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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.

2016 November 3

Writing feedback

Filed under: Uncategorized — gasstationwithoutpumps @ 09:15
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In his post Omics! Omics!: 10 Years of Omicing!, which reflects on the influences on his writing, Keith Robison says

The other person who deserves nearly infinite credit for making me think about my word choices is my father.  Sometimes he strays into being a pedant and enforcing rules which have fallen by the wayside, but he did make me think when I spoke and wrote.  I’ve seen some guidelines for helping students that counsel picking only a few major errors to mark, for fear of scarring the psyche of young writers.  Dad didn’t subscribe to that viewpoint in the least, and I’m the better for it.  In high school I treasured getting back a draft with red ink all over it; it’s a service I missed in college and beyond.  That meant he had read it and thought about it, and my work was always better for it.

I think that this attitude is one that we need to see more of, both among students and among faculty. I put a lot of time into trying to provide thorough feedback on student writing, even though I know that it is not always appreciated.  I also know a number of faculty who bemoan the low quality of student writing, but spend almost no time giving detailed feedback so that the students can improve.

There are times for triage—concentrating on the students whose work could benefit most from editing, while providing only minimal feedback to those who produce word salad or whose writing is very good—but I prefer to try to provide similar amounts of feedback for all students.  For the word-salad students, my comments are mainly on sentence structure and paragraph structure, to try to have their writing make sense at least at a local level. The students in the middle get a mixture of different comments from punctuation to overall structure of the paper, while the top students get mainly get comments on trivial little details that can polish their already good writing.

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 draw.io, 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.

 

2016 October 6

Using Google ngrams

Filed under: Uncategorized — gasstationwithoutpumps @ 23:08
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I’ve found https://books.google.com/ngrams to be a very handy tool while writing my book. It has helped me answer such questions as which is the preferred term, “bypass capacitor” or “decoupling capacitor”? “bandpass” or “band-pass”? “passband” or “pass band”?

https://books.google.com/ngrams/interactive_chart?content=bypass+capacitor%2Cdecoupling+capacitor&year_start=1940&year_end=2015&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cbypass%20capacitor%3B%2Cc0%3B.t1%3B%2Cdecoupling%20capacitor%3B%2Cc0

https://books.google.com/ngrams/interactive_chart?content=bandpass%2Cband-pass&case_insensitive=on&year_start=1920&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t4%3B%2Cbandpass%3B%2Cc0%3B%2Cs0%3B%3Bbandpass%3B%2Cc0%3B%3BBandpass%3B%2Cc0%3B%3BBANDPASS%3B%2Cc0%3B.t4%3B%2Cband%20-%20pass%3B%2Cc0%3B%2Cs0%3B%3Bband%20-%20pass%3B%2Cc0%3B%3BBand%20-%20pass%3B%2Cc0%3B%3BBand%20-%20Pass%3B%2Cc0%3B%3BBAND%20-%20PASS%3B%2Cc0

https://books.google.com/ngrams/interactive_chart?content=passband%2C+pass+band&case_insensitive=on&year_start=1920&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t4%3B%2Cpassband%3B%2Cc0%3B%2Cs0%3B%3Bpassband%3B%2Cc0%3B%3BPassband%3B%2Cc0%3B.t4%3B%2Cpass%20band%3B%2Cc0%3B%2Cs0%3B%3Bpass%20band%3B%2Cc0%3B%3BPass%20band%3B%2Cc0%3B%3BPass%20Band%3B%2Cc0%3B%3BPASS%20BAND%3B%2Cc0

I’m a little old-fashioned and will stick with “bypass capacitor”, but prefer “bandpass” and “passband”.

The tool is not always useful—I can follow the rise and decline of “mho”, but “siemens” has too many other uses to be able to determine when the standard name for the unit of conductivity overtook “mho”. It is rather a shame that “mho” did not become the standard, as it is “ohm” backwards and ℧ is such a cute symbol (being Ω upside down).  I am sticking with the standard in my book, though.

(Sigh, the iframes that had the interactive graphics worked fine in the WordPress.com editor, but when the post was published, WordPress stripped them out, leaving only the links.  You’ll have to click through to see the graphics—sorry about that.)

2016 September 29

GRE Analytic Writing favors bullshitters

Filed under: Uncategorized — gasstationwithoutpumps @ 22:33
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My son recently took the GRE exam to apply for grad school in computer science.  The test has changed since I took it in 1973, but it still looks a lot like the SAT exam, which has also changed since I took it in 1970.  The multiple-choice section is still primarily 9th and 10th grade material, so it is a bit surprising that only 5.5% of CS students, 11.4% of physics students, and 15.3% of math students get 170, the highest possible score, on the quantitative reasoning section. [All data in this post from https://www.ets.org/s/gre/pdf/gre_guide_table4.pdf]

The “quantitative reasoning” questions are primarily algebra and reading simple graphs, so the banking and finance students do best with 15.5% getting 170. The scores would be more valuable for STEM grad school admissions if they included some college-level math (calculus, ODEs, combinatorics, statistics, … ), but the general GRE has always been based on an extremely low math level.

The verbal scores are perhaps less surprising, with philosophy being the only major with over 3% getting a 170 (5.1%), and with some of the education and business majors doing the worst—except for computer science, where 8% get the lowest scores (130–134), with the next worst major being accounting with 2.7% having 130–134.  I wonder how much of the difference here is due to the number of native and non-native speakers, as computer science certainly attracts a lot more foreign students than most majors.

I was most interested in looking at the “Analytical Writing” scores, since I’ve not seen much correlation between them and the quality of student writing on the grad school applications I’ve reviewed over the last decade.  I was interested in two things: the mean score and the fraction that got 4.5 or better (the fraction getting 5.5 or better is too small to be worth looking at).  Again computer science and electrical engineering stand out as having extremely low means and small fractions of students having 4.5 or better.  I have not found any analyses of the GRE scores that separate native speakers of English from non-native ones—I wonder how much of the effect we see here is due to being native speakers and how much is due to curricular differences.

Here is the table of all the broad categories in the order that ETS provided them:

Subject

Mean writing

%ile ≥4.5

Computer and Information Sciences

3.1

8.8

Electrical and Electronics

3.1

6.7

ENGINEERING

3.3

12.6

Civil

3.3

13.2

Industrial

3.3

9.8

Mechanical

3.3

12.3

PHYSICAL SCIENCES

3.4

17.3

Accounting

3.4

12.3

Banking and Finance

3.4

10.7

Natural Sciences ─ Other

3.5

14.8

Materials

3.5

19.4

BUSINESS

3.5

15.2

Other

3.5

14.7

Agriculture, Natural Res. & Conservation

3.6

18.0

Mathematical Sciences

3.6

21.0

Chemical

3.6

21.6

Early Childhood

3.6

16.0

Student Counseling and Personnel Srvcs

3.6

17.3

Business Admin and Management

3.6

17.8

Health and Medical Sciences

3.7

19.0

Chemistry

3.7

23.8

Other

3.7

23.1

Other

3.7

21.3

Arts ─ Performance and Studio

3.7

24.3

Administration

3.7

21.9

Elementary

3.7

21.3

Special

3.7

19.5

Other

3.7

23.7

LIFE SCIENCES

3.8

21.3

Biological & Biomedical Sciences

3.8

26.0

Earth, Atmospheric, and Marine Sciences

3.8

25.4

Physics and Astronomy

3.8

26.8

Economics

3.8

27.8

Sociology

3.8

28.2

EDUCATION

3.8

23.9

Curriculum and Instruction

3.8

21.4

Evaluation and Research

3.8

23.6

SOCIAL SCIENCES

3.9

29.1

Psychology

3.9

26.6

Higher

3.9

29.7

Anthropology and Archaeology

4.0

34.7

Foreign Languages and Literatures

4.0

37.2

Secondary

4.0

33.9

Political Science

4.1

42.9

ARTS AND HUMANITIES

4.1

40.8

Arts ─ History, Theory, and Criticism

4.1

38.5

History

4.1

40.4

Other

4.1

38.6

English Language and Literature

4.2

45.2

Philosophy

4.3

52.7

 OTHER

Architecture and Environmental Design

3.4

13.1

Communications and Journalism

3.7

23.3

Family and Consumer Sciences

3.7

20.7

Library and Archival Sciences

4.0

34.3

Public Administration

3.8

23.7

Religion and Theology

4.2

46.5

Social Work

3.6

16.7

The table is more interesting in sorted order (say by %ile ≥4.5 on Analytical Writing):

Subject

Mean writing

%ile ≥4.5

Electrical and Electronics

3.1

6.7

Computer and Information Sciences

3.1

8.8

Industrial

3.3

9.8

Banking and Finance

3.4

10.7

Mechanical

3.3

12.3

Accounting

3.4

12.3

ENGINEERING

3.3

12.6

Architecture and Environmental Design

3.4

13.1

Civil

3.3

13.2

Other

3.5

14.7

Natural Sciences ─ Other

3.5

14.8

BUSINESS

3.5

15.2

Early Childhood

3.6

16.0

Social Work

3.6

16.7

PHYSICAL SCIENCES

3.4

17.3

Student Counseling and Personnel Srvcs

3.6

17.3

Business Admin and Management

3.6

17.8

Agriculture, Natural Res. & Conservation

3.6

18.0

Health and Medical Sciences

3.7

19.0

Materials

3.5

19.4

Special

3.7

19.5

Family and Consumer Sciences

3.7

20.7

Mathematical Sciences

3.6

21.0

Other

3.7

21.3

Elementary

3.7

21.3

LIFE SCIENCES

3.8

21.3

Curriculum and Instruction

3.8

21.4

Chemical

3.6

21.6

Administration

3.7

21.9

Other

3.7

23.1

Communications and Journalism

3.7

23.3

Evaluation and Research

3.8

23.6

Other

3.7

23.7

Public Administration

3.8

23.7

Chemistry

3.7

23.8

EDUCATION

3.8

23.9

Arts ─ Performance and Studio

3.7

24.3

Earth, Atmospheric, and Marine Sciences

3.8

25.4

Biological & Biomedical Sciences

3.8

26.0

Psychology

3.9

26.6

Physics and Astronomy

3.8

26.8

Economics

3.8

27.8

Sociology

3.8

28.2

SOCIAL SCIENCES

3.9

29.1

Higher

3.9

29.7

Secondary

4.0

33.9

Library and Archival Sciences

4.0

34.3

Anthropology and Archaeology

4.0

34.7

Foreign Languages and Literatures

4.0

37.2

Arts ─ History, Theory, and Criticism

4.1

38.5

Other

4.1

38.6

History

4.1

40.4

ARTS AND HUMANITIES

4.1

40.8

Political Science

4.1

42.9

English Language and Literature

4.2

45.2

Religion and Theology

4.2

46.5

Philosophy

4.3

52.7

Note that all the fields that call for precise, mathematical reasoning do poorly on this test, but those which call for fuzzy, emotional arguments with no mathematical foundation do well—the test is designed to favor con men. I believe that this is partly baked into the prompts (see the pool of issue topics and, to a lesser extent, the pool of argument topics), partly the result of having the writing being done entirely without access to facts (benefitting those who BS over those who prefer reasoning supported with well-sourced facts), and partly the result of having graders who are easily swayed by con men.

I believe that most of the graders are trained in the humanities, and so are more swayed by familiar vocabulary and rhetoric.  If ETS had science and engineering professors doing the grading (which they would have a hard time getting at the low rates they pay the graders), I think that the writing scores would come out quite different.

Of course, there are curricular differences, and science and engineering faculty are mostly not paying enough attention to their students’ writing (and I can well believe that CS and EE are the worst at that). But I don’t think that even engineering students who do very, very good engineering writing will necessarily score well on the GRE analytical writing test, which seems to favor rapid writing in only one style.

I will continue to give relatively little weight to Analytical Writing GRE scores in graduate admissions. The untimed essays that the students write for the applications are much closer to the sort of writing that they will be expected to do in grad school, and so much more indicative of whether their writing skills are adequate to the job. I will continue to interpret low GRE scores as a warning sign to look more closely at the essays for signs that the students are not up to the task of writing a thesis, but high GRE writing scores are not a strong recommendation—I don’t want grad students who are good at bull-shitting.

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