Gas station without pumps

2015 December 31

Blog year 2015 in review

Filed under: Uncategorized — gasstationwithoutpumps @ 17:06
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At this time of year, posts some rather pointless “year in review” for the blogs they host:  the one for my blog is at

Here are some of the stats from the wordpress stats page (which is rather difficult to get decent reporting from):

2015 all time
Posts  205  1,653
Comments ?  4,528
Views 101,150  513,069

I’m responsible for about 39% of the comments on my blog (pingbacks, replies to other commenters, and corrections to posts).  The other commenters are a somewhat different crew this year, with CCPhysicist, xykademiqz, Michael K. Johnson, Erich Styger, and gflint having the most comments.

The most viewed posts and pages of the year are the home page and pages mainly reached through search engines:

Title Views
Home page / Archives 27,544
How many AP courses are too many? 6,893
Making WAV files from C programs 3,010
Carol Dweck’s Mindset 2,661
Installing gnuplot—a nightmare 1,475
Why Discrete Math Is Important and The Calculus Trap 1,444
Engineering Encounters Bridge Design Contest 2014 1,382
Plagiarism detected 1,364
Circuits course: Table of Contents 1,268
West Point Bridge Designer 2011 954
labhacks — The $25 scrunchable scientific poster 933
Why no digital oscilloscope for Macbooks and iPads? 928
Journals for high school researchers 859
Physics posts in forward order 738
2014 AP Exam Score Distributions 719
Pressure sensor with air pump 709
Getting text from Amazon’s “Look Inside” 708
Algorithmic vs. Computational thinking 660
Homeschooling chemistry this year? 607
EKG blinky parts list and assembly instructions 591
Teaching voice projection 557
Conductivity of saline solution 540
Difficulties with the new Common Application 531
Spread on SAT2 raw scores 503

Of the top 20 most-viewed posts, only the Plagiarism detected post was written this year, but the popular posts are mostly more contentful posts than in previous years, which often favored posts that were little more than links to other sites, though students looking for bridge-design contest cheats are still a large chunk of the searches.  Two of my post popular pages (Circuits course: Table of Contents and Physics posts in forward order) are organizational aids to posts on the blog, and the circuits course page was updated 100 times in 2015, as 100 posts or pages were added to the blog for the applied electronics course (almost half the posts for this year).

I have no way of querying the stats for comments made this year—their stats are based either on the 1000 most recent comments or on all-time comments (it isn’t always clear which). The most commented-on posts based on whichever criterion they are using are also mostly not from this year (only the Why doesn’t anyone comment on blogs? post is from this year):

Post Comments
We create a problem when we pass the incompetent 27
Teaching engineering thinking 25
Why doesn’t anyone comment on blogs? 25
Why Python first? 21
Coursera Course Catalog 19
College tool box 18
Changes to UC admissions requirements 17
Storytelling to close the gender gap? 17
Student debt 16
A critique of CS textbooks 16

Other than internal links on my blogs, the biggest numbers of clicks were to Carol Dweck’s materials at Stanford, my web pages at UCSC, Wikipedia pages, Digi-Key product pages, and Art of Problem Solving pages.

Overall, I’m moderately satisfied with this year’s blogging.  The variety of posts has been down a bit (more than half the posts have had to do with electronics or teaching the electronics course, and those posts are not as popular as what I was writing a few years ago), but I’ve still got stub drafts for over 200 more posts, and another 500–600 bookmarks that haven’t even made it to stubs yet, so I won’t run out of material if I ever get the time and energy to do more blogging.

Twelfth weight progress report (one year)

Filed under: Uncategorized — gasstationwithoutpumps @ 15:57
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This post continues the series of weight progress reports from the previous one. This report marks one year from my New Year’s resolution at the beginning of 2015.  At the beginning of the year, I said I wanted to drop my weight by 10–15 pounds, by which I meant a target weight of 160–165 lbs 0r a BMI of 22.5–23 kg/m2.  During the course of the year, I re-defined my goal to a target weight of 155–160 lbs or a BMI of 21.6–22.4 kg/m2.  I reached that target range in April, and pretty much stayed there until the end of September, when I had a sudden spike in weight that took me about a month to correct.  November and December were not good for my weight, which has drifted up to hover around 161 lbs.

2015 weight record, showing successful weight loss followed by almost successful maintenance.

2015 weight record, showing successful weight loss followed by almost successful maintenance.

My weight has drifted outside my target range several times, and the holidays have been particularly bad for keeping it in bounds. I’ve adjusted my target weight to gradually relax the upper limit, to allow it to increase at 0.6 lbs a year, which would allow me to drift up t0 178 lbs over 30 years.  But I’m currently over even my relaxed limit, so I’ll have to go back to my  strict raw-fruits-and-vegetables-for-lunch diet, which I have not been keeping to very well lately.

My Body Adiposity Index now estimates my body  fat at 23.4%, while the estimate from BMI is 24.8%.  According to some calibration studies on people in Louisiana, neither estimate is particularly accurate—by that study, the correct value should be around 18±5%.

My exercise for December is way down also (only 2.48 miles/day of bicycling, down from 4.28 miles/day in November) and my total mileage for 2015 is only 1479.4 miles.  I was going to do some cycling with my son over break, but he got some mild gastrointestinal bug, and I’ve been a bit under the weather also, so we never got around to doing the bike rides we had planned. Even the short ride we attempted to UCSC to film a short video on oscilloscope usage got cancelled when he threw up halfway up the hill (the first symptom of the gastrointestinal bug, other than fatigue).



2015 December 27

Theater lights

Filed under: Uncategorized — gasstationwithoutpumps @ 00:02
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My son and I have started on his summer project while he is home for winter break—to build a moderately bright, adjustable color theater light for WEST Performing Arts, the children’s theater troupe he has worked with for the past 11 years (including the two years before they split off from Pisces Moon).

The design is still very much in flux (we’re on our third processor choice already), and we haven’t done any parts ordering or physical prototyping yet, just thinking about circuits, parts, and layout.  We are currently planning an RGBW light with DMX control, with 20W each of red, green, and blue LEDs, and 40W of warm white LEDs, all mounted in a PAR-38 can (using an old can from WEST, rather than buying a new can).  The light will be a simple flood, which is easier to construct than a fresnel or spot light, because we don’t have to concentrate all the light into a small spot for manipulating with lenses.  Currently WEST uses 75W or 100W incandescent bulbs in their PAR cans, so the LED light should be three or four times brighter.  There are RGBW lights from China that are about the same brightness as we’re aiming for, but they are larger and more expensive—we’re aiming for a budget of about $100 a light for parts.  (We’d not be able to sell them any cheaper than the commercial lights—this is just a hobby project to make one or two lights for the theater.)

The theater has a few 15W RGB lights with DMX control, the American DJ Mega Tripar Profile, but they are only 5W per channel (not really bright enough) and it is not clear what functionality the DMX controller for them has (we didn’t look at it or find out the model number).  Because the set was a very cheap lighting set, it probably can’t handle the greater functionality we’re planned for the RGBW lights, so we’ll probably have to find or design a simple DMX controller that can be run from a Mac laptop. There are some open-source DMX controller projects on the web, but their user interfaces may be a bit too complicated for the kids (or non-techy staff) running the light booth for WEST. It is not clear whether we can design a simpler interface for a small number of lights that provides easy access to all the functionality of the lights.  There is also the question whether a traditional control board with sliders or an all-virtual laptop-based controller is a better interface for beginning lighting techs.

We might even want to look at an iPad-based controller, like Luminair ($90), LightingPad (discontinued), and RunTheShow (free, but limited to controlling their particular hardware). LightingPad says that they have pulled the product until they can update for iOS8, which was released over a year ago—since iOS9 has come out before they updated to iOS8, it seems unlikely that they will ever be able to keep up with the churn in the iPads (a complaint I’ve heard from other iPad app developers—Apple makes it very difficult for older apps to keep running, requiring a full-time developer just to keep up with Apple breaking things on each release).  Hmm, I seem to have talked myself out of developing an iPad app, but we probably should make sure our hardware can run with controllers like Luminair.

For laptops, there are open-source projects like Elios and WhiteCat.  Elios is an open-source project in Java, but it hasn’t been updated for a couple of years, so may be a dead project.  WhiteCat seems rather complicated, based on the screenshots at, and most of the documentation is in French, which neither my son nor I reads.

Since we’re mainly interested in running on MacBooks, the OS-X-only code from LightKey may be usable.  They have a free version with 24 channels that might be usable, though upgrading to more channels gets into an expensive subscription model.

The controls we are planning for the RGBW light were 16-bit PWM on each of the 4 channels, plus a strobe frequency (in units of 0.1Hz, with 0–5 and 250–255 having special meanings—probably always off and always on).  Because the DMX512 protocol only has one byte per channel, the light would need 9 channels, and the free version of LightKey could only control 2 such lights.

The Tripar Profiles can be configured as anywhere from 1 to 7 channels:

  1. choice of 16 preset colors (“color macros”);
  2. 16 colors plus 1-byte dimmer;
  3. RGB;
  4. RGB plus master dimmer;
  5. RGB, dimmer, color macros;
  6. RGB, color macros, strobing, master dimmer;
  7. RGB, color macros, strobe or program speed, preset programs, master dimmer.

The preset programs are mainly for running the light as a standalone light show without a DMX controller, so we would not want to emulate that.  The 4-channel RGB,dimmer function is intended as a workaround for the low resolution of 8-bit PWM control—you pick the color at full brightness, then multiply by the dimmer setting to get the overall effect.  Since we are planning to use 16-bit PWM, we can get more precise color control even at dim light settings.  If we mix our light with the Tripar Profiles, we would probably use the Tripar Profiles in 4-channel mode (unless we needed strobing, in which case we’d use 6-channel mode).

I mentioned above that we’d been through three different processor choices.  At first we thought of using a Teensy board, because we’re familiar with ARM programming, the Teensy boards are easy to program, and they can be treated like a through-hole part for doing prototyping (by adding some header pins).  But the boards are a bit large, and a bit expensive ($11.65 for a Teensy LC), so we next considered using an ATtiny2313A processor (again, the ATtiny is easily programmed and I have some experience with the ATtiny13, which I used for the PWM on my desk lamps).  Unfortunately, the ATtiny2313A provides only 2 16-bit PWM channels (plus 2 8-bit channels), which is not really adequate.  Using two ATtiny2313A chips would work, but for less money and less board real estate, we can use a PIC32MX110F016B-I/SP and get 16-bit PWM on a 40MHz clock for a 610.4Hz PWM frequency.  The flexibility of the pin remapping on the PIC32 is attractive here, as it can simplify the routing of the board.

The processor not only has to interpret the DMX commands and provide PWM outputs, it also has to support the RDM (remote data management) protocol of modern DMX devices (the Tripar Profiles don’t, but there is no real excuse for not supporting RDM these days).

Here is a rough block diagram of the current design:

Each LED here is nominally a 10W LED module.

Each LED here is nominally a 10W LED module.

We’ve given some thought to the heat sink, fan, and mounting brackets for everything, but there is still more work to be done to make sure that we can really dump all the waste heat and keep the LEDs sufficiently cool.  We’re currently looking at about $80 in parts for the light (not including the can, which we’ll get from WEST) plus another $15 to make a USB-DMX interface that can handle the RDM protocol.  Those numbers may change a fair amount as we play with the design.

The two boards are each about 10cm by 5cm, which cost only $12 (for 10 copies) from Smartprototyping.  My son has done preliminary layouts of them, to see how big the boards would be and determine any mechanical problems we might encounter.

2015 December 26

Syllabi for splitting Applied Electronics into two courses

In order to split the Applied Electronics for Bioengineers course into two courses, as I suggested in Considering splitting Applied Electronics course, I need to fill out course approval forms to get the courses approved by the Committee on Educational Policy.  They’ve changed the forms this year, so that there are now three documents needed:

If I were requesting a general-education code for the course, I would also have to fill out one of the thirteen general-education forms (corresponding to the 13 possible general-education codes for a course at UCSC), listed at the bottom of the supplemental sheet.

The supplemental sheet was simplified this year, by pushing all the general-education forms out to separate forms, but the requirement for a course syllabus is new.  Basically, the supplemental sheet asks more or less the same questions as before, rephrased to “where on the course syllabus …?”  The “learning outcomes” question is new, as it reflects a relatively new bureaucratic approach to curriculum design.  The learning outcomes make a lot more sense at the course level than at the degree level, where the administration has been pushing for them.

Here are my first more-or-less complete drafts of my sample syllabi for the split course:

The split course is a pair of 4-credit courses, representing a total time of  about 250 hours (240–263 hours), 140 of which are contact hours (3.5 hours of lecture and 3.5 hours of lab a week).  I’m thinking in terms of MWF lectures (70 minutes each) and TTh labs (105 minutes each).  That should be easier to schedule than the 7-unit BME 101/L these courses will replace, which takes about 220 hours (210–232 hours), 95 of which are contact hours (3.5 hours of lecture and 6 hours of lab a week). The increased contact hours should result in students learning more, as many of our students are not very efficient at learning on their own.

One thing I’ll have to decide is whether to require all bioengineering majors to take both courses, or whether BME 51A is enough for the biomolecular concentration. For the bioelectronics and assistive technology: motor concentrations, both parts are needed both for the content and for the lab experience.  But for the biomolecular and assistive technology: cognitive/perceptual concentrations, the courses are mainly there to teach engineering design practices.  The assistive technology: cognitive/perceptual concentration relies on software courses for design content, and so BME 51A is probably enough for them, but there are very few design courses for the biomolecular concentration, as biomolecular lab work is very slow, and a full-year capstone sequence is barely enough for one iteration of one prototype.

2015 December 25

Christmas tree topper

Filed under: Uncategorized — gasstationwithoutpumps @ 19:26
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We celebrate a number of different holidays in our house around this time of year: Channukah, Winter Solstice, Christmas, Festivus, … .

For Channukah, we light the menorah with the traditional blessings, give trinket presents, eat latkes, and play dreidel. For Christmas, we decorate a tree, light up the porch, and give slightly larger presents. For Solstice, we eat round solstice cookies (basically shortbread). For Festivus, we have a tiny Fesitvus pole.

Channukah this year was a bit lower key than usual, as our son was still at UCSB for most of Channukah.  We saved the latkes until he got home and didn’t give presents or play dreidel.  We did light the menorah (except for 2 nights, when we forgot):


Christmas was also fairly low key—we didn’t get around to the porch lights this year, because of the rain early in the week and my son being a bit ill on Christmas Eve, when we would normally have put the lights up. We did bring in our usual live tree, and my wife decorated it. One novelty this year—we stuck on a different tree topper than usual. The clear plastic head was made a few years ago out of packing tape, using my head as a pattern. (Google “packing tape sculpture” for information about how to make such sculptures.) We had it out, because we hadn’t put it away after Halloween, so I stuck it on top of the tree. I liked the effect—particularly the way one of the branches ended up at the level of the eyes:


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