Circuit Design: An inquiry lab activity at Maui Community College
Katie Morzinski, Oscar Azucena, Cooper Downs, Tela Favaloro, Jung Park, Vivian U
aa r X i v : . [ phy s i c s . e d - ph ] S e p **Volume Title**ASP Conference Series, Vol. **Volume Number****Author** c (cid:13) **Copyright Year** Astronomical Society of the Pacific Circuit Design: An inquiry lab activity at Maui Community College
Katie Morzinski , , Oscar Azucena , , Cooper Downs , Tela Favaloro , JungPark , and Vivian U , Center for Adaptive Optics, University of California, Santa Cruz, CA 95064 Astronomy Dept., University of California, Santa Cruz, CA 95064 Electrical Engineering Dept., University of California, Santa Cruz, CA 95064 Institute for Astronomy, University of Hawai‘i at Manoa, 2680 Woodlawn Dr.,Honolulu, HI 96822 Electronic and Computer Engineering Technology, University of Hawai‘i,Maui College, 310 Ka‘ahumanu Ave., Kahului, HI 96732 Harvard-Smithsonian Center for Astrophysics, Mail Stop 66, SAO,60 Garden St., Cambridge, MA 02138
Abstract.
We present an inquiry lab activity on Circuit Design that was conductedin Fall 2009 with first-year community college students majoring in Electrical Engi-neering Technology. This inquiry emphasized the use of engineering process skills,including circuit assembly and problem solving, while learning technical content. Con-tent goals of the inquiry emphasized understanding voltage dividers (Kircho ff ’s voltagelaw) and analysis and optimization of resistive networks (Th´evenin equivalence). Weassumed prior exposure to series and parallel circuits and Ohm’s law (the relationshipbetween voltage, current, and resistance) and designed the inquiry to develop theseskills. The inquiry utilized selection of engineering challenges on a specific circuit (theWheatstone Bridge) to realize these learning goals. Students generated questions andobservations during the starters, which were categorized into four engineering chal-lenges or design goals. The students formed teams and chose one challenge to focuson during the inquiry. We created a rubric for summative assessment which helped toclarify and solidify project goals while designing the inquiry and aided in formativeassessment during the activity. After describing implementation, we compare and con-trast engineering-oriented inquiry design as opposed to activities geared toward sciencelearning.
1. Introduction
Maui, the second-most densely populated island in the state of Hawai‘i, hosts a suiteof research telescopes on the 10,000-foot summit of Haleakal¯a operated by the Uni-versity of Hawai‘i’s Institute for Astronomy (IfA) and the U.S. Air Force. Science,technology, engineering, and mathematics (STEM) employers on the island includethe observatories at Haleakal¯a as well as opportunities such as the Maui High Perfor-mance Computing Center at the Maui Research and Technology Center. Working toprepare Maui residents for Maui-based STEM careers are the Akamai Workforce Ini-1 Morzinski etal.tiative (AWI) and the Institute for Scientist and Engineer Educators (ISEE). ISEE hasgrown out of the former Center for Adaptive Optics (CfAO) Professional DevelopmentProgram (PDP, Hunter et al. 2008) and other education programs. Among the sponsorsof these programs are the National Science Foundation, the University of Hawai‘i, andthe Air Force.Undergraduate students on the compact island are served by the University ofHawai‘i, Maui College (formerly Maui Community College) in the central town ofKahului. At the time of teaching, the institution was called Maui Community College(MCC) and students could obtain an Associate’s degree in Electronics and ComputerEngineering Technology. As part of the Akamai Workforce Initiative and in partner-ship with ISEE, CfAO, and IfA, the process has begun to convert MCC to a four-yearinstitution called the University of Hawai‘i, Maui College. UH-Maui will o ff er a Bach-elor’s degree in Applied Science in Engineering Technology. Toward this end, PDP andISEE participants have been designing inquiry lab activities for UH-Maui to grow itscurriculum in electro-optics technology.An inquiry lab teaches process skills and content knowledge in a particular STEMfield by engaging students in learner-directed activities that mirror authentic scienceand engineering (Dow et al. 2000; Ash & Kluger-Bell 1999). Targeted facilitation isused to guide students toward the learning goals. This paper describes an inquiry oncircuit design prototyped in Fall 2009 at MCC.
2. Activity Description2.1. Overview
This activity fits into a formal course introducing electric circuits to college studentsmajoring in Electrical Engineering Technology, and assumes some prior exposure toOhm’s law (voltage is equal to current times resistance) and to series and parallel cir-cuits. A particular circuit (the Wheatstone Bridge) is used to study the content goalsof voltage dividers and analysis of resistive networks. In the activity “Starters”, theWheatstone Bridge circuit is introduced. This circuit features a voltage reading acrossthe bridge that is highly sensitive to small changes in resistance. Design goals arepresented as engineering challenges, and student teams choose one to address. In theFocused Investigation, teams work toward meeting their design goal by building, mea-suring, and analyzing their own variation on the Wheatstone Bridge circuit. Materialsrequired are breadboards, wires and connectors, resistors, rheostats or potentiometers,thermistors, multimeters, and power supplies. The duration of the lab is two 105-minuteclass periods. Table 1 shows the activity timetable.
This inquiry lab activity was designed by Oscar Azucena (Design-Team Leader), CooperDowns, Tela Favoloro, Katie Morzinski, Jung Park, and Vivian U as a new activity dur-ing the 2009 PDP. It was taught at MCC in Professor Mark Ho ff man’s class Electronics101: Introduction to Electronics Technology on Tuesday and Thursday, the 27th and29th of October 2009. There were twelve primarily first-year undergraduate students,interested in majoring in Electrical Engineering Technology.ircuit Design Inquiry 3
Table 1. Timeline for circuit design inquiry.
Day 1 Day 2
Introduction 15 min. Thinking tool 10 min.Starters 20 min. Focused investigation 40 min.Break 10 min. Break 10 min.(Facilitators sort questions) Poster preparation 15 min.Choosing a design goal 10 min. Sharing 15 min.Focused investigation 50 min. Synthesis 15 min.
Total Time 3.5 hrs.
As prior knowledge, earlier in the semester, students will have studied series and par-allel circuits and Ohm’s law, and will have used multimeters and power supplies. Thecontent goals for this lab are understanding voltage dividers and Kircho ff ’s voltage law,analyzing resistive networks (Th´evenin equivalence), and using the Wheatstone Bridgecircuit to solve an engineering problem. The process goals include building a circuitfrom a schematic diagram, testing a circuit using multimeters, and utilizing the engi-neering problem-solving process (particularly implementation, testing, and evaluationof a solution; see Figure 1). Attitudinal goals were teamwork, self-confidence in engi-neering skills, and motivation by real-world applications. Figure 1. The engineering problem-solving process.
Figure 2 shows the Wheatstone bridge circuit. Four resistors ( R , R , R , and R x ) areconnected between four circuit junctions ( A , B , C , and D ). Resistors R and R areconnected in series; resistors R and R x are connected in series; and the two legs areparallel to each other ( ABD k ACD ). The source voltage is V s and the output voltage V g is measured between B and C . When the voltage across the bridge is zero ( V g = balanced and the ratios of resistances are equal: R R = R R x . (1)In the specific example of Figure 2, R is a variable resistor (a rheostat or a poten-tiometer) and R x is a resistor of unknown value. R x will also be referred to as R forgeneralized Wheatstone bridges. Figure 2. Wheatstone bridge circuit. (Left) Schematic diagram. (Right) Breadboard.
The purpose of Starters in an inquiry is to generate curiosity and interest in students byexposing them to new phenomena or content they will be working with in the FocusedInvestigation. Facilitators (instructors) give directions about what to explore with eachStarter, and students are encouraged to write their observations and questions down onsentence strips (Figure 3). In the Starters for this inquiry we introduce the students tothe Wheatstone bridge, both in terms of what it means when the circuit is balanced aswell as its real-world applications. First, a schematic is shown (Figure 2, left) duringthe introductory presentation. Next, students see the circuit on a breadboard (Figure 2,right). During the Starters, students observe and measure the bridge in a few di ff erentconfigurations, with two students per station (i.e., two students per breadboard). Table 2describes the three Starters that are set up in three columns on the breadboard. Table 2. Starters, column on breadboard, and Wheatstone circuit set-up.
Starter Name Column Set-up of Circuits
Balanced vs. Unbalanced 1 Two of V g =
0, one of V g , R is a thermistorVariable Resistor and Linearity 3 R is a variable resistorIn Starter 1 (Balanced vs. Unbalanced), three Wheatstone bridges are presentedon a breadboard in column 1. The first two bridges are balanced (output voltage V g =
0) and the third bridge is unbalanced (output voltage V g , ff erent ways: one is balanced with all resistors beingequal ( R = R = R = R ), while the other is balanced with di ff erent values of resistorsircuit Design Inquiry 5 Figure 3. Questions and observations generated by the students during the Starters. in equal ratios ( R / R = R / R ). Students measure the output voltage and observe itsdependence on resistance. Note that when setting up the Starters, facilitators must becareful in choosing the appropriate resistors, as small di ff erences in resistance lead toeasily noticeable changes in output voltage, as the bridge is very sensitive to resistance.In Starter 2 (Thermistor) in column 2 of the breadboard, a thermistor (temperature-dependent resistor) is placed at R and students measure the output voltage as theywarm up the thermistor with their hands. Resistors R , R , and R x should be chosenin the linear regime such that students can balance the bridge by varying R at roomtemperature.Starter 3 (Variable Resistor and Linearity) is set up in column 3 of the breadboard,with a rheostat or potentiometer used at R . Students again measure the output voltage,this time observing the e ff ect while they vary the resistance R . The linearity of outputvoltage (Figure 4) with resistance can be explored with this circuit.Students write observations and questions down on sentence strips while doingthe Starters. Facilitators help with the setup and with using the multimeter to measureoutput voltage at V g . During a short break, facilitators sort the questions into the cate-gories under the Engineering Challenges in Table 3. Sample questions sorted into thecategories are shown in Table 4. Table 3 lists the engineering challenges o ff ered as options for the students’ investiga-tions. Table 3. Engineering challenges with a Wheatstone bridge.
Challenges for investigation
A. Build a perfectly balanced Wheatstone bridgeB. Build a Wheatstone bridge for operation in a linear regimeC. Use a Wheatstone bridge to build a thermometerD. Use a Wheatstone bridge to determine an unknown resistanceThe focused investigation is the heart of the inquiry and goes on for the rest ofDay 1 and the first half of Day 2. After student teams have chosen a design goal fromTable 2, they work to achieve that goal using the breadboards and circuitry available. Morzinski etal.
Figure 4. Output voltage V g as a function of variable resistance R x . The Wheat-stone bridge circuit is balanced where V g = V g isapproximately proportional to R x .Table 4. A partial list of the questions and observations generated during theStarters by students, each categorized into one of four design goals A-D. Build a perfectly balanced Wheatstone bridge
First two circuits in Starter 1 have no voltage readingWhy is the output voltage di ff erent in circuit 2 and 3?Each test point has a di ff erent set of resistorsThe circuit with higher resistor value has di ff . output voltage? Build a Wheatstone bridge with voltage change proportional to resistance
How does the voltage change with a variable resistor?Why does rheostat change by suddenly large then small amounts?Why does a rheostat switch from + to - ? Use a Wheatstone bridge to build a thermometer
Why does voltage decrease when I touch (apply heat) on the thermistor?How does temperature a ff ect a thermistor circuit? Use a Wheatstone bridge to build an Ohmmeter
If we change the value of a resistor, what will happen to the voltage?Why do u want a variable resistor?Purpose of the Wheatstone bridge?ircuit Design Inquiry 7(Students may not re-use the Starter circuits but must build their own circuits fromscratch, since building a circuit from schematic diagram is an important process skill inthis lab.)The di ff erences between the four engineering challenges in Table 3 are choice ofresistors. All students will build Wheatstone bridges, but the specifics of R , R , R , and R will vary. During much of the activity, students will test the output voltage at V g andthen swap or adjust their resistors to get the desired value. Students may need heavyfacilitation during the building stage if they are unfamiliar with breadboard circuitry orneed help using multimeters for measurements.In design goal A, “Build a perfectly balanced Wheatstone bridge,” the output volt-age V g of the bridge circuit should read exactly zero. This is achieved by carefullymeasuring and inserting resistors with the exact ratios R / R = R / R .In design goal B, “Build a Wheatstone bridge for operation in a linear regime,” avariable resistor (a rheostat or potentiometer) should be used for R , and the other threeresistors should be selected to ensure the output voltage is in the linear regime for agood fraction of the range of the variable resistor (Figure 4). The resulting Wheatstonebridge should have a voltage change proportional to resistance. The slope of the pro-portionality depends on the choice of resistors, and so it should be linear over a largevariation of the rheostat.In design goal C, “Use a Wheatstone bridge to build a thermometer,” a thermis-tor is used as resistor R , and the output voltage V g can determine temperature oncethe thermistor is calibrated (a conventional thermometer must be used to calibrate theWheatstone thermometer). Ice packs wrapped in absorbent cloth (to avoid condensa-tion shorting the circuit) and a hair dryer or the outside of a co ff ee cup can be used toprovide temperature variation.In design goal D, “Use a Wheatstone bridge to determine an unknown resistance,”the bridge is used in an unbalanced condition. Three resistors are known ( R , R , and R ) and any unknown resistor can be inserted into the fourth position ( R x ). The outputvoltage will vary, and this change can be used to determine the unknown resistance.At the beginning of the second day, we presented a thinking tool: a short lectureabout Ohm’s law ( V = iR ) and Kircho ff ’s laws (voltage law and current law) so thestudents can calculate the output voltage if the values of the resistors are known. Students conclude their investigations by making posters to present what they learnedwith the rest of the class. Column 1 in Table 5 lists the requirements for the posterpresentations, and was written on the board for the students. Column 2 in Table 5shows the correspondence of the poster requirements with the rubric we used to assesspresentations.During the synthesis, instructors tie the investigations together by clarifying thedetails of how to balance a Wheatstone bridge and its applications. Each teams’ workis referenced to point out how everyone learned something.
3. Elements of Inquiry Design for Engineering
This activity illustrates di ff erences in designing inquiry for engineering as opposed todesigning inquiry for science. Morzinski etal. Table 5. Final poster requirements for sharing, and correspondence to categoriesassessed with the rubric.
Item Poster Correspondence / your resistors ( R , R , R , and R ) so that Justificationyour circuit meets your design goal. In the Starters for the quintessential Light and Shadows inquiry usually studied by first-year PDP participants, learners are shown various phenomena related to light and shad-ows, and write their questions on sentence strips. During the gallery phase, learnersthen choose one of the questions to investigate. For the Circuit Design inquiry, learnerswrote questions and observations on sentence strips as in Light and Shadows. However,these questions were then sorted into the four categories listed in Table 3 as Engineer-ing Challenges or Design Goals. We utilized a di ff erent format more appropriate toengineering, as engineering is more the application of scientific principles. Therefore,our modification of the use of questions generated during the starters is an authenticadjustment for an engineering inquiry. We also modified the evaluation rubric for the engineering inquiry. The rubric PDPparticipants used to assess students’ learning in a science inquiry is designed to evaluatehow students answered their question; the categories for evaluation are claim, evidence,and reasoning.An engineering activity is more concerned with how a student was able to solvetheir problem and accomplished their design challenge; so the categories became pro-posed solution, support (including tradeo ff s and optimization), and reasoning or justifi-cation of how the solution worked.For the “support” category in this case we decided to focus on the students’ un-derstanding of the Wheatstone bridge by drawing a schematic diagram of their circuit(similar to Figure 2 left) or demonstrating understanding of the equation for calculatingthe output voltage of their circuit: V g = V s R x R x + R − R R + R ! . (2)For the “Solution” we were looking for a statement of how students met their designgoal. For the “Reasoning” we were looking for an explanation of the balance of resis-tance and how the output voltage V g depends on the resistor values R , R , R , and R x .The rubric is shown in Table 6.ircuit Design Inquiry 9 Table 6. Rubric used for summative assessment. O ff -track Emerging Accomplishing Mastering[0] [1] [2] [3]Solution(Claim) Solution doesnot addresstheir question Solution notcorrect ORSolution maywork but isconvoluted(i.e.,redundancy) Solution works / is correct Solution works / is correctAND stateapplication, orstate range ofvalidity andlinearity Support / Circuitanalysis
No diagram orequation Diagram withsome errors Diagram ORequation Diagram andequation
Reason-ing / Justifica-tion
Notinvestigatingbalanced vs.unbalanced oroutput voltageas a function ofthe 4 resistancelegs Incompleteunderstandingof V g as afunction of R , R , R , and R x Understandingof interactionof componentsand mechanismof Wheatstonebridge(balanced vs.unbalanced) Meets “accom-plishing”PLUSe ffi ciency ofdesign; orTradeo ff s; orLinear regime Scoring using the rubric was challenging, but it was important for discerning whether itwas a reliable and valid test of students’ learning. A valid test accurately characterizeswhat the students learned, while a reliable test gives similar scoring across time andassessor variation.Table 7 shows the scores given to each of the six teams by each of the six scorers(facilitators and teaching consultant). The maximum score possible was nine (9) points,and the mean class score was 6.2 points. The standard deviation provides some measureof reliability. The mean class standard deviation was 1.2 points, or 13% out of 9 points.This is more than one point uncertainty, implying that the rubric may not have been areliable test and can be improved.
Table 7. Summative assessment results. Each team of students was scored byeach facilitator using the rubric.
Scorer Team 1 Team 2 Team 3 Team 4 Team 5 Team 6A 7 8 6 6 7 6B 9 6 7 7 7 4C 8 8 6.5 4 5 6D 8 4.5 6 5.5 5.5 2.5E 6 6 5 7 4 5F 6 8 7 7 6 5
Mean 7.3 6.8 6.3 6.1 5.8 4.8Std. Dev. 1.2 1.5 0.8 1.2 1.2 1.3
4. Conclusions
The Circuit Design inquiry featured students learning important engineering processskills: they built a circuit on a breadboard to implement and test an electrical engi-neering question. Our modifications to adjust from a science inquiry to an engineeringinquiry included organizing student-generated questions under Design Goal challenge-style categories, and modifying the rubric to emphasize solving problems. While it maynot have provided reliable scores, the establishment of an engineering rubric helpedimmensely in clarifying our activity design goals and facilitation emphases. Overall,the inquiry went well and accomplished many of the learning goals, and the studentsseemed to enjoy it. Labs such as these, inserted into formal courses at UH-Maui, arehelping to train future STEM workers for the tech industry on the island of Maui.
Figure 5. Facilitators KM, CD, TF, OA, and JP sorting students’ questions.
Acknowledgments.
Design team member Vivian U was not able to travel to Mauito teach the lab, but she helped as much as the other team members (Figure 5) in design-ing the inquiry. Lisa Hunter was an observer and design-team consultant while at MCC,while Patrik Jonsson was a consultant at the PDP workshop. UH-Maui professors MarkHo ff man (the classroom teacher hosting this inquiry) and Elisabeth Reader providedadvice and assistance. This material is based upon work supported by: the NationalScience Foundation (NSF) Science and Technology Center program through the Cen-ter for Adaptive Optics, managed by the University of California at Santa Cruz (UCSC)under cooperative agreement AST ffi ce of Scientific Research (via NSF AST References
Ash, D., & Kluger-Bell, B. 1999, in Inquiry: Thoughts, Views, and Strategies for the K-5Classroom (Foundations Series, National Science Foundation), 79 ircuit Design Inquiry 11