Results of Combining Structure and Design in Electrical Engineering Laboratories

SOUKUP, Rodney¹ & BOYE, A. John²

Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511, U.S.A.
¹ rsoukup@unl.edu, http://www.engr.unl.edu/ee
² jboye@unl.edu, http://www.engr.unl.edu/ee

Abstract: The Curriculum in Electrical Engineering has contained two credit laboratories in both semesters of the junior year for about 15 years. Originally the laboratories were completely structured and contained experiments from several areas of the electrical engineering curriculum. In 1992 we made a decision to reduce the number of structured experiments and add open ended design experiments. Contrary to the comments of some attendees at the meeting where this idea was first presented [1] these laboratories are working very well. In the senior year we have discovered that the students oral and written communications skills have improved considerably and they are much better prepared for the final design laboratories, especially the capstone design laboratory in their final semester.

The structured part of the laboratories complement the lecture courses on analog electronic circuits, digital electronic circuits, continuous systems, electromagnetics, solid state device physics, communications, controls, and discrete systems. The design projects can be chosen by the students from 10 categories. The categories are somewhat different for each laboratory. The common choices for each laboratory are transistor amplifiers, operational amplifiers, oscillators, power supplies, filters, and other analog circuits. The first semester also has more advanced transistor amplifiers, basic digital circuits, logic circuits, and other digital circuits. Each student chooses only one project from each category, each of which contains three or more suggestions. This forces them to explore several areas for their designs. The second semester of the junior year is similar, but the non-common designs are chosen from more advanced digital circuits, fields and waves, communications, and control systems. These mini projects provide the students with an excellent background to enter the senior design laboratories.

Keywords: structure, design, laboratories

1 Introduction

Typically, most lower level electrical engineering laboratories merely demonstrate the material in one or two particular courses being taken concurrently with the laboratory. Also they are usually of the structured or "cook book" variety, giving a step-by-step procedure to follow. Design experiments are often left until the final year before they are attempted. In this paper we describe a two semester, two credit hours, third year required electrical engineering laboratory that we introduced several years ago. This laboratory contains experiments from a number of different courses; digital and analog electronics, electromagnetics, materials and devices, communications, and control systems. It contains a mixture of eight traditional structured experiments and four open ended design experiments each semester.

Each semester the laboratory meets for one three hour session for each of two weeks. During each of these two sessions, the student performs a different structured experiment. The third week the students demonstrate a design experiment upon which they have been working outside of the regularly scheduled laboratory period the previous two weeks. This typically takes about 15 minutes. This pattern is then repeated so that a total of eight structured and four design experiments are performed over a 12 week period. There is also a laboratory practical examination at the end of each semester. The schedule for one of these laboratories is shown in Figure 1.

Figure 1. Schedule of Laboratory Experiments

2 Structured Experiments

The eight structured experiments each semester are led by a graduate student teaching assistant under the supervision of a faculty member. The students are allowed to work alone or in pairs, but must work with a different partner each week. This forces them to meet and work with others. We also never allow three or more students to work together, since experience has shown that one of the three will usually not participate. A minor problem is the student who always wants to work alone. We do not allow this on a regular basis because we feel it is important for students to learn how to work in a team.

The structured experiments cover topics in required courses that the student should either have already taken or one which he or she is taking concurrently. For most of the experiments the material covered in a structured experiment should have already been covered in a class by the time the student performs the experiment. However, occasionally some of the material in an experiment is covered ahead of the corresponding class. Some believe that this is not good. However, it is felt that this can also be beneficial, since the student sees and performs experiments with the material before obtaining the thorough explanation. This should help to enhance the understanding of the material when covered in class. To help this situation, explanations of the necessary theoretical materials is given in the experiment description. Additional references are given from which the student can obtain further help.

The students purchase a laboratory manual which contains a written description of each of the structured experiments. Each description includes a brief review of the relevant theory, a pre-laboratory preparation section, often involving use of a computer, which the student completes before coming into the lab; an experimental step-by-step procedure section; and a number of questions relating the results of the experiment to the theory. The student is expected to keep a laboratory notebook with the results and he or she is not allowed to remove this notebook from the laboratory.

Experiment Descriptions

The first semester structured experiments include two experiments in each of four areas and were described in the earlier paper [1]. The second semester's experiments are discussed in the following.

1. Solid State Electronic Devices

   These two experiments are from material discussed in a lecture style course during the current semester. Not every student is required to take this other course at this time, but it is strongly recommended. This is somewhat of a disadvantage for these students, but the experimental description is written so that they can understand the experimental results without taking the other course.

   • The pn Junction Diode

     In this experiment the students are given equations describing the junction capacitance and the current-voltage characteristics. They then measure the capacitance and the current as a function of applied bias to see how well the equations fit the data.

   • Bipolar and Field Effect Transistor Properties

     In this experiment the equations describing the emitter, collector, and base currents as functions of the emitter-base voltage and the collector-base voltage are presented. For the MOSFET we explain how the gate oxide capacitance depends upon the gate voltage. The experiments are then carried out to determine if the experimental results are as predicted.

2. Modulation

   The theoretical background for this experiment is not covered before this laboratory except for a few students. Thus, a thorough explanation of amplitude modulation is give in the experiment write up. In the experiment, the student builds two types of am modulators and observes the outputs when a signal/carrier is the input.

3. Control Systems (Position Control of a dc Motor)

   This experiment attempts to demonstrate the theory of control systems. The material covered here is also not necessarily covered in another class before the experiment. In this experiment the students build a relatively simple control system and again determine the difference between the theory and actuality.

4. Signals and Systems (Discrete Sampling)

   In this experiment a thorough explanation of sampling is presented. The experiment consists of building an analog to digital converter to use as the sampling circuit. A digital to analog converter is also built and the two are connected to see how well the output compares with the input under several conditions.

5. Traveling Waves

   The three experiments in this grouping are all on material covered in a course which is required to be taken in parallel with this course. This other course should have progressed to the point where the material in these experiments has already been studied by the students.

   • Slotted Waveguide, Frequency and Impedance Measurements

     The operation of the slotted waveguide is investigated in this experiment. A standing wave pattern is generated, for which the operating frequency and an unknown impedance are measured using the slotted waveguide.

   • The Single-Stub Waveguide Screw Tuner

     A single-stub waveguide screw tuner is used to match a load impedance to the intrinsic wave impedance of a waveguide. Calculations are made with the assistance of a Smith chart.

   • Antenna Pattern and Propagation Measurements

     In this experiment the radiation pattern of a horn antenna is investigated. Using two antennas, the Friis transmission formula for a propagation link is studied.

The first semester experiments are clearly spelled out in the first paper [1]. The titles of the experiments will just be listed here. In both semesters, the last question to be answered in each write up is, "What suggestions do you have to improve this experiment?" We often learn things from the students in answer to this question.

1. Digital Combinational Circuits.
2. Digital Sequential Circuits.
3. The Current Mirror and Differential Amplifier.
4. The Wien Bridge.
5. Ampere's Law, Faraday's Law, and Inductance.
6. Measurement of B/H Characteristics and Dielectric Constants.
7. Time and Frequency Domain.
8. The Fourier Series.

3 Design Experiments

The four design experiments each semester are selected by the student from a list of about 30 projects divided into 10 categories. The students are allowed to only select one project from any one category. This forces the student to investigate more than the one or two areas for which he or she is most comfortable. There is a different list for each semester, with the second semester being more challenging than the first. However, in both cases, the projects only require the use of material learned in courses that the student has already had. We have attempted to change at least some of the selections each time we have taught the laboratory. This change is to help prevent the students from using experiments performed the previous semester by their friends. Students are again allowed to work alone or in pairs, with different partners for each design experiment. The students work on their own time for two weeks, building and testing their project. A faculty member is always available to answer questions during this time. The third week the students display their project to the faculty member in charge and answer verbal questions from him or her. About 15 minutes is allowed for each project demonstration. Finally the students each write a formal report on each project.

Project Descriptions

The list of projects is included in the laboratory manual. Each project is simply described by a one or two sentence statement of what is desired. The students are expected to perform the research necessary in order to do the project. Their grade is based partially on how close they come to meeting the specifications. Points are also given for extra effort or improving on the requirements. Some examples of the project descriptions follow.

• Design and build a system to control a passenger elevator in a seven story building.
• Design and build a class B transistor amplifier with a center frequency of 50 kHz and a bandwidth of 5kHz.
• Design and build a circuit using one operational amplifier whose voltage rises at a rate of 6 dB/octave when the frequency is less than ω₀ and whose voltage drops at a rate of 6 dB/octave when the frequency is greater than ω₀. You may choose the value of ω₀.
• Using discrete components only, design and build a Colpitts oscillator.

The above listed projects are some of the more popular ones. In this second laboratory they can choose from 30 suggested projects and can choose some of their own if the instructor agrees. In the first laboratory they also have 30 projects from which to choose.

The 10 categories for the first semester laboratory are: Basic Transistor Amplifiers; Miscellaneous Transistor Amplifiers; Operational Amplifier Circuits; Oscillators/Multivibrators; Filters; Power Supplies/Voltage Regulators; Other Analog Circuits; Basic Digital Circuits; Logic Circuits; Other Digital Circuits.

The 10 categories for the second semester laboratory are: Digital Circuits; Transistor Amplifiers; Operational Amplifier Circuits; Oscillators/Multivibrators; Power Supplies/Voltage Regulators; Filters; Other Analog Circuits; Fields and Waves; Communications; Control Systems.

4 Observations

In the most recent, fall 1998, senior exit interview and survey sheet, the students did not rate these laboratories above average. However, the problem most of the students had was with the equipment available to carry out the structured experiments and not with the laboratory in general. The projects and the variety of structured experiments are looked upon favorably. The equipment problem will be corrected in the near future and, hopefully these will be popular as well as valuable laboratories.

Since these are the first laboratories where the students have formal design projects the goal was to try to introduce the formal design procedure in a way that has encouraging and stimulating for the students. By the many favorable comments from students about the design projects, this seems to have been the highlight of the course for many. It was a good idea to include both structured and design experiments in the same laboratory. This seemed to be a good way of helping students make the transition from being guided step-by-step to being able to do independent open ended design. Even though they protested, it was good idea to have students write a formal laboratory report on the design projects. It was found that students need a lot of practice with written communications. This is particularly noticeable on the early reports. The comments from the instructors of the senior design courses are that the quality of the students reports are noticeably improved over the quality before we introduced these design projects in the junior year. Some students, especially at first, needed a lot of coaching and help on their design projects. There were some problems with experiments that were done before the theoretical background was covered in a corresponding course. However, this was at least partially overcome by including explanations and references in the laboratory description. Both the structured experiments and the list of design projects need to be revised at the beginning of each semester. This was necessary not only to clarify some of the explanations, but also to prevent students from merely using an experiment or project that some other student had done the previous semester. The students are graded on the design projects using the sheets in the Appendix.

5 Conclusions

A two semester junior level electrical engineering laboratory was described which included experiments from a number of different electrical engineering subdisciplines. In addition, both the structured approach and the open ended design approach were used. From our feedback it seems that students benefit from this approach and enjoy it as well. The laboratory schedule for both semesters is shown on the next page.

6 Appendix

ELEC 307 AND 317  

Project and Report Grading Sheet

PROJECT (0: lowest to 10: highest)

1. Meets specifications. (35%)

   Does the project work? Meets the minimum specification?

2. Difficulty/extra effort. (30%)

   How difficult is the project? Any additional improvements above the minimum specifications: Appearance, neatness, etc.?

3. Verbal explanation. (35%)

PROJECT TOTAL (100%)

Comments:

TOTALS

• Project (50%)
• Report (50%)
• GRADE (out of 10 possible)

REPORT (0: lowest to 10: highest)

1. Title page. (5%)

   Showing:

   • experiment title;
   • experiment number (1-30, as given in lab manual);
   • date(s) the experiment was performed;
   • date the report was finished;
   • author's name;
   • partner's (if any) name.

2. Abstract. (5%)

   A 3-4 sentence summary of the report.

3. Introduction. (5%)

   A 1 to 2 paragraph prelude to the experiment which stands alone from the abstract. Did the author understand what the lab was all about?

4. Background and theory. (5%)

   This section briefly should give the reader the necessary background and theory to understand the experiment.

5. Design (10%)

   This section explains and shows the design. Calculations go here.

6. Procedure and implementation. (10%)

   A brief recreation of the experiment explaining what was done, not a lengthy minute-by-minute account.

7. Results and discussion. (35%)

   The main part of the report. Results, including any measurements or investigations made. Include graphs, tables, and figures, if appropriate. Important observations. Comparison of the results with predicted theory and reasonable explanations of any difficulties or surprising results. Any recommendations that possibly could improve the results.

8. Conclusions. (10%)

   A 1 or 2 paragraph summary of the experiment. The main items learned. No new information should be included in the conclusion.

9. References. (---)

   If necessary. Proper credit given to anything copied!

10. English. (10%)

    Spelling, punctuation, and grammar.

11. Format: (5%)
    • all curves, tables, and figures labeled completely;
    • graphs labeled and interpreted slopes, breakpoints, etc. identified);
    • circuit diagrams accurate and labeled;
    • no smaller than 12 point type (that's the size of this type);
    • typed, double spaced, and written on one side of the page only;
    • no figures or equations included that are not referred to in the text;
    • report stapled in upper left corner, no plastic cover or paper clip;
    • two copies of report turned in.

REPORT TOTAL (100%)

References