# Gas station without pumps

## 2013 April 10

### 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

Information to accompany Request for Course Approval
Course #:
101
Catalog Title: Applied Circuits for Bioengineers

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

Information to accompany Request for Course Approval
Course #
101L
Catalog Title
Applied Circuits Lab

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 VIL, VIH, VOL, and VOH. 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.

## 2013 March 5

### Twenty-second day of circuits class

[Correction: Actually 23rd day—I forgot to increment the counter for the quiz day.]

On Friday, I had suggested that today I’d want to talk about

• how class-D amplifiers work. I’m sure it is very strange for a circuits class to cover class-D amplifiers, without ever having covered classes A, B, AB, and C, but that’s the way it worked out for us.
• LC high-pass filters before the loudspeaker.
• Zobel networks for compensating loudspeakers to get resistive behavior.

By this morning I had decided that I needed to talk change the order of the material and put off the LC filters until Wednesday, and the Zobel networks we may not get to at all, depending how things go.

I started today with a reminder of the square wave noisy toys we made in the tinkering lab, with a pFET in series with the loudspeaker, then I added an nFET down to a negative voltage source, so that we could get pulses of ±V to the loudspeaker.  I introduced the two main characteristics of a rectangular wave: the period and the duty cycle. I then talked about how averaging out the pulse could turn the duty cycle into a value (averaging 50% duty cycle gives 0, averaging 75% duty cycle gives V/2, averaging 25% duty cycle gives –V/2, and so forth).

Once they had the basics of pulse-width modulation, I went over the notion of a block diagram again, as the quiz had made it clear that many students really did not know what block diagrams were for, and had done the sort of random clouds of ideas that elementary school teacher who teach mind-mapping seem fond of.  (I find such random clouds of thoughts with arrows that have no particular meaning one of the most useless and irritating of educational fads.)  So I explained block diagrams as a way to decompose a design into smaller designs, with careful input and output specifications (the signals) between the blocks.

We then proceeded to start designing the block diagram for a class-D amplifier, starting from sound in (to a microphone) and sound out (from a loudspeaker) and working our way in towards the middle of the design.  I showed them how a decision at one point (like the power supply for the amplifier in the pre-amp section) could cause other decisions to ripple through the design: Vref was set in the middle of the power supply range, the output of the preamp became Vref±Vamp, with Vamp

We got as far as interpreting the voltage-to-PWM converter as a comparator taking input from the preamp and from a triangle wave generator, but we still need to look at level shifting for an input of the comparator, to get both to the same DC level.

I did get the students to figure out that the PWM frequency needs to be at least twice the highest frequency they want to amplify (yay! they remembered something from the sampling lab!).  They figured they needed at least 32kHz, and probably more than that. I told them that we were limited by how fast we could drive the FET gates up and down, so that we used the lowest frequency that was enough above 32kHz—typically 60–100kHz.

We’ll probably start on Wednesday reviewing the block diagram and examining the inputs of the comparator, then introduce the open-collector output of the LM2903.  Sadly, the LM2903 does not have an open-emitter option, as some comparators do, so we’ll need to look at sizing pull-up resistors for driving the nFET and the pFET.  I may want to rethink which comparator to use for next year, so that we can have more options, or perhaps add an external bipolar to get more drive capability for the FET gates, or even give up on FETs and use power bipolars instead.  After looking at pull-up sizing we’ll look at the LC filter between the FETs and the loudspeaker.  Only if we have time will we look at Zobel networks.

I thought that today’s class went reasonably well—we covered about as much as I expected to, and we got a better look at the process of breaking a design down into blocks and how precise connections between blocks let us propagate the consequences of design decisions.

After class, I had my usual Monday afternoon office hours in the lab.  There were a few questions about the quiz I had returned today.  You can tell that these are well-trained students, because they didn’t ask me about points, but about how to do some of the problems they missed.  (Incidentally, I had misgraded the group tutor’s quiz—he got a 72 not a 66—I’d stupidly misread which signal was the input and which the reference voltage to his amplifier.)

There were also 3 students finishing up last Thursday’s lab.  One pair had gotten the circuit working on a breadboard last Thursday and just had to lay out and solder the circuit.  They found one error in their design while doing the layout: they had been off by a factor of 10 on one of the capacitors and did not have a capacitor of the size they had designed for.  Rather than changing the resistor, they decided to solder 2 capacitors in parallel—a perfectly reasonable solution.  The other student had been ill on Thursday and had to do the whole pressure sensor lab by himself.  I ended up staying in the lab for 6 hours, so that he could finish and demo the working instrumentation amplifier soldered on the protoboard.  His first attempt at a demo revealed that he had changed a capacitor value between his schematic and his layout (from 4.7nF to 4.7µF) and so has a low pass filter with a corner frequency of 0.5Hz instead of 50Hz.  He learned how to use a solder sucker, replaced the capacitor, and his design worked fine.

While I was in the lab, I ended up helping a number of the EE101 circuits students with their first op amp lab.  Some were struggling with such basics as connecting power to the op amps (there wasn’t any drawn in the schematic they were using).  There were other major gotchas in the lab: like instructions telling them to look at the phase change in the signal at 1Hz for an input of 1V, without warning them that the gain would be so high that they would get clipping of the output.  Some students were also having trouble with weird high-frequency ringing in the output,which went away when I had them add bypass capacitors to their power lines.  It appears that the EE 101 class has gotten to week 9 out of 10 without having talked about bypass capacitors and without the students having learned how to limit the current on the power supplies.  I find it difficult to believe that the professors who wrote the lab assignments actually went to the lab and did the labs, or they might have noticed that the “cookbook” procedures they were having the students follow did not work in the real world.

Creating good lab experiences for a course is a lot of work (I’ve been putting in much more than 40 hours a week on the design of this course, testing and revising the labs), and I don’t think that the EE faculty have put in the time needed to do it.  The labs in EE 101 look boring, with essentially no design component, and apparently untested, even though I think that they have been used for years.

I was worrying about whether students in my class were learning enough for me to argue with the EE department that they should be allowed to take the signals and systems course and the bioelectronics course without taking EE 101 (those are the two required courses for the bioelectronics concentration).  Now I’m wondering whether the students taking EE 101 have learned anything useful, and whether the applied circuits course I’m teaching should be required instead of EE101 for the bioelectronics majors.  I’m not sure I’d trust my students to do well on an EE circuits theory test, but I think that they’d be a lot more useful in the lab than students who’d just had EE 101.

Speaking of tests, I did tell a couple of the students that we’d not have a final exam.  I’d rather get them to do both the class-D power-amp lab and the EKG design than cram for a test which they’ll forget again 2 days later.  The design reports they are writing for the course are probably better preparation for life as engineers (or, in some cases, as grad students) than yet another test.

## 2013 February 28

### Pressure-sensor lab went well

Filed under: Circuits course — gasstationwithoutpumps @ 21:32
Tags: , , , ,

The pressure-sensor lab went fairly well today.  We once again borrowed soldering irons from the RF lab (where my co-instructor teaches), but we did not borrow enough board holders, so a number of students had to solder with the boards just resting on the benchtop.  This was not a major problem, but having more board holders would be good.

Many of the students had done an adequate job of doing the design ahead of time, and even those who had not mostly managed to finish within 4 hours (but the lab is supposed to be scheduled for 3 hours).  Most groups managed to demonstrate working PC boards with instrumentation amplifiers amplifying the differential output of the strain-gauge pressure sensors, generally with gains in the range 100 to 300. I have one group coming in on Monday to finish the soldering—they took the more cautious approach of debugging on a breadboard first, and had to do a little redesign to make everything work.  I think that they’ll complete with no problems on Monday, as they had good notes on what their breadboarded circuit was, and had come up with what looked like a feasible layout.

Soldering was much more routine this time than on the first soldering lab.  Students were able to check their own work for cold-soldered joints, and only one group forgot to trim the extra wire length on the back of the board after soldering (they had a short when they put the board down, from two untrimmed leads touching).

Some students called me over to help them debug at one point, but I had to refuse, as they did not have  readable schematics that I could help them debug from.  After I told them why I couldn’t help them, they redrew their schematics, and I then helped them check the design against their soldered board.  It seems that they had soldered everything up correctly according to their schematic, and the DC voltages were right at all the nodes, but the twisted-wire cable to the pressure sensor had the wires scrambled. (Luckily, they had followed my advice of using 4 different colors for the wires, though they had not followed the red=+5v, black=0v convention—several students are still using colors at random.)  When they screwed the wires into the right terminals, their circuit worked.  It seems that schematics were not the only thing that they were sloppy with!

Some of the students used PDF markup tools to add the layout of their extra wires and parts to the prototyping board PDF worksheet.  That seems to have worked well for them, producing neater and more easily checked layouts that the pencil scrawls that I (and many of the students) used.  I hope they tell me in their lab reports what tool they used, so that I can recommend it for the EKG lab and for the pressure-sensor lab next year.  No one did the wire lists that I recommended, but there were relatively few wiring errors (and those were inherited from errors in the schematics, so wiring lists would not have helped).  I think I’ll leave the wiring lists out of the assignment next year.

One thing that surprised me (another moment of culture shock), was that the seniors in bioengineering did not know what a peristaltic pump was.  I was trying to connect what they were doing to something they already knew, only to find out that what I thought was familiar to them was novel.  I demonstrated the basic principle for a couple of them by hooking two ends of the flexible tubing up to the two ports of their differential sensor, and pinching the tube between a pen and the benchtop.  By pulling the tube through the squeezed area, I could get a large pressure difference between the ports.  Since peristaltic pumps are standard lab equipment in many of the labs they are working in, I was surprised that they have never used one or even known of their existence.  I’m now wondering whether I should do the demo demonstrating the principle in class on Monday for everyone.

## 2013 February 27

### Twenty-first day of circuits class

Filed under: Circuits course — gasstationwithoutpumps @ 20:04
Tags: , , , ,

This post has not been appearing on WordPress.com, so I’m going to try doing binary search on it to find the problem.

I started today’s class with questions about this week’s lab—students had fewer than I expected, so they are either very confident about their designs or so lost they don’t know what to ask. I guess we’ll find out in the lab tomorrow.

I showed them the tiny medical-grade pressure sensor that I had considered using, but ultimately rejected as too fragile, switching to a sturdier sensor with an easier-to-assemble breakout board. I also showed them my assembled prototyping board and talked about twisted-pair cables to minimize inductive pickup, keeping wires short on the board, using color-coded wires for the different types of signals (red for +5v, black for gnd, some other color for Vref, yet another color for signal, … ).

Instrumentation amplifier protoboard with circuit wired for the pressure sensor lab (top left connector to pressure sensor, bottom center connector to Arduino). Red is +5, black is GND, brown is Vref, yellow is low-gain, orange is high gain, and green is the feedback for the second-stage op amp.

I also covered one other topic relevant to instrumentation amps: common-mode rejection ratio.

After talking about tomorrow’s lab, I started on material for next week’s lab:

• AC power computation. I worry that I lost a few people, because I had to give them the $\cos(x)\cos(y) = 0.5(\cos(x+y) + \cos(x-y))$ trig identity and explain complex conjugation. The bottom line (that real power is $Re(\bar{V}\bar{I}^*$) should be useful in Monday’s class when we start looking at how much power is delivered to the loudspeaker at different frequencies with and without an LC filter.
• More complicated loudspeaker model. I did decide to switch from the linear model I had been using to a model with a frequency-dependent inductor, and I updated and released the handout for the power-amp lab today.

We ended class almost precisely where I expected us to, so for once my timing estimates were good.

On Friday we’ll have the quiz—the students wanted the TA to take it before they did, so that they could be assured that it was not as oversized and difficult as the first quiz, but he does not have any time before tomorrow evening, which would be the latest that I could incorporate any feedback. So we’re just going to have to rely on my estimates of how difficult the quiz is (fairly hard, but not as hard as the first one—I’m hoping for a median of 50% this time).

On Monday, I’ll want to talk about

• how class-D amplifiers work. I’m sure it is very strange for a circuits class to cover class-D amplifiers, without ever having covered classes A, B, AB, and C, but that’s the way it worked out for us.
• LC high-pass filters before the loudspeaker.
• Zobel networks for compensating loudspeakers to get resistive behavior.

If it looks like I’ll be running short of time, I’ll cut some of the Zobel network stuff, since I already decided that they would not add lossy compensation networks in their power amplifiers (I didn’t want to buy 10W resistors). Most of them will do LC filters, though, so I’d better cover that carefully, and of course the whole thing about how class-D amplifiers works is rather tricky, so Monday’s lecture will be pretty full.

## 2013 February 19

### Pressure-sensor lab handout written

Filed under: Circuits course — gasstationwithoutpumps @ 22:32
Tags: , , , ,

In All weekend and handouts still not written, I complained

I spent all day Saturday and Sunday (except for a few hours grading) working on the lab handout for the class-D power amplifier lab.  It was going great on Saturday, but I decided to include a portion of the lab on doing an LC output filter, rather than just directly connecting the speaker between ground and the FETs of the output stage as I had originally planned.  That opened a big can of worms.

and I concluded with

Since I need to do more experimenting with the class-D design to find the problems before handing it over to the students, I’ve moved that lab from week 8 to week 9, giving me another week to finish the handout (which is already 12 pages long, and not finished yet).  That means that I have 2 days to write the new lab 8: the instrumentation amplifier for the strain-gauge pressure sensor.  I’ve built and tested such an amplifier (even demoed it on the first day of class), so there aren’t any surprises waiting for me, but I have to write up not only an explanation of instrumentation amps, but also how to do layout for the protoboard.

Hmm, I just realized that I don’t have any posts on the blog for the rev3.0 instrumentation amp protoboard that I designed using the MCP6004 quad op-amp chip instead of the MCP6002 dual op-amp chip (still with the INA126P instrumentation amp chip).  My old test of the pressure sensor lab was with the old protoboard. Maybe I need to redo the pressure-sensor lab with the new board, to make sure that there aren’t any problems with the PC board design.

So I’ve got today and tomorrow to redo the pressure-sensor lab and write up the lab handout, plus finish the grading and figure out how I’m going to present sampling and aliasing on Wednesday, before the Thursday lab.  (I plan to use my son’s stroboscope, but I’ve not figured out what motion we’ll sample with it.)

Well, it is now Tuesday night ending my 4 day all-work weekend (all my weekends have been like that for quite a while).  I did get the grading done and the grades recorded. I also got the handout done for the pressure sensor lab—I even got feedback from my co-instructor on a draft (pointing out at least three things that I needed to fix).  I also designed and soldered up another amplifier today, this one adding a low-pass filter between the INA126P instrumentation amp and a second-stage op amp. The new protoboard works fine and is easier to work with than my first protoboard design (which wasted too much space in providing power connections—now I just take +5V and Gnd through small screw terminals).

I took the unfiltered instrumentation amp output and the higher-gain filtered output both out to screw terminals and looked at them with the Arduino.  There is less noise on the filtered output, but whether that is due to the filter or to the higher gain (so less discretization noise in the ADC) is not clear.  I’ll probably have to look at them with a higher resolution device than the Arduino ADC to see.

Incidentally, I really like the block of 4 screw terminals with 0.1″ pitch that I’m using for the protoboards and the pressure sensor breakout boards.  They may not be able to handle the current of the 3.5mm and 5mm screw terminals that Adafruit and Sparkfun use, but they take up less space and fit much more neatly on the 0.1″ grid.  They provide me with much easier and more secure connections than the header pins that I used to use.  (With the 0.1″ spacing, if I want header pins, I can just fasten a row of double-headed header pins into the screw connectors.)

I’m worried about how much time soldering the amplifier will take.  Despite all the admonishments I’ve given and will give them, I suspect that half the students will come to lab next week with the prelabs only half done—many won’t have done a carefully checked schematic and layout before coming to lab, so they’ll be rushing to do a half-assed one that is missing crucial connections or shorts power and ground.  And then their soldered board won’t work and they’ll spend many more hours trying to debug it than it would have taken them to check their schematic carefully in the first place before wiring things up.  I made everyone redo the lab writeups for the first soldering lab, because they’d mostly been very sloppy in their schematics (among other problems).  Even on the redone lab reports, after being told that they needed to fix and double-check their schematics, there were still a lot of the same sorts of errors, and the lab reports for lab 5 (the first audio amp lab) were not much better.

I wonder if all the engineering students have the same carelessness about details and poor lab notebook skills.  I have not been teaching students how to keep a lab notebook. I thought that had already been covered in their previous 4 years, and I tend to be a poor example: I had to reverse engineer my previous instrumentation amp circuit for the pressure sensor, because I couldn’t find the schematic anywhere—I then made a clean copy of the schematic with CircuitLab, and put a printout of the schematic and the board together in an envelope, so they would not get separated again. I also printed out the schematics for today’s amplifier design, and put them together with the design specs and the layout information in an envelope with the board I designed today.

I’ve been using this blog as my lab notebook for things related to the course, except for designs that I don’t want to give away to the students (which is why the schematic for the pressure sensor amplifier does not appear in this blog, which in turn is why I lost it).  I’ve only occasionally used a paper lab notebook, generally preferring “README” files in the computer directories associated with particular projects.  It’s not as good if I ever want to patent something, but it is a lot easier for me to maintain.

I still haven’t figured out exactly what I’ll do tomorrow in class.  I’ll bring my son’s stroboscope (a Xenon flash tube one made from a Velleman kit), but I’m not sure what I’ll use for periodic motion.  I’ll also need to prepare a “do-now” problem, to keep them sharp on their voltage dividers and op amps.

Next weekend will be dedicated (again) to doing the class-D amplifier lab handout, and building the class-D amplifier to make sure that the lab is doable.

Next Page »