Interactive Learning for Waveform Dynamics of Diode ... - IEEE Xplore

Interactive Learning for Waveform Dynamics of Diode Rectifiers and RC Filter in DC Power Supply Muhammad Ajmal Khan, Atique W. Siddiqui, Mohammed Abdul-Majid King Fahd University of Petroleum & Minerals (KFUPM) Dhahran-31261, Saudi Arabia E-mails: {ajmal, atique, majidm}@kfupm.edu.sa

Abstract-Electronics Students have always been struggling to understand the voltage waveform dynamics across different points in diode rectifiers, which leaves them confused and the grasp of DC power supply is always missing in their understanding. In this paper, we present Scenario-based elearning product ‘DC Power Supply Simulator’ developed using Macromedia Flash for an introductory technology course. This product is developed at the university to help students to understand the complicated concepts such as diode rectifiers, voltage dynamics of power supply, RC filter, etc. This DC-Power Supply Simulator consists of various components such as transformer, diodes, resistor and capacitor. The simulator strongly supports the visualization of the dynamics of the circuit while a user manipulates its parameters. The voltage waveforms at different places in the circuit are dynamically plotted in realtime as in an oscilloscope, a strong feature of this simulator.

I.

INTRODUCTION

Simulation-based educational modules are excellent illustrative tools, used exceedingly in student centered learning methodologies. It is an active learning technique, which stimulates users’ diverse cognitive skills and insight into a system by instantly staging the consequences of their actions and strategies. Such actions and strategies can be tested without the apprehension of failures or reprisal. Such tools allow a user to increase his understanding of a system in a short span of time. As compared to real world experience, this accelerated learning is one of the unequalled advantages of such tools. Such educational tools in academics are becoming wide spread and are categorized as scenario-, simulation-, and game-based e-Learning [1]. The realization of the efficacy of these products is growing [2]. Using new media and information technology in the classroom can not only make studying more attractive to the students, but might also make teaching much easier. In engineering classes complex technical problems have to be presented in a way which is easy to follow and understand, such as Flash animations [3], Java-Applets [4], simulators [5], interactive learning for signal and systems [6], etc. Learning on-line is one of the fastest-moving trends in higher education, as engineers and executives in technology industries are discovering [7]. An elating facet of these tools is the inherent concentration of a user on decision making. It is this intensity that gives these simulation-based educational tools its richness and

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effectiveness. Even though these interactive approaches are not considered to be a substitute of more formal approaches in teaching, it effectively complements these methods. Using Bloom’s taxonomy, the first three levels of knowledge, comprehension, and application, in most cases, are fully served. The fourth level of analysis could be presented fully or partially depending upon the type of the tool and the use of it by the instructor. The tool presented in this paper is developed in an academic project at the University. The motivation behind this project came from a workshop on increasing teaching effectiveness [8] and an undergraduate course that the authors are teaching. The course is an introductory technology course namely ‘Electronics-I’ which is a compulsory course taken by the undergraduate students in three departments; Electrical Engineering, Computer Engineering, and Systems Engineering and as an optional in various other departments at the University and its community colleges. The objective of the course is to develop the basic understandings of the electronics components such as diodes and rectifiers which are being used in various areas of electrical and electronics technology. To increase the effectiveness of the course, different scenarios of DC power supply simulator were developed in this project. According to taxonomy presented in [1] this product can be categorized as a scenario-based e-learning product. As the course is compulsory in three departments and optional in few other departments, average enrolment per semester is essentially high. In section II, the lab experiment setup of DC-power supply is presented and section III elaborates on the features, development, and operation of the DC-power supply simulator. Feedbacks from the instructors, who have taught this course, are presented in section IV. Section V shows the outcomes when this simulator was tested with the students. Finally, conclusions are presented in section VI. II. EXPERIMENTAL SETUP The DC power supply converts the standard 120V /220V, AC available at wall outlets into a constant DC voltage (usually in the range of 5 to 20 V). One of the most common electronic circuits to produce DC voltage which is used to power all types of electronics circuits, such as televisions,



satellite receivers, computers, mobiles, stereo systems, VCRs, CD players, voltage converters and stabilizers, and most laboratory equipments. A basic block diagram of a complete power supply is shown in figure 1.

Fig. 1. DC Power Supply Block Diagram.

III. DC POWER SUPPLY SIMULATOR This e-learning product reacquaints students with the fundamentals of AC (alternating current) and DC (direct current) voltages as well as introduces students to the basics of AC to DC conversion through the use of diode rectifiers. Electronic circuits are harder to understand where voltages and currents are not directly visible and must be measured indirectly with meters and oscilloscopes. This lack of visibility impedes learning about circuits in many ways. Thus one of the key objectives of this simulator is to assist the students to visualize the dynamics to various circuits and test the effects of various decisions they can make on the outcome of their circuits. The general objectives of this simulator are listed as follows:

The first block in a DC power supply is the power transformer. The diode rectifier can be either a half-wave rectifier or a full-wave rectifier (center-tapped and bridge). The variation in the magnitude of the rectifier output is considerably reduced by the RC filter block. In electronics course, students are taught diode rectifiers and DC-power supply circuits, and students realize these circuits in the electronics lab using various components, oscilloscope and multi-meter as shown in the figure 2.

Fig. 2. Experiment Setup for DC Power Supply.

There are various drawbacks noticeable with this physical set as compared to the virtual setup. A common happening, while using physical setup, is that the students burn components such as transformers, capacitors, resulting in their weakening poise and ease of handling. This leads to a more defensive or even ‘better not try’ approach in experimenting with their ideas. Another disadvantage that emanate from the physical setup is that the students are unable to visualize the voltage waveforms at different points simultaneously, and this leaves them confused and the grasp of voltage dynamics is always missing in their understanding.

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• To enhance student motivation and learning by providing them a hands-on experience in a virtual environment. • To provide an interactive way of understanding and experiencing the effects of various decisions making skills. • To supplement the class material regarding concepts used in various electronics courses. • To augment the application, analysis and decisionmaking skills of the students. • To encourage students to practice without the fear of burning components. The simulator is developed in Macromedia Flash 8. The programming is done in Flash ActionScript 2. The suite was selected because of its excellent animation and graphical abilities along with the programming capabilities provided by scripting language known as ActionScript. One of the aspects, in which this simulator varies with other similar kinds of electronics simulators, is the virtual oscilloscope display of waveforms during the course of the task. In real environment, a user usually connects one oscilloscope at a time, while in this simulator, a user observes the virtual display of all signals at each point of the circuit. This simulator has a fully interactive and dynamic interface, and all output results displays such as waveforms and voltages in real-time, rendering detailed dynamics of the circuit. The transformer primary winding turns has been fixed to 230 V and secondary turns are under user control to achieve step down voltage transformer. The transformer is completely interactive, where user controls and visualizes the variation of secondary turns as well as the output secondary voltage in the virtual digital meter. This output secondary voltage is then fed into the rectifier circuit. The rectified voltage is then passed through RC filter, where user has full control on it, to achieve his objectives by minimizing ripples with clear visualization in the oscilloscope.



A. DC Power Supply Simulator with Half-Wave Rectifier First, a simulator with half-wave rectifier has been developed to start with easiest task. Half-wave rectifier has only one diode which passes through positive cycle of sinusoidal waveform.

C. DC Power Supply Simulator with Bridge Full-Wave Rectifier Another power supply circuit, the bridge full-wave rectifier has been developed, as shown in figure 5. In this simulator, four oscilloscope displays are enough to visualize the voltage waveforms at different points.

Fig. 3. Simulator with Half-Wave Rectifier.

B. DC Power Supply Simulator with Center-Tapped FullWave Rectifier The simulator with center-tapped full-wave rectifier, shown in figure 4, is challenging one, where six virtual oscilloscope displays have been developed to provide complete visualization of voltage at all six points. This simulator enhances the students’ understanding with the help of realtime display of two waveforms, 180 degree out of phase, because of center-tapped transformer, it is worth viewing the secondary, rectified, filtered, and 180 degree shifted waveforms due to center-tapped transformer, coupled with the opportunity of reducing or enhancing the ripples by varying the filter capacitor and resistor, thus decreasing the discharge time and achieving almost constant voltage.

Fig. 5. Simulator with Bridge Full-Wave Rectifier.

IV. FEEDBACK FROM THE INSTRUCTORS As stated earlier, the course is compulsory. Accordingly, it is one of the highly populated courses in the University. The number of instructors who have taught this course, as a result, is sizeable. These instructors were asked by the authors to evaluate this e-learning product by filling a questionnaire accompanied with an informal interview for their feedback. The results of each question of the questionnaire, in terms of percentage response, are shown in table 1 below. The prime objective of this survey was to evaluate, in their opinion, the effectiveness of this e-learning product in the course. TABLE I INSTRUCTORS RESPONSE TO THE SIMULATOR

Percentage Response

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61 43 87 48 39 52 52 83 65 78

39 57 13 35 35 26 22 13 22 9

17 26 22 26 4 13 13

Strongly Disagree Disagree

Fig. 4. Simulator with Center-Tapped Full-Wave Rectifier.

is related to the course and lab supplements the course and lab enhances students’ learning has clear objectives increases effectiveness of the course has a suitable concept of help guides has appropriate language in text guides has a good quality of graphics has an easy navigation system has interesting animations & graphics

Neutral

1 2 3 4 5 6 7 8 9 10

Agree Strongly Agree

The DC Power Supply Simulator ….

-

-

The outcome shows positive response by the instructors. In their opinion, the simulator is very much related and has a very high potential of supplementing the lab material. There were mixed response as for the text guide impact is concerned; however most of them considered it to be a novel idea worth trying. The graphics and navigation of this elearning product was also considered to be suitable.

Following figure 8 shows the response of the students on navigation system of this e-learning product. 0.0 6.1

0.0

39.4

V. FEEDBACK FROM THE STUDENTS

54.5

This e-learning product was put to test for about three semesters. The students’ response was judged based on the changes in their motivation and overall learning on the topic. This response is evaluated mainly by student interviews, and questionnaire. During submissions of their assignments and lab work, the students were cross questioned about the core concepts and there was a significant enhancement in the students’ understanding. The responses during the interviews insinuate their liking of the idea and suggestions were made to have similar products for other lab experiments which may help them in their learning. The response, in terms of relation of this e-learning product to the course and lab material, was positive and is shown below in Fig. 6.

Strongly Agree

Agree

Neutral

Disagree

Strongly Disagree

Fig. 8. Quality of Graphics and Navigation System.

Response related to the use of such products was also encouraging. Students appreciated this e-learning product, and would like to see such types of products in other courses and labs. Their response is shown in figure 9. 30.3

0.0 3.0

0.0

0.0

3.0

0.0

15.2

66.7

Strongly Agree

Agree

Neutral

Disagree

Strongly Disagree

Fig. 9. Suggesting e-Learning Products for other Courses and Labs. 81.8 Strongly Agree

Agree

Neutral

Disagree

Fig. 6. Related to basic EE course and lab.

The students, in their opinion, suggested that the simulator has helped them in their learning and understanding, as shown in figure 7. A number of students revealed that this elearning product gave them the confidence to perform experiment without the fear of any possible failure or burning of lab equipment that happens otherwise resulting in material loss. 24.2

3.0

0.0

0.0

72.7

Strongly Agree

Agree

Neutral

Disagree

VI. CONCLUSIONS

Strongly Disagree

Simulation-based educational products have enormous potential as an active learning tool. Its use in engineering, management, and sciences education is common. However, the realization of its potential is on the rise. The authors still believe that the real momentum and focus to reap the benefits of this tool is yet to come, especially in engineering and sciences education. Although the concept of simulation-based educational products is not new in education, there is a great room available to increase its application in academics. This provides good opportunities for the research as well. From the instructors’ and students’ feedback, it is believed that this e-learning product has enhanced the students’ learning and understanding as well as students’ motivation by providing a hands-on experience in a virtual environment. This e-learning product has also augmented the application, analysis and decision making skills of the students. There can be few extensions to this product, such as; the virtual oscilloscope display can be improved with more realistic features and controls for signal display, and more complex combinations of rectifier and RC filter can be used.

Strongly Disagree

Fig. 7. Enhances Students’ Learning and Understanding.

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Such a product can be developed for an advanced level course in electronics. ACKNOWLEDGMENT The authors would like to acknowledge King Fahd University of Petroleum & Minerals for its support and funding in conducting this work. REFERENCES [1] [2] [3]

[4]

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

Randall Kindley, “The Power of Simulation-based e-Learning (SIMBEL)”, The e-Learning developers’ Journal, 2002. http://www.elearningguild.com/pdf/2/091702DES-H.pdf S. Carlson, “Can Grand Theft Auto Inspire Professors?” The Chronicles of Education: Information Technology, 2003. E. Ferre, Wai Shan Lau, Bee Ngo, Eve A. Riskin, Mani Soma, Richard Christie, Jennifer Harris, Laura J. Collins, Robert E. Lee, and Michael Campion, “Flash Animations in Introductory EE Courses”, IEEE Frontiers in Education Conference, November 2002. Uwe Drofenik, and Johann W. Kolar, “Interactive Power Electronics Seminar (iPES) - A Web-Based Introductory Power Electronics Course Employing Java-Applets”, IEEE Power Electronics Specialists Conference. Vol 2. N. R. Poole, “The application of simulators in teaching digital electronics”, IEEE Journal of Engineering Science and Education, Vol. 3, Issue 4, Aug. 1994 Page(s):177 – 184 S.G. Crutchfield, and W. J. Rugh, “Interactive Learning for Signals, Systems, and Control”, IEEE Control Systems Magazine, Vol. 18, Issue: 4, pp. 88 –91 (1998). R. Ubell, “Engineers turn to E-Learning,” IEEE Spectrum, Vol 37, No. 10, pp. 59-63, 2000. H. I. Ellington, A Workshop on Increasing Effectiveness as a University Teacher, Deanship of Academic Development, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia, 2002.

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