Supplemental sheets, draft 3

This post updates and replaces the Supplemental sheets, draft 2. It reflects the redesign of the course based on running a prototype version of the course in as a group tutorial in Winter 2013.

Lecture Course

Undergraduate Supplemental Sheet
Information to accompany Request for Course Approval
Sponsoring Agency: Biomolecular Engineering
Course #: 101
Catalog Title: Applied Circuits for Bioengineers

Please answer all of the following questions using a separate sheet for your response.
1. Are you proposing a revision to an existing course? If so give the name, number, and GE designations (if applicable) currently held.

This is not a revision to any existing course.A prototype version of the course was run as BME 194 Group Tutorial in Winter 2013. Notes on the design and daily running of that prototype can be found at https://gasstationwithoutpumps.wordpress.com/circuits-course-table-of-contents

2. In concrete, substantive terms explain how the course will proceed. List the major topics to be covered, preferably by week.

The Applied Circuits course is centered around the labs in the accompanying lab course.  Concepts are taught as needed for the labs, with design and analysis exercises in the lecture course cementing the understanding. The recurring theme throughout the course is voltage dividers: for change of voltage, for current-to-voltage conversion, for high-pass and low-pass RC filters, in Wheatstone bridges, and as feedback circuits in op amp circuits.  The intent of this course is to provide substantial design experience for bioengineering students early in their studies, and to serve both as as bridge course to entice students into the bioelectronics concentration and as a terminal electronics course for those students focussing on other areas.

1. Basic DC circuit concept review: voltage current, resistance, Kirchhoff’s Laws, Ohm’s Law, voltage divider, notion of a transducer.
   The first week should cover all the concepts needed to do the thermistor lab successfully.
2. Models of thermistor resistance as a function of temperature. Voltage and current sources, AC vs DC, DC blocking by capacitors, RC time constant, complex numbers, sine waves, RMS voltage, phasors. The second week should cover all the concepts needed to do the electret microphone lab successfully.
3. Low-pass and high-pass RC filters as voltage dividers, Bode plots. Concepts necessary for properly understanding digitized signals: quantized time, quantized voltage, sampling frequency, Nyquist frequency, aliasing.
4. Amplifier basics: op amps, AC coupling, gain computation, DC bias for single-power-supply offsets, bias source with unity-gain amplifier.  In the lab, students will design, build, and test a low-gain amplifier (around 5–10 V/V) for audio signals from an electret microphone. We’ll also include a simple current-amplifier model of a bipolar transistor, so that they can increase the current capability of their amplfier.
5. Op amps with feedback that has complex impedance (frequency-dependent feedback), RC time constants, parallel capacitors, hysteresis, square-wave oscillator using Schmitt triggers, capacitance-output sensors, capacitance-to-frequency conversion.   Topics are selected to support students designing a capacitive touch sensor in the accompanying lab.
6. Phototransistors and FETs for the tinkering lab and for the class-D amplifier lab. In preparation for the lab in which students model a pair of electrodes as R+(C||R), we will need a variety of both electronics and electrochemistry concepts: variation of parameters with frequency, impedance of capacitors, magnitude of impedance, series and parallel circuits, limitations of R+(C||R) model, and at least a vague understanding of half-cell potentials for the electrode reactions: Ag → Ag⁺ + e^-, Ag⁺ + Cl^- → AgCl, Fe + 2 Cl^-→ FeCl₂ + 2 e^-.
7. Differential signals, twisted-pair wiring to reduce noise, strain gauge bridges, instrumentation amplifier, DC coupling, multi-stage amplifiers.
   Topics are selected to support the design of a 2-stage amplifier for a piezoresistive pressure sensor in the lab.
8. System design, comparators, more on FETs. Students will design a class-D power amplifier to implement in the lab.
9. A little electrophysiology: action potentials, electromyograms, electrocardiograms. Topics are chosen so that students can design a simple 3-wire electrocardiogram (EKG) in the lab.There will also be a bit more development of simple (single-pole) filters.
10. The last week will be review and special topics requested by the students.

3. Systemwide Senate Regulation 760 specifies that 1 academic credit corresponds to 3 hours of work per week for the student in a 10-week quarter. Please briefly explain how the course will lead to sufficient work with reference to e.g., lectures, sections, amount of homework, field trips, etc. [Please note that if significant changes are proposed to the format of the course after its initial approval, you will need to submit new course approval paperwork to answer this question in light of the new course format.]

The combination of BME101 and BME101L is 7 units (21 hours per week).  The time will be spent approximately as follows:

• 3.5 hours lecture/discussion
• 3.5 hours reading background and circuits text
• 3 hours read lab handouts and doing pre-lab design activities
• 6 hours lab
• 5 hours writing design reports for lab

4. Include a complete reading list or its equivalent in other media.

No existing book covers all the material.  For the prototype run of the course, we relied heavily on Wikipedia articles, which turned out to be too dense for many of the students.  Other alternatives (such as Op amps for everyone by Ron Mancini http://www.e-booksdirectory.com/details.php?ebook=1469 Chapters 1–6 and Op Amp Applications Handbook by Analog Devices http://www.analog.com/library/analogDialogue/archives/39-05/op_amp_applications_handbook.html Sections 1-1 and 1-4) were also much too advanced.

In future we will most likely use the free on-line text All about Circuits as the primary text, with material not covered there (such as the various sensors) coming mainly from Wikipedia and the datasheets for the components.

5. State the basis on which evaluation of individual students’ achievements in this course will be made by the instructor (e.g., class participation, examinations, papers, projects).

Students will be evaluated primarily on design reports with some in-class or take-home quizzes to ensure that they do the needed reading on theoretical concepts.

6. List other UCSC courses covering similar material, if known.

EE 101 covers some of the same circuit material, but without the focus on sensors and without instrumentation amps.  It covers linear circuit theory in much more depth and focuses on mathematical analysis of complicated linear circuits, rather than on design with simple circuits.  The expectation for bioengineering students is that those in the bioelectronics track would take BME 101 before taking EE101, and that those in other tracks would take BME 101 as a terminal electronics course providing substantial engineering design.  The extra material in BME 101 would prepare the bioengineering students better for EE 101.

Physics 160 offers a similar level of practical electronics, but focuses on physics applications, rather than on bioengineering applications, and is only offered in alternate years.

7. List expected resource requirements including course support and specialized facilities or equipment for divisional review. (This information must also be reported to the scheduling office each quarter the course is offered.)

The lecture part of the course needs no special equipment—a standard media-equipped classroom with a whiteboard, screen, and data projector should suffice. Having a portable laptop-connected oscilloscope would make demos much easier to do, but is not essential.

The lecture course is not really separable from the associated lab course,whose equipment needs are described on the supplemental sheet for that course.

The course requires a faculty member (simultaneously teaching the co-requisite Applied Circuits lab course) and a teaching assistant or undergraduate group tutor for discussion sections and assistance in grading.  The same TA/group tutor should be used for both the lecture and the lab courses.

8. If applicable, justify any pre-requisites or enrollment restrictions proposed for this course. For pre-requisites sponsored by other departments/programs, please provide evidence of consultation.

Students will be required to have single-variable calculus and a physics electricity and magnetism course. Both are standard prerequisites for any circuits course. Although DC circuits can be analyzed without calculus, differentiation and integration are fundamental to AC analysis. Students should have already been introduced to the ideas of capacitors and inductors and to serial and parallel circuits.

The prerequisite courses are already required courses for biology majors and bioengineering majors, so no additional impact on the courses is expected.

9. Proposals for new or revised Disciplinary Communication courses will be considered within the context of the approved DC plan for the relevant major(s). If applicable, please complete and submit the new proposal form (http://reg.ucsc.edu/forms/DC_statement_form.doc or http://reg.ucsc.edu/forms/DC_statement_form.pdf) or the revisions to approved plans form (http://reg.ucsc.edu/forms/DC_approval_revision.doc or http://reg.ucsc.edu/forms/DC_approval_revision.pdf).

This course is not expected to contribute to any major’s disciplinary communication requirement, though students will get extensive writing practice in the design reports (writing between 50 and 100 pages during the quarter).

10. If you are requesting a GE designation for the proposed course, please justify your request making reference to the attached guidelines.

No General Education code is proposed for this course, as all relevant codes will have already been satisfied by the prerequisites.

11. If this is a new course and you requesting a new GE, do you think an old GE designation(s) is also appropriate? (CEP would like to maintain as many old GE offerings as is possible for the time being.)

No General Education code is proposed for this course, as all relevant codes (old or new) will have already been satisfied by the prerequisites.

Lab course

Undergraduate Supplemental Sheet
Information to accompany Request for Course Approval
Sponsoring Agency Biomolecular Engineering
Course # 101L
Catalog Title Applied Circuits Lab

Please answer all of the following questions using a separate sheet for your response.
1. Are you proposing a revision to an existing course? If so give the name, number, and GE designations (if applicable) currently held.

This is not a revision to any existing course. A prototype version of the course was run as BME 194F Group Tutorial in Winter 2013. Notes on the design and daily running of that prototype can be found at https://gasstationwithoutpumps.wordpress.com/circuits-course-table-of-contents

2. In concrete, substantive terms explain how the course will proceed. List the major topics to be covered, preferably by week.

The course is a lab course paired with BME 101, Applied Circuits for Bioengineers.  The labs have been designed to be relevant to bioengineers and to have as much design as is feasible in a first circuits course.  The labs are the core of the course, with lecture/discussion classes to support them. There will be six hours of lab a week, split into 2 3-hour sessions. Lab assignments will generally take two lab sessions, with data collection in the first lab session, and data analysis and design between lab sessions.   Some of the more straightforward labs will need only a single session.  Except for the first intro lab, these labs have been used in the prototype run of the class as 3-hour labs.  Most did not fit in one 3-hour lab session and would benefit from being split into two separate lab sessions with data analysis and design between the sessions.

1. Intro to parts, tools, and lab equipment (single session)
2. Thermistor
3. Microphone
4. Sampling and aliasing (single session)
5. Audio amp
6. Hysteresis oscillator and soldering lab
7. FET and phototransistor
8. Electrode modeling
9. Pressure sensor and instrumentation amp (soldered)
10. Class-D power amplifier
11. EKG (instrumentation amp with filters, soldered)

1. Intro to parts, tools, and lab equipment
   Students will learn about the test equipment by having them use the multimeters to measure other multimeters. What is the resistance of a multimeter that is measuring voltage? of one that is measuring current? what current or voltage is used for the resistance measurement? Students will be  issued their parts and tool kits, learn to use the wire strippers and make twisted-wire cables for the power supplies to use all quarter.  They will learn to set the current limits on the power supplies and  measure voltages and currents for resistor loads around 500Ω.  This lab will not require a written lab report.
   Lab skills developed: wire strippers, multimeter for measuring voltage and current, setting bench power supply
   Equipment needed: multimeter, power supply
2. Thermistor lab
   The thermistor lab will have two lab sessions involving the use of a Vishay BC Components NTCLE413E2103F520L thermistor or equivalent.
For the first lab session, the students will use a bench multimeter to measure the resistance of the thermistor, dunking it in various water baths (with thermometers in them to measure the temperature). They should fit a simple curve to this data based on standard thermistor models. A class period will be spent on learning both the model and how to do model fitting with gnuplot, and there will be a between-lab exercise where they derive the formula for maximizing | dV/dT | in a voltage divider that converts the resistance to a voltage.
   For the scond lab session, they will add a series resistor to make a voltage divider. They have to choose a value to get as large and linear a voltage response as possible at some specified “most-interesting” temperature (perhaps body temperature, perhaps room temperature, perhaps DNA melting temperature).  They will then measure and plot the voltage output for another set of water baths. If they do it right, they should get a much more linear response than for their resistance measurements. 
Finally, they will hook up the voltage divider to an Arduino analog input and record a time series of a water bath cooling off (perhaps adding an ice cube to warm water to get a fast temperature change), and plot temperature as a function of time.
   Lab skills developed: use of multimeter for measuring resistance and voltage, use of Arduino with data-acquisition program to record a time series, fitting a model to data points, simple breadboarding.Equipment needed: multimeter, power supply, thermistor, selection of various resistors, breadboard, clip leads, thermoses for water baths, secondary containment tubs to avoid water spills in the electronics lab. Arduino boards will be part of the student-purchased lab kit. All uses of the Arduino board assume connection via USB cable to a desktop or laptop computer that has the data logger software that we will provide.
3. Electret microphone
   First, we will have the students measure and plot the DC current vs. voltage for the microphone. The microphone is normally operated with a 3V drop across it, but can stand up to 10V, so they should be able to set the Agilent E3631A  bench power supply to various values from 0V to 10V and get the voltage and current readings directly from the bench supply, which has 4-place accuracy for both voltage and current. Ideally, they should see that the current is nearly constant as voltage is varied—nothing like a resistor.  They will follow up the hand measurements with automated measurements using the Arduino to measure the voltage across the mic and current through it for voltages up to about 4v.  The FET in the microphone shows a typical exponential I vs. V characteristic below threshold, and a gradually increasing current as voltage increases in the saturation region.  We’ll do plotting and model fitting in the data analysis class between the two labs.
   Second, we will have them do current-to-voltage conversion with a 5v power supply and a resistor to get a 1.5v DC output from the microphone and hook up the output of the microphone to the input of the oscilloscope. Input can be whistling, talking, iPod earpiece, … . They should learn the difference between AC-coupled and DC-coupled inputs to the scope, and how to set the horizontal and vertical scales of the scope. They will also design and wire their own DC blocking RC filter (going down to about 1Hz), and confirm that it has a similar effect to the AC coupling on the scope. Fourth, they will play sine waves from the function generator through a loudspeaker next to the mic, observe the voltage output with the scope, and measure the AC voltage with a multimeter, perhaps plotting output voltage as a function of frequency. Note: the specs for the electret mic show a fairly flat response from 50Hz to 3kHz, so most of what the students will see here is the poor response of a cheap speaker at low frequencies.
   EE concepts: current sources, AC vs DC, DC blocking by capacitors, RC time constant, sine waves, RMS voltage, properties varying with frequency.Lab skills: power supply, oscilloscope, function generator, RMS AC voltage measurement.Equipment needed: multimeter, oscilloscope, function generator, power supply, electret microphone, small loudspeaker, selection of various resistors, breadboard, clip leads.
4. Sampling and Aliasing
   Students will use the data logger software on the Arduino to sample sine waves from a function generator at different sampling rates.  They will need to design a high-pass RC filter to shift the DC voltage from centered at 0 to centered at 2.5v in the middle of the Arduino A-to-D converter range.  They will also design a low-pass filter (with corner frequency below the Nyquist frequency) to see the effect of filtering on the aliasing.
   EE concepts: quantized time, quantized voltage, sampling frequency, Nyquist frequency, aliasing, RC filters.
   Equipment needed:  function generator, Arduino board, computer.
5. Audio amplifier
   Students will use an op amp to build a simple non-inverting audio amplifier for an electret microphone, setting the gain to around 6 or 7. The amplifier will need a a high-pass filter to provide DC level shifting at the input to the amplifier. Note that we are using single-power-supply op amps, so they will have to design a bias voltage supply as well. The output of the amplifier will be recorded on the Arduino (providing another example of signal aliasing).
   The second half of the lab will add a single bipolar transistor to increase the current and make a class A output stage for the amplifier, as the op amp does not provide enough current to drive the 8Ω loudspeaker loudly.
   EE concepts: op amp, DC bias, bias source with unity-gain amplifier, AC coupling, gain computation.
   Lab skills: complicated breadboarding (enough wires to have problems with messy wiring). If we add the Arduino recording, we could get into interesting problems with buffer overrun if their sampling rate is higher than the Arduino’s USB link can handle.
   Equipment needed: breadboard, op amp chip, assorted resistors and capacitors, electret microphone, Arduino board, optional loudspeaker.
6. Hysteresis and capacitive touch sensor
   For the first half of the lab, students will characterize a Schmitt trigger chip, determining V_IL, V_IH, V_OL, and V_OH. Using these properties, they will design an RC oscillator circuit with a specified period or pulse width (say 10μs), and measure the frequency and pulse width of the oscillator.
   For the second half of the lab, the students will build a relaxation oscillator whose frequency is dependent on the parasitic capacitance of a touch plate, which the students can make from Al foil and plastic food wrap. In addition to breadboarding, students will wire this circuit by soldering wires and components on a PC board designed for the oscillator circuit. Students will have to measure the frequency of the oscillator with and without the plate being touched. We will provide a simple Arduino program that is sensitive to changes in the pulse width of the oscillator and that turns an LED on or off, to turn the frequency change into an on/off switch.  Students will treat the oscillator board as a 4-terminal component, and examine the effect of adding resistors or capacitors between different terminals.
   EE concepts: frequency-dependent feedback, oscillator, RC time constants, parallel capacitors.
   Lab skills: soldering, frequency measurement with digital scope.
   Equipment needed: Power supply, multimeter, Arduino, clip leads, amplifier prototyping board, oscilloscope.
7. Phototransistor and FET
   First half: characterize phototransistor in ambient light and shaded.  Characterize nFET and pFET.
   Second half: students will “tinker” with the components they have to produce a light-sensitive, noise-making toy.
   EE concepts: phototransistors, FETs.
   Equipment needed: breadboard, phototransistor, power FETs, loudspeaker, hysteresis oscillator from previous lab, oscilloscope.
8. Electrode measurements
   First, we will have the students attempt to measure the resistance of a saline solution using a pair of stainless steel electrodes and a multimeter. This should fail, as the multimeter gradually charges the capacitance of the electrode/electrolyte interface.Second, the students will use a function generator driving a voltage divider with a load resistor in the range 10–100Ω. The students will measure the RMS voltage across the resistor and across the electrodes for different frequencies from 3Hz to 300kHz (the range of the AC measurements for the Agilent 34401A Multimeter). They will plot the magnitude of the impedance of the electrodes as a function of frequency and fit an R2+(R1||C1) model to the data, most likely using gnuplot. There will be a prelab exercise to set up plotting of the model and do a little hand tweaking of parameters to help them understand what each parameter changes about the curve.Third, the students will repeat the measurements and fits for different concentrations of NaCl, from 0.01M to 1M. Seeing what parameters change a lot and what parameters change only slightly should help them understand the physical basis for the electrical model.Fourth, students will make Ag/AgCl electrodes from fine silver wire. The two standard methods for this involve either soaking in chlorine bleach or electroplating. To reduce chemical hazards, we will use the electroplating method. As a prelab exercise, students will calculate the area of their electrodes and the recommended electroplating current.  In the lab, they will adjust the voltage on the bench supplies until they get the desired plating current.Fifth, the students will measure and plot the resistance of a pair of Ag/AgCl electrodes as a function of frequency (as with the stainless steel electrodes).Sixth, if there is time, students will measure the potential between a stainless steel electrode and an Ag/AgCl electrode.EE concepts: magnitude of impedance, series and parallel circuits, variation of parameters with frequency, limitations of R+(C||R) model.Electrochemistry concepts: At least a vague understanding of half-cell potentials, current density, Ag → Ag⁺ + e^-, Ag⁺ + Cl^- → AgCl, Fe + 2 Cl^-→ FeCl₂ + 2 e^-.Lab skills: bench power supply, function generator, multimeter, fitting functions of complex numbers, handling liquids in proximity of electronic equipment.Equipment needed: multimeter, function generator, power supply, stainless steel electrode pairs, silver wires, frame for mounting silver wire, resistors, breadboard, clip leads, NaCl solutions in different concentrations, beakers for salt water, secondary containment tubs to avoid salt water spills in the electronics lab.
9. Pressure sensor and instrumentation amplifier
   Students will design an instrumentation amplifier with a gain of 300 or 500 to amplify the differential strain-gauge signal from a medical-grade pressure sensor (the Freescale MPX2300DT1), to make a signal large enough to be read with the Arduino A/D converter. The circuit will be soldered on the instrumentation amp/op amp protoboard. The sensor calibration will be checked with water depth in a small reservoir. Note: the pressure sensor comes in a package that exposes the wire bonds and is too delicate for student assembly by novice solderers. We will make a sensor module that protects the sensor and mounts the sensor side to a 3/4″ PVC male-threaded plug, so that it can be easily incorporated into a reservoir, and mounts the electronic side on a PC board with screw terminals for connecting to student circuits.  This sensor is currently being prototyped, and if it turns out to be too fragile, we will use a Freescale MPX2050GP, which has a sturdier package, but is slightly less sensitive and more expensive. (It also isn’t made of medical-grade plastics, but that is not important for this lab.) Note that we are deliberately notusing pressure sensors with integrated amplifiers, as the pedagogical point of this lab is to learn about instrumentation amplifiers.EE concepts: differential signals, twisted-pair wiring, strain gauge bridges, instrumentation amplifier, DC coupling, gain.Equipment needed: Power supply, amplifier prototyping board, oscilloscope, pressure sensor mounted in PVC plug with breakout board for easy connection, water reservoir made of PVC pipe, secondary containment tub to avoid water spills in electronics lab.
10. Class-D power amplifier
11. Electrocardiogram (EKG)
    Students will design and solder an instrumentation amplifier with a gain of 2000 and bandpass of about 0.1Hz to 100Hz. The amplifier will be used with 3 disposable EKG electrodes to display EKG signals on the oscilloscope and record them on the Arduino.Equipment needed: Instrumentation amplifier protoboard, EKG electrodes, alligator clips, Arduino, oscilloscope.

3. Systemwide Senate Regulation 760 specifies that 1 academic credit corresponds to 3 hours of work per week for the student in a 10-week quarter. Please briefly explain how the course will lead to sufficient work with reference to e.g., lectures, sections, amount of homework, field trips, etc. [Please note that if significant changes are proposed to the format of the course after its initial approval, you will need to submit new course approval paperwork to answer this question in light of the new course format.]

The combination of BME101 and BME101L is 7 units (21 hours per week).  The time will be spent approximately as follows:

• 3.5 hours lecture/discussion
• 3.5 hours reading background and circuits text
• 3 hours read lab handouts and doing pre-lab design activities
• 6 hours lab
• 5 hours writing design reports for lab

4. Include a complete reading list or its equivalent in other media.

Lab handouts: there is a 5- to 10-page handout for each week’s labs, giving background material and design goals for the lab, usually with a pre-lab design exercise.  The handouts from the prototype run of the course can be found at http://users.soe.ucsc.edu/~karplus/bme194/w13/#labs
Data sheets: Students will be required to find and read data sheets for each of the components that they use in the lab.  All components are current commodity components, and so have data sheets easily found on the web.  Other readings are associated with the lecture course.

5. State the basis on which evaluation of individual students’ achievements in this course will be made by the instructor (e.g., class participation, examinations, papers, projects).

Students will be evaluated on in-lab demonstrations of skills (including functional designs) and on the weekly lab write-ups.

6. List other UCSC courses covering similar material, if known.

CMPE 167/L (sensors and sensing technologies) covers some of the same sensors and design methods, but at a more advanced level.  BME 101L would be excellent preparation for the CMPE 167/L course.

Physics 160 offers a similar level of practical electronics, but focuses on physics applications, rather than on bioengineering applications, and is only offered in alternate years.

7. List expected resource requirements including course support and specialized facilities or equipment for divisional review. (This information must also be reported to the scheduling office each quarter the course is offered.)

The course will need the equipment of a standard analog electronics teaching lab: power supply, multimeter, function generator,  oscilloscope,  computer, and soldering irons. The equipment in Baskin Engineering 150 (commonly used for EE 101L) is ideally suited for this lab. There are 12 stations in the lab, providing a capacity of 24 students since they work in pairs rather than as individuals.  The only things missing from the lab stations are soldering irons and circuit board holders (such as the Panavise Jr.), a cost of about $45 per station.  Given that a cohort of bioengineering students is currently about 35–40 students, two lab sections would have to be offered each year.

In addition, a few special-purpose setups will be needed for some of the labs, but all this equipment has already been constructed for the prototype run of the course.

There are a number of consumable parts used for the labs (integrated circuits, resistors, capacitors, PC boards, wire, and so forth), but these are easily covered by standard School of Engineering lab fees.  The currently approved lab fee is about $131, but may need some adjustment to change exactly what tools and parts are included, particularly if the students are required to buy their own soldering irons (a $20 increase).

The course requires a faculty member (simultaneously teaching the co-requisite Applied Circuits course) and a teaching assistant (for providing help in the labs and for evaluating student lab demonstrations). Because the lab is such a core part of the combined course, it requires faculty presence in the lab, not just coverage by TAs or group tutors.

8. If applicable, justify any pre-requisites or enrollment restrictions proposed for this course. For pre-requisites sponsored by other departments/programs, please provide evidence of consultation.

Students will be required to have single-variable calculus and a physics electricity and magnetism course. Both are standard prerequisites for any circuits course. Most of the labs can be done without calculus, but it is essential for the accompanying lecture course.

9. Proposals for new or revised Disciplinary Communication courses will be considered within the context of the approved DC plan for the relevant major(s). If applicable, please complete and submit the new proposal form (http://reg.ucsc.edu/forms/DC_statement_form.doc or http://reg.ucsc.edu/forms/DC_statement_form.pdf) or the revisions to approved plans form (http://reg.ucsc.edu/forms/DC_approval_revision.doc or http://reg.ucsc.edu/forms/DC_approval_revision.pdf).

This course is not expected to contribute to any major’s disciplinary communication requirement, though students will get extensive writing practice in the design reports (writing between 50 and 100 pages during the quarter).

10. If you are requesting a GE designation for the proposed course, please justify your request making reference to the attached guidelines.

No General Education code is proposed for this course, as all relevant codes will have already been satisfied by the prerequisites.

11. If this is a new course and you requesting a new GE, do you think an old GE designation(s) is also appropriate? (CEP would like to maintain as many old GE offerings as is possible for the time being.)

No General Education code is proposed for this course, as all relevant codes (old or new) will have already been satisfied by the prerequisites.

Self-taught teacher

I recently got some praise on the AP Bio teachers’ forum for answering some statistical questions, which embarrassed me a little.  I always feel like an imposter when I help anyone with statistics.  Despite having a B.S. and M.S. in math, and a Ph.D. in computer science, I learned statistics rather late in life—my first course in it was a graduate stochastic processes course in 1999, when I was 44, and my second was a Bayesian statistics course in 2001.  Other than those two courses, I’m pretty much self-taught in statistics and have to rely heavily on Wikipedia and other on-line sources.

I occasionally answer biology questions on the forum also, though my biology has an even shakier foundation: one freshman bio course, one junior-level biochem class (without the prerequisite general and o. chem), one graduate protein structure class—again, I have to rely heavily on things I’ve heard from colleagues or seen on the internet.  I feel like a real imposter answering bio questions on the AP Bio teachers’ forum, since everyone else on the forum has had far more courses in biology than I ever will. I doubt that I have the knowledge to teach even an 8th-grade life science course, much less an AP bio course.

While I’m always willing to share what I know, I frequently have gaps in my understanding that I’m not even aware of.

Of course, I’ve gotten used to teaching things I’ve had to teach myself—several of the courses I’ve created have been in subjects where I had had no formal instruction:

• applied circuits for bioengineers (2013)
• technical writing (1987–1999)
• digital typography course (1996–1998). Just this month I met an alumnus of that course, who got into graphical design, then web design and programming as a result of that course—he regrets that he did not take any other computer courses in college.
• bicycle transportation engineering (1997)
• bioinformatics: models and algorithms (our core grad bioinformatics course, 1998–present)
• protein structure prediction (1996–2011)
• banana slug genomics (2010, 2011)
• how to be a grad student (1990–present)
• resource-efficient programming (2004)

Other courses I’ve created after only one prior course:

• VLSI design (1982–2000)
• digital synthesis of music (1989 and 1991)

For that matter, my first faculty position was a joint appointment between an EE and a CS department, teaching mainly EE courses, based on having a CS PhD and having taken 3 EE courses (digital logic, microprocessors, and VLSI design).

Of course, I’ve also taught several courses designed by others, often with little prior training in the field.  I find that more difficult than teaching a course that I’ve designed myself, even if it takes me six months or more to teach myself the material before designing a course (as with the circuits course).

Because so much of what I’ve taught is material that I’ve had to teach myself, I tend to take a different approach to teaching than many other faculty.  I see my role as trying to provide guidance for students to learn the material faster than I did, with less time chasing down blind alleys, not to just dump some pre-digested knowledge into their heads for them to memorize and regurgitate. I don’t teach them as I’ve been taught, but as how I wish I had been taught.  I tend to pose them problems to guide their learning, rather than giving them information, then expecting them to repeat it back to me. (I’m self-taught in pedagogy also, but that is normal for university faculty.)

I want them to learn skills (not facts) that can serve them as a basis for further learning—for example, in the circuits course, I wanted the students to be able to design and build simple amplifier circuits and to be able to write design reports.  I didn’t care so much whether they could work book problems as that they acquired the mental attitudes of engineers—that they could design and build things, that data sheets are worth consulting, that precise and accurate recording of what was designed and measured is essential, that often you have to check things for yourself (not blindly trusting the data sheets or simple models), that consistency and sanity checks are an important part of any problem solving, that breaking a problem into subproblems is an essential element of design in any engineering field, and so forth.  (I think they got some of that, but it takes more than 10 weeks for the attitudes to really become part of their worldview.)

I think that the flattery on the AP Bio teachers’ forum was to soften me up to mentor a bright high school student that the teacher knew.  I’m willing to serve as a mentor for smart and motivated kids interested in bioinformatics, but not in other branches of biology—I just don’t know enough in those fields to guide anyone.  Even in bioinformatics, I don’t find it easy to guide students below a certain level of training—I have a few programming projects I could use student help on, but I don’t have many ideas for students who aren’t already expert programmers.

I have one pending request from a high school student wanting to do computational protein work in my lab this summer—something I don’t really do any more.  I have no idea what to tell her—10 years ago, I had an active lab that I could have worked her into, but with the repeated failure of grant requests and my subsequent disillusionment with the whole grant rat race, I no longer have a lab. I’m now working more as a consultant on other people’s research (helping out with statistics, signal processing, genome assembly, and other things I’m self-taught in) and putting most of my time into teaching and creating new courses.

Class D with LC filter works

I had a class-D amplifier working at the beginning of January, but I’ve changed the specs a bit since then (adding the LC filter) , and the students have a different comparator chip than I used then (they have an LM2903, not an LM311), so I tried re-implementing it last night and this morning.

For the LC filter to work well, we want to use a fairly high frequency for the PWM (over 50kHz and preferably near 100kHZ), but there is a tradeoff.  Power is dissipated as heat in the FETs on every transition, because both the pFET and the nFET are simultaneously on as the gate voltage on the FETs passes through intermediate values.  To keep the amplifier efficient and to keep the FETs cool, we want to spend as little time as possible in the intermediate voltages, which means few transitions and transitions that are as fast as possible.

As I mentioned in Class D works,   “The LM2903 does have only a 20mA output current, rather than the 45mA output current for the LM311, which would mean a 330Ω pullup resistor, rather than 150Ω for the LM311 with a 6.6v supply  … . That means somewhat slower rise times for the gates of the FETs, which is probably the limiting factor on the efficiency of the amplifier. I suppose I could add a class A stage with a bipolar transistor to drive the FET gates if I needed faster rise times, but I think that the current design is working well enough for a 1-week lab exercise, so I won’t mess with it unless I need to.”

I had not re-read those notes last night, and was having trouble getting a high enough PWM frequency for the LC filter to offer much reduction in signal.  At the frequencies I wanted to use, the FETs got hot.  The problem is that the gate capacitances of the two FETs are huge (around 675pF and 500–750pF according to the spec sheets, adding up to 1.2–1.4µF), so the rise and fall time of the signals is limited by how fast the comparator can charge and discharge that big a capacitance.  Last night I was trying a pullup resistor of 1kΩ, which was clearly not providing enough current.

Today, I tried putting the two comparators of the LM2903 in parallel, providing twice as much pull-down current, and shrinking the resistor until the low voltage was about 0.8V (enough to turn off the nFET).  The rise time to Vdd-1V is about 0.8µs and the fall time to 1V is about 1.2µs, so I might do better with a slightly larger pullup,  to balance the rise and fall times.  Of course, I’ve been doing my testing with just a 6.6v single-sided supply, and they’ll be doing their design with a 5v or 6V supply for the preamp and a separate ±9v dual supply for the power stage, so some of the parameters may change, but it looks like I can go up to about 100kHz now for the PWM frequency without the FETs overheating, even after running for an hour.

One problem that may be reduced with the bench supplies is the coupling of noise back into the power source.  I’m seeing a 10mV fluctuation in my 6.6V that is synchronized to the FETs switching.  At first I thought that this was causing big problems with the comparator, since the gate voltage waveforms had flat spots in the rise and fall that corresponded to the places where the noise on the power supply was biggest.  But I now think that the problem is a different one: capacitive coupling between the gate and drain (called reverse-transfer capacitance on the data sheets).  As the FETs change state, the voltage on the drain changes rapidly in the opposite direction to the change on the gate, and the capacitive coupling is enough to keep the gate voltage from changing much as the drain voltage changes. This capacitance is about 10% of the gate capacitance, so a 6v swing on the drain would make about a 0.6v swing on the gate, which is about what I’m seeing, and the flat spots on the gate transitions correspond precisely with the rise and fall of the drain voltage.

I’ve provided a couple of plots to show the waveforms at the FETs and at the loudspeaker.

Gate (yellow) and drain (green) voltages on the FETs with about a 100kHz PWM frequency. The scales are 2µs/division and 1V/division, with the center horizontal at 3V. The rise and fall times for the gate are a little more than a microsecond.
I used the Bitscope BS10U Pocket Analyzer to record the waveform, but I had to use Photoshop elements to make the image usable (changing the stupid black background to a white background, and fixing the other colors to have barely adequate contrast). [Click image to see larger version.]

Voltage waveform on the loudspeaker (after an LC filter) with a whistled input.  The loudspeaker voltage really is a pretty good triangle wave at 100kHz, with an added audio waveform.  Because the loudspeaker acts as an inductor at 100kHz, there is very little current (hence little power) in the triangle wave.
The center line is 2.5V and the scale is 0.5V/division. The horizontal scale is 100µsec/division.
I used the Bitscope BS10U Pocket Analyzer to record the waveform, but I had to use Photoshop elements to make the image usable (changing the stupid black background to a white background, and fixing the other colors to have barely adequate contrast). [Click image to see larger version.]

I’m wondering whether using the larger voltages needed for getting full power out of the loudspeaker will result in further slowing down of the gate voltage swing and more power dissipation in the FETs.  I’ll probably have to take my breadboard into the lab on Monday, and try it with the bench supplies.

Another problem with the power amp lab is feedback squeal.  The microphones are omnidirectional and the loudspeaker is generally close enough that by the time we get obvious amplification, the amplification is enough to cause feedback. Even with only enough gain to get about a 3.5V peak-to-peak swing on the loudspeaker I trigger squeal. For next year, I may want to think of a different sound source for them to amplify than a microphone.

The inductors I bought (AIUR-06-221K) are not shielded, and a 90kHz has significant energy out to about 3Mhz, so I wondered whether the amplifier would interfere with an AM radio.  It turned out to be a little hard to test, because my MacBook Pro laptop interfered with the AM radio up to about a meter away.  Eventually I put the inductor on a long piece of speaker cord, so that I could test the radio far enough from my laptop.  The inductor interfered with the radio when it was within about 10cm—not nearly as much as the laptop, but you’d definitely want shielding before putting an amplifier like this into an AM radio.

I checked that the loudspeaker really was acting like an inductor at the PWM frequency, by putting it in series with a 0.25Ω resistor (two 0.5Ω in parallel).  With no input to the amplifier, the waveform across the resistor was a very small square wave (with a lot of noise and harmonics) while the waveform across the loudspeaker+resistor was a triangle wave, 90° out of phase.  When I whistled into the mic, the audio signals at the loudspeaker and resistor were in phase and with a ratio of about 29 (compatible with a 7Ω impedance for the speaker).  The voltage was about 2.4V p-p across the speaker and the current about 350mA p-p through the speaker, so I was getting about 0.4W RMS into the speaker, a long way from its 10W limit.

Idea for phototransistor/FET lab

Based on the conversation I had with the students at the beginning of class yesterday, I came up with an idea for a lab that uses both the phototransistor and an FET that should be fairly fun and easier than many of the labs we’ve done.  The students were saying they would enjoy a musical application—the student who mentioned it was thinking of a light harp, where the “strings” are light beams that you break with your hands to trigger synthesized notes.  It would be pretty easy for them to make a circuit that detects the presence or absence of light, but all the fun parts of such a lab are in the programming, which is not part of this class (and which most of the students have no training in).

I decided to try making a sound that the students could control in some way with a phototransistor, but not necessarily a particularly musical sound.  The obvious application of an FET is to put it in series with the loudspeaker and a power supply and turn the FET on and off.  The relaxation oscillator that they did for the hysteresis lab this week could be used to drive the FET (at least, if we lower the frequency down into a comfortable part of the audio range). The students don’t have another 74HC14N chip, but they don’t need one, since all four nodes of the hysteresis oscillator (+5v, out, in, GND) are available at the screw terminals of the board they soldered.

Since we are interested in increasing RC, we can do it by increasing C—adding another capacitor in parallel with the one on the board. All they need to do is connect wires from the board to a breadboard, add capacitance to lower the frequency, and connect the output to the gate of the FET.

So we’ve got sound (pretty loud sound if they use a high pitch) out, all we need is control.  The simplest thing I could think of was to put the phototransistor across the capacitor.  In bright light, it conducts a large current, discharging the capacitor and keeping the input low (thus keeping the output high).  In darkness, it conducts essentially no current and the oscillator oscillates as it did before we added the phototransistor.  At intermediate light levels, it conducts some current, which means that it takes the oscillator much longer to charge the capacitor up to the high threshold, so the output-high time is stretched.  If the current through the resistor is slightly larger than the current through the phototransistor, the oscillator oscillates at a low frequency.  If it is much higher, the oscillator output is stuck high, and if it is much lower, the oscillator oscillates at its maximum frequency.  So by shadowing the phototransistor, one can modulate the frequency of the output.

One problem with the design as a toy is that the resistor used determines the amount of ambient light needed to shut the thing off.  I had to add resistors in parallel with the one already in the oscillator to make the current large enough to oscillate even in dim light, and I needed to increase the current a lot more to have any control in sunlight.  When I had the current that high, though, the oscillator would not shut off with just room lights at night.

I suppose I can make a virtue out of this problem, though, by having the students measure the range of currents that they get from the phototransistor (with a bias voltage around the V_IH threshold) for the lighting in the room and the shadowing they can do with their hand, then pick the resistance they would need to use in parallel with the existing resistor. After that, they could compute the capacitance they would need to add to get a reasonable high frequency in darkness.

This is a simple design exercise, gets another use out of the hysteresis oscillator board, and is sort of fun to play with (though the pulse-train buzzes do get annoying to listen to after a short while—I’m sure I’ll have a monster headache by the end of the lab session. I’ll try to write up this lab as soon as I get Monday’s quiz written.

I’m now thinking that next year I’ll rearrange the first 6 labs into several shorter labs:

1. buying parts kit and familiarization with it.  Marking bags of capacitors, learning to use multimeter to measure resistors.
2. thermistor lab using multimeter  (and make sure we have water hotter than 70°C and colder than 10°C)
3. thermistor lab using voltage divider and  Arduino
4. microphone lab getting DC characteristics with Arduino
5. microphone lab setting DC bias and learning to use the oscilloscope
6. hysteresis oscillator on breadboard
7. soldering hysteresis oscillator design
8. phototransistor and FET lab
9. characteristics of stainless steel electrodes
10. characteristics of Ag/AgCl electrodes
11. audio amplifier with op amp, dual power supply
12. audio amplifier with op amp, single power supply

That order would give us more time to develop the notion of impedance before the electrode lab, as well as more time to learn to use gnuplot, but after 6 weeks will be in about the same place I hope to be at the end of next week after 6 weeks.  It might be necessary to spend two of the shorter labs on the dual-power-supply op amp, but we’ll see.

 

Fifth day of circuits class

I feel pretty good about today’s lecture, though things got a little rushed at the end.

Three-resistor voltage divider for the first question.

I started with a “do now” question, similar to the one from Monday. Actually, I started with 2 questions. The first just asked what the output voltage would be for a 3-resistor voltage divider. The second repeated the question from Monday, but with the additional constraint that the power supply was 5 volts:

You have sensor whose resistance varies from 1kΩ to 4kΩ with the property it measures and a 5v power supply.  Design a circuit whose output voltage varies from 1v (at 1kΩ) to 2v (at 4kΩ).

Several students realized that the first question was a hint for the second one and that the variable resistor had to be RB or RC, and could set up the equations and solve for RA and RC.  This is a better performance than on Monday’s “do now”, but only about 1/3 of the class got it completely, and several of them were not confident of their results, so we again took time to go over the whole solution. I think that everyone (or almost everyone) understood the design process and how to set up and solve the equations by the end of the presentation, which I drew out of the students as much as possible.  I also mentioned that we could have solved the problem with a different circuit (putting RC in parallel with RB instead of in series), but did not further elaborate on that point.

The do-now plus going over the solution took about 33 minutes, which is a little more time than I’d like to be spending on these questions.  It would be good to get the time down to 15 minutes, but I don’t see how to do that without losing half the class.  If the problems are easy enough that everyone gets them, then there is no point to taking up any class time with them, and if they are hard enough that 1/3 to 2/3 of the class don’t get them, then they need to be gone over in class.

After the do-now, we spent a little time discussing the “fit” command of gnuplot, since the students have to fit models to the data they collect tomorrow, and I’m not providing them a script this time (though they can modify the script that was provided in the first lab).

Finally, we got to the theoretical meat of the class—we discussed what sound was (ending up with variations in pressure for a fluid, though we discussed briefly transverse and shear waves in solids).  Then I introduced microphones as transducers, trying to get the students to remember their elementary mechanics, so that we could do pressure→force→displacement→1/capacitance→voltage for electret mics.  The hardest part was getting students to remember that a spring-mounted object had force proportional to displacement (a lot remembered the energy was somehow related to displacement squared and got stuck on that formula).  I suspect that the local physics department would not be seeing a high score on the Force Concept Inventory for students coming out of their physics classes, as a lot of them seem to have concentrated on cramming formulas rather than learning fundamental concepts.  Someone did remember Q=CV and someone else could reason from wanting voltage proportional to displacement to needing constant charge which let me introduce both conventional capacitance microphone (with a large resistor to voltage source) and electrets.  I also explained that the electret had an enormous resistance, so we couldn’t get any measurable current out of it, and we needed an FET transistor to convert the voltage to a current.

Because both the do-now and extracting vague memories of physics from the students took longer than I had planned, we were a bit rushed for the last part of the lesson, which was a simple model of I_ds vs V_ds for the FET output stage of the electret mic. I asked for advice on drawing the plots for resistors and for current sources, and got the appropriate straight lines.  I then drew a smooth transition between them and claimed that the simple FET models usually consisted of a linear region at low voltage (which my co-instructor refers to as the “triode” region, a usage I’ve seen in some other presentations) and a saturation region at high voltage, and that we usually try to stay out of the sublinear region in between.

I also said that the saturation region is not really constant, but has a slight upward slope, since they will be measuring the I-vs-V characteristic of the electret microphones tomorrow, and they will certainly be observing that.  The lab handout gives them 4 models to fit: linear, constant current, an empirical blend of the two, and a model that allows current increase in the saturation region.  Neither the 3rd nor the 4th model match the ones usually used in circuit simulators, but I had trouble fitting parameters to those models, even with voltage-modulated channel lengths, so I gave up and produced simple models with few parameters that can be fit pretty easily. We’ll be revisiting FETs again before the power-amp lab (where they’ll use pMOS and nMOS power FETs to make a class-D amplifier). Somewhere around then, I’ll have to give them some usable models for how saturation current varies with gate voltage, which I deliberately did not cover in this lecture.

I’m a bit worried about how big tomorrow’s lab is.  There are again 2 parts:

• the DC characterization of the mic using the Arduino to gather data (plus a few hand-collected points for higher voltages than we can subject the Arduino to)
• designing a pull-up resistor to bias the mic into its normal operating range (in the saturation region) and observing the microphone output on the oscilloscope.  I also asked students to hook up their loudspeakers to the signal generators, to provide known inputs to the mic, and some other little stuff, but I’ll probably be happy if everyone gets the first part done and manages to observe waveforms on the scope.

On Friday, most of the lecture will be standard EE stuff by my co-instructor (probably current sources, Thévenin equivalents, and Norton equivalents).  I may have a do-now question at the beginning of the class, if I can come up with one that I think is pedagogically useful.