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2018 April 1

Starting new quarter

Filed under: Circuits course — gasstationwithoutpumps @ 17:20
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Tomorrow the new quarter starts, and I hardly feel like I’ve had a break—I was grading continuously through Monday, working on my book through Friday, and setting up Canvas with all the assignments today. I also spent several hours this week reading course syllabi and student petitions for the Committee on Courses of Instruction meeting that is tomorrow afternoon and a little time reading senior thesis proposals from students wanting to start senior theses next quarter.

It probably doesn’t help that I’m on the third week of a cold—it has settled down to being a minor cough, but it is still making me more tired than usual and interfering with my sleep (the cough is worse when I’m lying down).

There is a new draft of Applied Electronics for Bioengineers posted—those who have already bought the book should have gotten an e-mail about the free update.  The minimum price for the book has gone up by 1¢, as Leanpub now has a $5 minimum, and I had set my book at$4.99 minimum.  There are not many changes this time, because I did not have a lot of writing time last quarter:

• Beefed up the chapter on lab report guidelines.
• Many typo and minor wording fixes (mainly ones reported by students in class).
• Replaced Waveforms 2015 references with Waveforms 3, due to name change by Digilent.
• Added paragraph to thermistor lab about doing design around standard parts.
• Also added specific discussion of using parallel resistors for current sensing in power-amp lab.
• Added the missing section on high-pass active filters.

By being somewhat generous on my grading for the final lab report, I managed to keep the number of failures for Winter quarter down to two—one flaked so much that all five labs had resulted in the partner requesting doing separate lab reports and the other did not do the last lab.  This is about the usual failure rate (2–3%). Still, I was not happy with how many C grades I had to give—I’d like to see a higher distribution Spring quarter.

Several of the students in my course had previously taken EE101 (circuits) or were taking it concurrently.  I checked, and there was essentially no correlation between the EE101 grade and the grade in my course (Kendall tau correlation about -0.03 for not-taking/taking and +0.07 for grade among those who took—neither is a statistically significant relationship with p-value>0.64).

I think that what would make the biggest difference in the grades is better writing from the students—many of the lab reports were a struggle to get through, with poor organization, poor paragraphing, poor grammar, poor word choices, poor punctuation, and poor formatting.  Only about 10% of the class was writing at a level I would consider acceptable for college students, and I’ll be stressing writing more in Spring quarter.

The grading last quarter was stressful, and I expect it will be again this quarter.  Grading at home during finals week resulted in me putting on five pounds—I kept rewarding myself with snacks after getting through another couple of papers.  I’m hoping that I can get the students to write a little better and a little more tersely this quarter, so that the grading will be less stressful (and I can take the weight off again).

I’m hoping that I can convince more of the students to get out of answer-getting and point-scoring mode (see Just scoring points) on the quizzes and rework any problems they get wrong—I’m tired of asking essentially the same question in quiz after quiz and having students still miss it.

2017 September 22

Spike in views on Monday

Filed under: Uncategorized — gasstationwithoutpumps @ 12:06
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I had double my normal readership on Monday 18 Sept 2017, which surprised me as I had not put out any posts recently.  I checked the statistics and found that the bump was mainly from one post: Engineering vs. Science, which got 173 views on Monday and 185 all week.  The referrals were from classroom.google.com, so apparently someone required reading the post for a class—I’ve no idea who, as the classroom links are somewhat anonymous (I have links, but would need to be in the class to follow them).

Because of that class assignment, the  Engineering vs. Science post is my most viewed site this week and this month, though not for the quarter—three others still beat it:

It always surprises me which of my posts become the most popular.  The top 10 for the past year were

The “home page” hits are large because all new posts read by subscribers get counted there. The next 9 are all posts with original content by me (unlike some of my all-time most-viewed posts, which were mainly pointers to other things on the web).

2017 February 25

More writing advice from the electronics course

Filed under: Circuits course — gasstationwithoutpumps @ 20:13
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I spent the entire long Presidents’ Day weekend grading and still did not clear my backlog (the cold I’ve had for the past two weeks has really reduced my ability to work long hours).  I did get a homework set graded and a design report set graded during the 3-day weekend, but I was left with a set of 18 redone lab reports that I still hadn’t gotten to.  Wednesday produced another set of redone reports (so I now have about 35), and Friday produced another homework set (which I just finished grading after spending all Saturday—I haven’t even gotten dressed yet and it is almost 8pm). Tomorrow I’ll tackle the first set of redone reports, assuming my cold lets me do anything tomorrow.

In Disappointment with chain stores, I commented on no longer wanting to grade in the Peet’s coffee shop I used to grade in, and commenter “Mike” wanted to know what solution I came up with. This winter, I’ve mainly been grading in my breakfast room at home, using a tiny laptop (an 11″ MacBook Air, which we bought for travel and for lecturing) when needed to look things up (data sheets, my solution sets, the exact wording in the book, …).  This has worked out ok this year, though I do tend to wander into the kitchen for snacks a bit too often.  Still, the snacks at home are healthier than in a coffee shop!

Here are some general comments that I shared with the whole class, based on the most recent design reports:

Content:

Many students reported using a 3.3V power supply without measuring it, resulting in inconsistent information, such as VOH > 3.3V.  PteroDAQ reports the power-supply voltage on the GUI and in the metadata for the data file, so the data was available, even if the students hadn’t thought to measure it while in lab.

Formatting:

• Equations are parts of sentences, not figures and not objects dropped randomly on the page. Treat them grammatically as noun phrases.
• Explicit figure credit is needed any time a figure is copied or adapted. The caption must say something like “figure adapted from …” or “figure copied from …”. Failure to do so is plagiarism, and I’ll have to start academic integrity proceedings if students fail to do proper figure credits in future.
• Don’t bury the lede. Start with the design goal, not with generic background. A lot of students still wanted to give me a bunch of B.S. about what hysteresis was, before telling me that they were designing a capacitive touch sensor using a relaxation oscillator built around a Schmitt trigger.

Grammar:

• The subjunctive mood marked by the auxiliary verb “would” is used for many things in English, but technical writing primarily uses just one: contrary-to-fact statement. “The inverter that we would be using” says that you didn’t use that inverter and are about to say why. A lot of students seem to think that “would be” is some formal form of past tense—they’ve seen it in writing, but never understood what it means.  I fault their middle-school English teachers for not stressing the importance of more advanced grammar than the bare minimum, but the fault could have been corrected in high school or in college composition classes, but still persists.
• Students are still using way too much passive: “It was decided …” should be replaced with “We decided …”.  Part of the problem here is that much of the writing they are exposed to overuses passive also—excessive passive is a common writing error for scientists and engineers, not just students.

Wording:

• “Firstly”, “secondly”, “lastly” ⇒ “first”, “second”, “last”. These are already adverbs and don’t need an “-ly” ending.  Strangely, I never see the corresponding problem with “next”, though it is in the same class of words that are simultaneously adjectives and adverbs.
• There are a lot of words that are compound words as nouns, but separable verb+particle pairs as verbs. For example, “setup” is a noun, but “set up” is a verb. Other examples include layout, turnaround, pickup, putdown, stowaway, flyover, and setback.
• Avoid the unit abbreviation mm2, as it is too hard to tell whether you mean m(m2) or (mm)2. Most often, the (mm)2 interpretation will be made, but a lot of students used it for m(m2).  (Same for cm2.)
• Many students are using “proportional” wrong, for any increasing function. The phrase “f proportional to d” means f=kd for some k, not just that f increases with d. Similarly, “T inversely proportional to d” means T=k/d for some k, not just that C decreases with d.

Punctuation:

• Capitalize at beginning of sentence and proper names only: “Schmitt trigger” not “Schmitt Trigger”, “Figure 3” but “many figures”. Figure names, table names, and equation names are proper nouns, so should be capitalized: “There are three figures on the last page: Figures 4, 5, and 7”.
• Unit names are not capitalized (hertz, volts, amps, …), but symbols for units from people’s names are (Hz, V, A)
• Hyphenate a noun phrase used as a modifier for another noun: “Schmitt-trigger inverter” but “Schmitt trigger”.

2017 January 29

Filed under: Circuits course — gasstationwithoutpumps @ 22:14
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I just spent my entire weekend grading 37 design reports for the thermistor lab—it has not been a fun weekend.  The coming week or two will be grading hell, as I have homework due for the 72-person class Monday, Wednesday, and Friday (with another lab report due next Monday), and no grader or TA.

This lab report was the first of the quarter, so there were a lot more problems with the submissions than I expect to see on future lab reports.  I’ve tried to collect some of my notes on the more common writing errors for this blog post, with the intent of trying to work them into the chapter on lab reports in the textbook:

• Some students had wordy introductions. I want reports to start with a clear, concise statement of the engineering goal, not a dump of any random factoid that might be vaguely related to the report.
• Report should be standalone—not referring to homework. If something in the homework is needed, incorporate it!
• Use paragraphs with one topic each. Every paragraph should start with a topic sentence, and the rest of the paragraph (if there is any) should support and amplify that topic sentence. It is better to have one-sentence paragraphs than to ramble from topic to topic without a paragraph break.
• Fit your model to your data, not your data to a model. You should never be changing your data to make it fit your theory—you should be changing your theory to fit your data.If you say you are fitting your data to your model, you are claiming to commit scientific fraud.
• Best-fit curves are not necessarily lines—students don’t have a “line of best fit” in this lab, because the models we’re fitting are nonlinear.
• Figure captions should be paragraphs below figure, not noun phrases above figure. Any anomalies or interesting features of the figure should be pointed out in the caption.  Most of the crucial content of the report should be in the figures and captions, because that is all 90% of readers ever look at in a science or engineering paper.
• Refer to figures and equations by number, rather than “schematic below” or “equation above”.
• Don’t use screenshots for schematics or gnuplot output—export graphics properly as PDF files and incorporate them into the report so that they can be printed at full resolution even when scaled.
• Many students use way too much passive voice.  Using passive voice is a way to hide who did something or deny responsibility (see Nixon’s “mistakes were made”) and should not be necessary in a design report.
• Use past tense for things that have been done, not present tense.  Also, “would” is not some formal version of the past tense—it is a marker for the subjunctive mood in English, which has a whole lot of different uses.  In technical writing, the most common use of subjunctive is for “contrary to fact”.  If you say “I would put the thermometer in the water”, I immediately want to know why you don’t—I expect to see the sentence continue with “, but I won’t because …”
• “Software” is an uncountable noun, which means that it can’t be used with the indefinite article “a”.  There are a lot of uncountable nouns in English, and there isn’t much sense to which words are countable and which aren’t—even closely related languages with similar notions of countable and uncountable nouns mark different nouns as uncountable.  I’ve only found one dictionary that marks countability of English nouns—the Oxford Dictionary of American English, which is available used for very little money.
• Equations are part of a sentence (as a noun phrase), not random blobs that can be sprinkled anywhere in the paper.  No equation should appear without a textual explanation of its meaning, and the meaning of its variables.
• There was a lot of misuse of “directly proportional” and “inversely proportional”: A directly proportional relationship plots as a straight line through zero. The voltage output in the thermistor lab is not directly proportional to temperature—it is increasing with temperature, but the function is sigmoidal, not linear.  Similarly, an inversely proportional relationship between x and y is a direct relationship between 1/x and y. It plots as a hyperbola. The resistance of a thermistor is not inversely proportional to temperature, as the resistance is proportional to $e^{B/T}$  not $B/T$.
• Read the data sheet carefully!  A lot of students claimed that their thermometers were good to 150°C, but the data sheet said that the thermistor they were using had a maximum temperature range of  –40°C to 105°C, not 150°C.
• Students need to use the right metric prefixes.  For example, “kilo” is a lower-case “k” not an upper-case “K”.  This becomes even more urgent for “micro” (µ), “milli” (m), and “mega” (M).  At least one report needs to be redone because the students claimed a value around 200MΩ, when they (probably) meant 200mΩ.  What’s a factor of a billion between friends?
• Some students are clearly not used to using the prefixes, because I saw a lot of values around 0.0001kΩ, which should have been written 0.1Ω (or even 100mΩ).  Even worse, a lot of students just wrote 0.0001, with no indication what the units were (that triggered a number of “redo” grades on the reports).
• “Lastly” is not a word—”last” is already an adverb. The same goes for “first”, “second”, and “third”. Perhaps it is easier to keep this in mind if you think of “next”, which is in the same class of words that are both adjectives and adverbs. For some reason, students never write “nextly”.
• The ×  symbol (\times in LaTeX) is only used for crossproduct, not for scalar multiplication (except in elementary school). The normal way to show scalar multiplication is juxtaposition of the variables, with no operator symbol.
• “Before” and “after” make no sense in the voltage divider circuit. You can sometimes use those terms in a block diagram that has a clearly directed information flow from inputs to output, but not for talking about the two legs of a voltage divider.

2017 January 7

Book draft 2017 Jan 7

Filed under: Circuits course — gasstationwithoutpumps @ 17:03
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I’ll be releasing an updated version of the Applied Electronics for Bioengineers text on LeanPub today.  I’ll probably raise the minimum price next week, to reflect the improved quality, but I’ll give people a few days to get the book at the old price.  (Remember that the LeanPub model allows you to get all future editions of the book free, as long as I continue publishing through them, so there is no reason to wait until a new edition comes out.)

I’ll list the changes in two sections: changes that were made since the October 2016 release, then changes that were made in the Oct 2016 release (because I don’t seem to have posted those to the blog).

Changes since October 2016

• Fleshed out assignment schedule and moved to Preface.
• Rearranged several of the early chapters (without significant content change) for better ordering of assignments.
• Added mention of Analog Discovery 2 to oscilloscope chapter, replaced some Bitscope traces with Analog Discovery~2 traces.
• Added bonus frequency response activity to pressure sensor lab.
• Added Lego-brick pictures for the optical-pulse-monitor lab.
• Revised all chapters and labs from the microphone chapter to the EKG lab (the second half of the course).  Many of the changes were minor revisions (typo fixes, indexing, changing to numbered exercises, spell check).
• Added exercises to the microphone chapter and moved some exercises from the microphone lab to the microphone chapter.
• Moved some of the oscilloscope introduction from the microphone lab to the sampling lab.
• Rewrote DC analysis of microphone to use function generator, rather than potentiometer, for variable voltage.
• Added R+L figure to loudspeaker chapter, rather than referring to impedance chapter.
• Moved inductor description to new chapter just before loudspeakers.
• Added RMS power exercise and R-L plot exercise to loudspeaker chapter.
• Moved some intro amplifier material from preamplifier lab to pressure-sensor lab, reflecting change in order of labs.
• Moved some instructions about color coding wiring from preamplifier to an earlier lab.
• Added mention of using earbuds instead of loudspeakers for preamplifier lab.
• Redid Miller plateau oscilloscope trace using Analog Discovery 2, using smaller gate resistor to get higher speed.
• Added cross-section of a power nFET (still needs to be redrawn)
• Fixed clipping on several schematics (the Vdd power symbol gets clipped if at the top of the schematic—a known bug in SchemeIt).
• Put inductive load in the single-nFET driver schematic, including flyback diode.
• Added explanation of why the crude model for computing slew rate is so far off.
• Removed most references to obsolete AOI514 nFETs (using NTD4858N nFETs instead).  This required gathering new data to characterize the transistors.
• Redid the section on open-collector outputs for LM2903 comparators.
• Added table of conductivity for NaCl solutions.
• Added section on 4-electrode conductivity measurements.
• Moved information about nulling ohmmeters when measuring resistance from electrode lab to loudspeaker lab.
• Reiterated some of the EKG safety info in the EKG lab.

Changes between April 2016 and October 2016

• Added more background to first chapter (logarithms, picture of complex plane) and started chapter numbering at 1 instead of 0.
• Rearranged chapters for new lab order, with all the audio labs after the pressure sensor and optical pulse monitor.
• Updated information on using lead-free solder.
• Added a generic block diagram to lab report guidelines, and added definition of “port” to the block diagram discussion.
• Added subsection on Thévenin equivalent of voltage divider.
• Added section on series and parallel connections to resistance chapter, to reflect lower prerequisite expectations of course.
• Moved some gnuplot exercises into thermistor lab from sampling and aliasing, to reflect new lab order, also moved PteroDAQ installation instructions.
• Added picture of metal thermometer to thermistor lab.
• Added voltmeter connection schematic to DAQ chapter.
• Moved details of PteroDAQ out of DAQ chapter to separate appendix.
• Added potentiometer schematic and photo to resistance chapter.
• Split data acquisition from sampling and aliasing into separate chapters.
• Improved figure showing aliasing and Nyquist frequency.
• Added pictures for wire stripping and flying resistors to sampling lab.
• Added scaffolding for oscilloscope probe exercise.
• Hysteresis measurement changed to use function generator.
• Moved multi-stage amplifier discussion to beginning of amplifier chapter and beefed it up.
• Added introduction to differential amplifiers before instrumentation amps and op amps.
• Added pH meter block diagram to beginning of amplifier chapter.
• Moved discussion of clipping to the end of the instrumentation amplifier section.
• Added active low-pass filters to amplifier chapter.
• Added chapter on transimpedance amplifiers with section on log-transimpedance amplifiers and rewrote pulse-monitor lab to use logarithmic current-to-voltage conversion.
• Added discussion of absorbance of melanin, fat, and water to blood section.
• Moved the instrumentation amplifier internals to new chapter, before the EKG chapter.
• Simplified the sensitivity calculation for LEDs and phototransistors, making the exercise more productive.
• Added text to caption of microphone preamp photo.
• Moved loudness section from the amplifier chapter to the microphone chapter.
• Added notes at end of loudspeaker lab to improve student reporting of models.
• Added more safety information to EKG chapter
• Made all exercises be numbered, and changed most of the prelab questions into numbered exercises.
• Added equipment-needed lists to the beginning of each lab.
• Redrew several block diagrams using draw.io, and added captions to several figures to indicate what drawing tool was used.
• Changed caption formatting to be more distinctly different from body text.
• Cleaned up several schematics.
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