Circuits I & II suggestions.

Discussion in 'General Electronics Chat' started by WBahn, Jul 12, 2013.

Mar 31, 2012
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Okay folks, here is your chance!

I will be teaching both a Circuits I and a Circuits II section this next semester. I am soliciting suggestions on specific tidbits that you think should be touched on in these courses but that frequently isn't.

These courses, at this school, are basically as follows:

Circuits I (EENG281):
Level: Sophmore
Prereqs: Physics II (Intro E&M)
Description: This course provides an engineering science analysis of electrical circuits. DC and single-phase AC networks are presented. Transient analysis of RC, RL and RLC circuits is studied as is the analysis of circuits in sinusoidal steady-state using phasor concepts. The following topics are included: DC and single-phase AC circuit analysis, current and charge relationships, Ohm's Law, resistors, inductors, capacitors, equivalent resistance and impedance, Kirchhoff's Laws, Thevenin and Norton equivalent circuits, superposition and source transformation, power and energy, maximum power transfer, first order transient response, algebra of complex numbers, phasor representation, time domain and frequency domain concepts, and ideal transformers. The course features PSPICE, a commercial circuit analysis software package.

Circuits II (EENG382):
Level: Junior (but many take it as a sophomore)
Prereqs: Circuits I and Diffy-Q
Description: This course provides for the continuation of basic circuit analysis techniques developed in EENG281, by providing the theoretical and mathematical fundamentals to understand and analyze complex electric circuits. The key topics covered include: (i) Steady-state analysis of single-phase and three-phase AC power circuits, (ii) Laplace transform techniques, (iii) transfer functions, (iv) frequency response, (v) Bode diagrams, (vi) Fourier series expansions, and (vii) two-port networks. The course features PSPICE, a commercial circuit analysis software package.

Things to note:

1) The courses only deal with linear systems, so no diodes or transistors at all; those are introduced in a parallel course to Circuit II.

2) There is no hands-on laboratory component associated with either course (there use to be, and I am not happy that there no longer are). So it is, sadly, simulation based.

3) The Circuits I course is a multisection course with common homework and exams, thus I have very limited flexibility to make changes. But I can certainly include a limited number of small, related topics to help motivate practical, real-world thinking.

4) The Circuits II course is a single-section course and so I have a much greater degree of control and flexibility.

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Because there does not seem to be a lab component of any kind, one of the things I am thinking of doing is at least demonstrating live circuits in class on a regular basis. The problem here is that the classes will be held in another building and so I need to haul over any equipment that I would need.

I am thinking about getting a reasonably cheap USB scope so that I can use the projector to display the scope traces. Anyone have any recommendations? It would be wonderful to find something that has a function generator, at least two channels, a few programmable voltage outputs, a few ADC inputs (for multimeter type measurements), and perhaps some digital I/O. I don't care too much about bandwidth since I can tailor the demos to match the capabilities.

I'm also willing to give up features, especially if I can end up with something cheap enough that I can recommend it to students that it might be something worth investing in. Part of my goal is to get them to develop an interest in hand-on electronics, especially since it is being squeezed out of formal engineering education.

2. tracecom AAC Fanatic!

Apr 16, 2010
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What a shame!

3. Gibson486 Active Member

Jul 20, 2012
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woah....your circuits and I and II is usually just circuits I in other universities and colleges....

4. LvW Well-Known Member

Jun 13, 2013
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Hello WBahn,

I have not too much teaching experience for the subjects in circuits I.
However, I have for circuits II. Therefore, I have some recommendation:

1.) With the aim to demonstrate the relation between time and frequency domain I think it is very instructive to show that the denominator of the transfer function for second-order frequency-dependent circuit in the s-domain (like filters) is identical to the characteristic polynomial in the time domain. Thus, one can emphasize the meaning and the importance of the Laplace transformation.

And you can show that the roots in the time domain are identical to the system poles in the frequency domain.
In this context, I know from my experience that many students have problems in visualizing the meaning of a „pole“. In particular, why such a mystery like a „pole“ gives a corner frequency for s=jw.
More than that, sometimes students are confused because they do not know when
they have to use s=sigma+jw and when simply s=jw.

2.) In context with Laplace-transformation, complex frequency plane and Bode-diagram it would be fine if you could also treat some basics about feedback (reasoning, advantages, disadvantages) and stability of feedback systems (Black`s formula, Nyquist plot). However, this requires some knowledge about active devices (opamps) - perhaps an ideal amplifying block (VCVS) would be sufficient as a first step.

3.) By evaluating Black´s formula and the various feedback alternatives it would be a logical step to derive the oscillation condition (loop gain) and to introduce the basic concept of a feedback oscillator.

________________

The above thoughts just came into my mind reading your question. may be I have some additional subjects later.
Regards and good luck
LvW

5. LDC3 Active Member

Apr 27, 2013
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It is limited to about 20kHz since it uses the sound card, but you can use WinScope as an oscilloscope. It will make the projection easier since it is in real time. Most USB scopes store the data and then transfer it since the transfer usually takes longer than the acquisition.
Of course, you can always use an USB camera to video a real oscilloscope or data analyzer.

6. wayneh Expert

Sep 9, 2010
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An incredibly useful tool that is rarely taught is "secondary" knowledge; knowing how certain you can be about what you think you know. Weather forecasters get daily feedback and become humble quickly. They tend to be the best profession at knowing how well they know what they think they know. Physicians tend to be the worst, having absurdly high levels of confidence when in fact there is great uncertainty.

An experienced practitioner learns that simulations and models have limits, and that lab measurements are imperfect and can cause artifacts. But I've had new technicians think that reporting a pH value to 3 or 4 decimals reflects their great skill in the lab. Good grief.

It's a complex topic to convey and I don't know how you teach humility to young college engineers. It's not something they are used to thinking about, having been the "smart kids" in school for their whole lives to date.

I think a series of fun exercises - maybe call them the Friday Foolers - where you draw them all in to make the same mistakes due to their hubris, would be a memorable message.

7. LvW Well-Known Member

Jun 13, 2013
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Yes - agreed, This reminds me that in analog electronics no formula is really "correct" - nearly everything is an approximation only (a capacitor is not a pure capacitor, a resistor has capacitive properties,...). Of course, this applies to active elements in particular. Insofar, all the symbols we use for these elements are also "models" only with neglected imperfections.

And it is one of the most important tasks for an engineer to know for each application if the used equations/formulas are allowed to be applied or not.

Typical examples to be found in textbooks (often without mentioning the application limits):
*Gain of a common emitter stage G=-Rc/Re
*Gain for an inverting opamp: -R2/R1.

8. tshuck Well-Known Member

Oct 18, 2012
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The lack of an associated lab class is terrible, that was where I truly learned the concepts...

Perhaps showing the limitations of the simulator/theory would help the students understand that ideal components do not exist. I didn't see anything on op amps, but showing a finite frequency response was something that sent things home for me.

I think the demonstrations would be a great idea to supplement the lack of hands-on experiments.

In any case, good luck!

9. GopherT AAC Fanatic!

Nov 23, 2012
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This points to the need for a discussion on component tolerances and "Error Budget" in any circuit design. It doesn't have to be a lecture or homework, just sprinkle it in during each lesson. The students will catch on that it is a "way of life" for an engineer, and not a one-time lesson.

And thermal effects/drift associated with electrical devices of all types.

It is also a good time to discuss metrology, accuracy and precision

In other words, don't let anyone leave your class thinking they can put a 100k resistor in parallel with a 1 ohm resistor to make a 0.99999 ohm resistor.

10. DerStrom8 Well-Known Member

Feb 20, 2011
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My obvious answer would be Ohm's Law (and Watt's Law), but I would also include things like calculating wire resistance from cross-sectional area and length (can come in handy), basic component descriptions (primarily resistors, current sources, and voltage sources for circuits I, and throw in capacitors, diodes, and maybe even transistors to a degree in circuits 2), brief discussion of transformers, motors, and generators. Also I recommend looking at Thevenin and Norton, superposition (simple ones, of course), and things like that.

During my time working at the university I was able to observe some of the classes that came in the lab, and these were some of the things they discussed. Also I recommend encouraging frequent breadboard use and experiments, to verify that calculations are correct. Teaching how to use DMMs, O-scopes, waveform generators, and the like would be a great skill for them to learn as well.

The key is to expect that they are coming in without knowing a thing about electronics, since that tends to be the way it is these days.

Good luck!
Best wishes,
Matt

Mar 31, 2012
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FYI: The text is "Electric Circuits" by Nilsson & Riedel, 9th Ed. My reviewing of the text thus far leaves me with mixed impressions. One thing that I know I am going to hate, but I fully expected it, is that the authors are sloppy with their units and omit them in most of their examples within the work and just tack them on at the end. But, I'm used to dealing with that. It will take about the first month for the students to realize that I am serious about units and another month to develop the habit. In the second half of the course they will be pretty good at tracking their units without even thinking about or realizing that they are actually doing so.

Mar 31, 2012
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I don't know about "usually". Everyplace I have been affiliated with uses one course for introductory circuits and a separate course for transform methods. Plus two more courses in electronics that focus on transistor circuits. But I am not surprised that some universities would choose to combine these into a single course, though I imagine they don't cover all of these topics, at least not to the same depth, and either cover them elsewhere or leave them out entirely. In fact, the authors of the text we are using, which has 18 chapters, map out some options for single-semester coverage that leave out either four or five chapters.

Mar 31, 2012
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For the most part (not completely) these are Circuits II issues. One of the things that I am real big on is insisting that students understand where the relationships and techniques come from and not just how to apply them as a cookbook recipe. I agree that all of these things are points that are very hard for many students to get their minds wrapped around, and so will be frequently drawing their attention to the links between these concepts.

I don't know how much I will be able to do with feedback concepts. They take an entire course in feedback control systems just after Circuits II and they deal with feedback and stability in the Electronics course (transistor circuits). We do cover introductory opamps, but a quick glance through the book doesn't seem to deal with stability considerations at all -- might have overlooked it, but I don't think so. The text appears to only focus on ideal opamps and only devotes a bit over two pages to a "more realistic model" of the opamp. That model adds input resistance, output resistance, and finite openloop gain -- nothing more. But, I now that this is addressed in much more depth in the electronics course when the students are in a much better position to actually see where these non-ideal behaviors come from and how to account for and mitigate them. So I'm not too concerned about the introductory nature of the coverage in this course.

I seriously doubt I will be able to talk about oscillators at all in either course. Again, these are addressed (but not all that deep) elsewhere in the curriculum.

Mar 31, 2012
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I don't have a problem with being limited to 20kHz on the upper end. But I think that being limited to 20Hz on the lower end (i.e., being AC coupled) is going to be very restrictive since many of the things I will want to demonstrate will be DC circuits.

But it is definitely worth considering, at least as part of the solution. Thanks.

Mar 31, 2012
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As anyone that has seen very many of my posts knows, I have two big rules that I always drive home:

1) Always, always, ALWAYS track your units.

As part of #2, I expect students to make estimates of what they expect the answer to be, including some kind of uncertainly bound. It's too cumbersome to require that they demonstrate this on every problem they work, but I generally do so on nearly every example problem I work in class and also have homework and exam problems that are intentionally too hard to work in a reasonable time frame and all they are asked to do is to estimate and/or bound the expected result.

I also expect students to check their answers and they lose points if they don't.

I strive to always use realistic component values in examples and problems that I come up with (which I could say the same for most authors). I also generally restrict myself to standard component values. I generally require that they memorize the E24 series of multipliers and be able to derive their ideal values mathematically based on the concept behind them.

Out of curiosity I just tested myself to see if I could write down the E24 sequence, something that I have not done for probably twenty years. The only one I missed was 16.

I give many problems in which they have to design a circuit to achieve a particular goal. First they come up with the mathematical values, but then I require that they use E24 values. I also require that they do worst case analysis. Related to this I have them to sensititivity analyses to determine which components need tighter component tolerances and which ones can be loosened up. This is much easier to do with transistor circuits, but I can still get them in the habit of knowing how to do it and enough practice at it that they aren't afraid to do so.

In the vein of your Friday Foolers, I try to give out "cookie problems" in which I give them a non-trivial problem, often with a twist, and give a big cookie (like a 12" chocalate chip cookie from a local bakery) to the first person that turns in the correct answer with correct justification and reasoning. I will also throw up interesting problems in class for discussion and solution.

Mar 31, 2012
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This school has always had a reputation for having more hands-on practical lab and field learning opportunities than most other schools. Sadly, even though many of the labs have been replaced by simulation exercises, this is probably still the case because most other schools seem to have gone down this road just as fast or even faster.

It's a trend that I hate and that I think is short-sighted and that does a serious disservice to the students. If anything we need extensive hand-on experiences even more than before because of the fact that fewer students are entering the curriculum with a personal passion for the field gained as a hobbyist (such as a ham background) and, instead, are coming in with no background and no interest at all but only because they've been led to believe that and engineering degree is a ticket to a big paycheck.

But I have another arrow in my quiver on this point. I am involved with a group of hardcore techies that meet on campus weekly and I offer weekly help sessions that just happen to bump up into those meetings in the same room. Few students take advantage of the help sessions once they figure out that I'm not going to just show them step-by-step how to work their homework, but a few do and they often get interested in the techie meeting.

The Circuits I course covers opamps in a pretty rudimentary way. I don't know to what degree opamp circuits are utilitzed in Circuits II (in the text), but I will almost certainly add them here and there if they aren't.

17. amilton542 Active Member

Nov 13, 2010
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An introduction to Lagrangian Dynamics so as to model electromechanical systems.

Mar 31, 2012
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That, I can guarantee, is NOT going to happen.

Why do you think that an sophmore/junior introductory circuits class is the appropriate place to introduce Lagrangian dynamics? It would strike me as being better situated in a dynamics course or a controls course.

19. MrChips Moderator

Oct 2, 2009
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I can't say that I have memorized the E24 series.
I can say that I have not only memorized the E12 series but I can decode the color code of any value in the E12 series in the same way I can interpret Morse code by just hearing the sound byte, as an example.

I can't really give much advice on the Circuits I and Circuits II content because it seems we don't go into that much depth as your courses.

Our courses put more emphasis on the practical side of electronics and the laboratory experience is essential. I have seen efforts underway to eliminate labs but that would be a fatal error. I would quit teaching instantly.