Thai Conf Final 30mar2004 1340

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4th

Global Congress on Engineering Education © 2004 UICEE

Bangkok, Thailand, 5 - 9 July, 2004

INTRODUCTION

On March 17, 2004 a panel of San Jose State Universityinstructors spoke to faculty members about the use of online

teaching tools. According to the panel discussions greatstrides have been made in the direction of using the internet for education, either in full on-line courses or in using the internet

in web-assisted courses. “Corey Gin, academic coordinator atthe SJSU Center for Distributed Education, which hosted the

event, said there are about 41 totally online courses beingtaught on campus this semester, with about 150 blended courses, which use online resources to supplement what istaught in the classrooms.”[1] The web-courses take advantage

of all kinds of tools in addition to lecture presentations. In this paper the author describes other novel tools aiding us in theeffort of instruction, in particular, the instructions in a circuitand experimentation lab. A virtual instrument from NationalInstruments is used for demonstrating the control and measurement of experiments. The fact that this instrument iscontrolled by a personal computer makes it possible to alsocontrol it via the internet. In addition, customized programswere developed using LabView, a graphical programming

language, which let the user at a remote location apply

specified dc-voltages and ac-signals to circuits in our lab and which allows him/her to make circuit measurements.

THE PRESENT INTEGRATED CIRCUIT DESIGN LAB

The Integrated Circuit Design Lab in the ElectricalEngineering department at San Jose State University (SJSU)

covers the lab portion of EE124 Electronic Design II. EE124has 4 credit units, including the lab portion which has a onecredit unit weight. Each semester we have 6 lab sections,

whereby there is a 16 student per section limit. The lab has 10lab stations. 8 lab stations are used by the students who doubleup in groups of two. One lab station is for the instructor used

for experimentation and demonstration. The 10th lab station isconsidered to be a spare station. If any equipment breaksdown, then the instruments from the spare station may be used.

The EE124 lab complements the lecture, where students learndesign techniques for integrated circuit design. In the labstudents hone their skills in circuit design, simulation, buildingand troubleshooting, measurement techniques, circuitcharacterization and evaluation. They are responsible for

recording their data in lab notebooks, and for reporting their results in reports and by presentations.

The experiments covered are listed in Table 1.

Table 1: Circuit and Instrument Experiments in EE124 Lab

Expt.

#

Experiment

1 Diode Characteristic

2 Transistor Curve Tracer

3 Current Mirror

4 Differential Amplifier

5 Transconductance Amplifier

6 Feedback Amplifier 7 Op Amp Frequency Limitation

8 Oscillator

9 Filters

10 Spectrum Analyzer

There is a considerable equipment investment in the EE124Lab. Each lab station has an oscilloscope, function

generator/arbitrary waveform generator, digital multimeter and a triple output power supply. Also each lab station has a PC(with monitor, keyboard and mouse) connected to theinstruments by a GPIB interface bus. In addition the laboratory

Real life measurements in a circuit design laboratory via the internet

Udo Strasilla

Department of Electrical EngineeringSan Jose State UniversitySan Jose, California, USA

ABSTRACT: A pilot program has been set up in our Analog Circuit Design Lab where remote measurements may be performed via the internet. Our initial stimulus to go this route is the fact that students often cannot finish their lab experiments within theallotted time when an instructor is present. For reasons of security and shortage of funds to keep a supervised lab open longer,students are not allowed in the lab at non-class times. The success in enabling students to perform experiments at home over theweb demonstrates that less endowed universities could also invest in a measurement lab accessible on the web. Their cost inestablishing such lab would be 10% of the cost of equipping a traditional circuit measurement lab. Both, an Educational Laboratory

Virtual Instrument from National Instruments and customized LabView programs linked with data acquisition hardware, are used not only for in-lab demonstrations but also for remote measurements. Examples for some of the remote controlled experiments are:

the measurement of a diode characteristic, characterization of a transistor similar as done by a curve tracer, and the measurement of the frequency response and linearity of amplifiers and filters.



has capacitance meters, a transistor curve tracer and a spectrumanalyzer. Acquisition records show that the cost of the labequipment is at least US$70’000. If it were not for

contributions from industry, in particular from HewlettPackard, this lab would be in poor shape. Our chairman, Prof.Freeman, calculated that if our labs would only rely on statefunds, they could be upgraded only every 80 years.

THE TRADITIONAL WAY TO USE THE CIRCUIT

DESIGN LAB

The lab experiments are described in our EE124 Lab Manual[2] which is updated every semester, whereby circuitspecifications are changed in order to avoid “recycling” of old lab reports. According to the lab manual instructions thestudent should prepare for each experiment at home by

familiarizing him/herself with the theory, by performing the paper/pencil design and by performing circuit simulations toverify the design. Also students should breadboard their circuit at home, so they may use lab-time more efficiently for measurement and evaluation. In the beginning of the lab theyare given a quiz to test their understanding of the previous

experiment(s) and their preliminary preparation. The labinstructor gives a short lecture reviewing subtleties of the

previous experiment and giving pointers on the newexperiment with emphasis on areas where difficulties areanticipated. The instructor often attempts to demonstratemeasurements on a demo circuit, showing measurementtechniques, expected waveforms and troubleshootingtechniques.

There are a couple of shortcomings using above approach.First, valuable lab-time is lost by the in-lab tutorial and by the

demo. This portion could be addressed as effectively byhaving tutorials on the web. Secondly, the demo - as wellintended as it is - is problematic when 16 students crowd around the instructor and stretch their neck trying to get aglimpse of the oscilloscope. Sometimes a student might

accidentally bump into the arm of the instructor handling probes, thus causing open or short circuits or components to pull out. The solution for this demo-problem will bedescribed in the next chapter, where ELVIS comes to the

rescue.

The largest shortcoming in the lab is the fact that students canrarely finish the lab experiment in their allotted time of 3hours. If one hour is lost due to the introductory tutorial, demoand quiz, then the students have only 2 hours to finish the

experiment. Though the experiment is designed such that theyshould be able to finish the experiment in that time, this doesnot allow for Murphy’s law, which states that “if anything cango wrong, it will!” Instructors often are generous in staying

longer in the lab. But many students cannot take advantage of this due to conflicts with other classes. Understandably, due tothe huge department investment in this lab, and due to safetyissues, access codes cannot be given to the students. Also, dueto the budgetary crunch, our department cannot afford the

hiring of student assistants who could supervise the lab at other times than the official lab times. It is encouraging that the

internet allows a solution to this dilemma by making remote-controlled experiments possible over the web. Efforts done onthis front will be discussed in the second next chapter of this paper.

CIRCUIT MEASUREMENT DEMONSTRATION USINGELVIS

The Fall 2002 Professional Development Grant of $2500allowed the author, who also is lab coordinator for the EE124Integrated Circuit Design Lab, to purchase the ELVISinstrument from National Instruments. ELVIS is the acronym

for Educational Laboratory Virtual Instrumentation Suite. It isa LabView-based design and prototyping environment for

university science and engineering laboratories. ELVIS is a

powerful measurement instrument which practically contains12 instruments in one package. [3] As shown in Fig. 1 itconsists of a box containing hardware function generators, power supplies, connectors and a protoboard on the top. Acircuit built on the protoboard may be powered and excited bya signal generated from within the ELVIS box or generated by

software within the computer. ELVIS connects via a cable tothe digital/analog data acquisition (DAQ) card mounted within

the computer. Software invoked ac-signals and dc-voltages aresent from the PC DAQ-card to the circuit. The resultingsignals are measured on the PC.

Fig. 1 ELVIS, the Laboratory Virtual Instrument

The heart of the instrument is the LabView software resident inthe PC. In 1986 National Instruments introduced Lab View, agraphical test development environment that pioneered the

concept of “virtual instrumentation”. Table 2 shows thevarious instruments into which ELVIS could morph to. Someof these instruments, for example power supplies, functiongenerator and oscilloscope may be run simultaneously, thusduplicating the basic instruments of our lab-bench.

Table 2: Various Instruments Built into ELVIS

Inst # Instrument Type

1 Digital Multimeter

2 Oscilloscope

3 Function Generator

4 Variable Power Supplies

5 Bode Analyzer (Frequency & Phase)

6 Dynamic Signal Analyzer (Spectrum)

7 Arbitrary Waveform Generator

8 Digital Reader

9 Digital Writer

10 Impedance Analyzer

11 Two-Wire Current-Voltage Analyzer

12 Three-Wire Current-Voltage Analyzer



ELVIS is ideal for demonstrations in our EE124 Lab. It has been used in the author’s lab section starting this springsemester 2004. The demo circuits are built on the pressboard

on top of the ELVIS box. The various power supplies and signals are hooked up to the appropriate points and the desired signals are monitored using the meter or scope feature of ELVIS. When the instructor demonstrates the behavior of thecircuit he/she may manipulate the voltages, signals and scopesettings from the PC. Due to the fact that the circuit is never

touched during the demo, the setup is quite robust. An LCD

projector connected to the PC allows projection of theinstrument panels to the classroom screen.

Some of the demos performed in the EE124 lab are illustrated in Figures 2 and 3. Fig. 2 shows an oscilloscope display of theinput and output voltages of a differential amplifier to bedesigned by students. It well demonstrates the performance of a differential amplifier where a “useful” triangular differential

signal “corrupted” by a square-wave common-mode signalamplifies only the triangle signal while discarding the

common-mode portion. This is a useful feature of amplifiersin applications like medical instrumentation, where small brainwaves buried within common-mode ac-signals need to beamplified first before they can be recorded by an EEG or

Electro-Encephalo-Graph.

Fig. 2: ELVIS (Educational Laboratory VirtualInstrumentation Suite) Oscilloscope Display of a DifferentialAmplifier Circuit Input and Output Voltage

Fig. 3 demonstrates the characterization of a band-pass filter by

means of a Bode plot analyzer. It shows the gain and phase of the filter in decibels and degrees, respectively, as the sine-waveinput frequency is varied between 10Hz and 35 kHz. Our labdoes not have a conventional Bode plot analyzer due to its

expense. Students wishing to analyze filters or amplifiers haveto go through the painstaking process of measuring inputvoltage, output voltage and phase at one frequency, and thenrepeating the measurements for successive frequencies.

Also ELVIS may be used as a spectrum analyzer. A spectrumanalyzer works on the principle that it can dissect any signalinto its frequency components, similar as a prism separates alight-beam into its various rainbow colors. If a pure sine-waveis analyzed, only one frequency spike should result at thefrequency of the sine-wave. A square-wave contains thefundamental frequency of the square-wave plus the odd harmonics. If the square-wave is filtered by a band-pass filter,

then the fundamental frequency is unchanged while the higher harmonics are attenuated, progressively more at higher frequencies.

Fig. 3: ELVIS used as Bode plot Analyzer Measuring theFrequency Response of a Band-Pass Filter

REMOTE EXPERIMENT CONTROL ANDMEASUREMENT VIA THE INTERNET

The most exciting application for using Lab View and associated instruments is their capability to control experimentsand to make measurements via the internet. This way, studentswho are not able to finish their experiment within the allotted

lab time may finish the experiment at home. It is understood that they most likely will not have a chance to connect their own circuit to the lab instrumentation setup. Most likely theinstructor will hook up his/her well-tested demo circuit.However, they still will get the measurement experience and will have the chance to gain a deeper understanding of the

circuit operation.

LabView is such a powerful high level programming language,that independent of ELVIS it is not too difficult to developyour own programs for simulation and data acquisition. Theauthor acquired data acquisition cards at the tune of about$800/card using the Fall 2003 Professional DevelopmentGrant. The graphical programming language and the powerfulvirtual sub-instruments (vi’s) made available by National

Instruments facilitate the programming part considerably asopposed to programming by C or C++.

So far three of the experiments listed in Table 1 were programmed such that they can be used remotely: the Diode

Characteristic, the Transistor Curve Tracer and the DifferentialAmplifier. These act as showcase to demonstrate thecapability of remote controlled experimentation.

Fig. 4 shows the front panel of the diode experiment. Ingeneral the web-experiments have three modes which may be

accessed by virtual switches or by pull-down menus:a) the tutorial mode, where theoretical concepts may be

explored by using simulations; b) the manual measurement mode, where the student’s

measurements on a lab-bench may be re-enacted;c) the automatic mode, where a voltage sweep or signal-

frequency sweep is performed within certain limits,



and where the resulting data are automaticallydisplayed in a graph. On a lab-bench in our lab thestudent normally does not have this feature. This

mode shows him/her the methods used in industry for automatic characterization and screening of chips.

Fig. 4: Remote-Controlled Diode Measurement

Experiment

The tutorial mode of the diode experiment (not shown in

Fig. 4) gives the student the chance to play around withvarious scenarios. For example, the student knows that

the diode equation is: t d nV V

S d I I

/exp= whered

I and

d V are the diode current and voltage, respectively, as

shown in the circuit of Fig. 4. t V depends on physical

parameters and temperature, S I depends mostly on the

cross-sectional area of the diode, whereby n is a fudgefactor depending on the vagaries of the silicon-process

during manufacture. By being able to vary these parameters and studying the resulting diode-current versusvoltage plot, the student can imitate the effort of

manufacturers, who try to pin down theS

I and n-values,

so they may enter these in their device models, allowingthem to achieve better circuit simulation results. In fact,the student may experimentally match the theoretical curve

against the measured curve, in order to determine theS I

and n-values of the diode under test.

Fig. 4 shows the end-result of a diode voltage sweep in the

automatic mode. The meters shown follow the sweepslowed down on purpose by the program. Of course in themanual mode they are necessary for data recording. Inthe automatic mode the virtual voltage control knob iscovered by the graph, so that only relevant information is presented.

To demonstrate what the graphical program looks like, theLabView program of the diode tester is shown in Fig. 5.

This program contains two so-called sub-vi’s, similar tosubroutines in a C-program, which are supplied by National Instrument as part of their software package and which deal with the communication to the DAQ-card.

Fig. 5: Demonstration of the LabView Program for theDiode Experiment

Fig. 6 shows a remote controlled transistor beta tester. Asnapshot of the automatic mode is taken, where thecollector current family of a bipolar NPN transistor is

displayed as function of base current steps. From this thestudent should be able to determine the transistor current

gain BC I I /= β and the Early resistance or . In

addition to the tutorial mode (accessible by a push button)

and the switch-controlled manual/automatic mode, thisexperiment also has a quiz feature, accessible by a push button.

Fig. 6: Remote-Controlled Transistor MeasurementExperiment

Fig. 7 demonstrates the manual control feature of thedifferential amplifier experiment. In this case adifferential dc-input voltage may be varied between -10Volt and +10 Volt. The resulting dc-voltages and dc-

currents for various id V voltage settings are then

displayed in the small boxes next to the points of interest.This test is important prior to ac-signal measurements inorder to determine the linear operating region of thecircuit. This type of measurement is more powerful than

the traditional measurement on the lab-bench because nomeasurement leads need to be traced and correlated to theactual circuit. With one glance the student gets a feel for

the behavior of the circuit at a particular id V -voltage.



Fig. 7: Remote-Controlled Differential Amplifier Experiment

ASSESSMENT OF THE VALUE OF THISINNOVATION FOR TEACHING IN A LABORATORYENVIRONMENT

The method described above is a powerful teaching toolfor lab-courses. It promises to make existing labs moreefficient by giving students the chance to work through

tutorials on the internet, to perform remote measurementson real circuits and to analyze the data in preparation for on-line quizzes.

It appears that other departments at San Jose StateUniversity or at other universities may be interested in this

approach. Any department involving measurements and control could apply these LabView features, for example

the Physics Department, Meteorology Department and even the School of Medicine. Within the School of Medicine out-patient monitoring via the internet may beachieved.

The cost of a remote measurement station includingELVIS is not prohibitive. For US$7000, ELVIS, DAQ

cards and the PC may be purchased. In addition the purchase of the LabView software or obtaining a site

license needs to be entered into the equation. In thisregard the Electrical Engineering Department is fortunatesince the College of Engineering has a site license for LabView.

To be fair, one should be aware that the possible price

reduction from US$70’000 to a US$7’000 when switchingfrom a hardware lab to a remote controlled internet lab,

involves compromises. A real hardware lab supported by

ELVIS and an internet lab module is still the optimumsolution. This way the student gets the best of bothfeatures. He/she still will have to interact with other students as team member and with the instructor. He/shewill still have to build a circuit and experience the real-lifefrustration if the circuit doesn’t work the first time. Then

he/she will have to apply trouble-shooting techniques. Butin addition, the student would get the benefit of an

excellent measurement demo by the instructor usingELVIS, of tutorials on the web, as well as the chance tocontinue measurements at home.

It appears that the establishment of a remotecontrol/measurement capability should open upopportunities for faculty for obtaining grants or

sabbaticals. Even an economical remote lab may beestablished for extension courses. If a school, particularlyin an underdeveloped country, cannot afford a hardwarelab, then a remote lab will still give that school a chance toallow its students valuable measurement experience.

The applications of the real life internet features of

LabView are limitless. Proof of this is a senior projectfinished in May 2003, where students demonstrated successfully that a robot in our lab may be remotelysteered from any part of the world via internet. [4] Theremote user sees on the computer screen what the videocamera mounted on the robot sees. The robot may bemaneuvered around our lab and hallways, it may pick upobjects at will under the guidance of a remote user -

anywhere in the world - who manipulates the virtualcontrols on the computer screen by moving/clicking a

mouse.

CONCLUSION

A powerful tool is demonstrated which enhances circuitlab instructions in several ways. Using an EducationalLaboratory Virtual Instrument demonstrations may bedone easily whereby the measurement techniques may be projected on the screen. The same experiment may then be remote controlled via the web. Using LabView inconjunction with data acquisition cards additionalcustomized lab experiments may be set up which may becontrolled remotely via internet. Features may be added to

allow internet tutorials, measurement evaluations and quizzes.

ACKNOWLEDGEMENT

The initial LabView work was supported by a Lockheed grant. The use of the LabView software is made possibledue to a site license at the College of Engineering of SanJose State University. The purchase of ELVIS, the

Educational Laboratory Virtual Instrumentation Suite, dataacquisition cards, peripheral equipment and educationalmaterial were supported by professional developmentgrants. Thanks are due to student assistant Cuong Nguyenfor the artwork in designing the instrument front panels.

REFERENCES

[1] Jakk Jones; “Faculty members hear online teachingadvice”; Spartan Daily; San Jose; 3/18/2004

[2] Tom Matthews; EE124 Lab Manual, Integrated Circuit Experiments; Maple Press; San Jose; Spring 2004[3] Barry Paton; Introduction to ELVIS; Dalhouse

University; National Instruments Corporation; January2004[4] Cameron Vandersteen, Justin Rodriguez, Thuc Nguyen; Control Over-the-Internet of a Radio Controlled Robot; Senior Project; El. Eng. Dept.; San Jose StateUniversity; May 2003

[5] National Instruments; Datasheets and Literature;http://www.ni.com

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Thai Conf Final 30mar2004 1340