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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 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.

 

2015 November 25

Buy Nothing Day

Filed under: Uncategorized — gasstationwithoutpumps @ 20:00
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Today I got a message from Leanpub, the site where I’m selling drafts of my Applied Electronics for Bioengineers book, suggesting that authors provide a discount for Black Friday, the biggest shopping day of the year in the USA (or one of the 10 biggest, depending whose figures you believe).

My family doesn’t engage in the demented frenzy of orgiastic consumerism that the day after Thanksgiving has become in the US.  We, instead, stay home and celebrate Buy Nothing Day.  The celebration is simple: we stay home and buy nothing that day—not venturing out into the crazy traffic of drivers too stoked on the thought of bargains to look out for pedestrians, not doing on-line ordering, not even ordering pizza by phone (though we did do that one year, when we didn’t have enough food in the house for dinner).

Despite our family’s habits, though, I’m going along with Leanpub and offering a discount on my book:  From Friday 2015 Nov 27, through Monday Nov 30 (“Cyber Monday”), I’m lowering the minimum price on my book from $3 to $2.50.  As always, this includes not just the PDF of the current book, but all future updates for as long as I’m publishing the book with Leanpub.

Quite frankly, I doubt that the 50¢ difference (17% OFF!) will result in any more sales. Most of the purchasers of the book are paying more than the minimum anyway (average currently is $4.89, and that includes several people whom I gave free coupons to).

2015 November 5

Book draft 2015 Nov 5

Filed under: Circuits course — gasstationwithoutpumps @ 22:39
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I released an updated version of the Applied Electronics for Bioengineers text today.  This draft involved several changes:

  • Added modifier for “resistor” at end of Section 5.1
  • Changed “load resistor” to “bias resistor” in microphone chapter and lab.
  • Fixed microphone schematics to use polarized microphones.
  • Figure 11.2 changed to use only one differential channel on PteroDAQ.
  • Brief explanation of RMS added to Section 3.2
  • Small fixes to Chapters 9–16 and indexing terms added.
  • Index cleaned up.
  • 60Hz FM figure added to Chapter 14
  • Updated power discussion in Sections 0.5, 12.3, 23.1
  • Updated to include Teensy 3.2
  • Major rewrite of Chapter 23 (Class D power amp)

I’m still not finished with the Class D chapter, but I managed to test today an H-bridge circuit using a 9V power supply, which could provide ±9v signals to a loudspeaker (the full 10W that the loudspeaker can take).  I did not actually drive the loudspeaker that far, but I confirmed that the H-bridge was providing the full voltage range for PWM and that I was getting clean signals at the loudspeaker for loudness I was willing to tolerate listening to.

I’m now convinced that an H-bridge design is a simpler approach to teach the students, as well as being more useful for students who go on into the “assistive technology: motor” concentration.  Modifying the H-bridge to use logic-level signals from the comparator but high voltages for the power FETs turned out to be quite simple.  I just added a small nFET and a couple of resistors to make an inverter with a small voltage swing on the output:

Q1 and the resistors R1 and R2 form an inverter for driving the pFET.  Sizing R1 and R2 determines the voltage swing on the pFET gate  (Q2) and how fast the turn on and turn off are.  Of course, when Q3 is on, there is a current through it that is wasted (not delivered to the load), but I was able to keep that down to about 15mA.

Q1 and the resistors R1 and R2 form an inverter for driving the pFET. Sizing R1 and R2 determines the voltage swing on the pFET gate (Q2) and how fast the turn on and turn off are. Of course, when Q3 is on, there is a current through it that is wasted (not delivered to the load), but I was able to keep that down to about 15mA.

2015 September 7

Book draft 2015 Sep 7

Filed under: Circuits course — gasstationwithoutpumps @ 18:33
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I released an updated version of the Applied Electronics for Bioengineers text today.  This draft involved several changes:

  • Minor improvements to title page and copyright page.
  • Acknowledgements page added.
  • Various minor fixes in the Preface and Chapters 0–7, including more indexing.
  • Added figure and explanation of series and parallel connection to Chapter 0.
  • Added background info on capacitors and complex numbers to Chapter 0.
  • In Lab 1, fixed some PteroDAQ references to mention the Teensy boards.
  • Table of capacitor values added to Chapter 7.
  • Added an exercise to RC filters (Chapter 8)
  • Added an exercise to voltage dividers (Section 5.2)
  • Added PDF bookmarks for contents, list of figures, list of tables, bibliography, and index.
  • Cleaned up bibliography and added a few entries.
  • Protoboard design put online (https://users.soe.ucsc.edu/~karplus/bme101/pc-boards/op-amp-proto-rev0/) and properly pointed to.
  • Microphone preamp photo added to Lab 7.
  • In Chapter 18 (Pressure sensors), I collected new cuff-pressure data and added descriptions and pictures of the breath-pressure apparatus (plus breath-pressure data).  The new cuff-pressure data is more consistent with my normal blood pressure.
  • Chapter 19 (Instrumentation amps) lightly edited.
  • Lab 8 (pressure sensor lab) has had more scaffolding added to the sensitivity calculations.
  • Chapter 21 (Optoelectronics) extensively edited.
  • Added mention of isolation to Chapter 27 (EKG)
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