Gas station without pumps

2016 June 14

Things to do for book

Filed under: Circuits course — gasstationwithoutpumps @ 15:24
Tags: ,

I’ve finally finished my grading for the quarter, after a solid week of grading, and so I can now catch up on some of my administrative tasks (like checking the articulation framework documents, trying to find an undergraduate director for bioengineering for Fall quarter, checking the 30 or so senior exit portfolios, and so forth).

I can also start thinking about the tasks for me on revising my book, which will take up big chunks of summer and fall:

  • Move the book files into a source-code control system, probably mercurial, and use and off-site backup, probably BitBucket.  I should have had the files in a source-code control system from the beginning, but I never got around to setting it up.  This is a couple of years overdue, and I shouldn’t make any more updates to the book until I’ve done it.
  • Rearrange book to put labs in new order, moving all the audio labs into the second half, and moving the instrumentation amplifier and transimpedance amplifier into the first half.
  • Revise parts list for next year’s labs.
    • May want to use a different phototransistor (without the filter that makes it less sensitive to visible light).
    • Choose nFET with lower threshold voltage (maybe pFET also).
    • Find better resistor assortment.
  • Add hobbyist add-ons to the labs, for people who want to go beyond what we can do in class.  For example, I could add
    • designing a triangle-wave generator to the class-D amplifier, so that it can be self-contained,
    • sound input from a phone jack to class-D amplifier (with info about TRRS plugs)
    • logarithmic transimpedance amplifier for optical pulse monitor, to make it tolerant of different light levels and finger thicknesses
    • optical pulse monitor using reflected (actually back-scattered) light instead of transmitted light, so all the optics is on one side
    • motor controller based on H-bridge used in class D
    • temperature controller using thermistor, FET, and power resistor
    • galvanic skin response measurement?
    • oscillator design other than Schmitt trigger relaxation oscillator?  Maybe a Colpitts oscillator with the big inductor (though even with 10μF and 220μH, the frequency would be rather high for audio use)?
    • make Schmitt trigger out of comparator chip
    • EMG controller (either with analog envelope detection or with software envelope detection)
  • Insist on LaTeX for design reports.  I had too many reports with terrible math typesetting, incorrect figure numbering, and bad font substitutions with Microsoft Word or Google docs reports.  I’ll need to include a short tutorial in the book, with pointers to more complete ones.
  • Make it clear in the book that design reports build on each other, but each report needs to be self-contained—for example, the class-D amplifier report should contain circuits, results, and some discussion from the microphone, loudspeaker, and preamp labs; and the EKG lab report should include some information from the blood pressure and pulse monitor labs.
  • Add more background physics and math at the beginning of the book, to review (or introduce, for some students) topics we need.
  • Should I add a short lab characterizing the I-vs-V curve for an nFET and a pFET?  If so, where would I fit it in?  What about for a diode (could be LED)?
  • Bypass capacitor discussion should be moved to between the preamp lab and the class-D lab.  I need to talk more about power routing and location of bypass capacitors for the class D lab (it is important that the bypass capacitors be between the the noise-generating FETs and rest of the circuitry, which is noise-sensitive).  May need to introduce the concept of the power wiring not being a single node, so that “clean 5V” and “dirty 5V” are different nodes.
  • Class-D lab should have students measure and record the amount of current and power that their amplifier takes with no sound (removing the mic?) and with loud sound input, both with and without the LC filter.
  • Class-D lab should require students to show oscilloscope traces of the gate and drain of an nFET and of a pFET in the final H-bridge, both for turning on and for turning off.
  • EKG, blood pressure, and pulse monitor prelabs should have students compute the attenuation of 60Hz interference (relative to the signal in the passband) for low-pass filters that they design.

I should also review what students had to say about the course (look at discussion in previous post, for example).



  1. IMO, the best tutorial for LaTeX is to provide a sample file. In your case, that would be a “lab report” that uses each of the features you expect them to use, including some typical equations (both in-line and display). The tutorial should also tell them how to export the figures that you showed how to include in your LaTeX input, for each auxillary program you have them use, and include what the output is going to look like from that file. For me, the steepest part of the learning curve was all the junk at the top and bottom of a LaTeX file. Writing in it is easy once you have that.

    My other suggestion is that I-vs-V for a diode (both ideal and real) makes sense as part of the background physics. It is something we sometimes, but rarely, do in my intro lab class so I doubt they have seen it. (Check with your physics department.) Do you have a first week that doesn’t accomplish much, where you could do a resistor and an LED and then extend it to include a FET? Once you have the setup for one, the rest is straightforward.

    Comment by CCPhysicist — 2016 June 19 @ 18:40 | Reply

    • Students have told me that they do very little in the Physics E&M lab with electronics, and I’m pretty sure that they don’t do I-vs-V plots of any components (not even resistors).

      The first week the students are learning to solder and adding headers to their microcontroller boards, so there isn’t time then.

      If I rearrange the course to put all the audio stuff in the second half of the course, then I need to replace the microphone lab in the first half with something else. I could do I-vs-V curves for an LED then, but I need something for them to learn to use the oscilloscope. Juggling all the different threads of what they need to learn so that they can get enough lab skills and enough theory to do the design work is very tricky!

      I probably should include a boilerplate LaTeX design report—probably not in the textbook, but pointed to by the text. I’ll probably need to rewrite one of my blog posts (not one too closely related to class lab project) as a design report in the style I expect.

      Exporting PDF from SchemeIt and is pretty simple, but gnuplot installation to get PDF output is still a mess of awkward dependencies.

      Comment by gasstationwithoutpumps — 2016 June 22 @ 10:52 | Reply

      • Yes, starting with the objectives and working backward is the key, and labs are always complicated by the tradeoff between skills (thank God we don’t teach them soldering!) and theory only complicates things (some of our labs lead lecture, more in some semester calendars than others). My only advice is to consider which ones are the highest priority, that is, either the ones you want/expect them to retain or the ones you need them to use. That is what our chemistry group did when they redesigned their lab, because they had to discard labs some to make room for what they wanted to accomplish, and I am thinking along the same lines. My trend is toward a “just in time” approach where a skill is encountered one week in a simple lab and then applied the next in a more complicated lab. Probably not good for long-term retention of what they learn, but effective from a time-management standpoint.

        Comment by CCPhysicist — 2016 June 26 @ 09:18 | Reply

        • I have several different constituencies even within the bioengineering major, with different interest levels and different essential skills. A big part of the problem is balancing the objectives, rather than tweaking the course design to meet a fixed set of objectives.

          I want all the students to get design experience and a lot of technical writing feedback—two things that engineers always need more of. For the biomolecular concentration students, those are the only essential objectives, but they are very important, as biomolecular work is so slow that they get little design experience in their other courses until their senior design project. The debugging practice is particularly important, as most students are not used to having to figure out what they did wrong—they expect teachers to point out their mistakes to them. If they want to be productive as engineers (or almost any other white-collar profession), they need to learn to identify and correct mistakes themselves, not waiting for someone else to do it for them.

          The bioelectronics and assistive technology: motor students have more direct use for the content of the course—I’ve tried to make every lab relevant for one or both of those concentrations. I’m also trying to give the students enough of an intuitive understanding of complex impedance and voltage dividers that the applied math of standard circuits course makes sense to them—they were struggling with it a lot when it was their first introduction to electronics.

          For all the students, I want them to get an understanding of a number of cheap hand tools (wire cutters, wire strippers, long-nose pliers, soldering iron, calipers, micrometer, … ), and a sense that they can make things themselves. If I can get a third of the students to be electronics hobbyists (or makers of some other sort), I’ll be well pleased.

          The “just-in-time” component of the course for me is giving them just enough theory to be able to do the design projects. Lab skills are mostly used over and over (fundamental ones like using multimeters or soldering) or only once (micrometer, drill press, … ).

          Comment by gasstationwithoutpumps — 2016 June 26 @ 10:57 | Reply

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