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2017 April 16

Recent theater events

Filed under: Uncategorized — gasstationwithoutpumps @ 20:46
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I have been so busy lately that I haven’t had a chance to do a blog post about the theater I’ve seen lately. The electronics course has mostly been responsible for my being busy—from March 20 to March 27 I was grading the huge pile of design reports for BME 51A, and classes started again on April 3.  Two weeks into the new quarter, I’ve just finished grading the third set of homeworks for BME 51B, and I’m already tired of grading.  (There are still six sets of exercises and five 5–10-page lab reports to come.)  I have a non-course pile of “grading” to do also: I’m on a committee to evaluate 22 project reports from across the School of Engineering for Deans’ and Chancellor’s Awards.  I’ve looked at four of them so far, and I have about a week to finish them.  They are a bit bigger than the little design reports (7–67 pages), but generally better written, and I don’t have to read them closely—just rank them to figure out which are the most award worthy.

But since I have my homework graded, I’ll take a break to list some of the plays I’ve seen lately:

date title playwright theater company
March 25 Dance of Death Strindberg Jewel Theatre
March 29 Julius Ceasar Shakespeare Oregon Shakespeare Festival
March 29 Shakespeare in Love Norman/Stoppard/Hall Oregon Shakespeare Festival
March 30 Henry IV, Part One Shakespeare Oregon Shakespeare Festival
March 31 Hannah and the Dread Gazebo Jiehae Park Oregon Shakespeare Festival
March 31 Mojada: a Medea in Los Angeles Luis Alfaro Oregon Shakespeare Festival
April 15 The Nether Jennifer Haley SeeTheatre

 

The Strindberg play did not quite sell out the Colligan Theater, but it was well attended by the usual crowd of white-haired theater goers.  Julie James gave herself one of the leads (what’s the point of owning a theater company if you don’t get to play lead?), but this time she was well-cast in a part that matched her skills, unlike some of her earlier attempts to play parts for women 20 years younger. The play was well-acted, but the directorial decision to use MP3 players and laptops jarred with the text in several places.  The set was a bit generic, but the costumes were good. Overall, I think that we all enjoyed seeing the play, but have no particular desire to see another production of it ever—it just isn’t that gripping a story.

Over  Spring break, my son and I both traveled by bus with people from Santa Cruz Shakespeare (staff, board members, and donors) up to Ashland, Oregon to see 5 plays there, to get a backstage tour, and to get a tour of the new production facilities in Talent, OR. My wife was unable to go, as her spring break is a week later than UCSC’s and UCSB’s.

Of the five plays we saw, Shakespeare in Love was the most fun, Mojada had the strongest emotional impact, and Hannah and the Dread Gazebo  was the most thought-provoking.  The two Shakespeare plays were the weakest productions.

The Julius Ceasar was a rather lack-luster production, with little attempt to get inside the characters’ heads, just showing us the public faces.  I found the Brutus (played by Danforth Comins) particularly disappointing, portraying Brutus as a weak and vacillating figure, rather than a man of strong principles who was so moral that he attributed high principles to everyone around him.  The dance theater elements really left me cold—it felt like I was watching a poorly produced music video on YouTube. The kata at the end seemed endless and monotonous. Others in our group had much more positive reactions to the play, and the reactions seemed to split based on whether or not people liked to watch dance.  The dance fans loved the play, and the non-dance fans did not.

The Henry IV, part 1 had a good Falstaff (G. Valmont Thomas) who was an excellent physical comic, and they really played the Eastcheap tavern scenes for all they could milk out of them, but the second half of the play fell flat.  Some of the cross-gender casting worked well (Lauren Modica as Glendower, for example), but I was not thrilled by Alejandra Escalante as Hotspur.  Don’t get me wrong—Ms. Escalante did a superb job of acting, but the machismo of the part made it very difficult.  (Note: I’m not at all opposed to cross-gender casting—last year’s female Hamlet at Santa Cruz Shakespeare was by far the best Hamlet I’ve seen.)  I think it would have been more interesting (though even more difficult) to make Hal be the female character—the father’s disappointment at not having a worthy son and Hal’s subsequent attempt to live up to the father’s dreams could have worked quite well as a female role, though the desire to keep the same actor for Henry IV, part 2 and for Henry V would have required a much bigger commitment to a female lead.  Some of our party thought that Falstaff’s comic acting was too much like minstrel shows, with too much caricature of black culture.  Others were uncertain whether Mr. Thomas was being directed to this caricature, or whether it was just his style of comic acting—I’m sure that black comics actors are forever wrestling with the dilemma of how to be funny to a wide audience without being disrespectful to their peers.  I’d be interested in hearing how black theatergoers react to his Falstaff.

Shakespeare in Love is a delightful romp through a lot of Shakespearean references (as well as big parts of Romeo and Juliet), and the actors and actresses all seemed to be thoroughly enjoying themselves.  The play is pretty close to the movie (at least as I remember the movie), which is unusual in a stage-play adaptation of a movie.  I was impressed by the teen actor playing John Webster (Preston Mead)—he did a good job of portraying a particularly ghoulish character.I think that this play will have the widest audience appeal of any of the five we saw.

Hannah and the Dread Gazebo was the strangest play I’ve seen in some time, with a lot of dream sequences and non-linear story telling. All the money for the set was spent on a massive wall that tilted down to make a rooftop.  We were told that the counterweight for the wall weighed 8000 pounds, and that combined with the rest of the wall, the total weight was around 10000 lbs.  The counterweight was not taken out of the theater on the twice daily set changes, but the rest of the set was. I was particularly impressed with the lighting design (by David Weiner), as the set took on very different characteristics with no change in the set pieces, just from the lighting.  The only disappointing set piece was the “gazebo” at the end, which was symbolically represented by a chandelier—this felt like a we’ve-already-overspent-our-budget move, rather than an artisitic choice. The quick costume changes needed by the Shapeshifter (Jessica Ko) were also technically very challenging (some of the changes had to happen on stage, as there was only 5–10 seconds for them). The play had an emotional resonance for some of the Asian-Americans in our group and perhaps a few other second-generation immigrants, but I found it more of an intellectual puzzle than an emotional play (despite being a second-generation immigrant myself).  I really needed more time to ponder it, but we had Mojada to see the same evening, which rather cut short my time for rumination.

Mojada was definitely a gut-punching play (as you would expect from any adaptation of Medea). The script kept many of the elements of Euripedes’s play, though a number of characters were conflated to reduce the cast size.  The acting was strong, but I found the set rather distracting—trying to make an L.A. slum apartment look like Baba Yaga’s hut was a little too strained.  They might have been better off producing the play on a bare stage.

The high point of the trip to Ashland was not the five plays (though they were definitely worth seeing—or the 3 non-Shakespeare ones were).  The high point was visiting the production facilities in Talent, OR. The custom-built space is a Makerspace par excellence for theater lovers. They have all the usual tools: 3D printers, laser cutter, CNC router, CNC lathe, machine shop, two wood shops (props and scenery), spray paint booth big enough for a car, robotics workshop, … with huge amounts of space. One wall of the paint shop has a grid large enough to hang the largest flies that any of their theaters can use, with theatrical lighting for it so that they can paint the backdrops vertically, rather than having to lay them on the floor. Their scene shop has a full-size mockup of the theater stages, complete with a 14-foot-deep pit for testing lifts to the stage, and that mockup is a small fraction of the whole scene shop.

Almost half the building is taken up with storage for costumes and props. The costume collection is amazing, and they rent out everything to theater companies and schools (with a big discount for community theaters and schools).  Almost everything is photographed and indexed on the web (https://www.osfcostumerentals.org/OSF-Costume-Rentals).  The props are not so well indexed nor do they have a formal rental program, though they have occasionally rented out pieces on a case-by-case basis.

This wall of shoes is part of the shorter wall of the room—the long wall would not fit in any of my pictures, nor would the many rows of racks double-height racks of clothes.

I took a few pictures in the costume storage area, but none were able to capture the sheer magnitude of the space and the overwhelming number and variety of costumes. This picture shows just a tiny fraction.

The most recent play I’ve seen is Jennifer Haley’s The Nether, which is still showing at Center Stage (through April 29). The play is intended to be thought-provoking (about what standards should apply to online entertainments), but the themes are a bit tough for many audience members: child abuse and murder of virtual characters.  Like in many science fiction works, there was a bit too much exposition, but the actors managed to keep things moving despite that. The highlight of the play was the performance by Olivia Gillanders, a fourth-grade student who played the role of Iris, the child avatar that is abused and murdered (off-stage). Nick Bilardello as Mr. Doyle and Andrew Davids as Mr. Sims were also quite good.  I felt that the April Bennett (as Detective Morris) and Robert Gerbode (as Woodnut), did decent jobs, but were not up to the caliber of the rest of the cast—their delivery was sometimes a bit wooden, and the characters lacked the intensity of the others.  Part of that may be in the script—the characters didn’t have as good lines—but they could have done more with what they had to work with.

The set was very simple, being split between an interrogation room (stage right) and the virtual world called the Hideaway (stage left).  The interrogation room was done in greys and ultra-utilitarian furniture, while the Hideaway attempted to be a lush Victorian parlor (not quite successfully, as the theater company lacked the budget, but well enough to give the impression of a virtual-world Victorian parlor).

I felt a little sorry for the actors, as the house was only about half full last night (I don’t think I’ve ever been to a production at Center Stage that was not sold out before, as the house only seats 89 including the wheelchair spot). The play is worth seeing, and there are two more weekends (tickets at http://www.brownpapertickets.com/event/2729920). I recommend that people buy tickets, even if they can’t go, in order to keep small theater companies from going bankrupt in Santa Cruz.

In addition to these plays, other recent cultural events include Viva La Lehrer IV (April 8 @ Kuumbwa Jazz, a celebration of Tom Lehrer songs) and a visit to the crochet coral reef on display at the Porter Sesnon Gallery at UCSC (which my wife and I went to April 14).

The Lehrer songs were fun, though I could quibble with some of their selections and how much time they gave to the weaker performers compared to the stronger ones—I don’t feel any need to go to Viva La Lehrer again for about another 5 years.

The CO2CA-CO2LA Coral Reef exhibit runs at the Sesnon gallery until May 6.  I recommend it for kids as well as for adults (one part is mounted in a dark room that you explore with flashlights).

2017 April 11

Maybe eliminate bench equipment next year

Filed under: Circuits course — gasstationwithoutpumps @ 22:40
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One of the BELS (Baskin Engineering Lab Support) staff had an interesting proposal for next year: maybe, instead of tying up a lab with $200,000 worth of bench equipment next year, the applied electronics course could have students rent a box containing an Analog Discovery 2 (with USB cable and power supply).  Each box would cost about $200, and students could rent them for about $30 a quarter (there is precedent for this approach—it is used in the first programming course for Computer Engineering).  As long as the failure rate for the USB oscilloscopes is low enough, the rental would cover replacement about every three years.  Furthermore, students could purchase the boxes at the end of the course for cost minus the rental rate.  Given the attractiveness of the instrument to bioelectronics students and to hobbyists, I suspect that about 1/3 of the boxes would get bought each year.

The initial investment is relatively modest (about $20,000 for 100 boxes) and the change would make it much easier to schedule the labs next year—all that is needed is a room with enough electrical outlets and enough tables and chairs (not even fancy lab benches).  We’d also need to have soldering irons and fume extractors, but those have already been purchased (though we may need to get more, as they keep getting used for other courses and other needs.

I’m now trying to decide between two options:

  • Stick with the conventional bench equipment we have.
  • Switch to using the Analog Discovery 2 exclusively (with maybe a handheld DMM for use as an ohmmeter)

The conventional bench equipment approach has the advantage of teaching the students how to use equipment that they are likely to see again in other courses or in research labs. The Analog Discovery 2 is not suitable for high-frequency work, so students going into work that need higher bandwidth will have to learn conventional bench equipment—the current course is the best training available to the students and helps them considerably in the EE lab courses, where they are expected to figure out the rather complicated bench equipment on their own. The bench equipment approach also requires no extra expenses for the students.

The Analog Discovery 2 approach has the advantage of allowing the students to do almost all the labs anywhere.  With the lab time for 5 sections coming to 16 hours a week, not having to share a lab with another course would be a welcome relief, both for us and for them.  (Also, we wouldn’t have to deal with all the damage that the untrained, unsupervised students in the first EE class do to the equipment.)  The Analog Discovery 2 provides an easier-to-use interface for all the equipment than the rather clunky old interfaces of the bench equipment in the lab—some of the labs that now take hours could be done in a few minutes, because of the better integration of the instrumentation. Furthermore, the students would be able to buy at very low cost a piece of equipment that would serve them very well in other courses and as hobbyists.

If we did go with the Analog Discovery 2, I would have to rewrite big chunks of the book to adapt the labs and remove (or separate to different sections) references to the bench equipment. I’m already planning to do a fairly major overhaul of the book this summer and fall, so that’s not a major argument one way or the other.

Faithful readers, advise me! Should I stick with the bench equipment or should I move to BELS renting out Analog Discovery 2 boxes next year?  What other factors should I consider in making the decision?

Co-instructor wanted for applied electronics course

Filed under: Circuits course — gasstationwithoutpumps @ 22:04
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I am looking for someone to be a co-instructor with me for the Applied Electronics for Bioengineers course at UCSC next year (January 2018–june 2018).  There are two reasons for my wanting a co-instructor:

  • I want to train someone to take the course over from me when I retire (in about 3–4 years).  Right now, I’m the only person who has ever taught the course, and there are no other faculty at UCSC particularly interested in taking it over. My department has no other faculty who know enough electronics, and the EE and CMPE departments are having enough difficulty covering their own courses, so I need to find someone from outside our usual faculty.
  • The course is expected to grow to 100 students next year, and I can barely handle the grading load and lab supervision for 70 students this year (71–73 students last quarter, 68 students this quarter).  If I could split the grading load with another person, we would each have a large, but manageable load.  I might be able to hire undergrad graders to do the homework grading, but not the lab reports, which require good feedback on the writing.

I’ll be hiring undergraduates to help answer questions in the lab, as I’ve been doing this year, but I would want the co-instructor to be present for about half the lab sections.  I think that we’ll have 5 sections of 20 students each, so I’d do 2, then we’d do one together, then the co-instructor would do 2.  The total number of hours a week would be about 3.5 attending/giving lectures, 9.5 hours lab, 8 hours grading, for about 21 hours a week.  I don’t know what the pay would be (depends on qualifications on paper), but the pay would probably be meager by engineering standards—I’d guess it would work out to about $40/hour, though it might be more if the lab time is properly accounted for in the pay rate.

If any of my local readers are interested in the possibility of being a co-instructor, please contact me (karplus@soe.ucsc.edu).  If you know someone who might be interested, please pass on the information.

 

2017 April 10

Electret microphone hysteresis

Filed under: Circuits course,Data acquisition — gasstationwithoutpumps @ 09:05
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In attempting to determine the I-vs-V characteristics of an electret microphone, I stumbled across a phenomenon that I’m still having difficulty explaining.  What I was looking for was a plot like this one:

I-vs-V DC characteristics for an electret microphone. The linear and saturation regions are nicely distinguished and there is little noise.

In previous years I had collected the data with PteroDAQ, but this plot was done with my Analog Discovery 2, which combines both the function generator and the data acquisition. Because I was in a bit of a hurry, the first time I tried doing the characterization, I used a shorter period for the function generator, and got a somewhat different plot:

The hysteresis observed here was unexpected. The loop is traced clockwise, with the upper curve for increasing voltage and the lower curve for decreasing voltage.

At first I thought that the effect was a thermal one, like I saw when characterizing power MOSFETs, but a thermal phenomenon would get more pronounced at slower sweep rates (more time to heat up and cool down), while the hysteresis here could be reduced by sweeping very slowly. Also, the hysteresis did not rely on running large currents—the mic was dissipating less than 1mW at the most, and changing the voltage range did not change the hysteresis much.

My next conjecture was a capacitive effect, which I tentatively confirmed by either adding a capacitor in parallel with mic (increasing the hysteresis) or a capacitor in parallel with the 5.1kΩ sense resistor (which reduced the hysteresis or even reversed it).

I tried playing with the frequency of the excitation waveform, to see what happened to the hysteresis:

This pretty plot shows the transition from nearly DC (the curve that looks like the first one of the post) to something that looks almost like a resistor, with current going up linearly with voltage, as the frequency is increased.

Because the hysteresis did not seem to depend on the amount of the sweep, I picked a voltage well into the saturation region (4V), and tried doing a Bode plot of impedance for the mic for a relatively small signal (±1V). I then fit the Bode plot with an (R1+C)||R2 model:

The parallel resistor corresponds to the slope of the DC I-vs-V curve around a bias of 4V. The model fits the data so well that the curve for the data is hidden by the model curve.

I also tried a Bode plot for a DC offset of 2V and an amplitude of ±300mV:

Like with the 4V DC bias, I got an extremely good fit with the (R1+C)||R2 model. The parallel resistance is different, because the slope of the I-vs-V plot is a little higher (so smaller resistance) at 2V than at 4V.

Because the network tool in WaveForms 2015 provides phase information as well as magnitude information, I did my fit first on magnitude, then on phase. The phase fitting was also extremely good:

I show only the 2V phase plot here—the 4V one is similar, though the biggest phase shift is -56.5° at 3.5V, rather than -45.1° at 4.6 Hz.

So I have an excellent electrical model of the behavior of the electret mic at a couple of different bias voltages, with a simple explanation for one of the parameters of the model. I’m still mystified where the capacitance (about 1.7µF) and the other resistance (about 8kΩ) come from. I suppose, theoretically, that they could be tiny surface mount components inside the can of the mic, but I see no reason for the manufacturer to go to the trouble and expense of doing that. The pictures of a disassembled mic at http://www.openmusiclabs.com/learning/sensors/electret-microphones/ suggest a rather low-tech, price-sensitive manufacturing process.

Incidentally, until I looked at those pictures, I had a rather different mental model of how the electret mic was assembled, envisioning one with a simple membrane and the electret on the gate of a MOSFET. It seems that the electret is put on the surface of the membrane and a jFET is used rather than a MOSFET. After thinking about it for a while, I believe that a jFET is used in order to take advantage of the slight leakage current to the gate—the gate will be properly biased as a result of the leakage. The OpenMusicLabs post showed a 2SK596 jFET (an obsolete part), which has an input resistance of only 25—35MΩ, easily low enough to provide bias due to leakage currents. If the gate is biased to be about 0V relative to the source, then the jFET is on by default,

The 1.7µF capacitance is huge—many orders of magnitude larger than I could explain by a Miller effect (unless I’ve screwed up my computations totally) as all the capacitances for the jFET are in the pF range, and the multiplier for the Miller effect should only be around 5–50 (1–10mS times the 5.1kΩ load), so I’m still at a loss to explain the hysteresis. I checked to see whether the effect was something in my test setup, by replacing the mic with a 10kΩ resistor, but it behaved like a 10kΩ resistor across the full range of frequencies that I used for testing the mic—this is not some weird artifact of the test setup, but a phenomenon of the microphone (and probably just of the jFET in the mic).

I suppose I should buy a jFET (maybe a J113, that has a 2mA saturation current with a 0V Vgs) to see if other jFETS have similar properties, connecting the gate to the source with a small capacitor to imitate the electret biasing.

Incidentally, while doing this experimenting, I found a bug in the Waveforms 2015 code: if you sweep the frequencies downward in the network analyzer (which works), on output to a file the frequencies are misreported (as if they had been swept upward). I reported this on the Digilent Forum, and they claim it will be fixed in the next release. The time between the report and the acknowledgement was only a few hours, which is one of the fastest responses I’ve seen for a software bug report. (They didn’t say when the next release will be, but they’ve had several since I bought my Analog Discovery 2 four months ago, so they seem to be releasing bug fix versions rapidly.)

2017 April 4

Second Santa Cruz Mini Maker Faire

Filed under: freshman design seminar,Robotics — gasstationwithoutpumps @ 10:37
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The Santa Cruz Mini Maker Faire (http://santacruz.makerfaire.com/) is 2017 April 29, 10 a.m.–5 p.m. at Gateway School (126 Eucalyptus Ave in Santa Cruz, near Lighthouse Field).  I have been accepted as an exhibitor again, and I’ll have with me some of the freshmen from my freshman design seminar course.  This year was the most successful run of that course, with all three groups being able to demonstrate their projects.

Two of the groups collaborated to do an EMG-controlled arm.  One group did the electromyograph amplifier, the other built a MeArm from a kit and programmed a Teensy board to read the EMG output and use it to control the arm.  On their public demo during exam week, they had two working channels, to control the shoulder and gripper of the MeArm.  With a little practice, the operator was able to pick up a light object with the arm.  These groups will be joining me at the Maker Faire.

The third group build their own gripper out of medium-density fiberboard, using the scroll saw and drill press in the fab lab.  They were able to demonstrate the gripper, but did not have time to build the wrist that they had also planned.  I don’t know whether this group will be joining me at Maker Faire or not.

I’ll have a number of demos from the applied electronics course also—I still need to figure out what I’ll display and how I’ll lay things out on the table.

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