# Gas station without pumps

## 2012 June 20

### Another way to think about course design

Filed under: Uncategorized — gasstationwithoutpumps @ 00:27
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Continuing the series about designing an applied electronic circuits course for our bioengineering majors (with more project ideas and another project idea), I want to talk about another lab-oriented view of what we want the course to teach—what lab skills they should have by the end of the course. Eventually, I’ll get around to textbook-concept view of the course, but I’m trying to stay away from that for a while, since the course we are trying to replace was faulted for being far too theoretical.  I want to start with the practical goals first, and work out form there what are the most important theory topics and what order they should go in.

Again, this is all very preliminary brainstorming—I have to talk with my co-instructor about what lab skills are feasible to teach in the class, which ones he sees as essential, and which are beyond the scope of the class.  Here is a tentative list of technician-level skills that every engineer should have:

• Reading voltage, current, and resistance with a multimeter.
• Using an oscilloscope to view time-varying signals:
• Matching scope probe to input of scope.
• Using triggering.
• Reading approximate frequency from display.
• Measuring time (either pulse width or time between edges on different channels)
• Using a bench power supply.
• Using a signal generator to generate sine waves and square waves.  Hmm, only the salinity conductance meter uses an AC signal so far—I may have to think of some other project-like labs that need the signal generator.  Perhaps we should have them do some capacitance measurements with a bridge circuit before building a capacitance touch sensor.
• Using a microprocessor with A/D conversion to record data from sensors.
• Handling ICs without frying them through static electricity.
• Using a breadboard to prototype circuits.
• Soldering through-hole components to a PC board.  (I think that surface-mount components are beyond the scope of the class, and freeform soldering without a board is too “arty” for an engineering class.)

There are probably a lot more skills to add to this list, which I haven’t thought about yet, and details within these skills that I’ve not thought about.  Luckily, my co-instructor has been teaching beginning students how to use electronic lab equipment for over 15 years, so I’m sure he knows what needs to be covered.

The bigger problem here is motivating students to want to develop these skills quickly—the EE and computer engineering students see the skills as directly related to their chosen profession, but the bioengineers will need to know why anyone would care about resistance, voltage, or current.  Getting a simple biosensor in right from the beginning would probably help.  I wonder if we should start with a thermistor lab for resistance, voltage, and current measurement.  How soon can we cover voltage dividers, so that they can design a resistance-to-voltage converter for interfacing to the ADC on an Arduino? Can we do that in the first lab?

1. [...] The relevant posts so far are Changing teaching plans More on electronics course design Yet another project idea Another way to think about course design [...]

Pingback by More musings on circuits course: temperature lab « Gas station without pumps — 2012 June 20 @ 13:13

2. [...] The author of Gas Station Without Pumps has posted this thought-provoking list of technician-level skills every engineer should have: [...]

Pingback by Technician-level skills every engineer should have « Shifting Phases — 2012 June 20 @ 18:36

• Thanks—your thoughts on the technician-level skills is helpful to me. (I imagine that Steve, who has taught the use of this equipment forever, could do it in his sleep, but I still need to think about what I want the students to get.) I think you’re right that chip resistors are not too hard to solder (though I do find them significantly harder than through-hole parts). Gull-wing parts are not too bad also (I did some soldering of pressure chips this year). But we have only 10 lab sessions of about 3 hours each, so I don’t want to spend a lot of time having the students learn to solder. They are mainly going to be bioengineering students, so soldering will not be a frequent task for them later on.

Comment by gasstationwithoutpumps — 2012 June 20 @ 20:11

3. I like to have students test sensors early — it builds a bridge between abstract “invisible” concepts like voltage, and real-world experiences like sound, light, and heat. The one that seems to make the biggest impression on my students is sound, maybe because recording and audio-processing apps have previously introduced them to the electrical “picture” that sound makes. Having them talk into a mic and see their own voice on the scope seems to be a powerful way to help them internalize electrical concepts in a hurry. The same is true of connecting a signal generator to a scope, then to a speaker — it’s as if they don’t fully “believe” that electricity can make sound until they hear the difference between a sine wave and a square wave.

I’m looking back through your project ideas and it doesn’t look like there are any acoustic applications. Is it worth considering something like an electronic stethoscope? It would motivate the use of an amplifier as well as a signal generator for test signals.

Comment by Mylène — 2012 June 21 @ 20:57

• Just realized that I had intended to answer your post’s final question, but never did. Students might be ready to make sense of a voltage divider on the first day, but probably would not be able to build it independently. There are a lot of new skills at play: figuring out the layout of the breadboard, remembering which leads go with what, making sense of a meter, remembering how to connect the meter, using hand tools and hook-up wire, conventions about notation on a schematic and values on components, etc. A couple of scaffolding ideas: set out the experiment nearly complete at each lab station, and have the students make one or two modifications. Or, make a step-by-step screencast and have students follow the directions (if you have computer workstations at each lab station). They will have little ability to troubleshoot if things don’t work, so you will probably be doing a lot of running around. It might be a good opportunity to compile a list of common troubles, to be used in another class to brainstorm about how to troubleshoot.

Another thought: I assume they will need to read and maybe sketch simple circuit diagrams. Translating between a circuit diagram and a breadboard circuit requires visual-spatial skills that are very challenging for a lot of my students (especially if the breadboard is not laid out in the same orientation as the diagram). If they have taken a previous E&M course that used circuit diagrams and simulation software, they may be frustrated to find that something they thought they knew well now seems foreign. If you gave them a built circuit and asked them to sketch it, it would probably yield useful information about their spatial skills and/or electrical misconceptions.

Comment by Mylène — 2012 June 21 @ 21:10

• I like the idea of having students draw schematics from breadboards, but I think that we might want to do that as homework before the first lab, using color photos on the web of some simple layouts. Of course, it depends on what day of the week the lab is scheduled, whether we will have any time before the first lab.

If we have resistors in the pictures, it will give them practice at the resistor color code also.

Comment by gasstationwithoutpumps — 2012 June 22 @ 11:38

• I will add a stethoscope to the list of possible projects—that’s a good thought. I’d not thought about starting the oscilloscope lessons with talking into a mic. We’d have to think a bit about what sort of mic to use. Perhaps the simplest would be to have a small loudspeaker that could be used for either generating sound or as a mic.

Hmm, cheap loudspeakers seem to be hard to find. I can get electret microphones for about 75¢ each (CUI Inc CMA-4544PF-W, from DigiKey), but they need a power supply and a series resistor. I happen to have one of these cheap electret microphones, and just tied hooking it up with a 4.7kΩ series resistor and a nominally 5v wall wart. It works fine, but the ripple from the wall wart is huge (about 50 mV) and the signal from the microphone is only about 200mv. Adding an RC filter to the power supply cleans it up, so I think the students would not have much trouble with the much cleaner outputs from their bench supplies.

Comment by gasstationwithoutpumps — 2012 June 22 @ 11:35

• That’s the same mic I use. My students seem to get a kick out of using various signals — their voices, their MP3 players, some of the test-tone generating apps that are available for smartphones.

Comment by Mylène — 2012 June 22 @ 15:41

4. [...] a previous comment, I had remarked on the difficulty I was having finding cheap loudspeakers.  I did a little more [...]

Pingback by Speakers and function generator « Gas station without pumps — 2012 June 23 @ 12:54