# Gas station without pumps

## 2014 March 12

### Plan for rearranged circuits labs

Filed under: Circuits course — gasstationwithoutpumps @ 22:50
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The Applied Circuits for Bioengineers class starts on 2014 March 31. The big change from last year’s prototype run of the course is that we’ll have two 3-hour lab sessions a week, not just one, so I need to rewrite all the lab handouts to split the work (and, in many cases, increase it slightly). There are also a couple of labs that I want to replace or redo extensively, to make them more useful or require less assistance to the students.

This post, which I’ve been working on fairly solidly all week, is an attempt to schedule the labs for the quarter.  There are 20 lab slots (2/week for 10 weeks), and I plan to use them all, though I might keep one or two open late in the quarter for students who need extra time to catch up after illness or other absence.  Currently I’m planning for the Wednesday lectures between the two halves of the lab to be a data analysis and presentation day, often using Gnuplot.

One big question for me is when lab design reports will be due. If I make them due on Fridays, I can grade them over the weekend and get the feedback to students by the next class, but students will have very little time for the writeup. If I make them due on Mondays, I might not be able to get them back to the students for a week, but students will have more time for the writeup. Currently I’m leaning towards Friday due dates, as students should be writing up the labs the same day they do them, and Wednesdays will be a good time for them to ask questions about the lab data.

 Monday 2014 Mar 31 Administrivia: structure of course, rotating partners, labs not cookbook—need to read carefully before coming to lab. Pre-lab homework. Demo pressure sensor or EKG? Ohms law, voltage dividers. Homework: install gnuplot on own computers, read Wikipedia on thermistors and the Steinhart-Hart equation, draw voltage divider with schematic capture tool (probably Digi-key’s SchemeIt) Tuesday 2014 Apr 1 Unpacking parts, labeling capacitor bags, using wire strippers, making clip leads, measuring input resistance of multimeter, measuring thermistor resistance at many temperatures. Wednesday 2014 Apr 2 Do-now resistance-to-voltage converter. Gnuplot: fitting thermistor theory to measured data. Derivatives of voltage w.r.t. temperature to maximize sensitivity (and linearize output). Homework: install data logger on own computer and KL25Z, record accelerometer? Thursday 2014 Apr 3 Soldering headers onto KL25Z boards, downloading data logger to KL25Z, if not already done. Measuring voltage of thermistor voltage divider, recording voltage vs. time. See soldering instructions at Soldering headers on a Freedom board and Jameco soldering tips Friday 2014 Apr 4 Voltage-divider do-now exercise. Other temperature measuring devices (RTDs, thermocouples, silicon bandgap temp sensors). Monday 2014 Apr 7 Three-resistor do-now question. Feedback on design reports, i-vs-v plots, how electret mic works.  AC voltage (sine wave: amplitude, peak-to-peak, RMS voltage). DC blocking capacitors, RC filters (without complex impedance). Tuesday 2014 Apr 8 Measure I-vs-V DC characteristic of resistor and of electret mic, both with multimeter and with KL25Z board. Wednesday 2014 Apr 9 Gnuplot: plotting transformed data, fitting various models to i-vs-v (resistor, current source, blending of resistor and current source, more complex model). Thursday 2014 Apr 10 Look at mic with resistor load on oscilloscope (AC & DC coupling).  Capacitor for own AC coupling. Loudspeaker on function generator? Friday 2014 Apr 11 Another 3-resistor do-now question. Voltage sources, current sources, load lines, Thévenin and Norton equivalents. Monday 2014 April 14 Hysteresis. Applications: cleaning up noisy signals to on/off signals, feedback control. Differential equation for capacitor, derived from Q=CV, RC time constant. Basic idea of hysteresis oscillator (demo of touch tensor?) Tuesday 2014 Apr 15 Characterize hysteresis in Schmitt trigger chip using data logger. Breadboard hysteresis oscillator with various R and C values, measuring frequency or period (oscilloscope or frequency meter?) Wednesday 2014 Apr 16 Analysis of hysteresis oscillators: deriving formula for frequency. Homework: estimate increase in capacitance of touch sensor when touched.  Design hysteresis oscillator that will change period by factor of 2 or more when sensor touched.$e^{j \theta}= \cos \theta + j \sin \theta$, polar representation as magnitude and phase, $e^{j \omega t}$, current through capacitor for sinusoidal voltage, complex impedance. Thursday 2014 Apr 17 Make and test touch sensor with breadboard oscillator. Solder hysteresis oscillator. Note:I’ll have to write touch sensor code for KL25Z.Estimate capacitance of touch from change in period of hysteresis oscillator. Friday 2014 Apr 18 High-pass and low-pass RC filters as voltage dividers. Gnuplot plots and Bode plots for amplitude. Make sure they see ω=0 and ω=∞ simplifications, and straight-line approximations (f, 1/f, constant) away from corner frequency.  Introduce dB and dB/decade rolloff. Monday 2014 Apr 21 RC filter/voltage divider quiz/midterm Tuesday 2014 Apr 22 Impedance of stainless steel (polarizing) electrodes in different NaCl concentrations (at several frequencies). Wednesday 2014 Apr 23 Gnuplot: Functions for impedance: Z_C, Z_L, Z_parallel. Fitting R1+(R2‖C) models to data, maybe fitting other models?Polarizing and nonpolarizing electrodes. Properties of stainless steel (corrosion resistance in oxidizing environments, biocompatibility, poor choice for electrodes) Thursday 2014 Apr 24 Impedance of Ag/AgCl (non-polarizing) electrodes in different NaCl concentrations (at several frequencies) Friday 2014 Apr 25 Intro to op amps, unity gain buffer, transimpedance amplifier. Monday 2014 Apr 28 Theory of sampling and aliasing Tuesday 2014 Apr 29 Characterizing impedance of loudspeaker vs. frequency Wednesday 2014 Apr 30 Gnuplot: fitting models for loudspeaker impedance. Thursday 2014 May 1 Sampling and aliasing lab. Awkward that this gets split from sampling and aliasing theory, but I want to analyze loudspeaker data this week. Friday 2014 May 2 Inverting and non-inverting amplifier. Monday 2014 May 5 System thinking and block diagrams: developing for audio amplifier Tuesday 2014 May 6 Low-power single-stage audio amplifier with op amp Wednesday 2014 May 7 Do now: transimpedance amplifier.  Models for photodiodes and phototransistors.  (other photosensors?) Develop block diagram for phototransistor amplifier with bandpass. Thursday 2014 May 8 Photodiode and phototransistor with transimpedance amplifier.Fingertip pulse sensor? (doable at 3.3v with 700nm red LED, but I put a 627nm red LED in parts list—I’ll have to test with that also—may need higher gain to compensate for greater finger opacity at that wavelength).  Need higher gain for IR also.  I’d also need to drill a dozen blocks of wood for making the fingertip alignment blocks.  May need to use bandpass filtering (2-stage).  Too complicated for one day? Friday 2014 May 9 Op-amp quiz/midterm Monday 2014 May 12 Review of op amps based on quiz? Tuesday 2014 May 13 Measuring nFET current with constant VDS and varying VGS, also with constant VGS and varying VDS. (Diode-connected also?) Wednesday 2014 May 14 Gnuplot: fitting nMOS transistor models to measured data. Thursday 2014 May 15 Catch up lab day? measuring pFET current? Friday 2014 May 16 class D amplifier  concept.  nFET & pFET as switches. Monday 2014 May19 Developing class D block diagram Tuesday 2014 May 20 class D audio amplifier day 1(preamp and comparators) Wednesday 2014 May 21 Gnuplot: analyzing loudspeaker load, adding LC filter in front of loudspeaker to make sharp cutoff without ringing. Thursday 2014 May 22 class D audio amplifier day 2 (output stage) Friday 2014 May 23 Strain gauges and Wheatstone bridges. Instrumentation amps.  Homework: block diagram and design for pressure sensor. Monday 2014 May 26 Memorial Day, no class Tuesday 2014 May 27 Pressure sensor day 1: design and soldering instrumentation amp prototype board Wednesday 2014 May 28 catch up day? Thursday 2014 May 29 Pressure sensor day 2: further debugging.Recording pressure pulses from aquarium air pump?  Would need to buy some more air pumps. Friday 2014 May 30 Action potentials in nerve and muscle cells? Monday 2014 Jun 2 Why EKG signals differ based on placement of electrodes.  (Vector model) Tuesday 2014 Jun 3 EKG day 1:  breadboard and debugging (confident students could go directly to soldering) Wednesday 2014 Jun 4 Catch up? Thursday 2014 Jun 5 EKG day 2: soldering, debugging, and demo.  Last day for any catchup labs. Friday 2014 Jun 6 Catch up? Monday 2014 Jun 9 4–7 p.m. Final exam? (probably not needed, except as a lab catch-up day)

I’m not 100% satisfied with this schedule, and things will probably slip as I discover unexpected difficulties in student preparation, but I think it is likely to run more smoothly than last year, and last year was not bad.

If any of my readers have suggestions on improvements that could be made in the labs or the order of topics, please let me know. I have to buckle down and (re)write the lab handouts soon!