Wikipedia books, another approach for a free/cheap textbook

I’ve been thinking about another approach to providing a low-cost textbook for the circuits class: bundling a number of Wikipedia articles into a Wikipedia book, like the Introduction to Electronics one.  The idea is an appealing one, as many of the Wikipedia articles are excellent (better written than many textbooks), we can customize what topics to include, small errors in the text can be corrected, and students can either access the “book” online, download it in in PDF, ZIM, or OpenDocument format, or even pay for a printed copy.  The downloaded or printed copies will be frozen, while the live Wikipedia book gets updated every time one of the contained articles is edited.  We could provide frozen copies on the course web site, as a precaution against major rewrites removing information we expect students to read.

The Introduction to Electronics Wikipedia book does not have exactly the subjects we would need for our course, but several of the articles there are appropriate.  One attraction of this approach is that we can tailor our book to have exactly the content we need (assuming the articles we need exist) in the order we want. We can design our course by listing the topics we need in the order we need, and automatically have a text that matches. Given the somewhat idiosyncratic nature of our course (from basic circuits to EKG design, with side trips into electrodes and possibly fluidics modeling), we’re going to have to cobble together multiple sources anyway, so a Wikipedia book may be a good way to create the main text.  No matter what text we use, we’ll have to supplement with manufacturers’ data sheets, which can’t be included in a Wikipedia book because of copyright restrictions.

One disadvantage of Wikipedia books is that the articles in Wikipedia are by different authors and have no implicit ordering, so concepts cannot be developed in a gradual manner.  Individual articles are written at very different levels of sophistication, and some articles will have only a few sections that are relevant to the course.  The book would not be as smooth as a well-written textbook, but better than many of the poorly written ones on the market. I believe that we can add some manually created text (part of the book, but not part of Wikipedia) to introduce chapters, but I’m not exactly sure how (probably it involves including pages that are part of Wikipedia user space rather than public space).

Note: Wikipedia books are different from WikiBooks, which are from a project to create crowd-sourced free textbooks.  The electronics books currently available from WikiBooks are very incomplete and not as well written as Wikipedia articles, so I don’t think that they will be useful this year.

I started playing a bit with Wikipedia’s “Book Creator” and found it to be a very awkward interface.  Clicking on pages to add them to the book being created worked ok, but dragging the pages around to reorder them did not and the claimed button for adding chapters never appeared.  Furthermore, once you save a draft book, the book creator assumes you want to start a new one, so clicking on pages can’t add to an existing draft.  It seems that the book creator is damn near useless after the first 5 minutes, and after that you just have to edit the book like any other Wikipedia page.

All about circuits, a possible supplemental text

I’ve been dipping into All about circuits, a free electronic textbook written (mostly) by Tony R. Kuphaldt, as a possible textbook for the circuits class.  I like that it is free, as that makes it much more likely that students will have ready access to it (many decide not to buy expensive texts, and end up trying to borrow them from friends).

The format, as 100s of HTML files, is a bit awkward to read, but fairly easy to search with Google (by adding “site:allaboutcircuits.com” to the keywords ins the search box), so indexing is not really an issue.  The book starts at about a middle-school level, but gets up to the beginnings of circuit theory (Thevenin’s Theorem,  RC and L/R time constants, Reactance and impedance—R, L, and C, …).  The Operational amplifier chapter looks usable, though it does not have a design focus—circuits are presented as almost magical rather than carefully analyzed from first principles (as is done in more theoretical circuits books) or from design rules of thumb (as is done in books like Horowitz and Hill).

I think that All about Circuits can be a good supplemental text for students who need something at a lower reading and math level than Horowitz and Hill, for review of physics electricity and magnetism concepts, and to fill in gaps in prior education (such as complex numbers).

I don’t know that I want to use Horowitz and Hill as the main text, though, as it is pretty expensive for such an old electronics book. I wonder if there is another free book that is somewhat higher level than All about Circuits that can be combined with it to make a textbook at the right level for the range of students expected in the class.

I think we may need a more mathematical presentation of some of the material, if the students are to be able to continue into later electronics classes. This may not matter, because the chair of the EE department has made it pretty clear that no subsequent electronics course would use this course as a prerequisite, and that students would have to take the “real” circuits course in order to take any further electronics courses.  Of course, if he holds to that for the bioelectronics class, then he’ll have almost no students in that class, since few if any of the bioengineers will subject themselves to the dry, repetitive linear algebra manipulations of the standard circuits class in order to take a bioelectronics class that doesn’t even include a lab component.  If we get to teach our applied circuits course, we should be able to convince the professor creating the bioelectronics course to accept it as a prereq in place of the standard circuits course.

Possible textbook, Horowitz and Hill

Having rejected Medical Instrumentation: Application and Design, 4th Edition. ISBN-10: 047167600 as being unsuitable for the circuits class, despite some relevant material, I decided to start looking from a different angle.  Instead of looking for a text targeted at bioengineers that talks about circuits for EKGs, I decided to look for one that covered basic circuits material with the appropriate applied emphasis, even if the application were different.

I started by looking at a classic EE textbook, The Art of Electronics, 2nd edition by Paul Horowitz and Winfield Hill (copyright 1989) ISBN-10: 0-521-37095-7 hardback 0-521-42228-0 paperback.  Amazingly this 23-year-old electronics book is still in print and still sells at high prices  ($97 new and $70 used at Amazon). I was rather hoping that such an ancient book would have gotten cheap by now, but it seems to have retained its value better than just about any other EE I’ve heard of.

I understand that a third edition was scheduled for March 2012 and is now expected in early 2013.  Given the extensive lists of parts in the book, many of which are long gone from the market, such an overhaul is way overdue.  Perhaps the best thing they could do is throw out Chapters 10 and 11 (on microcomputers and microprocessors) as impossible to maintain and concentrate on the stuff that remains more stable for decades, since the 3rd edition is undoubtedly going to be the last one.

I’ve read the first 30 pages of Chapter 1: Foundations, and it seems to have exactly the right mix of practical advice with theoretical underpinnings for the applied circuits course.  It even starts with exactly the topics we thought to start with—resistance and voltage dividers, followed by impedance and generalized voltage dividers.

We can’t use all of the book in a 10-week course, but it looks like we can skip Chapters 2 and 3 (on bipolar and FET transistors respectively) and jump immediately to Chapter 4 on op amps.  I think that we should also use scattered sections from later in the book (like on voltage references, instrumentation amplifiers, and noise in amplifiers).  I’ll have to go through the book carefully to figure out how much of it we can use, and whether that is enough to justify the $70–100 price to the students.  Based on a quick look through today and reviews by people who have used the book, it seems likely that this is a book to encourage students to buy and keep.

There are a number of Amazon reviewers who disliked the book—most were trying to teach themselves electronics using the book and found the explanations too terse without a professor or TA to answer questions and expand on the material. Since we will be available, those criticisms are not really relevant for a course textbook, though it is good to know that some students find even the intro material daunting, and so we should have a slower-paced, more tutorial option available for such students.

Before I dive too deeply into Horowitz and Hill, I’ll also look into the recommendations of intro books by “Wise Warthog”, who gives a number of different suggestions for people with different needs.  He recommends a free e-book Lessons In Electric Circuits  by Kuphaldt for those just getting started, but warns that it may be too slow for some people, and suggests alternatives.

 

 

Medical Instrumentation, Chapters 9–14

As I mentioned in Medical Instrumentation, first 5 chapters, Medical Instrumentation, Chapter 6,  and Medical Instrumentation, Chapters 7 and 8, I’ve been slogging through one of the potential text books for the circuits course: Medical Instrumentation: Application and Design, 4th Edition. John G. Webster. Publisher: Wiley, 2009. # ISBN-10: 0471676004; # ISBN-13: 978-0471676003.  Here are my notes on the rest of the book (I plan to return it tomorrow to the library).

Chapter 9

MEASUREMENTS OF THE RESPIRATORY SYSTEM
Frank P. Primiano, Jr.

I only skimmed chapter 9, as there did not seem to be much of use for the circuits course.

Richard had suggested making a rotating-vane flowmeter using a toy siren-whistle as the turbine and a photodetector to determine its speed.  I investigated that possibility, but the siren whistles have very low drag on their turbines and continue to spin for a couple of seconds after the air flow has stopped.  One might be able to use that for a wind-speed indicator, but the response time is far too slow for measuring air flow due to breathing.

The section on measuring gas concentrations is intellectually interesting and may be of some value to bioengineers, but doesn’t seem relevant for the circuits course.

Chapter 10

CHEMICAL BIOSENSORS
Robert A. Peura

It’s nice to know how a pH probe works and how blood gases are measured, but I don’t see a lot we can do in the circuits class.
The plot of the absorptivities of carboxyhemoglobin, oxyhemoglobin, reduced hemoglobin, and methmoglobin in Figure 10.6 are interesting, and are needed for explaining how a pulse oximeter works, as well as why 940nm LEDs should be a good choice for detecting arterial blood pulses, since reduced hemoglobin has about 3/5th the extinction coefficient of oxyhemoglobin there.  An even longer wavelength (say 1000nm) would be even better, since the ratio drops to about 1/4, if LEDs and phototransistors for that wavelength were readily available, but 950nm is about as long a wavelength LED as is available.

I considered doing a pulse-oximetry lab, but the difficulty of calibrating the device made it seem pointless.  That’s too bad in a way, as the technique relies inherently on considering the AC rather than the DC component of the signal.

Chapter 11

CLINICAL LABORATORY INSTRUMENTATION
Lawrence A. Wheeler

Nothing in this chapter seems relevant to the circuits class.  I had at one point considered doing a very early lab in which electric fields were illustrated by measuring voltages at different points in an electrophoresis gel, but that didn’t seem worth the messy setup.  Most of the bioengineers will do gel electrophoresis in other labs anyway.

Chapter 12

MEDICAL IMAGING SYSTEMS
Melvin P. Siedband

Nothing in the imaging chapter seems relevant for the circuits class.

Chapter 13

THERAPEUTIC AND PROSTHETIC DEVICES
Michael R. Neuman

It doesn’t look like there is anything in Chapter 13 for our course.

Chapter 14

ELECTRICAL SAFETY                               638
Walter H. Olson

14.1       Physiological Effects of Electricity   639

Useful figure and definitions of different levels of shock hazard.

14.2       Important Susceptibility Parameters   641

Perhaps a bit too much information for students to process about current needed for hazard.

14.3       Distribution of Electric Power   646

Fairly straightforward description of electric distribution in buildings.  Students should know this already, but most likely don’t.

14.4       Macroshock Hazards   650

Somewhat wordy description of hazards, repeating previous sections.

14.5       Microshock Hazards   653

Important for those who are making direct electrical connections to the heart, which we are NOT.

14.6       Electrical-Safety Codes and Standards   658

As boring as the title makes it sound.

14.7       Basic Approaches to Protection Against Shock   659

Short and nearly contentless.

14.8       Protection: Power Distribution   660

Good description of GFCIs, but the schematic in Figure 14.15 is not explained, and how it works is not obvious.

14.9       Protection: Equipment Design   663

Reasonable description of double insulation and isolation barriers.  Doesn’t seem to indicate that optical couplers are now the dominant method (though I believe they are) for information transfer across the isolation barrier—they give it only as one of three possible options.

14.10     Electrical-Safety Analyzers   667

One paragraph, not much content.

14.11     Testing the Electric System   667

Doesn’t really say how to do it, just that the usual 3-LED tester used by construction workers and home electricians is inadequate.

14.12     Tests of Electric Appliances   669

Basically repeats material from the National Fire Protection Association standards (NFPA99-2005).

Problems   673
References   674

Chapter 14 has some good material on electrical safety, but is probably too much information for the circuits course.  I’m going to have to find a more concise description that students will actually read and remember.

Bottom line

There are bits and pieces of Medical Instrumentation that could be useful to our students, but not enough of the content is relevant to the course to use it as a text and the parts that are relevant are too long for the book to be useful as a reserve book in the library.  It was probably worth my time to read (most of) the book, but I doubt that it will be worthwhile for the students.

Medical Instrumentation, Chapters 7 and 8

As I mentioned in Medical Instrumentation, first 5 chapters and Medical Instrumentation, Chapter 6, I’ve been slogging through one of the potential text books for the circuits course: Medical Instrumentation: Application and Design, 4th Edition. John G. Webster. Publisher: Wiley, 2009. # ISBN-10: 0471676004; # ISBN-13: 978-0471676003.  I need to return the book to the library this week (interlibrary loan periods are short), so I’ll probably just skim the book after Chapter 8, to see if there is anything we can use.

 

Chapter 7

BLOOD PRESSURE AND SOUND                                 293

Robert A. Peura

7.1         Direct Measurements   295

We’re not sticking catheters into people, so this is irrelevant to our class.

7.2         Harmonic Analysis of Blood-Pressure Waveforms   300

A bad presentation of Fourier analysis, giving only amplitude (not phase), but saying “When we compare the original waveform and the waveform reconstructed from the Fourier components, we find that they agree quite well, indicating that the first six harmonics give a fairly good reproduction.”  You can’t get a reconstruction like that without the phase information, which they never even mention!

7.3         Dynamic Properties of Pressure-Measurement Systems   301

Uses RLC transmission-line circuits to model pressure in a catheter.  The idea of using electrical analogs to model physical systems is an important one, but I’d rather do it with a system that we can actually build and test in the lab.  The number of formulas in this section is large enough that probably only a small fraction of students ever read it.

7.4         Measurement of System Response   308

The describe a way to get the step response of a pressure-sensor-catheter system (by using a bursting rubber membrane to get a step decrease in pressure) and sinusoidal response (using an underwater loudspeaker).  They do not talk about differentiating the step response to get the impulse response, nor using autocorrelation with random excitation to get impulse response.  This section feels like something out of the 1970s.

7.5         Effects of System Parameters on Response   310

Catheter wall stiffness and de-aerating water are important from a fluid dynamics standpoints but are not interesting for a circuits class.

7.6         Bandwidth Requirements for Measuring Blood Pressure   311

Rather trivial discussion of bandwidth, though the mention that looking at the derivative of pressure  increases the bandwidth requirement is an important one that students could easily overlook.  They claim that the amplitude-vs-frequency characteristic of a catheter-manometer system should be flat (to within 5%) for the first 20 harmonics.  For a rapid heart rate of 240 bpm, that means a high frequency of about 80Hz.  That is trivial for electronics, but tough for fluid in a narrow tube.

7.7         Typical Pressure-Waveform Distortion   311

Fairly good discussion of the effects of an underdamped and overdamped system, as well as he effects of air bubbles and “catheter whip”.  Unfortunately, they don’t talk about what “damping” is and seem to confuse it with “inadequate frequency response”.  I would not give this section to someone who didn’t already have a firm grasp of the concepts, as it is likely to lead to serious misunderstandings.

7.8         Systems for Measuring Venous Pressure   313

Medically interesting, perhaps, but nothing new for sensors or circuits.

7.9         Heart Sounds   314

A good description of heart sounds and their correlation to the EKG and blood pressure waveforms.  Talks about the rather non-flat frequency characteristics of stethoscopes, and problems with applying the stethoscope and of leakage at the earpieces.  They talk about the lack of success of electronic stethoscopes on the market and attribute it physicians’ unfamiliarity with the sounds heard through electronic stethoscopes.

7.10       Phonocardiography   318

One paragraph on recording heart sounds.

7.11       Cardiac Catheterization   318

We’re not sticking catheters into people’s hearts!

7.12       Effects of Potential and Kinetic Energy on Pressure Measurements   323

Standard fluid dynamics stuff (Bernoulli’s equation) applied to blood flow.  The stuff about hydrostatic pressure and which way a catheter port points relative to blood flow is undoubtedly important in blood pressure measurements, but is not really relevant to our circuits class.

7.13       Indirect Measurements of Blood Pressure   325

Now we’re finally getting to stuff that could conceivably be useful for the course: non-invasive techniques involving pressure cuffs and listening to the blood flow.  The oscillometric method (which senses the pressure in the cuff) is popular in home blood pressure meters.  I don’t think that we want to put together the cuff and other mechanical parts of a blood pressure meter, but it would give us an excuse for using a pressure sensor.

7.14       Tonometry   330

Measuring pressure in the eye (and in arteries) by force sensors flattening the object being measured. Not really suitable for our circuits course.

Problems   335
References   336

Overall, there is little in Chapter 7 of any use for the circuits class. We could, perhaps, make an electronic stethoscope or oscillometric blood pressure cuff.  The notion of modeling fluid pressure using electronic analogs is an important one, but we can’t use the example here in the lab.

Chapter 8

MEASUREMENT OF FLOW AND VOLUME OF BLOOD                338
John C. Webster

8.1         Indicator-Dilution Method That Uses Continuous Infusion   338

We’re not sticking catheter in arteries.

8.2         Indicator-Dilution Method That Uses Rapid Injection   341

We’re not sticking catheter in arteries.

8.3         Electromagnetic Flowmeters   338

We’re not cutting people open to stick $500 cuff probes around arteries.

8.4         Ultrasonic Flowmeters   350

Ultrasonic flowmeters using Doppler shift measurements are kind of cool, but I don’t know that we can get decent transducers for a reasonable price. Hmm,  there is a 7.2MHz transducer that is 22mm in diameter (a bit big for aiming at a blood vessel!) with wire leads for about $4 each in quantities of 5).  I think that the mechanical design problems here could get to be too big for the circuits course.  The electronics is a bit tricky also, as they would have to deal with RF (around 7MHz) and detecting the slightly shifted Doppler return (which is modulated by a noise band, not a simple shift) in a huge carrier background. Probably too difficult for this course.

8.5         Thermal-Convection Velocity Sensors   361

We’re not sticking heated probes into people’s blood vessels.

8.6         Chamber Plethysmography   364

A rather bulky apparatus that we have no reason to build.

8.7         Electric-Impedance Plethysmography   366

We could try building the 4-electrode plethysmograph, but it seems like a lot of trouble for a not very interesting result.  The authors even say “electrical-impedance plethysmography has been used to measure a wide variety of variables, but in many cases the accuracy of the method is poor or unknown.”  We’d probably have to make our own band electrodes also, as the only commercial ones I’ve been able to find are for neonatal EKGs and so are much too small for adults.

8.8         Photoplethysmography   372

This section has the detection of blood flow by shining light through tissue, which I experimented with a bit, but I’ve not found a good way to mount sensors so that they work properly.  They do recommend 940nm LEDs and  phototransistors, in both transmission and reflection setups.  They do mention a problem that I was facing: “large artifacts due to motion saturate the amplifier”.  They point out that when patients are in shock, vasoconstriction reduces peripheral blood flow, so these sensors may not be able to detect the pulses.  Their suggestion of shining the light through the nasal septum is useful in surgery, no doubt, but probably not appropriate for the circuits course.

I’d still like to get this to work reliably without a lot of mechanical setup, because I really want to have a light-sensor application.

Problems   374
References   375

Bottom line

I still don’t think that we can make Medical Instrumentation our main text book, and there isn’t much in Chapters 7 and 8 that we could use.  I wish I could get the light-based pulse sensor working without so much hassle—I’ll have to try it again.

One concept worth looking at is the electrical-circuit analog for mechanical devices.  It might be worthwhile to set up a lab involving pressure measurements at either end of a long tube and modeling the tube as an electrical circuit.  This would give me an excuse for using pressure sensors like the Freescale MPXHZ6250A, which we used in the remotely-operated underwater vehicle as a depth gauge.  That gauge has a 1msec response time (10% to 90% of response to a step input), which is fast enough for most of the experiments I can think of for them to do.