Gas station without pumps

2013 March 20

Bar exam for circuits class

Filed under: Circuits course — gasstationwithoutpumps @ 13:45
Tags: , , , ,
Front of T-shirt

Front of T-shirt

Back of T-shirt.  The silkscreen is intended as a white silkscreen over a black T-shirt.

Back of T-shirt. The silkscreen is intended as a white silkscreen over a black T-shirt.

Because the applied circuits course did not have a final exam, the students asked if we could get together at a bar for a beer during the exam time instead (which my son quipped should be considered a “bar exam”).  Because we had some underage students in the class, I chose Caffe Pergolesi as a site (they serve beer but also coffee, hot chocolate, and coffee-house snacks).  The café was surprisingly crowded for 4 p.m. on a Tuesday (probably due to it being the first day of exam week), and I had to sit out on the deck, because there were no tables available inside.  At first I was a bit worried that no one would show up (a common problem for parties I’ve tried to have in the past, so I’ve stopped attempting to have parties), especially when no one was there by 4:10.  But the students started trickling in and we eventually had all the students in the class—even those who had sent e-mail saying they couldn’t make it.

I showed the students the T-shirt design, modified according to their suggestions the day before, and they approved it.  I still need to check with the screen printer that the SVG files I have will work—I think that the back is ok (it is a single black rectangle for the T-shirt with a single path for the white layer on top), but I’m worried about the front. The text, slug, and small thought bubbles should be fine, but the black images on the large thought bubble are currently objects on top of the white thought bubble, and I’ve not figured out how to get Inkscape to make them cuts through the thought bubble to the black T-shirt underneath.  The Inkscape “path difference” operation, which worked for the back of the T-shirt doesn’t do the right thing with these images.  So far I’ve gotten 7 orders for T-shirts from the class (including one for me and one for my son), and I’m hoping for another 5 or 6 to amortize the setup costs.  I think that we’ll have about $90 in setup plus $12/shirt, so 7 shirts would be about $25 each and 12 shirts would be about $20 each (long sleeve shirts a couple of bucks more).

I used the time to get feedback from the class about how it should be modified in future, starting from a handout I’d given them the day before.  Here are some of my notes from the discussion.  If I’ve missed anything, I hope that students will send me e-mail.

  • Parts and tools to eliminate:  velcro cable ties (unused), long-nose pliers (low quality and not used), thermometers (change to lab equipment), LEDs (not used).
  • Parts and tools to add: inductor for class D amplifier, soldering iron.  A soldering station like the one I have (and similar to the ones they used in the lab this year) would add $20 to the cost of the course.
  • It may be worthwhile upgrading the screwdriver set, as the under $2 set was really low-quality and some of the screwdrivers failed (blade slipped in handle, so that screwdriver did not turn with handle).
  • I had been worried about the high price for the large assortment of resistors ($13.35 for 1120 resistors, 10 each of 112 sizes), but the students liked that they always had whatever resistor size they needed, and were contemptuous of the approach used in EE101 of providing students with only about 20 resistors of the precise sizes that the faculty had decided the students would use.
  • One student suggested having a protoboard for designing the class D amplifier, since that is something they might want to keep.  I’ll have to think about that, as it doesn’t strike me as an immediate win, though I can see wanting to keep the power amplifier.  One problem is that the class-D amplifier is not as generic a project as the instrumentation amplifiers, so it is harder to come up with a general-purpose protoboard. Also, most students ended up having to do a lot of experimenting to get the biasing to work out for the power FETs, which could be difficult on a PC board.  The class-D amplifier also needs a bit more space than the two instrumentation amp projects, so a PC board for it would have to be bigger ($2/board instead of $1/board).  Having the same protoboard for both the pressure-sensor lab and the EKG lab meant that time spent learning how to use the protoboard was amortized over two projects, which would not be the case for a special-purpose power-amp board.
  • One student suggested adding a voltmeter for home use, but the problem there is that voltmeters that can read AC voltage correctly for 100kHz signals are mostly in the $100-and-up range.  The $5 voltmeters that could be put in a kit for everyone to buy are not useful for some of the labs.
  • Students suggested that the first quiz should be given as homework instead of a quiz—a good idea, since the questions were too hard for the students as a quiz, and having time to think about them and discuss them with each other would lead to more learning.
  • The students do not think that adding a textbook to the class would help, but being directed to the All about Circuits readings more often (including the worksheets) might help.  They generally found the Wikipedia articles too detailed and too broad to be helpful in learning the material.  They got fairly good at at searching the web for keywords and finding lecture powerpoints from other courses that were relevant.  No one found a steady source of good material though—the searches tended to find different sources for each topic.  The students reported being able to find data sheets fairly easily and consulting them fairly often, so at least one of the goals of the course was met.
  • One student reported that soldering the instrumentation amp for the pressure sensor lab seemed a bit pointless to some, as they don’t buy the pressure sensors to connect to, so a permanent board is not much use. The benefits (soldering practice and less noise pickup from long wires) may not justify the extra effort of soldering.
  • We discussed re-ordering the labs, moving the electrode measuring and modeling lab later, and the sampling and aliasing lab earlier.  A possible new order is
    1. Thermistor
    2. Sampling and aliasing
    3. Microphone
    4. Audio amp
    5. Hysteresis oscillator
    6. FET and phototransistor
    7. Electrode modeling
    8. Pressure sensor
    9. Class-D power amplifier
    10. EKG

    That order could cause some difficulty for the sampling lab, which needs RC filter design (hence complex impedance), so maybe swapping the mic and sampling labs would be better.

  • We also discussed the idea of having 2 labs a week (both Tuesday and Thursday), with a data analysis day in between (to teach gnuplot scripting and fitting models).  None of the students had done model fitting (other than straight lines) in any other course, so this is a skill worth spending a bit more time on in class.  Having 2 105-minute labs a week (the standard TTh time slot) would probably not be enough, as that is barely more than the 3-hour lab weekly lab this quarter, and the setup time would probably eliminate any gains.  I’d probably have to schedule 2 time slots per lab (say 10–1:45, 2–5:45, or 6–9:45).  If the course grows to full size, I would be spending 8–12 hours in the lab on Tuesdays and Thursdays, without break.
  • If I do have more lab time next year, I could start a little slower, using the first week to have students learn to identify all the parts, mark the capacitor bags with the capacitor sizes, learn to use the ohmmeter and power supplies, … .  Some of the later labs would have no more time than this year, but some of them needed no extra time.
  • Students would like several explanations to come earlier in the course relative to the labs—FETs before the microphone lab, PN junctions and phototransistors before the tinkering lab, block diagrams earlier in the course, … .  I agree, and moving the first labs a week later could help with that.  I’ll be doing a day-by-day topic planner before resubmitting the course approval paperwork.  One problem with teaching block diagrams earlier is that—like outlining in writing—they’re really only useful once the complexity of the design gets high enough that subdividing the problem is useful.
  • The students were pretty pleased with the data logger software that my son wrote.  The biggest complaint was about the logger freezing when recording a long run at high sampling rate (a known problem).  I believe that he is developing a fix for that problem, which will generally result in faster live charts.  Students also like the idea of being able to produce eps, pdf, png, or svg output directly from the data logger, so that they didn’t feel the need to make screenshots.  Providing starter gnuplot scripts (which they could then add to in order to do model fitting) was also attractive to them.  There was one request for icon-based executables (avoiding the command line), but I actually prefer for engineering students to have to learn to use command-line tools—I was shocked that they had gotten to their senior year and had not learned how to use command lines.
  • Students thought that the current prereqs for the course were fine—they did not see a need to add a programming prereq, unless the course was changed in a major way to include Arduino programming (which I’m not tempted to do, as there are already courses on campus covering that).  They did think that the course needed to remain an upper-division course, but that sophomores might be able to handle it by the Spring (which is when it will be scheduled in future).
  • Some students thought that the course could be reduced to 9 labs (from 10)—mainly to reduce the number of reports written.  I think that we could achieve that by putting the microphone lab and audio amp lab together and having 3 lab sessions with only one report.  We might be able to combine the hysteresis lab and the tinkering (FET and phototransistor) lab into one report also.
  • The students really liked the undergrad group tutor we had—saying that he was the best TA they’d ever had.  I believe that he is graduating this year (as are all the students in the course), so I don’t know whether we’ll be able to get as good an assistant next year.
  • Students liked having learned gnuplot, though they initially struggled with it and hated it.  Once they got past the initial learning, they found it useful for senior theses and courses other than the circuits course.
  • Overall, students thought that the class had met most of the learning goals I had set for it, and several of them wished the course had been available to them earlier—some of them might even have opted for the bioelectronics track (they were all biomolecular track), had they taken this course early enough (and if EE would accept it as prereq to the other upper-division courses needed for bioelectronics).  I’m certainly going to try to convince the EE faculty that this course can serve as more than adequate preparation for courses like signals and systems (better than the existing circuits course).

The students in the class gave me two bottles of wine as a thank-you for the course—that is a first for me in 30 years of being a professor.  Most often students are glad to have survived my courses, but don’t generally appreciate them until several years later.

The student appreciation certainly isn’t because I’ve been grading leniently—the class is mostly in the B- to B+ range, and some had to go through 2 or 3 drafts of the lab reports to get to even that level. There may be one or two A- grades (I still have the last 2 lab reports to grade, so I don’t know yet—I’m hopeful, but I’m not going to give out As unless the work justifies them).

I think that the recognized that I was genuinely interested not just in the material but in getting them to do real engineering design and to think like engineers.  Several have taken to heart the “try it and see” mantra and have learned to appreciate the value of “sanity checks”.  I think that the value of a UC education lies mainly in these high-contact “artisanal” courses, not in the mega-lectures and cookbook labs that they have mostly been suffering through.  (To be fair, many of them are working on senior theses in various faculty labs, so they have had high-contact educational experiences—just not structured as a required course.)



  1. […] of the student suggestions from the “bar exam” was to design a protoboard for the class D amplifier, so that they could keep it as a permanent […]

    Pingback by Triangle-wave oscillator | Gas station without pumps — 2013 March 23 @ 23:09 | Reply

  2. […] previously recommended that students get a cheap soldering station like the one I have, and even recommended that the […]

    Pingback by Broken soldering iron | Gas station without pumps — 2013 September 17 @ 11:51 | Reply

  3. […] to do a design like the ones I’ve done for other classes (see Cyberslug t-shirt designs and Bar exam for circuits class), but the students seemed more interested in coming up with their own design (which I see as a good […]

    Pingback by Fifteenth day of freshman design seminar | Gas station without pumps — 2014 March 3 @ 19:57 | Reply

  4. […] of the students asked about the circuits-class t-shirt I was wearing, and I explained that I’d created the shirt for last year’s class and […]

    Pingback by First day of S14 circuits class went ok | Gas station without pumps — 2014 March 31 @ 21:22 | Reply

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