Paper ID #11922

Embedding Engineering Design in a Circuits and Instrumentation Course

Dr. Jacquelyn Kay Nagel, James Madison University

Dr. Jacquelyn K. Nagel is an Assistant Professor in the Department of Engineering at James Madison Uni-versity. She has eight years of diversified engineering design experience, both in academia and industry,and has experienced engineering design in a range of contexts, including product design, bio-inspired de-sign, electrical and control system design, manufacturing system design, and design for the factory floor.Dr. Nagel earned her Ph.D. in mechanical engineering from Oregon State University and her M.S. andB.S. in manufacturing engineering and electrical engineering, respectively, from the Missouri Universityof Science and Technology. Dr. Nagel’s long-term goal is to drive engineering innovation by applying hermultidisciplinary engineering expertise to instrumentation and manufacturing challenges.

Mr. Stephen Keith Holland, James Madison University

S. Keith Holland received his PhD in Mechanical and Aerospace Engineering from the University ofVirginia in 2004. He served as the Vice President for Research and Development with Avir Sensors,LLC prior to joining the Department of Engineering at James Madison University (JMU). At JMU, hedeveloped statics, dynamics, circuits, instrumentation, controls, renewable energy, and engineering studyabroad courses. His current research interest include material development for solar energy applicationsand optoelectronic device development for non-destructive testing and evaluation.

Brian Groener , James Madison University

c©American Society for Engineering Education, 2015

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 Embedding Engineering Design in a Circuits and Instrumentation Course

Abstract

The junior level circuits and instrumentation course at James Madison University is a 4-credit course with three lectures and one laboratory each week. Fundamentals of DC and AC circuit analysis are covered along with instrumentation topics. The laboratory portion of the course reinforces the concepts learned in lecture and assignments while building skills in circuit prototyping and measurement. Lab exercises have traditionally been a time when students follow a given procedure, collect data, and interpret the data. The highly structured experience often leads to students focusing on the procedure and not fully thinking through the concepts being covered. To encourage a deeper understanding of course concepts and how they translate to physical systems, two open-ended design projects were offered in place of structured labs in the most recent offering the circuits and instrumentation course.

The design projects are undirected experiences that build on the directed experiences in the lecture and lab. Students are challenged to work in teams of four to design, build, test a specific type of circuit. Project one focused on a calibrated instrument that reported the weight of a sample using a strain gage. Project two focused on the design of an analog filtering circuit. No instruction is provided for the projects, rather, a set of design requirements, timetable, and supplemental materials (e.g., data sheets, vendor design briefs, past labs relevant to the design requirements) are given. Students were required to synthesize multiple weeks of course content into a single design project.

This paper reports on our observations and findings for embedding design experiences into a circuits and instrumentation course, as well as descriptions of the design projects. Qualitative and quantitative assessment of student perceptions of learning achieved through the projects was performed using surveys and reflections.

Introduction

The relatively young engineering program at James Madison University has been designed to train the Engineer of 20201,2. The program was developed from the ground up to not be an engineering discipline-specific program, but to provide students training with an emphasis on engineering design, systems thinking, and sustainability. Our vision is to produce cross-disciplinary engineer versatilists. At the heart of this program is the six-course engineering design sequence which provides instruction on design theory (thinking, process, methods, tools, etc.), sustainability, ethics, team management, and technical communication (both oral and written), while incorporating elements of engineering science and analysis. Students apply design instruction in the context of two projects during the six-course sequence—a cornerstone project spanning the fall and spring semesters of the sophomore year, and a capstone project spanning the junior and senior academic years. The curriculum of our non-discipline specific engineering program, shown graphically in Figure 1, combines a campus-wide, liberal arts general educational core with courses in math, science, engineering design, engineering science, business, systems analysis, and sustainability3,4. Individual skills taught developmentally through the curriculum, beginning with the freshman year, are blended with engineering design theory and utilized in projects in the design sequence. The engineering design sequence is meant to be the core or spine of the engineering curriculum. During the engineering design courses, students not only learn engineering design tools and methods but also learn about creativity, sustainability, business, ethics, values, engineering science, math, and manufacturing. It is during this engineering design sequence where students are provided with a hands-on environment to apply the theory learned in other courses5. Similarly, the engineering science courses provide an opportunity to apply the theory and problem solving processes learned in the engineering design courses.

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Figure 1: Schematic illustrating the engineering curriculum4. Introductory electrical engineering courses have traditionally focused on problem solving and analysis theorems, which are often complemented by laboratory experience. What this structure lacks is a way to motivate the students, and provide experience with building practical circuits. To make a required course relevant, practical, and engaging while still providing the necessary instruction in fundamentals open-ended projects are often added6-9. Engineering curricula often heavily emphasize scientific and mathematic calculations. While computational mastery is critical for engineering students, it is also important for students to use quantitative results to reason about problems within systems and make necessary adjustments. Projects allow students to practice this aspect of engineering10.

The viewpoint at James Madison University on design projects is that they challenge students to synthesize multiple course concepts and work in teams to create something practical or relevant, thus reinforcing the need for learning the theoretical concepts required in a course. Therefore, each engineering design and the majority of engineering science courses implement a course project. All projects within the curriculum are team-based; therefore training in teamwork is a thread throughout the design sequence of the curriculum. Beginning in their first year, students work in small teams toward a project goal (changes each semester and by instructor) and receive training in the context of how group processes and collaborative learning influence the professional development of an engineer. Formal training in team building, team dynamics, and team management begins in the first semester of the second year in ENGR 231 – Engineering Design I. In this course students are taught the five stages of team development by Tuckman and spend the first three weeks working on team assignments to tease out each members’ behavior and values that impact or influence the role they take within a team. Additionally, students learn about constructive and destructive conflict, characteristics of successful teams, team structures, and elements of effective team meetings. And teams synthesize this information into a team code of conduct. Following Engineering Design I students developmentally build on the foundational knowledge of teamwork in the design sequence. Thus, teamwork is not taught in the engineering sciences courses.

YEAR

1

Calculus 1 Liberal Arts Core Liberal Arts Core Liberal Arts Core Physics 1YEAR

1Calculus 2 Liberal Arts Core Introduction to

Engineering Liberal Arts Core Physics 2

YEAR

2

Calculus 3 Liberal Arts Core Engineering Design 1 Liberal Arts Core Chemistry 1

YEAR

2Linear Algebra &

Different Eq. Statics & Dynamics Engineering Design 2

Engineering Management 1 Chemistry 2

YEAR

3

Thermal-Fluids 1 Instrumentation & Circuits

EngineeringDesign 3

Engineering Management 2 Liberal Arts Core

YEAR

3Thermal-Fluids 2 Materials &

MechanicsEngineering

Design 4 Liberal Arts Core Liberal Arts Core

YEAR

4

Sustainability Fundamentals Systems Analysis Engineering

Design 5 Technical Elective Liberal Arts CoreYEAR

4Sustainability & Design (LCA) Technical Elective Engineering

Design 6 Technical Elective Liberal Arts Core

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 In this paper we explain the open-ended lab design projects offered in the junior level circuits and instrumentation course at James Madison University. The projects were offered across two sections with different instructors in a single semester. The following section provides background information on implementing open-ended or design projects in introductory circuits courses and labs. The next section describes the circuits and instrumentation course at James Madison University to provide some context for the lab projects. The remainder of the paper focuses on the lab design projects including assessment, student feedback, and observations. The paper ends with recommendations and future work.

Literature Review of Circuits and Instrumentation Course Projects There is mounting evidence that pedagogies of engagement result in higher learning and greater retention11,12. A deeper level of learning beyond surface learning occurs when students actively engage in the topic, rather than passively accept information. To be actively involved in learning, students must engage in such higher-order thinking tasks as analysis, synthesis, and evaluation, which are not facilitated through traditional lecture or labs that explain every step. Introductory computer and electrical engineering courses have traditionally focused on theory and quantitative analysis, which are often complemented by laboratory experience. What this structure lacks is a way to motivate or engage students in learning. It has been shown that, “The shift toward more theory in the engineering curriculum has produced graduates with far less experience in the practice of engineering and design than those of years past”13. Consequently, some programs have begun to build introductory circuits courses around the laboratory or offer open-ended design projects. Colorado University completely restructured their electrical engineering labs in 1999 in order to provide its graduates with more engineering practice. These labs consist of a main eight week design project in which students undergo the complete design-build-test cycle of a project of their choosing14. Past themes have included Rube Goldberg contraptions, sensors measuring a physical quantity, and assistive devices for people affected by cerebral palsy. Moreover, the design focused labs significantly increased retention numbers and helped to give meaning to physics and calculus courses15. Illinois University created a new introductory course encouraging self-directly learning and skill development through the design of an autonomous electric vehicle16. This allows students to apply what they have learned throughout the course and develop creative problem solving skills when faced with difficulties while working on their project. The University of Manitoba observed an increase in student motivation, engagement, and enrollment when it switched its structured laboratories to open-ended projects with design components17. The theme based laboratories foster a discovery learning approach, practical thinking to construct the system, and exposure to system level design concepts, which are common to all engineering disciplines17. At Iowa State University the engineering program has developed an introductory computer engineering course encouraging problem-based learning, which has been central to engineering education. It is particularly relevant to the integration of new system design concepts and technologies into introductory courses18. This adaptation allows students involved and interested in various disciplines to take the course and be able to succeed. These project experiences not only solidify scientific fundamentals, intuition of electrical concepts, and an understanding of systems-level design issues, but also better prepare students for the rest of their college experience and life in the workforce. Like problem solving, design is a focus that can be found across all engineering disciplines. Part of Marquette University’s Department of Electrical and Computer Engineering’s mission statement reads, “it is important to note that since engineers’ problems are sometimes creative, sometimes analytic, and sometimes experimental, their educational experience must give practice in each of these areas and in all types of problems. Significant design experience is an essential part of the engineer’s education”19. In many cases, the beginning engineering student is thrown into upper-level engineering courses without an adequate introduction to the basic material. This, at best, causes undue stress on the student as they feel unprepared when faced with unfamiliar material, and at worst, results in students dropping out of the

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 program or changing majors when they discover that their chosen field of engineering is not what they thought it was14. Using design in electrical and computer engineering courses forces students to analyze and comprehend the material they are being taught and acts as an essential way to increase the breadth of knowledge being learned. At the U.S. Naval academy, electrical engineering courses are designed to connect concepts across the curriculum. Learning about design and its application introduces students to MATLAB and digital systems, which are then further explored in upper level courses8. These projects ended up being so successful that students would stay after their lab period to test ideas beyond what was asked for by the professor. One engineering education survey focused on the ability to learn in groups as compared to individual work. The results indicated that, “Relative to the students who only worked individually, the students who worked in teams were significantly more likely to agree that the course had achieved its stated learning objectives”20. Working in groups allows students to collaborate and work through common issues, and results in building a support network that motivates them to succeed. Regardless of engineering discipline, students should graduate with engineering practice experience, the ability to problem solve, and the ability to design. These three core competencies are also engineering educational objectives as dictated by ABET criteria21. Increasing the design component in the undergraduate curriculum better prepares graduates for engineering practice, the end result being a well-rounded engineer. Traditional engineering courses provided graduates with little, if any, experience in engineering application. Electrical and computer engineering courses and labs that have moved towards an active learning approach through design and open-ended projects or labs offer the greatest benefits and opportunities to students, and allow students the chance to better prepare themselves for the workforce. Circuits and Instrumentation Course The ENGR 313 – Circuits and Instrumentation course at James Madison University introduces students to the fundamentals of circuit analysis and instrumentation topics. The course covers fundamental DC and AC circuits and analysis techniques and instrumentation while providing exposure to common electronics equipment and laboratory tools through laboratory investigations. Specific course outcomes and the relation to ABET criteria (a, b, e, and k) are detailed below. Upon successful completion of this course, students will be able to:

1. Develop and solve mathematical models of multi-component circuits using Kirchhoff’s current law, Kirchhoff’s voltage law, and Ohm’s law (a)

2. Describe and mathematically model the characteristics and behavior of first- and second-order dynamic systems and circuits (a)

3. Understand and use terminology related to DC and AC circuits (a) 4. Use complex impedance and frequency domain analysis to mathematically model the periodic

input response behavior of dynamic circuits and systems (a) 5. Understand the fundamentals of instrumentation and measurement (a) 6. Use common electronics laboratory tools and devices (b, k) 7. Design, construct, and test circuits to perform specific tasks using resistors, capacitors, diodes,

transistors, operational amplifiers, etc. (a, e) 8. Work as individuals and as team members to design and conduct laboratory experiments, analyze

data, and communicate results (k) An overarching goal of the course is to provide students with the skills necessary to design and analyze multidisciplinary systems that include electrical components and make informed decisions regarding data collection using instrumentation. Our world is increasingly becoming data driven and integrated,

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 thus as an engineer is it crucial to understand the fundamentals of electrical circuits in order to tackle the interesting and challenging problems of the future. Another objective for the course within the James Madison University engineering curriculum is to prepare students for the electrical portion of the Fundamentals of Engineering Exam. To achieve these objectives, the 4-credit (5 contact hour) course is designed as a combined lecture and laboratory experience. The primary lecture and laboratory topics used throughout the course are outlined in Table 1. Since the course’s inception, an open ended design, build, and test project has been incorporated as a culminating element to reinforce the course concepts, encourage integration with engineering design principles, and develop practical experience with development and troubleshooting. During more recent offerings, two open ended projects have been incorporated, approximately at mid-semester and end-of-semester. This paper investigates the impact of such open-ended projects on the student perceptions of applying and integrating engineering design with engineering science concepts to develop and implement an effective design that appropriately addresses requirements and constraints. Table 1: Circuits and Instrumentation Lecture and Laboratory Topics

Lecture Topics: 1. Basic laws (Ohm’s Law, Kirchhoff’s Laws) 2. Circuit Analysis Techniques and Theorems 3. First and Second Order System response

modeling using differential equations 4. Frequency Analysis and Bode Plots 5. Operational Amplifiers 6. Measurement uncertainty 7. Sample Aliasing and Nyquist Sampling

Theorem 8. AC Power analysis 9. Complex Impedance Analysis

Lab Topics: 1. Common laboratory equipment (Multimeters,

solderless breadboards, function generators, oscilloscopes, soldering irons, etc.)

2. Resistors and Diodes (non-ohmic devices) 3. Solar Cells and i-v characteristic curves 4. Strain Gauges and Wheatstone Bridge circuits 5. First and Second Order System response 6. Operational Amplifier circuits 7. Filter circuits 8. Design/Build projects

Circuits Laboratory Design Projects The design projects for the ENGR 313 course were developed to provide relatively undirected experiences to compliment the directed experiences in the lecture and lab. Formal instruction on project completion was not provided to students; rather, a set of design requirements, a recommended timetable, and supplemental materials (e.g., data sheets, vendor design briefs, past labs relevant to the design requirements) were provided. Students were challenged to synthesize multiple weeks of course content into a single design project, and engage in self-directed learning. Two design projects were given in one semester, one at week 5 to be completed by mid-term, and one at week 10 to be completed during finals week. The following subsections describe the two lab projects. Lab Design Project 1 - Designing a Calibrated Instrument The first project posed to the students was intended to reinforce DC circuit and instrumentation concepts. These concepts included linear calibration and uncertainty, resistive circuit networks, and design of operational amplifier circuits. In this project, student teams were provided aluminum cantilever beams of varying length and thickness with a pre-mounted, 120 Ω, F = 2.1, three-wire strain gage bonded to the top surface. Each team was challenged to design and prototype an analog circuit that would transform the beam and strain gage into a weight measurement device. Students were instructed that the device should have subsystems as illustrated in Figure 1. Additionally, vendor specification sheets and

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 application notes for the three-wire strain gage and the provided operational amplifiers were provided. Brief introductions to strain gages, Wheatsone bridges, and operational amplifiers were also provided as supplementary documents for student self-learning. Prior to and during this project, no direct instruction on Wheatstone bridge design was covered in the class or laboratory component of the course. Each student team, comprised of three or four students, was responsible for constructing and integrating all of the sub-systems to meet the project requirements, as outlined below. At the end of the project period, each team was required to meet with the instructor to demonstrate the operation of the circuit. During this demonstration, the instructor was to hang an unknown weight (between 0.1 N and 3.0 N) from the end of the cantilever beam and the student team was challenged to report the weight back to the instructor. In order to expose students to additional laboratory and prototyping equipment, a requirement of the project was for students to receive soldering training and to solder the designed Wheatstone bridge on a copper clad prototyping board. In addition to the completed prototype, students were also required to prepare a brief technical report, codifying the final design (through the use of schematics), the instrument calibration data (sensitivity and uncertainty), and recommendations for design improvements. A full description of the project, as provided from the students, can be found in the appendix.

Figure 1: Block diagram of the conceptualized instrument. Lab Design Project 2 - Designing An LED Audio Frequency Indicator Project The second laboratory design project was selected to reinforce the concepts of frequency dependent AC circuit responses and filtering circuits, which was covered during the second half of the semester. To accomplish this, students were challenged to design an audio frequency filtering circuit coupled to LED lights. Essentially, the project requested the design of a three-band audio crossover filter, wherein specific frequencies of input would result in different colored LEDs being lit. The input of this prototype circuit was specified to be a portable media/music player and, for testing and verification purposes, a laboratory function generator with a defined output amplitude. No requirements were placed on the method of filtering (i.e., active vs. passive); however, each project was required to have the subsystems as defined in Figure 2. At the conclusion of the laboratory project period, teams presented their designs and prototype to the instructor. As part of the presentation, students were required to demonstrate operability of the circuit with both the function generator and the portable media player input. During this time, students were also questioned about the frequency dead-band and/or overlap regions of the LED outputs and other challenging points as identified during the presentation. In addition to this presentation, teams were also required to submit a design brief, clearly indicating their design (via schematic), predicted (theoretical) frequency response behavior, and comparison to observed behavior, as well as suggestions for improving the design. A complete description of the project, as provided to the students, can be found in the Appendix.

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Figure 2: Block diagram of the conceptualized audio frequency sensitive led circuit. Circuits Laboratory Design Project Assessment The delivery of the course laboratory design projects was comprised of two course sections, totaling n = 45 students. The student population across the two sections included 15 (33%) female and 31 (67%) male students. Each author was responsible for one class section. Topics and laboratory pacing between course sections was similar throughout the semester and the two course projects occurred simultaneously. Quantitative Assessment One measure of success for the design project experiences was the number of successful project completions. Out of 12 teams, 10 demonstrated a working prototype for the first project and 10 teams developed and demonstrated a successful prototype for the second design project. To assess student perceptions about the learning goals for these project assignments, post-project surveys were administered to the students. The ten questions posed on each survey were: Q1. Rate how this project helped to meet the following course outcome: Design, construct, and test

circuits to perform specific tasks using resistors, capacitors, diodes, transistors, operational amplifiers, etc.

Q2. Rate how this project helped to meet the following course outcome: Use common electronics laboratory tools and devices (multimeters, solderless breadboards, function generators, oscilloscopes, soldering irons, etc.).

Q3. Rate how this project helped you to meet the following course outcome: Understand the fundamentals of instrumentation and measurement.

Q4. Rate how this project reinforced your understanding of the course concepts related to the project. Q5. Rate how this project improved your understanding of circuits used for instrumentation. Q6. Rate how this project improved your understanding of designing to a set of requirements. Q7. Rate how this project improved your understanding of subsystems within an instrument and how

they interact. Q8. Rate your agreement with the following statement: Because of this laboratory project, I am more

interested and excited about electrical circuits. Q9. Rate your agreement with the following statement: Because of this laboratory project, I feel more

confident in my ability to design and build electrical circuits. Q10. Rate your agreement with the following statement: Because of this laboratory project, I

recognize the need for and an ability to engage in lifelong learning.

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 Survey questions 1-3 map directly to the course outcomes 5-7. Survey question 4 indirectly maps to course outcomes 1-4, depending on the project, and was worded such that it can be applied to both projects. The course concepts involved in the project are given in the project descriptions. Survey question 5 is not linked to course outcome 5; rather, its purpose is to gage the students’ system perspective of circuits and their use. We do not expect our students to become practicing electrical engineers, but we do expect our students to use instrumentation to take measurements in order to tackle the interesting and challenging problems of the future. Survey questions 6 and 7 are aimed at understanding students’ perception of how engineering analysis techniques learned in engineering science courses inform the process of design learned in engineering design courses. Authentic design projects across the curriculum lead students to break down the mental barriers that design is different in engineering science courses, and work toward an integrated perspective of engineering. Furthermore, understanding subsystems and how they interact is a qualitative reasoning skill that is often introduced in engineering design and plays a significant role in developing a system perspective of circuits. Survey questions 8 and 9 were given to understand students’ interest and confidence in working with circuits. Because the engineering program at James Madison University is non-discipline specific we would like to understand student interest and motivation. Survey question 10 maps directly to ABET criteria j and is aimed at gaging the students’ perception of engaging in self-directed learning. Students evaluated each question on a scale of 0-3 (0 – Strongly Disagree, 1 – Disagree, 2 – Agree, 3- Strongly Agree). The average and standard deviation of the n = 45 responses to the project 1 and project 2 survey questions are shown in Figure 3. It is noted that, with few exceptions, the average and standard deviation scores for each question remained consistent between the project surveys. Questions 6 and 7 showed a slight improvement in the perceived understanding of designing to requirements and the understanding of subsystem interactions.

Figure 3 – Results of post-project survey response scores, including error bars representing the ±1

standard deviation estimate from the responses. Table 2 provides a tally of the responses received by question for each project. Notably, for Q6 and Q7, a larger number of students indicated that the projects contributed to their understanding of requirements and subsystem interactions. The largest number of students did not feel that the laboratory projects added to their interests in electrical circuits (Q8) or to their ability to design and build circuits (Q9) after the projects.

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  Table 2: Tally of responses per question and post project survey. Degree of shading represents the frequency of responses (dark shading indicating a more frequent response).

Project 1 Project 2 Question 3 –

Strongly Agree

2 – Agree

1 – Disagree

0 – Strongly Disagree

3 – Strongly

Agree

2 – Agree

1 – Disagree

0 – Strongly Disagree

Q1 20 24 1 0 22 22 1 0 Q2 24 21 0 0 27 18 0 0 Q3 14 27 4 0 16 25 4 0 Q4 16 24 5 0 17 24 4 0 Q5 15 26 4 0 16 26 3 0 Q6 9 33 3 0 16 28 1 0 Q7 17 24 3 1 20 24 1 0 Q8 9 22 11 3 9 22 12 2 Q9 13 21 9 2 12 23 10 0 Q10 15 24 6 0 13 30 2 0

Student Feedback and Comments The intention of the laboratory design projects was to reinforce the learning of the theoretical concepts required in the course in a student- or learner-centered manner. As such, the laboratory projects include multiple aspects of an authentic design and build experience, including designing to set of requirements, sub-system integration, bridging theory and practice, qualitative and quantitative reasoning, and practical applications. There are multiple ways to meet the set of requirements, thus students needed to engage their engineering science and design skills. To assess student perceptions about the project assignments and their educational value, the following open-ended questions were asked in the post-project surveys: Q11. What was the most valuable aspect of lab project #? Q12. What was the least valuable aspect of lab project #? Q13. Use the space below to add any additional comments. The following student comments are grouped based on the educational aspects of the projects, and provide insight on what the students’ valued. The responses and feedback were positive and in favor of the projects educational value. Negative comments reflected the perceived difficulty of the projects. The majority of the negative comments related to the lack of procedures and instructions. 1) Aspect of Lab Design Project: As a complementary experience to the course and lab directed instruction, the laboratory design projects aimed to reinforce the theoretical concepts learned in the course and provide context for how they can be applied. Student Feedback – Example #1: “The  most  valuable  aspect  of  the  lab  project  was  probably  being  able  to  design,  build,  and  test  a  circuit  that  allowed  for  a  practical  application  of  the  material  learned  in  class.  It  was  not  only  a  strong  example  of  applying  that  information,  but  the  project  enhanced  my  understanding  of  the  material  greatly.  It  was  also  insightful  realizing  how  important  it  is  to  understand  the  interactions  between  subsystems.“    

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 Student Feedback – Example #2: “The  most  valuable  aspect  of  the  first  lab  project  for  me  was  the  process  of  having  to  work  through  the  initial  confusion  and  frustration  of  a  novel  system  to  learn,  then  apply,  then  address  problems  (bound  to  occur),  and  ultimately  find  functional  success.” 2) Aspect of Lab Design Project: Projects in industry do not have a right answer; rather, they have a set of requirements to meet. This was emulated by providing a general framework for the project through block diagrams and a set of requirements to design for. Student Feedback – Example #1: “Being able to actually design, build, and solder our own circuits to meet specific criteria and goals.” Student Feedback – Example #2: “Employing the design process to a circuits project was a good experience because it was a novel application that broadened my awareness of the capacity of the design techniques we have learned.” 3) Aspect of Lab Design Project: Many engineered products are designed at the subsystem level and teams work together to integrate them into the final product. Understanding the interdependencies of sub-systems that are integrated together to create a system is key for design, analysis, testing, and troubleshooting. Student Feedback – Example #1: “The  most  valuable  aspect  of  Project  1  was  being  able  to  put  together  the  sub-­‐systems  of  the  design  and  when  they  were  not  working  well  together  we  had  to  figure  out  how  to  troubleshoot  the  issues.  This  made  us  really  understand  what  was  happening  in  the  circuit  design.  “ Student Feedback – Example #2: “The most valuable aspect of lab project 1 for me was discovering the roles of different circuit subsystems and how they all interact to accomplish a goal. Since many practical applications involve the interaction of different electrical subsystems, I think that the hands-on experience through this lab helped enhance our understanding of integration of subsystems. I also think this lab enhanced problem solving skills and application of knowledge because there was not a procedure or specific set of instructions to follow; this approach is similar to how actual engineering problems should be addressed outside of a classroom setting.”   4) Aspect of Lab Design Project: Building connections between theory and practice are important for problem solving and developing an engineering intuition. Practicing the theory engages other modes of learning and provides a stimulus for learning. Student Feedback – Example #1: “The most valuable aspect of this project was seeing how these components interact together in a real world circuit. Schematics are drawn in a way that is easy to understand, but being able to practice actually putting these things together is also very important.” Student Feedback – Example #2: “Getting to actually build the circuit and test it out made me realize how the slightest errors can cause problems. Building the circuit also made me understand how it worked because I had to make it with my own hands and double check each others work.” 5) Aspect of Lab Design Project: Qualitative and quantitative reasoning A complete education in engineering design must not only focus on the numbers and calculations, or quantitative reasoning. Qualitative reasoning through understanding the requirements and developing representations (i.e. schematics) must also take place as it enables a true understanding of the system being designed. Student Feedback – Example #1: “The  most  valuable  aspect  of  this  lab  was  being  able  to  put  two  "lessons  from  class"  (the  Wheatstone  bridge  and  the  Op-­‐Amp)  together  for  a  real  application:  to  calibrate  a  strain  gauge.  It  was  very  satisfying  to  see  four  weeks  of  hard  work  demonstrating  the  

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 predicted  behaviors.  Even  though  the  calibration  did  not  lead  us  to  predict  the  mystery  mass  within  a  95%  confidence  interval,  we  were  able  to  verify  that  our  system  behaved  as  desired,  just  without  the  accuracy  required.    Going  through  the  process  of  drawing  a  schematic,  simulating  the  circuit,  building  the  circuit,  testing  the  circuit,  troubleshooting,  and  verifying  a  successful  circuit  is  very  helpful.  I  will  be  using  these  methodical  steps  for  future  projects.”    Student Feedback – Example #2: “The  importance  of  researching  and  designing  before  you  dive  into  something  complicated  such  as  this  project  and  also  how  methodical  you  must  be  when  building  a  circuit  as  complicated  and  with  as  many  places  to  make  mistakes  as  this  project  had.” 6) Aspect of Lab Design Project: The projects provide an opportunity for designing and building circuits that have practical applications both in engineering and non-engineering fields. The projects also provide exposure to what is likely inside devices they have already used, seen on a website, or can purchase. Student Feedback – Example #1: “The  most  valuable  aspect  of  lab  project  2  was  how  each  subcomponent  had  a  purpose  and  aided  in  the  success  of  the  system  as  a  whole.  The  iteration  that  took  place  between  designing  each  subcomponent  led  to  a  deeper  understanding  of  the  system  as  a  whole.  I  liked  how  the  system  we  were  designing  is  similar  to  LED  speaker  systems  that  you  can  buy.  It  gave  me  a  better  understanding  of  how  to  approach  real  circuit  systems.”    Student Feedback – Example #2: “It  was  really  cool  to  create  something  that  actually  did  something.  It  has  so  many  different  applications.”   Feedback on what was least valuable in the project: Student Feedback – Example #1: “Overall  it  was  a  good  lab,  but  it  came  too  soon.    I  did  not  know  how  to  successfully  build  a  circuit  on  a  breadboard  or  a  circuit  board  before  that  lab.    I  would  have  liked  it  if  we  did  those  labs  separately  and  then  did  a  cohesive  project  after  we  got  a  better  understanding  of  how  each  of  the  circuits  worked.    Student Feedback – Example #2: “Even though we were given a blackbox schematic of the different components, it was very difficult to determine how to design the components. It would have helped if we had briefly discussed how an attenuator, a buffer, and a comparator can be implemented. I do agree that because we had to research on our own, we experienced what it is like to be a practicing engineer that is given a problem and expected a solution with little guidance.”  Student Feedback – Example #3: “Not being able to troubleshoot the system effectively caused a lot of frustration and led to me feeling like the project was not worth my time.” Student Feedback – Example #4: “Would have liked more help on certain aspects of the project; felt totally lost and helpless a lot.” Discussion and Observations From a student perception perspective, the circuits design projects strongly met the course outcomes of (1) Design, construct, and test circuits to perform specific tasks using resistors, capacitors, diodes, transistors, operational amplifiers, etc.; (2) Use common electronics laboratory tools and devices (Multimeters, solderless breadboards, function generators, oscilloscopes, soldering irons, etc.); and (3) Understand the fundamentals of instrumentation and measurement. Further, it appears from responses to survey questions 6, 7, 11, and 12 that the repeated project exposure reinforced the importance of designing to requirements as well as the importance of understanding subsystem

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 interactions during design. Additional research is needed, however, to fully understand the influencing factors. Unfortunately, the projects did not appear to increase motivation or interest in the subject matter at hand. For many of the students the circuits design projects were the first experience they had with designing, prototyping, and troubleshooting a circuit to meet a certain goal. Having the entire process left open-ended was a bit daunting to many of the students. This, however, reinforced life-long learning, teamwork, and being resourceful. Another observation was with regard to subsystem design and testing, and system integration. Students would often construct the entire system before testing and would get frustrated when trying to troubleshoot the circuit. Teams that could not identify the source of error within their circuit were encouraged to test subsystems first before integrating. With coaching, the student teams were able to understand the systems perspective of the circuit design and how outputs of one subsystem became inputs to another. In both of the circuits projects a recommended timeline was provided for each that clearly articulated what needed to be accomplished each week to ensure a successful project. It was observed that most students did not follow the timeline in the first project and spent many hours in the days leading up to the deadline. Teams that drastically underestimated the time requirements did not complete the project and presented a partially working design. As a result of this experience, during the second project, the majority of students took full advantage of open lab and instructor consultation hours, knowing that refinements and testing would take up much more time than they previously estimated. By having two projects in the circuits course, students had a better idea of what to expect in a circuits design project as well as learned from past mistakes. Instructors noted that teams devoted more up-front time to understand the project requirements, research the subsystems and components of the system, consider the input-output relationships of the subsystems, and carefully consider methods for implementing solutions. Recommendations and Future Work The curriculum of our non-discipline specific engineering program combines a campus-wide, liberal arts general educational core with courses in math, science, engineering design, engineering science, business, systems analysis, and sustainability. Thus, design projects are integrated throughout the curriculum to help tie together fundamental concepts. Furthermore, the projects are emphasized as a learning opportunity where the end result (whether it was fully functional or not) was not quite as important as the lessons learned during the course of the project. This makes it a more enjoyable environment focused on experimentation, discovery, and improvement. One recommended change is to add slightly more structure to the first design project, to better model the thought processes of designing a circuit to meet a set of requirements. Additional research is also needed to verify if the importance of designing to requirements as well as the understanding subsystem interactions during design was attributed to the repeated project exposure in a single course, other factors, or some combination. Overall, the laboratory design projects were successful at motivating the students to learn the course concepts as well as fundamental engineering skills, and will continued to be offered in some capacity. References 1. National Academy of Engineering. The Engineer of 2020: Visions of Engineering in the New Century. Washington DC:

National Academies Press; 2004. 2. National Academy of Engineering. Educating the Engineer of 2020: Adapting Engineering Education to the New

Century. Washington D.C.: The National Academies Press; 2005. 3. Nagel RL, Pappas EC, Pierrakos O. On a Vision to Educating Students in Sustainability and Design—The James

Madison University School of Engineering Approach. Sustainability. 2012;4(1):72-91.

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 4. Nagel RL, Pierrakos O, Pappas EC, Ogundipe A. The Integration of Sustainability, Systems, and Engineering Design in

the Engineering Curriculum at James Madison University. ASME 2011 International Design Engineering Technical Conferences (IDETC). Vol DECT2011. Washington, DC: ASME; 2011.

5. Pierrakos O, Nagel RL, Pappas E, Nagel JK. A New Vision for Engineering Design Instruction: On the Innovative Six Course Design Sequence of James Madison University. 119th ASEE Annual Conference & Exposition. San Antonio, TX2012.

6. Sterian, A., Adamczyk, B., & Rahman, A. A Project-Based Approach to Teaching Introductory Circuit Analysis. 38th ASEE/IEEE Frontiers in Education Conference, pp. 1-6, 2008.

7. Macias-Guarasa, J., Montero, J., San-Segundo, R., Araujo, A., & Nieto-Taldriz, O. A Project-Based Learning Approach to Design Electronics Systems Curricula. IEEE Transactions on Education, 49(3), 389-397, 2006.

8. Jenkins, B., Field, C.T. Practical Circuit Design in an Elementary Circuit Theory Lab. Proceedings of American Society for Engineering Education Conference, St. Louis, MO, USA, 2000.

9. Firebaugh, S., Jenkins, B., Ciezki, J. A Comprehensive Laboratory Design Project for Teaching Advanced Circuit Analysis. Proceedings of American Society for Engineering Education Conference, Salt Lake City, Utah, USA, 2004.

10. Michaud, Francois, et al. "Designing toy robots to help autistic children-an open design project for electrical and computer engineering education." Proc. American Society for Engineering Education, 2000.

11. Smith, K.A., Shepard, S.D., Johnson, D.W., Johnson, R.T. Pedagogies of Engagement: Classroom-Based Practices. Journal of Engineering Education, 94(1), 87-101, 2005.

12. Freeman, S., Eddy, S.L., McDonough, M., Smith, M.K., Okoroafor, N., Jordt, H., Wenderoth, M.P. Active learning increases student performance in science, engineering, and mathematics. PNAS 111 (23) 8410-8415, 2014. doi:10.1073/pnas.1319030111

13. Dutson, A.J., Todd, R.H., Magleby, S.P., Sorensen, C.D. A Review of Literature on Teaching Engineering Design Through Project-Oriented Capstone Courses. Journal of Engineering Education, 86(1), pp. 17-28, 1997.

14. Adhami, R., Meenen, P.M., Wayne, D. Fundamental Concepts in Electrical and Computer Engineering with Practical Design Problems. 2nd ed. Boca Raton, FL: Universal, 2007.

15. Carlson, L.E., Sullivan, J.F. Hands-on engineering: learning by doing in the integrated teaching and learning program. International Journal of Engineering Education, 15(1), pp. 20-31, 1991.

16. Uribe, R.b., L. Haken, and M.c. Loui. A Design Laboratory in Electrical and Computer Engineering for Freshmen. IEEE Transactions on Education, 37(2), pp.194-202, 1994.

17. Shafai, C., and Kordi, B. A Laboratory-Centered Approach to Introducing Engineering Students to Electric Circuit and Electric Systems Concepts. Proceedings of the Canadian Engineering Education Association, Winnipeg, Manitoba, Canada, 2012.

18. Striegel, A. Problem-based Learning in an Introductory Computer Engineering Course. 32nd Annual Frontiers in Education Conference, pp. 7-12, 2002.

19. Yaz, Edwin E. "Department of Electrical and Computer Engineering." Marquette University Bulletin. Marquette University.

20. Oakley, B.A., Hanna, D.M., Kuzmyn, Z., Felder, R.M. Best Practices Involving Teamwork in the Classroom: Results From a Survey of 6435 Engineering Student Respondents. IEEE Transactions on Education, 50(3), pp. 266-72, 2007.

21. ABET, Criteria for Accrediting Engineering Programs, 2012 - 2013. ABET Board of Directors, 2011.  

 

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 ENGR  313—CIRCUITS  AND  INSTRUMENTATION  

   Lab  Project  #1  —Designing  a  Calibrated  Instrument  

 INTRODUCTION    This  lab  project  is  a  3-­‐week  project  for  teams  of  four  students.    Throughout  this  project,  you  will  need  to  use  the  knowledge  and  experience  that  you  gained  in  class  and  lab  to  design,  build,  test,  and  calibrate  a  functional  weight  measurement  device  based  on  a  strain  gage  mounted  to  a  cantilevered  beam.    Each  team  is  required  to  design,  build,  demonstrate,  and  report  their  design.    This  document  outlines  the  requirements  for  this  project.    This  first  lab  project  will  be  weighted  as  7.5%  towards  your  final  grade  in  the  course.    PROJECT  DESCRIPTION    Students  will  form  their  own  project  teams  comprised  of  four  students.    Each  team  must  meet  the  weekly  deliverables,  and  give  a  demonstration  of  their  design  in  lab  during  the  week  of  October  13th.      Each  team  must:  

• Derive appropriate equations to model the system and inform the circuit design process • Create a schematic of the final circuit design • Include a Wheatstone bridge and instrumentation amplifier in the design • Construct and test the designed circuit • Calibrate the instrument and provide a calibration plot with uncertainty • Measure (using LabVIEW, multimeters, etc.) and provide ample documentation to prove that the

designed circuit meets the project criteria • Sign up for and attend solder training • Solder the Wheatstone bridge portion of the circuit design • Each individual must complete weekly progress reports detailing their individual contributions to the

project during the previous week • Give a demonstration of the working design • Write a report that explains the design, analysis, testing, and calibration of the instrument, as well as how

modeling assisted with the design, deviations of the performance from expectations based on mathematical modeling, and how the limitations were overcome

 Demonstrations  of  the  calibrated  instrument  will  occur  in  lab  during  the  week  of  October  13th.    Your  instructor  will  be  available  during  normal  class  laboratory  times  to  answer  questions  and  assist  teams.    Evening  laboratory  hours  (5  pm  –  8  pm)  are  also  available  for  teams  to  work  on  the  project.      

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 PROJECT  REQUIREMENTS    Design,  build,  and  test  a  calibrated  instrument  to  measure  and  report  the  weight  of  mass  attached  to  the  device.  This  instrument  must  have  the  subsystems  defined  in  Figure  1.  

 Figure  2:    Required  Subsystems  of  Instrument  

A  pre-­‐mounted  120  Ω,  F  =  2.1,  three  wire  strain  gage  will  be  provided  to  each  team.    Your  team  will  be  required  to  research  the  principles  of  strain  gage  operation  and  how  strain  measurements  are  performed  using  a  Wheatstone  Bridge.    Each  team  must  then  design  and  implement  a  Wheatstone  Bridge  circuit  to  measure  the  strain  induced  on  an  aluminum  bar  fitted  with  a  strain  gauge  having  a  gauge  factor  of  F  =  2.1.  The  bridge  circuit  must  be  adjustable  so  that  an  output  of  0  V  can  be  achieved  in  the  no-­‐strain  condition.  The  input  voltage  to  the  Wheatstone  bridge  must  be  1.5  V.  Further,  the  Wheatstone  Bridge  circuit  components  must  be  soldered.    To  measure  the  voltage  difference  across  the  Wheatstone  Bridge,  each  team  must  research,  design,  and  implement  an  instrumentation  amplifier  using  the  LM  324N  op-­‐amp  that  improves  the  sensitivity  of  the  Wheatstone  bridge  output  voltage.    Bonus  points  opportunity:  The  teams  that  solder  this  instrumentation  amplifier  circuit  in  addition  to  the  Wheatstone  bridge  circuit  will  receive  bonus  points.      Finally,  design  and  implement  an  interface  that  reports  the  output  of  the  instrument.    The  interface  must  convert  the  instrumentation  amplifier  output  value  to  the  value  of  weight  applied  to  the  end  of  the  cantilever  beam.    This  interface  can  be  a  manual  or  automated  design.    Bonus  points  opportunity:  The  teams  that  build  a  LabVIEW  interface  that  will  automatically  convert  the  amplifier  output  value  to  a  weight  value  in  real-­‐time  will  receive  bonus  points.      The  calibrated  instrument  must  be  able  to  accept  an  input  within  the  range  of  10-­‐300  grams.    Your  team’s  instrument  will  be  validated  by  placing  an  unknown  (to  your  team)  weight  on  the  instrument.  Based  on  your  circuit  output,  your  team  should  be  able  to  determine  the  value  of  the  weight  applied,  including  the  uncertainty  in  the  measurement.    PROJECT  TIMELINE    All  project  teams  will  follow  the  timeline  given  in  Table  1.    Demonstrations  of  the  calibrated  instrument  will  occur  in  lab  during  the  week  of  October  13th.    Table  2:    Lab  Project  1  Timeline  

Week   Pre-­‐lab      During  Lab  September  22  

  Learning  about  strain  gages,  and  open  lab  time  to  explore  Wheatstone  bridges  or  amplifiers    

September  29  

Simulated  Wheatstone  bridge  and  instrumentation  amplifier  designs;  Discussion  post  on  Canvas  of  individual  contribution  

Prototyping  the  Wheatstone  bridge  and  instrumentation  amplifier  

October  6   Functioning  and  soldered  Wheatstone  bridge  circuit;  functioning  instrumentation  

Calibration  of  instrument  design  

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 amplifier  circuit  on  breadboard;  Discussion  post  on  Canvas  of  individual  contribution  

October  13   Calibration  and  uncertainty  data;  Discussion  post  on  Canvas  of  individual  contribution  

Demo  final  design  with  unknown  weight  

 

DEMONSTRATION  OF  CALIBRATED  INSTRUMENT  

During  the  final  week  of  lab  project  #1,  each  project  team  will  demonstrate  their  calibrated  instrument  using  the  apparatus  shown  in  Figure  2.    A  randomly  chosen  weight  between  10-­‐300  g  will  be  placed  on  the  end  of  the  beam  with  the  pre-­‐mounted  strain  gage.    The  interface  of  the  designed  circuit  will  report  the  weight  applied  to  the  end  of  the  beam.  (Note  that  the  beam  deflection,  and  hence,  the  resulting  strain,  will  depend  upon  the  moment  generated  by  the  weight.    Be  sure  that  your  group  has  a  pre-­‐defined  method  for  ensuring  that  the  applied  load  will  be  placed  at  the  same  distance  from  the  point  of  attachment  during  instrument  testing  and  calibration.)  

             

 

 

 

 

 

 

 

 

 

 

Figure  3:    (Left)  Example  Pre-­‐mounted  Strain  Gage  on  Beam  (Right)  Instrument  Test  Apparatus  

     

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 PROJECT  DELIVERABLES      All  project  teams  will  work  toward  the  following  two  deliverables:  

• A fully functioning instrument with the subsystems of Wheatstone bridge, instrumentation amplifier, and interface. Wheatstone bridge must be soldered.

• A professional, type-written project report that details the design, analysis, testing and calibration of the instrument. All reports must have the following sections:

o Introduction – includes an overview of the project and explains what is included in the document o Design Team – includes a description of team member roles, who worked on each subsystem of

the design, and explains how work was assigned. All the weekly individual contribution reports should be placed in an Appendix.

o Design & Analysis – includes the methods of design and analysis, descriptions, schematics, simulations, and equations relevant to each subsystem listed in Figure 1, the overall system schematic, equations used by the interface, and how the design meets the given requirements. Include images of the subsystems and overall design. Should be organized into subsections.

o Calibration – includes the method of calibration, and calibration information including a plot with uncertainty. All the raw information should be placed in an Appendix.

o Testing – includes methods of testing the design, preliminary testing results, and results from the demo testing during the week of Oct. 13th. Include images of testing.

o Discussion – includes what was observed during testing, how mathematical analysis informed the design, why deviations of performance from expectations based on mathematical modeling occurred, how the limitations were overcome

o Conclusion – summarize the project, results, and key take-aways of the design o References – follow APA format o Appendices – should include at least two appendices: compiled weekly individual contributions,

and raw data from calibration.  The  professionalism  of  the  report  will  also  be  graded.    This  includes  appearance,  organization,  graphics,  grammar,  tone,  and  clarity  of  writing.    The  due  dates  for  the  project  deliverables  are  given  in  Table  2.    Table  3:    Due  Dates  for  Deliverables  

Week  Due   Deliverable      October  13   Fully  working  design  October  20   Project  report        

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 ENGR  313—CIRCUITS  AND  INSTRUMENTATION  

   Laboratory  Project  2  —  LED  Audio  Frequency  Indicator  

   INTRODUCTION    This  laboratory  project  will  require  you  to  use  and  integrate  concepts  from  class  and  previous  labs,  as  well  as  research  new  topics,  to  complete  the  design  of  an  audio  frequency  LED  indicator  circuit.    Self-­‐selected  project  groups  of  3  or  4  students  must  design,  build,  test,  and  present  the  final  design,  justifying  technical  decisions  with  appropriate  research  and  calculations.    The  remaining  laboratory  periods  will  be  “open  lab”  periods  devoted  to  this  project  work.    PROJECT  DESCRIPTION    Your  engineering  team  has  been  approached  by  a  company  that  wishes  to  include  audio  frequency  sensitive  LED  lighting  into  clothing  and  electronic  devices.  The  company  has  asked  you  to  devise  a  proof-­‐of-­‐concept  prototype  to  demonstrate  how  LED  lights  can  be  made  sensitive  to  audio  frequencies  from  a  portable  music  player  (iPod,  etc.).  For  this  project  you  will  need  to  design  and  demonstrate  a  circuit  capable  of  providing  audio  frequency  selective  lighting  response.    Audio  or  sound  is  the  result  of  air  compression  waves  that  occur  at  different  frequencies.    These  slight  pressure  variations  in  the  air  are  detected  by  our  ears  and  interpreted  as  sound  by  our  brains.    Recording  equipment  captures  these  air  pressure  variations  and  stores  the  time-­‐history  of  these  pressure  variations.    These  signals  can  then  be  reproduced  (re-­‐played)  at  a  later  time.  The  recorded  pressure  variations  are  reproduced  by  sending  an  electrical  signal  that  represents  the  recorded  information  to  a  speaker,  which  in  turn  cause  air  compression  waves.    Therefore,  recorded  audio  (music)  signals  are  comprised  of  many  different  frequencies  of  sinusoidal  waves  that  are  all  combined  together  (recall  that  a  pure  tone  is  a  sinusoidal  wave  at  a  single  frequency).    The  volume  of  the  audio  is  determined  by  the  amplitude  of  the  sinusoidal  waves  while  the  tone  or  pitch  is  determined  by  the  frequency  of  the  waves.    In  many  audio  playback  and  speaker  systems,  it  is  customary  (for  sound  quality  reasons)  to  “divide”  the  audio  frequencies  among  multiple  speakers.    Low  frequency  signals,  which  result  in  low,  bass  tones,  are  sent  to  a  large  speaker  element,  often  called  the  bass  speaker  or  subwoofer.    Midrange  frequencies,  which  are  typical  of  many  musical  instruments  and  the  human  voice,  are  sent  to  a  smaller,  midrange  speaker.    Finally,  high-­‐frequency  signals,  associated  with  instrument  overtones  and  high  pitch  instruments  are  directed  to  a  small  speaker,  often  referred  to  as  the  tweeter.    The  frequencies  associated  with  each  ranges  is  given  in  Table  1.    Table  1:  Frequency  ranges  and  audio  classifications  Frequency  Category  (Speaker)  

Audio  Classification   Frequency  Range  

Low  Range  (Woofer)   Sub  Bass    Less  than  60  Hz     Bass   60  Hz  –  250  Hz  Midrange  (Midrange)   Midrange   250  Hz  –  2  kHz  High  Frequency  (Tweeter)   High  Midrange   2  kHz  –  6  kHz     High  Frequencies   Larger  than  6  kHz    An  electronic  circuit,  known  as  an  audio  crossover  filter  or  network  is  usually  used  to  accomplish  this  frequency  selection  and  direction  process  for  speakers.    For  this  project,  your  team  will  design,  construct,  test,  and  demonstrate  a  crossover  filter.    However,  

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 instead  of  driving  speakers  with  your  audio  filter,  you  will  drive  LEDs.    In  this  manner,  the  LEDs  will  light  up  when  the  circuit  is  provided  with  an  input  signal  at  a  particular  frequency.    The  requirements  for  this  prototype  are:  

• The circuit must accept audio input (voltage) from a portable audio device. For this proof of concept prototype, we will use a mono, or single channel output, as opposed to traditional stereo playback.

• To demonstrate the single frequency filtering capabilities, your team must devise a method for mimicking the audio device output using a laboratory function generator.

• The audio filter will distinguish at least three frequency ranges, corresponding to the low-range, midrange, and high frequency ranges shown in Table 1.

• When a low frequency signal (less than 250 Hz) has a peak-to-peak voltage that is larger than 3 dB below the maximum amplitude output of the audio device output, a red LED must be lit.

• When a midrange frequency signal (between 250 Hz and 2 kHz) has a peak-to-peak voltage that is greater than 3 dB below the maximum amplitude output of the audio device, a yellow LED will be lit.

• When a high frequency signal (greater than 2 kHz) has a peak-to-peak voltage that is greater than 3 dB below the maximum amplitude output of the audio device, a green LED will be lit.

 This  design  may  be  accomplished  using  active  filters  (i.e.,  op-­‐amps)  and/or  passive  filters  (i.e.,  inductors).    Your  designed  circuit  will  be  tested  by  your  instructor  using  a  function  generator  and  must  also  be  demonstrated  using  the  selected  audio  device  and  group  selected  audio  tracks.    The  output  amplitude  of  the  function  generator  will  be  set  to  the  maximum  output  amplitude  for  these  tests.    The  function  generator  will  then  be  attached  to  your  circuit,  including  the  circuit  required  to  reduce  or  amplify  the  function  generator  output  to  match  that  of  the  expected  output  of  the  audio  device.  The  frequency  of  the  function  generator  output  will  then  be  varied  (set  to  different  frequencies)  to  verify  that  the  circuit  meets  the  design  requirements.  

 MATERIALS  PROVIDED    Each  group  may  use  the  following  equipment  and/or  components  within  their  electronics  design:  

• A maximum of two (2) DC power supplies • One (1) solderless electronics breadboard • A maximum of two (2) LM324N Quad Op-Amp integrated circuits (ICs) • Common circuit components (resistors, capacitors, inductors, LEDs, jumper wire kits, etc.) • Access to standard 3.5 mm audio (mono channel) jacks with pigtail (wire leads) for integration with

portable audio player devices.  Note  that  your  group  is  not  required  to  use  all  of  these  components  for  the  final  design.        ADDITIONAL  INFORMATION  AND  SUGGESTED  APPROACH    Most  portable  audio  players  are  designed  to  reproduce  audio  by  driving  “earbud”  style  speakers  with  a  typical  resistance  of  32  Ω.  To  evaluate  the  output  of  the  audio  player,  you  will  need  to  mimic  these  conditions  and  measure  the  typical  output  voltage  of  the  device  (using  an  oscilloscope)  across  such  a  load  (i.e.,  earbuds).  Also,  remember  that  the  amplitude  of  the  output  will  vary  based  upon  the  setpoint  “volume”  of  the  audio  player,  so  it  will  be  advantageous  to  select  a  consistent  volume  level  for  the  design.  To  be  able  to  accurately  test  your  circuit  at  precise  audio  frequencies,  it  will  be  necessary  to  interface  your  design  with  a  function  generator.    The  function  generator’s  output  (when  the  amplitude  output  is  set  to  its  maximum  value)  will  most  likely  not  produce  the  same  voltage  as  the  audio  player;  therefore,  it  will  be  necessary  for  your  team  to  devise  a  resistive  circuit  that  will  either  attenuate  or  amplify  the  signal  provided  by  the  function  generator  to  a  level  that  mimics  the  voltage  input  provided  by  the  audio  player.        Because  there  is  a  desire  to  not  disturb  the  quality  of  the  audio  signal  input  into  the  speakers,  your  circuit  

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 will  need  to  include  a  circuit  that  “buffers”  the  frequency  selective  LED  circuit  from  the  audio  signal.    Amplification  of  the  audio  signal  may  be  necessary.    For  reference,  the  signal  model  for  the  desired  circuit  can  be  represented  by  the  block  diagram  in  Figure  1.    

 Figure  1  –  Block  diagram  of  the  conceptualized  audio  frequency  sensitive  LED  circuit.  

 A  recommended  timeline  for  development  of  this  proof-­‐of-­‐concept  prototype  is  suggested  in  Table  1.    Note  that  the  final  prototype  must  be  demonstrated  to  the  client  (your  instructor)  during  the  week  of  December  8th  (Finals  Week).    30  min.  timeslots  will  be  made  available  as  the  date  gets  closer.    

Table  1  –  Suggested  timeline  for  project  implementation.  Week  of…   Recommended  Project  Tasks  November  3   • Explore low-pass, high-pass, and bandpass filters to understand how they

work • Characterize the output of the audio device • Characterize the output of the laboratory function generator • Design and implement a circuit to mimic the maximum amplitude output

of the audio device using the function generator November  10   • Design and implement an amplifier or buffer circuit to measure the

voltage across the headphone load • Identify and evaluate (using mathematical modeling and simulation)

designs for low-pass, high-pass, and bandpass filters • Begin implementation of filter circuits

November  17   • Complete and test filter circuits and modify individual filter circuit designs, as required, based on results

• Identify methods to light LEDs when frequency input is within the desired range at the required -3 dB level

• Begin integrating LEDs with filter circuits November  24   Thanksgiving  Break  –  Enjoy!  December  1   • Complete the integration of the LEDs with the filtering circuits

• Test the completed prototype with the function generator and compare with expected results

• Test the completed prototype with the audio player and confirm desired operation

December  8   • Present the design and demonstrate desired functionality during chosen timeslot

• Turn in lab project #2 report        

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 DELIVERABLES  AND  EVALUATION    Each  team  will  present  their  completed  circuit  to  the  instructor  for  evaluation  during  a  30  minute  evaluation  period  (to  be  scheduled  as  a  team  with  your  instructor).    Prepare  a  10-­‐12  minute  presentation  about  your  group’s  design  for  presentation  at  the  beginning  of  the  evaluation  period.  This  presentation  should  include  a  demonstration,  technical  description  of  the  circuit’s  functionality,  and  schematics.  Following  this  presentation,  the  circuit  operation  will  be  verified  and  questions  about  the  design  and  operation  of  the  circuit  will  be  asked  of  each  team  member.    These  sessions  will  be  scheduled  for  the  week  of  December  8th  (final  exams  week).    In  addition  to  your  proof-­‐of-­‐concept  prototype  demonstration  and  presentation,  each  team  must  provide  the  following  written  technical  design  information  in  the  form  of  a  brief  technical  report  (due  at  the  time  of  the  scheduled  evaluation  period).    The  report  should  include  the  following:  

• Full system schematic of the designed prototype circuit, including values for all components and power supplies used in the design.

• Images of prototyped circuit. • Justification for the selection of components used to perform the frequency selective filtering. This

should include descriptions, mathematical models and calculations. Provide citations for all references used.

• Explain the performance of the designed circuit. Include Bode plots of predicted and measured frequency selectivity performance of the circuit.

• A summary of “lessons learned” and suggestions for further refinement and commercial implementation of the prototype circuit.

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