.org/30169
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