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Proceedings of the 2011 ASEE Gulf-Southwest Annual Conference University of Houston

Copyright © 2011, American Society for Engineering Education

Session T3B-1

INCORPORATION OF NI MYDAQ EXERCISES IN ELECTRIC

CIRCUITS

Catherine Chesnutt and Mary C. Baker

Department of Electrical and Computer Engineering Texas Tech University

[email protected]

Abstract

Students often struggle with conceptual courses that involve abstract concepts without hands-on examples. Electric circuit theory courses are typically taught in the second year of the Electrical and Computer Engineering curriculum, and often do not involve a laboratory component, or have a laboratory component that is taught independently from the course. In order to engage students in the learning process throughout the course and to give them a hardware component to connect with the theory aspects of the course, each student was given an NI MyDAQ for the duration of the semester. The MyDAQ is an inexpensive data acquisition device that can be used in the Labview environment, and acts as a multimeter, oscilloscope, DC power supply, or signal generator. This makes it possible to both assign hardware homework to students consisting of specific circuits, as well as to encourage students to independently explore circuits in their own time. This paper describes a series of exercises to be used with the NI MyDAQ in the introductory circuits class. The long term goal is to integrate the devices throughout the curriculum, beginning with the introductory course in the freshman year.

Introduction According to research done in the past decade, poor performance and dropouts among freshman engineering students can be in part accounted for with poor matching of learning and teaching styles. Previous studies [1,2] argue that the most common learning style among engineering students is sensing as opposed to intuitive, active as opposed to passive, and [2] global as opposed to sequential. In other words, engineering students learn quickest through a first-hand observation of the world around them, experimenting and gathering data, tinkering with the physical objects that represent abstract concepts, and understanding the big picture. This learning style is unfortunately undermined by most of the present teaching methods which are auditory, intuitive, passive, and sequential in nature [1,2]. The application of particular teaching methods to specific learning styles has been found to produce positive results [3]. One study builds specific laboratory experiments based on the concepts that outline mental challenges that young engineers must learn to think in terms of: discovery, evaluation and investigation [4]. This paper proposes that a sensory, active component to the traditional undergraduate circuits course is



Fig. 1: The NI MyDAQ and its components [5]

crucial in producing young engineers who have gained a fundamental understanding of the material, and provides a set of eight active hardware assignments to be used with the NI MyDAQ.

Designing the Labs

Students were given a handbook that introduced them to the MyDAQ and Labview environment. Students who chose to purchase the student edition of Labview were able to utilize the MyDAQ in their time as opposed to spending time in a structured, formal laboratory environment. Each laboratory is designed with a specific purpose. There are a few concepts in introductory circuits courses which are, to the average sophomore, new, abstract, and strange at best. Some of these concepts include voltage division, Thevinin’s and Norton’s theorems, phase-shifting, and DC vs. AC. Sometimes students learn these concepts when they are first taught, but often they take them an entire four years to grasp. This is likely because while they may work many problems which use these concepts on paper, they do not physically get to handle them, and even eventually when they are building projects in other lab classes, they might not actually realize they are implementing those concepts. In other words, a student might know physically how to build something without understanding the concepts behind what actually makes it work, because he or she never related the mathematical problems he worked in class to the hardware. The assignments focus on closing this gap between the mathematics underneath the concepts and their physical implementation, which essentially matches the engineering student’s learning style to the engineering student’s laboratory. If this can be done well, students will understand more of why and how their projects work and will be able to design and build them better. If engineering students are expected to learn how to design and build devices, it makes sense that they ought to be taught the concepts they will need to do this in a similar manner.

Using the National Instruments MyDAQ

An ideal device for such an integrated laboratory experience is the NI MyDAQ, shown in Fig. 1.



Fig. 2: MyDAQ Software Suite includes digital multimeter, oscilloscope, function generator required for circuits hardware assignments.

Although it is capable of more, the features which are needed for hardware assignments are its ability to input and output analog and digital signals and its ability to be used as a digital multi-meter. It handles I/O from two analog input and two analog output channels, along with eight digital I/O channels. National Instruments provides a software suite for the MyDAQ, shown in Fig. 2, which has an instrument panel that includes Labview VI’s for an oscilloscope, digital multi-meter, function generator, and bode-plot analyzer which are all configured to work with the MyDAQ, so that students do not require Labview experience to use it. Based on the MyDAQ platform, we developed a series of hardware-based homework assignments that complemented areas of instruction in the lectures. Students were provided with a MyDAQ for the semester and were encouraged to explore both the hardware assignments as well as the additional features of the MyDAQ. Each assignment is documented with detailed descriptions of what the student should do, and includes pictures and schematics of what the setup should look like.

Hardware Assignment Descriptions Voltage Division It is assumed that the student is already familiar with the voltage division formula and schematic on paper shown in Fig. 3. The hardware assignment provides the student a simple way of understanding this concept: to actually do it. The student is given a picture of a breadboard, shown in Fig. 3, which shows where to place the resistors and the input and output voltage wires, and then told to reproduce this on their own board. The instructions to connect the input and output voltages to the MyDAQ are explained in detail, and pictures of the MyDAQ itself and where to connect the wires are provided. The goal is not to make the student try to figure out



Fig. 3: Voltage Division schematic corresponding to voltage division formula !!"# = !!"!!

!!! !! and an

instructional breadboard schematic.

how to hook things up, but so they can see the concept they have been taught in a physical, tangible way which reflects the sensory, active learning style that most engineering students have. The student is told to first calculate the output voltage using the voltage division formula, then measure the actual output voltage from the breadboard using the same parameters, and then to compare the two and give reasons for any discrepancies. This introduces the student to the concept that the implementation will not always reflect the initial calculations on paper. Since this first lab uses DC, another voltage division lab is given when the students begin to learn about AC, which repeats the same steps using AC instead of DC (Lab #8). Thus, the students receive reinforcement for the voltage division concept while being introduced to the difference between DC and AC, using something they are already familiar with as a platform.

Thévenin and Norton’s Theorem The second lab (Lab #2) provides a way to experiment with Thévinin’s and Norton’s theorems in much the same way as the voltage and current divider labs. The student first calculates equivalent voltage and current on paper, then measures it physically and records any differences between the two. The student is asked to consider why the measured values differ from the calculated ones. Again, the breadboard schematics are set up to help the student relate it to the paper schematic as much as possible. Current Division A current divider lab using DC (Lab #3) is also given shortly after the DC voltage division lab. It aims to provide the student with a better understanding of how the two are different. Current and voltage division can be ambiguous on paper, but being able to physically measure what the current is at a given point in the system helps fill in gaps in understanding, especially when the breadboard schematic is arranged in the same way as it is drawn on paper, shown in Fig. 4. This exercise shows the student that current is not measured in the same way that voltage is, and



Fig. 4: Current Divider lab breadboard schematic designed to closely resemble the actual schematic.

Fig. 5: Breadboard and schematic for an RC circuit

provides a greater understanding of the problems they work in homework. The student is asked to calculate the currents across R1, R2, R3 and R4, measure them using the MyDAQ’s multi-meter, and record them, as well as why or why not they would expect the values across the resistors to differ.

RC Response A fourth lab (Lab #4) has the student build an RC circuit and discover the time constant of the circuit by watching the oscilloscope as DC is applied and then removed with a switch. The student estimates time constant by looking at the oscilloscope, and then calculates what it should be by hand. The student is asked to consider what they think the purpose of the R1 resistor is, as well as what would happen if they tried to run the circuit without this resistor. The breadboard schematic, shown in Fig. 5, is not as intuitive as the voltage and current divider labs, but should

help the student begin to think about how to relate a breadboard arrangement with a paper schematic. An example of the time constant graph they see is shown in Fig. 6. AC Circuits and Phase Shift



Fig. 6: Oscilloscope showing time constant of RC circuit

Fig. 7: Oscilloscope showing phase shift in an RC circuit

A lab following the RC circuit lab (Lab #5) is an AC assignment that illustrates phase shift. It takes the same RC circuit and shows the student the difference in phase that takes place between the input and output of an RC circuit. An AC current is applied to the circuit and two analog input channels are used simultaneously to view the voltage at the resistor and capacitor, producing a graph on the oscilloscope similar to the one in Fig. 7. The student is asked to consider whether the two graphs look out of phase, and which one they think is leading or lagging the input. The student is then instructed to switch the wires connecting the capacitor voltage and then reconsider which one they think is leading the input. This familiarizes the student with the concept of different phases within the same circuit.

Conclusions

The use of a device such as the MyDAQ with hands-on hardware assignments for introductory circuits students not only helps to match the education method to the learning styles of the students, but also provides a convenient way for the students to explore circuit building on their own. It is easy to force students to do laboratories that make them work with circuits; it is not so easy to create the desire in those students to play with circuits. The MyDAQ can be taken anywhere and used with virtually any computer, and assignments can be done on it that previously needed to be done in a classroom laboratory setting. This type of work fosters the student’s natural desire to discover while building and tinkering with components, which is an essential part of deep learning. In addition, although students need no prior knowledge of Labview in order to use the MyDAQ, there are many available VI’s which are configured to work with it and can be used to write more complex programs in Labview. The MyDAQ laboratory manual described here also contains more optional assignments including building low and high-pass filters and a band-pass filter for students who wish to familiarize themselves with the frequency analysis they would learn in a linear systems class following circuits.



The MyDAQ has a wide range of possible applications and is versatile and easy to use. The students who purchased the MyDAQs in the circuits class will be able to continue using them in their junior and senior level classes. A present goal is now to incorporate the MyDAQ into the subsequent curriculum of the students who have experienced it. The frequency filtering assignments in the MyDAQ manual should be a good beginning for incorporating it into a linear systems course. Since this and many other following courses are project intensive, the MyDAQ provides students with a device that they are already familiar with which can then be used in numerous projects.

References [1] Felder, Richard M., “Learning and Teaching Styles in Engineering Education,” Journal of

Engineering Education, 78(7), 674-681, (1998). [2] Hanselman, Duane C., “Signals and Linear Systems: A Teaching Approach Based on Learning Styles

Concepts,” IEEE Transactions on Education, 35, No. 4, (1992). [3] Ayre, Mary and Nafalski, Andrew, “Recognizing Diverse Learning Styles in Teaching and

Assessment of Electronic Engineering,” IEEE Frontiers in Education Conference, T2B-18, (2000). [4] Cooley, Wils. L., McConnell, Robert L. and Middleton, Nigel T., “Matching Laboratory Courses to

Engineering Activities,” IEEE Frontiers in Education Conference, 5C4, (1994). [5] National Instruments. (2010). Ni Developer Zone. [Online]. Available: National Instruments Website:

http://decibel.ni.com/content/docs/DOC-12888

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