33. International Symposium IGIP / IEEE / ASEE 2004, September 27-30, Fribourg, Switzerland

Laboratory Exercises for Analog Circuits andElectronics as Hardware Homework with Student
Laptop Computer Instrumentation
Marion O. Hagler
Department of Electrical and Computer Engineering
Mississippi State, MS 39762 USA
hagler@ece.msstate.edu
Abstract—This paper describes some prototype hardware homework
projects that use inexpensive software running on student laptop PCs andan inexpensive digital multimeter. These projects were prepared to assess
the feasibility of using hardware homework to provide interactive andexperiential laboratory experiences in the first in a sequence of circuit
analysis and electronics courses.
Keywords-laptop PC; oscilloscope; spectrum analyzer; laboratory; LabVIEW.

1. INTRODUCTION
Although laboratory experience has always been an integral part of engineering
education, contemporary understanding of how interaction and active experience
with learning environments can boost learning underscores the fundamental
importance of laboratory experience even more [1]. This paper describes an effort to
exploit recent developments in technology to make the laboratory experience early
during a sequence of analog circuits and electronics courses more intensively
interactive and experiential by extending its availability beyond formal laboratory
and classroom settings.
Since 1999, the Bagley College of Engineering at Mississippi State University(MSU) has required each entering undergraduate student to purchase a laptop
computer and software that meet certain specifications [2]. As part of a restructuring
its sequence of courses in circuit analysis and electronics, the Department ofElectrical and Computer Engineering at MSU is now preparing to transfer thelaboratory hours that have been associated with the first course in the sequence to acourse later in the sequence, where the laboratory projects can be more complex. At
the same time, the laboratory experience in the first course will be strengthened byrequiring students to construct circuits and make measurements on them with theaudio capability built into their laptops and with an inexpensive digital multimeterthat they purchase for their own use. Students will accomplish the construction andmeasurement activities not in a laboratory or in a classroom, but at home. These
projects, therefore, are in essence hardware homework.
Hardware homework in the first course in the circuit analysis and electronics course
sequence not only will offer more frequent and sophisticated laboratory activities
than the present formal laboratory course, it also will employ students' laptops insubstantive interactive learning and thereby give students additional tangible returnon the financial investment in their laptops. In addition, this approach opens thepossibility of offering the first course in the circuit analysis and electronics sequence
through distance learning, a possibility that would help break scheduling bottlenecks
133. International Symposium IGIP / IEEE / ASEE 2004, September 27-30, Fribourg, Switzerlandthat occur when students transfer to Mississippi State from 2-year colleges – acommon occurrence – to complete the requirements for degrees in electrical andcomputer engineering.
In a course for first year undergraduate students in electrical and computerengineering at Mississippi State, hardware homework has been used since 2001 togive a laboratory experience without a formal laboratory [3]. Earlier, hardware
homework was used occasionally in an electronics course at Texas Tech University[4]. The recent availability of inexpensive software, such as the DSSF3 Light
Realtime Analyzer, that enables the audio capabilities of a PC to function as arelatively sophisticated real time signal generator, oscilloscope, and spectral analyzer
extends the range of laboratory exercises beyond those possible with the digitalaudio editors used before [5]. In contrast to powerful (and expensive) virtual
instrument software such as LabVIEW, Realtime Analyzer relies on the sound card
built into PCs for data acquisition and thereby permits simple and inexpensive signal
acquisition, processing and display in the audio frequency range [6].
This paper describes some prototype hardware homework projects that use aninexpensive digital multimeter and Realtime Analyzer running on each student’s
laptop PC to assess the feasibility of using hardware homework to provide thelaboratory experience in the first in the sequence of circuit analysis and electronics
courses at Mississippi State University.

2. RESISTIVE CIRCUITSKey objectives in the sequence of circuits and electronics courses are for students tolearn how to measure the performance of circuits, how to analyze the circuit
performance with mathematics and software, and how to compare and combine theresults of measurement and analysis to achieve the level of understanding needed forthe design of systems that meet performance specifications. Microsoft Office isrequired on each student laptop so Microsoft Excel is available. The Department ofElectrical and Computer Engineering at MSU requires, in addition, each student topurchase and install MATLAB Student Version [7]. Students also are expected todownload and install the latest free demonstration version of the OrCAD PSpicecircuit simulator [8].
Resistive circuits that consist of voltage sources, operational amplifiers, and resistors
offer an environment for integrating software and hardware into an experientiallycomplex interactive learning environment. Consider, for example, a simple two-loop
circuit that consists of 5 resistors and two 9V batteries configured with a single
battery in each loop. In practice, the value of each resistor is specified, but not theirplacement in the circuit. Students build the circuit with components and a board thatthey purchase at a local electronics store or online [9]. An inexpensive (less thanUS$25) digital multimeter available from the same source permits easy and accurate
measurements of voltages and resistances.
Homework based on this circuit consists of multiple parts with completion dates
spread over the first several weeks of the first course in the sequence. Of course,
these assignments would be complemented by other problem assignments during
this time, and not all parts would be assigned during a particular offering of thecourse. The individual parts range from constructing the circuit and comparing
measured, analytically calculated, and simulated values of mesh currents and node2

33. International Symposium IGIP / IEEE / ASEE 2004, September 27-30, Fribourg, Switzerland

voltages to investigating Thevenin’s theorem and the maximum power transfer
theorem.
As an illustration of one part related to the maximum power transfer theorem, Fig. 1
shows an Excel plot of power absorbed by a load resistor connected across a pair ofterminals in the circuit as a function of the load resistance. The light symbols
correspond to theoretical points, while the dark symbols correspond to measured
values.

Figure 1. Screen shot of Excel plot of the power dissipated in the load resistor vs. its resistance.

In a second example, students would consider a 741 op amp IC connected in an
inverting amplifier configuration, a practical implementation of a voltage controlled
voltage source. Students can plot the output voltage vs. the input voltage and deducethe voltage gain of the amplifier from the slope of the curve. Students can deduce theThevenin resistance of the amplifier at its output terminals and can observe when the741 IC begins limiting the output current to prevent damage to the IC. When that
happens, students note that the amplifier no longer behaves as a linear circuit, andconsequently that the Thevenin equivalent circuit is no longer valid.

3. CIRCUITS WITH CAPACITORS AND INDUCTORS
Teachers can use resistive circuits, an inexpensive digital multimeter, and widely
available software to construct surprisingly rich interactive and experiential learning
environments. Most practical circuits contain inductors and capacitors, however, andthus require a signal generator, oscilloscope, and spectrum analyzer for
implementation of effective learning environments. Although the venerable freedemonstration version of Cool Edit 96 enables a PC to act as an excellent audio
signal generator and provides oscilloscope and spectrum analyzer functions byrecording an audio waveform and then processing it, Cool Edit is no longer available
for inexpensive purchase [4]. At a cost of about $90, Realtime Analyzer (DSSF3Light version) provides more contemporary and sophisticated implementations of asignal generator, oscilloscope, spectrum analyzer and other functions in real time,and hence permits a PC to function much more like more capable instruments thatstudents will use later [5]. Fig. 2 shows a 2000 Hz square wave generated byRealtime Analyzer and displayed with its oscilloscope. Note the capability of theoscilloscope for two-channel display, adjustable triggering, and screen copy,
although these features are not used in this particular example figure.
333. International Symposium IGIP / IEEE / ASEE 2004, September 27-30, Fribourg, Switzerland

Figure 2. Realtime Analyzer oscilloscope view of a 2000 Hz square wave from its signal generator.

Fig. 3 shows an inverting integrator circuit built with a 741 IC, a 10 nF capacitor, a
10,000 Ohm resistor, and several ancillary components. Fig. 4 shows the (triangularwave) output of the inverting integrator when the 2000 Hz square wave shown inFig. 2 is applied to the integrator input. Students can compare the relative
magnitudes of the input and output waveforms with analytical calculations and withthe results of OrCAD PSpice simulations. If the laptop provides a stereo input, theoscilloscope can display simultaneously the input in one channel and the output inthe second channel. In that case, students can compare the relative phases of theinput and output waveforms.

Figure 3. An inverting integrator circuit built with an 741 op amp IC, a 10 nF capacitor, a 10,000 Ohm
resistor, and ancillary components.

433. International Symposium IGIP / IEEE / ASEE 2004, September 27-30, Fribourg, Switzerland

Figure 4. Triangular wave output of the inverting integrator when the input is the square wave shown inFig. 2.

To illustrate spectral measurements, consider a simple RC (resistor capacitor) low
pass filter circuit with R = 4700 Ohms and C = 10 nF. To measure its spectral
response, drive the input to the filter with white noise generated by Realtime
Analyzer and the laptop sound circuitry. Measurement shows that the spectrum of
the laptop audio output is flat to within a few decibels between 200 and 19,000 Hz.
Fig. 5 shows the spectrum of the output from the low pass filter as it is driven bywhite noise from the headphone output of the laptop. Phasor analysis indicates thatthe frequency at which the spectrum should fall by 3 decibels from its low frequency
value should be about 3400Hz, a value consistent with Fig. 5, which also shows thatbetween 5000Hz and 10000Hz the spectrum drops by about 6 decibels, the value
indicated by analysis. Of course, students can compare the measured results withanalytical phasor calculations plotted with Excel and with OrCAD PSpicesimulations.

Figure 5. Spectrum of the output of the RC low pass filter driven by white noise.

Fig. 6 shows illustrates the capability of Realtime Analyzer to measure and display
the impulse response of circuits.

5

33. International Symposium IGIP / IEEE / ASEE 2004, September 27-30, Fribourg, Switzerland

Figure 6. Impulse response of an RLC band pass filter.

4. DISCUSSION AND CONCLUSIONSThe list of parts and tools needed for construction of the circuits mentioned includes
a digital multimeter, 9V batteries, resistors, capacitors, 741 op amp chips, general
purpose printed circuit boards, IC sockets, shielded cables with alligator clips, long
nosed pliers, solder, and a soldering pencil. The total cost is less than US$80 [9].
Students in the Department of Electrical and Computer Engineering at Mississippi
State University have been required to purchase most of these parts and tools during
a first year course [3]. The main incremental cost to the students, therefore, would be
the cost of the Realtime Analyzer (DSSF3 Light) software, about US$90 andapproximately the cost of a typical contemporary engineering textbook.
The promise of the prototype exercises described here to provide intenselyinteractive and experiential learning environments, in combination with the low
incremental costs to the students, has led the faculty of the Department of Electricaland Computer Engineering to approve work aimed at implementing hardware
homework in the revised first course in the sequence in circuits and electronics in theDepartment beginning in the fall semester of 2005.

REFERENCES
[1]
[2]
[3]

[4]

[5]
[6]
[7]
[8]
[9]

P. C. Wankat, The Effective, Efficient Professor. Allyn and Bacon: Boston, 2002, pp. 42-43.
Computer Initiative, http://www.engr.msstate.edu/prospective_students/computer_initiative/.
M. O. Hagler, "Hardware Homework As Active And Experiential Learning For First Year Students
In Electrical And Computer Engineering," Proc. 2003 Frontiers in Education Conference, CD-ROM
file /papers/1450.pdf. Also, http://fie.engrng.pitt.edu/fie2003/papers/1450.pdf.
M. Hagler and D. Mehrl, "A PC with Sound Card as an Audio Waveform Generator, a Two-Channel
Digital Oscilloscope and a Spectrum Analyzer," IEEE Trans. Ed. Vol. 44, p. 199, 2001. Also, CDROM file /15/BEGIN.HTM or http://www.ece.msstate.edu/~hagler/May2001/15/BEGIN.HTM.
DSSF3 Light, http://www.ymec.com/products/dssf3e/
LabVIEW, http://www.ni.com/labview/
MATLAB Student Version, http://www.mathworks.com/academia/student_version/
OrCAD, http://www.orcad.com/downloads/orcadlite10/
RadioShack, http://www.radioshack.com
6