Gas station without pumps

2015 March 30

First day of S15 circuits class: demo failure

Filed under: Circuits course — gasstationwithoutpumps @ 16:23
Tags: , , , ,

I went into the class with a fairly short to-do list—much shorter than last year’s. I managed to cover the following:

  1. Went over syllabus .I showed them the syllabus and managed to go over scheduling of labs, partner work, and online texts, but did not get to some of the boilerplate about cheating and about disability services.  Oh well, it is enough that the boilerplate is on the syllabus.
  2. Demoed pressure sensor  with PteroDAQ on KL25Z board. I hooked everything up and it didn’t work. I fixed one problem of a loose wire (using the jeweler’s screwdriver, but it still didn’t work. I did manage to show them PteroDAQ and used gnuplot to show them a pressure trace I had recorded in the BME88A demo last quarter.
  3. Reading the book and doing design well before lab.
  4. Assigning reading due tomorrow and Thursday.
  5. Partners changing every week, so no one gets a free ride for very long and no one has to suffer with a freeloader.

I was thinking that I’d use the chalkboard a lot, so I used the small screen in the classroom (this classroom is ridiculously over-equipped with projectors, even having a project for a screen at the back of the classroom) rather than the big one, which covers most of the chalkboard. But I ended up using the projector to show them parts of the book and to use the document camera to show the KL25Z board and instrumentation amp protoboard, and barely used the chalkboard at all.

The rearrangement of the labs, with soldering on Tuesday, sampling and aliasing on Thursday, and the thermistor labs next week does give me a little leisurely start-up than last year, as I don’t have to get to Ohm’s law and Kirchhoff’s current law until the voltage-divider lecture on Friday.

Overall, I’m fairly happy with how the first day of class went, despite the demo failure.  I’ll debug the demo and show them either in lab tomorrow or in class on Wednesday.  I just hope I haven’t fried the instrumentation amplifier with static—they’re expensive and I don’t know whether I have any spares on hand.

Update 2015-Mar-30 17:58:  When I got home I checked out the board to figure out what might be wrong.  After probing for a while with the voltmeter, I determined that the wire that had come loose from its screw terminal and that I had fixed in class was not the only wire that had come loose.  The one next to it had also come loose.  It still looked ok, but wasn’t making contact.  Opening the screw terminal, reinserting the wire, and tightening it down again fixed the problem.



  1. It’s a little-know fact that ever electronic demo board includes an “inopportune moment” detector. Once the detector determines that the number of watching eyeballs exceeds the minimum threshold value–always greater than two–the detector triggers the deeply-embedded Murphyizer circuit to either render the hardware either completely useless or cause it to catch fire and eventually reduce to a smoldering heap. Of those monitoring the experiment, the threshold trigger value is inversely proportional to their stature, their seniority relative to the person attempting to demonstrate the circuit, or their ability to provide effective public ridicule.

    Comment by prevailingtech — 2015 March 30 @ 17:03 | Reply

    • The problem was another loose wire. Screw terminals are better than breadboards, but still subject to wires getting disconnected.

      Comment by gasstationwithoutpumps — 2015 March 30 @ 18:02 | Reply

    • I have got to cut and save this. I knew there had to be some reason at least half my intended demos fail miserably when attempting them before an audience.

      Comment by gflint — 2015 March 31 @ 09:43 | Reply

  2. This is clearly an example of Resistentialism.

    Comment by John Hassler — 2015 March 31 @ 06:19 | Reply

  3. Assign the syllabus as homework. Make it the first day’s reading assignment. Ideal for flipping the classroom. Send them a pdf before the first class if the “LMS” isn’t available before the first day of class. If needed, give them some actual homework on the boilerplate! (Short quiz in Canvas or whatever?) I try to limit class time to things like showing them how to access an on-line resource (what link goes to that link and others) or setting the tone for the class (active work in groups). But I do show them the calendar so they know what they have to do that first week for the lab, etc.

    Sorry about the hard luck with the demo, but I like that you will use diagnosis as a further demo. Might help them deal with their own frustration if you lead in with “Yesterday I learned to check EVERY contact!”

    Comment by CCPhysicist — 2015 April 5 @ 09:41 | Reply

    • I did redo the demo in the next class, explaining what had gone wrong. I also warned them that wires coming loose was an even bigger problem with breadboards than with screw terminals, and that they should check their connections carefully.

      I don’t use a learning management system (which is a good thing, because the one our campus provides has already had a couple days of outage in the first week of the quarter). I did send them the link for the syllabus ( and for the book (which I’m not making public yet) before the quarter started. I’ve also set up an e-mail group for the class, so that I can send them announcements and they can send each other questions or help.

      I’ve got enough homework to grade with a pre-lab assignment due every Monday and a design report every Friday. Even if they can’t behave like adults and read stuff when I tell them to, I’m not going to treat them like 9th graders and give them busywork quizzes. The pre-lab assignments will check that they’ve gotten the key ideas from the reading and can apply them to design problems. Which reminds me—I need to write the prelab assignments for the week 3 lab.

      Comment by gasstationwithoutpumps — 2015 April 5 @ 09:51 | Reply

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