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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.

Having undergrad graders in Spring quarter rather than a TA may help, as I have a couple of very competent undergrads who can provide writing feedback on the prelab assignments in a timely fashion.  The foreign TA I had last quarter took a long time getting feedback to students and was not really able to provide writing feedback—not a bad TA for an EE course, but not up to the heavy grading demands of this course.  The graders will be grading the homework and the prelab assignments, but I’ll still be grading the quizzes (which only take about 2–3 hours a week to grade) and the final lab reports (which will take about 150–200 hours to grade for the 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 August 19

Progress on my book

Filed under: Circuits course — gasstationwithoutpumps @ 16:05
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I have been slogging through the book, updating it to include feedback I got on it from students and notes I had made on grading assignments, and revising the labs to use the Analog Discovery 2 rather than conventional bench equipment.

I was a little disheartened when I noticed that I’ve just finished updating through Lab 3, out of the 12 labs. That looks like I’m only a quarter of the way through the rewrite, when I had hoped to be almost halfway by now. When I look at it in terms of pages, though, I’m much further along—I’ve revised through page 142, and there are 360 numbered pages before the references (not counting the 37 Roman-numeral pages), so I’m about 40% of the way through the rewrite. That’s a little behind schedule, but not terrifyingly so, especially since it is the beginning labs that needed the most changes to convert to using the Analog Discovery 2.

There are still 132 to-do notes scattered through the book, some of which are in sections I’ve counted as “done” for the summer, so I’m not going to run out of work on the book any time soon.

The PDF file is currently at 411 total pages, with 179 figures (203 distinct images, as there are some figures with subfigures) and 13 tables. It is up to 22.8Mbytes, which I could probably reduce by a few MBytes by better compression of some of the JPEG figures.

I’ve previously thought that it would be good to be able to make paper copies of the book available to students (see Textbook should be on paper), but the print-on-demand services seemed too expensive.  I was apparently not looking at reasonable services, as IngramSpark’s “print-and-ship” calculator says I can now get a single copy (perfectbound paperback, standard color, simplex cover) for about $24 (including shipping and sales tax).  Ordering 50–100 copies doesn’t reduce the price much (still $20 a copy—all the reduction is in shipping).  Unfortunately, their “weight and spine width” calculator says that my page length is out of range for an 8.5″×11″ book, but if I reduce my trim size slightly (t0 8.25″×10.75″), I can print with them and the cost is about a dollar more.  (There may also be an initial setup charge to create the book the first time, including things like getting an ISBN.)

If the book gets much fatter, I’d have to switch to a smaller trim size, which would make the book fatter still, and the increase in the number of pages would increase the cost.  I think that a 7″×10″ trim (which would allow up to 1140 pages) would cost about $3.50 more than an 8.5″×11″ book for the same content, assuming that I reduced the margins and the text block, but didn’t change font sizes.

Paper books through distribution channels are expensive: to get $4 a book (about what I get from the $5 e-book sales through Leanpub), I’d have to have a list price of about $42 a book based on IngramSpark’s publisher’s compensation calculator.

2017 July 22

Logos no more

Filed under: Uncategorized — gasstationwithoutpumps @ 11:19
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On Thursday this week, I spent most of my afternoon waiting in line to check out at a bookstore.  The main used-book store in town, Logos, is going out of business after 48 years and they have started their closing sales (which will probably last another month or two).  Thursday was the first day of their sale, and though prices were not particularly low (20% off their usual prices), a lot of people wanted to mourn the passing of the bookstore (and use up their store credit before all the “good” books were gone).  The result was so many people wanting in that the fire marshal insisted on a rule that a person could only enter the store when one left.  But the wait to get in was not all that bad (about 30 minutes)—the delays were in checking out, as the store had only four registers in operation and none of the cashiers had ever been trained for speed (bookstores gain more from social interaction at the register than from high-speed transactions).  I was in line to check out for about an hour, and my wife, waiting in the other line, was in line for about 3 hours.  Most of the 125 people that the fire marshal permitted were waiting in one or the other checkout lines.

Here is how the Sentinel started their article  Logos, a beloved Santa Cruz bookstore, falls victim to a changing retail economy:

For the first time since the summer of the moon landing, Santa Cruz will soon be without Logos, the used-book emporium that has been part of the downtown landscape since the days of the Pacific Garden Mall.

In about six weeks, after a long everything-must-go liquidating sale, Logos will shut its Pacific Avenue doors for good.

John Livingston, the store’s owner and operator for its entire 48-year run, said that he put the store up for sale a year ago. Facing little interest and no serious offers, as well as sharply declining revenues, he has decided to close his business.

Since the rebuilding after the 1989 Loma Prieta earthquake, the anchor businesses downtown have been Bookshop Santa Cruz near the north end of Pacific Avenue and Logos near the middle.  (More recently, Cinema 9 has also drawn a lot of people downtown.)  The rest of the businesses are mostly a mix of surf shops, boutiques, gift shops, and eateries.  (After dark, only the restaurants and bars are open, and the highest crime rate in the city seems to be about closing time for the bars downtown.)

For a while around the turn of the century, Santa Cruz was the chief battleground between independent bookstores and chains (the owner of Bookshop Santa Cruz was the president of the Independent Booksellers Association and both Crown Books and Borders opened stores in downtown Santa Cruz with the avowed intent of crushing Bookshop Santa Cruz—both are gone, but Bookshop Santa Cruz remains).  Logos was mostly ignored in this fight, as there were no large chains trying to get into the used-book business, which has long relied on customer browsing, impulse purchases, and store owners who know both their customers and their stock—not a business that scales well.

Between a third and a half of my over 3000 books have come from Logos, and they have been where I’ve sold back my surplus and duplicate volumes.  A bookstore that primarily sells new books (like Bookshop Santa Cruz) may be better for authors, but browsing the stacks of a used bookstore for books that are long out of print or undeservedly forgotten is a pleasure that cannot be duplicated by on-line shopping.  I’ve bought a few books online, when I knew precisely what I wanted and it wasn’t available locally, and I’ve bought new books from Bookshop Santa Cruz, but most of my purchases have been used paperbacks from Logos.

These purchases were a result of browsing—I needed a book (or 10) for bedtime reading, and I had only vague ideas about what I wanted: usually science fiction or fantasy, with characters I could identify with and decent world building (both of which are rarer than they should be in the genre). Browsing is very difficult in on-line purchasing, and new bookstores tend to be too stuffed with the latest fad books (where they make what little profit they get) to have much that I’m interested in reading and haven’t already read. (OK, that may be more a commentary on the narrowness of my tastes than on the contents of the store.)

I mourn the passing of an era—soon there will be no places left to browse through stacks of paperbacks, looking for treasures amongst the dross.  Logos had decent book buyers, so the ratio of treasure to recyclable paper was higher than at many bookstores (though it always irked me that they would buy back only about a quarter of my surplus books—they’d sold the books once, why did they think they couldn’t sell them again?).

My wife has even more cause to mourn Logos than me, as about half the books she acquired for her school library were from Logos. Almost as many were from Friends of the Library books sales, but that source is much less reliable and requires very fast decision making for children’s books, as they are snapped up quickly.

For those, like me, who appreciated the pleasures of finding strange and wonderful books and being able to buy them for very low prices, take a little time in the next couple of weeks to visit Logos for remembrance’s sake.

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, 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.

2016 October 8

Release notes for book (Oct 2016)

Filed under: Circuits course — gasstationwithoutpumps @ 17:10
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I’ve just finished doing a rewrite pass over the part of the textbook needed for BME 51A, which I’ll be teaching starting in January. I’ve been working on this rewrite pass since June, so a little over 4 months. I’ll be spending the next couple of months doing a rewrite pass for the part of the book needed for BME 51B, but that should go a little quicker, as there are about half as many pages in the second “half”, and I think they are in somewhat closer to the desired form than the part I just finished.

There are still a lot of “to-do” notes in the margins of the book, even in the part I just “finished”, but they are all fairly small things, I think. This blog post will be my release notes for this version of the book, summarizing what I changed.

The biggest change was a rearrangement of the order of the labs, so that there are now two amplifier labs in the first half, and all the audio labs are in the second half.  Lots of things (like the table of equipment for labs and the schedule of lectures) needed to be revised to fit.  I still have some work to do on the lecture schedule.

I moved the sampling and aliasing lab after the thermistor lab, so that there is more time in lecture to talk about time-varying signals before the lab.

I expanded the  op-amp chapter into a more general amplifier chapter, and now discuss multi-stage amplification from the beginning, because the instrumentation amp lab for the pressure sensor is now the first amplifier lab. I also added active low-pass filters to the op-amp chapter.

I rewrote the optical pulse-monitor lab, which now calls for a more robust design using logarithmic current to voltage conversion.  I’m still experimenting with different ways of holding the phototransistor, so I may need to redo all the photographs, if I come up with a better design. The optical properties of blood section of the optoelectronics chapter now discusses melanin and fat, and the effect they can have on optical pulse monitoring.  I added a new chapter on transimpedance amplifiers, and added log-transimpedance amplifiers to the chapter. The difficult sensitivity analysis for the pulse monitor has been removed, as the log-transimpedance design does not require great care in setting the gain.

I added more coverage of expected background material, so that students who had not had physics electricity and magnetism courses could still follow along.  I found that a lot of the students didn’t remember anything from physics anyway, so I had to cover the essentials over again, and so I reduced the prerequisites for the course to calculus and high-school physics. I also added a section on logarithms.

I added a bunch more figures, bringing the numbered figures up to 145 (and several of those are multi-part figures). I also improved the typesetting of the captions, so that they are better distinguished from the main body text. Several of the block diagrams were redrawn with, and I added some new block diagrams and a bit more discussion of how to use block diagrams effectively. I cleaned up a few of the schematics also.

I added a few more exercises, added autonumbering, and converted the somewhat vague prelab assignments into numbered exercises, so that I can assign blocks of numbered exercises without worrying that students may have missed part of the prelab assignment. The oscilloscope probe exercise that caused a lot of problems last year has been rewritten with more scaffolding.

I added “equipment-needed” lists to the beginning of each lab.

I changed some of the labs that had used potentiometers to sweep voltages to use function generators with a slow triangle wave instead. This should save quite a bit of time, particularly for the hysteresis lab, where I described how to trigger on the output of a Schmitt trigger changing to record the input thresholds.

I created a new appendix for some of the PteroDAQ details, which I removed from the DAQ chapter.

I added more index terms and fixed a number of glitches in the index.  Index entries with subindexing now stay together in one column, rather than being split between columns and pages.

I’ve started boxing “important” things (and I may change to highlighting them), but choosing the right things to box will probably take another full pass over the book.

I fixed all the overfull-hbox errors through Chapter 24.


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