Misconceptions in Electronics Design using Simulation Nissim Sabag1, Elena Trotskovsky2 and Shlomo Waks3 1
ORT Braude College of Engineering, Karmiel, Israel,
[email protected] ORT Braude College of Engineering, Karmiel, Israel,
[email protected] 3 Technion-Israel Institute of Technology, Haifa, Israel,
[email protected] 2
Abstract Lifelong learning is one of the prominent characters needed to a novice engineer during his or her career. With this in mind, educators in the engineering field should make strong efforts to rid their students of misconceptions. We believe that in professional work, the engineer will find it harder to overcome his or her misconception without external help. Consequently, helping the students to overcome misconceptions during the period of studies is very important because it can contribute to the maturation of novice engineers and assist them in their future career. Simulation is an efficient tool to help engineers and students in electronic circuits designing and testing. Nevertheless, circuits do not function in simulation exactly as in the real world. The article presents examples showing the potential danger of misconceptions generated by simulation. In the current study, we interviewed three teachers and twelve students, and observed the students’ activities while implementing their electronic circuits design using simulation. The results show that using simulation only leaves the student with the impression that the circuit designed correctly. The student might think that the simulation results are the same as real life results. The student's actively involvement straightens the misunderstanding and might turn it into misconception.
Keywords: misunderstandings, misconceptions, simulations, circuits design 1. Introduction During the past two decades, access to academic studies has increased. More and more engineering colleges are competing for high-achieving students to register. Consequently, there is a wide range of students today, in the sense of cognitive abilities and knowledge base, studying for engineering degrees. This diversity in abilities and educational background, accompanied by previous misunderstandings and misconceptions from daily life and intuitive ideas, place the engineering educators in the front line of the battle against mistaken interpretations of science and engineering knowledge by the students.
International Conference on Engineering Education and Research 1 July - 5 July 2013, Marrakesh
Engineering educators are in charge of helping the students to arrive at the correct understanding. Therefore, it is extremely important to find pedagogical ways to avert future difficulties that novice engineers may face after leaving university or college.
2. Research objective and question The research aims at making a contribution to the educational research knowledge concerning students' misunderstandings and misconceptions while using simulation. The following question was derived from the study objective: How do EEE students express these misunderstandings and misconceptions?
3. Literature review It was established that misunderstandings expressed by the students in the course of project design in synthesis and systems thinking (third classification level) are characteristic of most engineering disciplines. In what follows, we further describe educational literature research of project based learning and engineering systems thinking. 3.1. Misconceptions: definitions and roots According to the classical approach to errors and misconceptions [1], students come to class with early theories based on their daily experience, that is, with intuitive perceptions. Systematic errors in thinking are the results of these perceptions [2]. There are many definitions for the term students’ misconceptions. Cromley and Mislevy suggest that, "There are ideas derived from daily experience that students bring to their learning experience and that contradict scientific understanding and [are] often resistant to change” [3, p.3]. The most common term for students' prior ideas – misconception – emphasizes the mistaken character of prior knowledge. Still, a misconception can also be defined differently – e.g., as alternative conceptions, preconceptions and naïve beliefs. Different definitions "reflect differences in how researchers have characterized the cognitive properties of student ideas and their relation to expert concepts" [4]. Researchers use other terms to describe similar phenomena of misunderstanding: phenomenological primitives or p-prims [4], naïve conceptions [5], intuitive [6], or naïve knowledge [7]. Regardless of which definition is the correct one, all these terms refer to students' prior knowledge, which is inconsistent with or contradicts the new scientific knowledge that they are learning. As a result, this situation causes cognitive conflict and conceptual change. 3.2. Misconception in science and engineering education Smith, diSessa and Roschelle’s study [4] defines the main directions taken by educational research of misconceptions during the past twenty years. Most studies in this field aim at identifying various misconceptions in numerous science and engineering disciplines. For example, misconceptions in the following areas were widely researched: classic mechanics [5, 8], quantum mechanics [9], light [10], International Conference on Engineering Education and Research 1 July - 5 July 2013, Marrakesh
magnetic induction [11], floating and sinking [12]. Even the University of Dallas has posted on its website a guide to enhancing conceptual understanding that includes a list of preconceptions and misconceptions in all areas of physics [13]. Also, the report of research on students’ misconceptions describes huge numbers of misconceptions in eleven conceptual areas of chemistry [14]. On the other hand, the research of misconceptions in engineering disciplines is less advanced and developed [15]. Usually, such research deals with identifying specific misconceptions in concrete topics; for example, highlighting an individual’s misconceptions on electrical circuits [16]; or misunderstanding of the concepts of frequency response in signals and systems [16]. Group of researchers studied various engineering students’ misconceptions in digital electronics: misconceptions about the flip-flop state [17]; misconceptions about medium-scale integrated circuits [18]; misconceptions about number representation [19]. 3.3. Simulation and misconceptions The use of simulation to assist statistical learning was investigated in [20] and it was revealed that a simulation tool could correct the students’ misconceptions and enhance their understanding. Nevertheless, the authors admit that tool is not beneficial to all learners. In [21], the use of computer simulation of basic fluid flow and heat transfer processes to correct misconceptions and improve learning of engineering principles was investigated. The studies above dealt with the advantages of using simulation to overcome misconceptions. In the current paper, we bring some examples showing that simulation might the source of some misconceptions.
4. Method The participants in the study were 12 students studying for a B.Sc. degree in electrical and electronic engineering and three lecturers. We present examples of the students’ work. They were involved in designing small projects as one of the requirements in the framework of a digital electronics laboratory. Our purpose was to understand their way of thinking. The nature of this activity dictated using qualitative tools. Therefore, the students' work was observed and videotaped, their final reports were analyzed, and the students were interviewed. The lecturers were also interviewed. All the data collected was coded so that the students names were replaced by S1-S12 and the lecturers were coded as L1-L3.
5. Results The students designed small projects using a simulation program (Multisim). The Multisim emulates an electronics lab. It enables the use of virtual, or so called "real" components and the use of virtual measuring equipment. The simulation has advantages such as ease of use, simplicity of building and debugging electronic circuits, clear and colourful representation of experiment results, and others. Nevertheless, the program has some serious disadvantages. Some components can function without connection to
International Conference on Engineering Education and Research 1 July - 5 July 2013, Marrakesh
power supply; this could cause a dramatic misconception in the student’s mind as demonstrated in that following student-lecturer conversation: S1 asked for the lecturer's help:. It doesn't work. I don't know why. L1: Did you check the supply voltage? S1: Why, is it important? L1: Of course it's important. Without supply voltage, the circuit will not function.
The citation above shows an example in which a student really believed that an electronic circuit can operate without power supply. Another example is the case of open input in digital components. Using TTL (Transistor Transistor Logic) digital components dictates the connection of all the inputs to a known binary level '0' or '1'; otherwise, the component might malfunction in some instances. The simulation refers to the open inputs as a '0' level, thus a misconception may be born. The next case is about two students (S2, S3) who performed their first small project using real components. The circuit included a three-inputs-OR gate but used only two inputs and neglected the third one. The OR output showed a constant '1' level regardless of the inputs combination. The same circuit acted correctly in simulation but not with real world components. The students asked for the lecturer's (L2) help as reproduced in the conversation below: S2: It doesn't work. S3: Look, the output is always '1' even though we put '0' in the inputs. L2: What do you think is the problem? S2 and S3: The OR gate is damaged... we have to replace it. Despite the students' wrong answer, the lecturer let her students to replace the component with a new one; of course, it did not help. L2: What do you think now? S2 and S3: We don't know. L2: How many inputs are in your gate? S2 and S3: Three L2: And how many of them are you using? S2 and S3: Two. The conversation went on, but the students did not use any of the lecturer's clues till, at last, the lecturer said, “You left the third input open; it's not allowed, especially with the TTL family.” S3: But we did the same with simulation and it worked then …
As we can see from the example above, the students found it hard to believe that the open input affected the circuits operation. This is the way that misconceptions are created. A well-known requirement in the digital world is the compatibility of logic levels when a mixture of digital families is in use in the same circuit. For example, an output logic level '1' is represented by voltages in the range of 2.7V–5V for the LS-TTL family (Low-power Schottky TTL is a subfamily of TTL), while the input voltage level of logical '1' in the CMOS (Compatible Metal Oxide Semiconductor) family is greater than 3.5V. So, in case of connecting a TTL output gate to a CMOS input gate, there might be a mismatch that causes a malfunction. As a result, this type of connection is not allowed when using real components. Yet, the Multisim simulation allows such a connection.
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An example of a student's small project with such a mismatch is presented here. Students S4 and S5 performed complementary projects; S4 designed an F/V (Frequency to Voltage converter) and S5 designed a V/F (Volt to Frequency converter). In the final presentation, the output of one project was connected to the other project's input, so the input and output of the chain of projects can be easily compared. Student S4 used an AND gate (7408N) and three NOT gates (7404N) of the TTL family and a binary counter (4024BP) of the CMOS family, as shown in Figure 1. The real circuit did not function, of course. S4 asked for the lecturer's help. To give a clue, L2 asked S4, "Do you know about different logic levels in the TTL and CMOS families?" S4 answered, Yes, I learned about that. I learned that in Digital Electronics. But I did not think that it is significant. Different logic levels did not concern me. I have not encountered this problem.
It did not concern the student even though she had previously tested the same circuit with Multisim simulation.
Figure 1: Part of a Frequency to Voltage Converter demonstrating a mixture of TTL (7404 gates) and CMOS (4024 counter) components
An additional example of electronic circuit malfunction in reality, yet relatively correct operation in simulation described below. One of the most important problems in digital electronics is the timing problem. Thus, D flip-flop has two input signals – a data input D and a Clock input. For positive edge-triggered D flip-flop (data input D can affect the output only on the rising edge of the clock signal), the signal in D input must be stable a certain time before and after the positive edge of a clock signal. If signal D changes during this time interval, the output might not be appropriate. The main problem concerning the timing issue is that simulation components have constant propagation delay time, whereas in practice, the propagation delay changes randomly within a given interval. Student S6’s mission was to develop a Manchester code Encoder. The student used D flip-flops, among other components in his design. In this case, we focus on the timing issue, as presented in Figure 2, and ignore the incorrectness of the designed code. International Conference on Engineering Education and Research 1 July - 5 July 2013, Marrakesh
Figure 2: Timing diagram of S6's encoder
The two illegal spikes on the output signal are emphasized by ellipses; as seen in Figure 2, the D flip-flop's input changes exactly on the clock's positive edge. In the first ellipse, the output is a spike while in the second ellipse, the output varies constantly. Nevertheless, the simulation supports simultaneous changing of data and clock in different ways. When asked by lecturer L3, the student S6 explained this phenomenon as follows: I sample the data every positive edge of the clock. Here, in this point (ellipse 1), clock sees '0' in the data, so output is '0'. Here, in this point (ellipse 2), clock sees '1' in the data, so output is '1'. The circuit works; that is the fact.
In fact, S6 displayed more than a single misconception. First, he ignored the different responses of the circuit in the first and second ellipses; second, the propagation delay is on a scale of tens of nanoseconds, and the signals presented in Figure 2 are about thousands of times longer. The student had to change the measuring scaling he made his conclusion.
5. Conclusion The well-known phrase is ascribed to Karl Marx, "Practice alone constitutes the criterion of truth." We find it most appropriate to our case in which we want to put in a right proportion the importance and the limitations of using simulation in engineering education. Simulation has many clear advantages such as ease of use, simplicity of building and debugging electronic circuits, clear and colourful representation of experiment results, and the ability to create extreme conditions that cannot be tested in the real world. Running a simulation is the initial stage in the project design process in industry. Yet, the real world outcomes are the only results that count. In this paper, we have described examples showing that students who designed projects using simulation first, failed in performing the same circuit with real world components. The understanding acquired by using simulation blocked the students' ability to overcome their misconceptions. The most extreme example is S6 who insisted, "The circuit works; that is the fact." Some disadvantages of using simulation that can cause development or reinforcement of students' misunderstandings and misconceptions were presented. We recommend to our colleagues not to use simulation alone in engineering education. Actual experiments from the real world as well as design projects should be integrated into engineering education. We also suggest that it is the teacher's role to enlighten the students about differences between simulation and real world outcomes. International Conference on Engineering Education and Research 1 July - 5 July 2013, Marrakesh
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