Gas station without pumps

2016 March 26

Oscilloscope tutorial video

Filed under: Circuits course,freshman design seminar — gasstationwithoutpumps @ 23:08
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I’ve released an intro tutorial on using the digital oscilloscopes in the lab:

The tutorial is fairly short (12 minutes, 23 seconds), and so only covers the basics of using the oscilloscope, not the myriad of features that the scopes in the lab have.

Incidentally, it took us about 2 hours to shoot the video, 2 hours for me to edit it, 2.5 hours to render it, and 5 hours to upload it to youtube.  (I would have uploaded it to Vimeo, where I already had an account, but they limit non-paying customers to 500MB a day, and the 1080p video was 1.6GB—it’s not worth paying $10 a month to upload one video.)

I’ll probably do more videos this summer, if students find this one useful, but since the production takes about 50 times the running time, don’t expect a lot of videos from me!

2016 March 25

2015 Peace Corp Volunteers

Filed under: Uncategorized — gasstationwithoutpumps @ 16:32
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One hears a lot these days about how the current generation of students is much more service-oriented than previous generations, but I’m not sure that is true.

I was just looking at the 2015 listing of Peace Corps volunteers by college, which gives the 2015 numbers and, for a few colleges, the cumulative numbers since 1961.

College 1961–2015 average 2015
University of California, Berkeley 3,598 102.8  54
University of Wisconsin—Madison 3,145 89.9  69
University of Washington 2,888  82.5  72
University of Michigan 2,596  74.2  51
University of Colorado Boulder 2,411  68.9  62

All five colleges for which they gave historical figures (35-year totals) had substantially fewer volunteers in 2015 than the long-term average. It would be interesting to see plots of the total numbers of volunteers by year as well as volunteers per college by year, but I did not see a quick way to get that information from the Peace Corps website.  I wonder if Peace Corps volunteerism is counter-cyclical, like grad school education, with students choosing to volunteer when finding paying jobs is tough anyway.

I was pleased to see several California public universities in the listings:

College category rank 2015 volunteers
University of California, Berkeley large 7 54
University of California, Los Angeles large 13 42
University of California, Davis large 14 41
University of California, San Diego large 15 39
University of California, Santa Barbara large 15 39
Cal Poly large 24 30
Humboldt State medium 8 54

It is interesting to see more Peace Corps volunteers from the elite institutions (UC) than from the larger, but lower-status Cal State campuses.  (Note: Cal Poly is the most selective of the California State campuses and is functionally more like a UC.)

Accepted for Mini Maker Faire

Filed under: Uncategorized — gasstationwithoutpumps @ 00:02
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My application for the Santa Cruz Mini Maker Faire (mentioned in Santa Cruz Mini Maker Faire 2016Applying for Mini Maker FaireApplying for Mini Maker Faire round 2, and Applying for Mini Maker Faire round 3), was accepted this week.  I’ll have a 30″×72″ table to display on.

I’ve ordered a yard of 56″-wide “Performance Piqué” fabric, which is costing me $33, because I’m paying an extra $12 for faster processing (having dithered so long about the design).  That is, I’ve changed the design again, to something less busy:



The 150dpi image that I sent to Spoonflower was 7.7MB as a PNG file, which is not too large.  I’m curious to see how bad the gradient looks when printed on fabric.

I’ll have to spend some time once my son has gone back to college setting up the table in his room as the display table, to see how much stuff I can reasonably put in the display.  Here is what I’m currently thinking of:

  • A pulse monitor with a 2.8″ TFT display driven by a Teensy 3.1 board and using the op-amp protoboard with a transimpedance amplifier on it to amplify the phototransistor signal.  I got that working this week (not written up yet for the blog), but I’m still playing with other ways of mounting the LED and phototransistor, since the two ways I’ve tried so far are both subject to severe motion artifacts.  I need a way to immobilize the LED and phototransistor, but still move it quickly from person to person.
  • An analog oscilloscope with a pair of function generators, to show Lissajous figures (kids can adjust the frequency and amplitude of one of the function generators).
  • PteroDAQ running on my laptop and a Teensy LC board, with EKG and pressure-sensor input.  I’ll have to wear the EKG electrodes, but the blood pressure cuff can be set up separately.  I’m a little worried about being tethered to the EKG, and about the blood pressure cuff readings being a bit too hard to read in the raw PteroDAQ output—I normally have to bandpass filter to get the fluctuations and low-pass filter to get the corresponding pressure.  I may want to think about other things I could show with PteroDAQ.
  • Bitscope and microphone preamplifier?
  • Desk lamp using LED boards
  • Strobe using LED boards  (which reminds me—I wanted to put together a program which could switch between dimmer and strobe functions with a single shorting jumper).
  • Tool display? (soldering iron, board holder, multimeter, flush cutters, …)
  • Business cards for my book (designed, but not ordered yet)
  • Handout with book and blog information (not designed yet—probably will be quarter-page to keep printing costs down)

If anyone has other ideas for stuff I should do, I still have a little time to put something together, but classes start next week and I’ll be putting in full time on the Applied Electronics course, so it can’t be anything complicated (unless I already have it soldered up on a board).  I’ve also dedicated both my Teensy boards (for the pulse monitor and PteroDAQ), so I’d have to do things with either an Arduino or the FRDM KL25Z board.


2016 March 19

Introduction of a technical paper

Filed under: Uncategorized — gasstationwithoutpumps @ 12:19
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I was recently pointed to a post The 5 pivotal paragraphs in a paper | Dynamic Ecologythat gives advice about how to structure a scientific paper.  Most of the advice is good, but I disagree with one statement:

First paragraph of the introduction—you should use this paragraph to embed and contextualize your work in the context of a large classic, timeless, eternal question. What drives species richness. Or controls abundance or distribution. Or gives the best management outcome. Or explains why species are invasive. Or controls carbon flux. You of course are not going to fully answer this question. Indeed no one person, and probably even no generation of scientists will fully answer this question, but ask a really big question. You can then use this big question setup to spend the rest of the introduction summarizing past attempts to answer this question, and show how they have all failed to address the key issue you are about to address.

The first paragraph of the introduction should be the specific point of the paper, not general BS. I read far too many papers (particularly student papers) where there is a huge wad of background dumped before the author gets around to telling me what they are writing about.  It irritates me—especially when I already know most of the background.

Don’t bury the specific goal of the paper at the end of the introduction—your readers may never get that far if you start out with general BS. Start with the specific goal of this paper—not the overall goal of a long-term research project or (even worse) the fundamental dogma of biology.

There is a term for this in journalism—it is known as “burying the lede”, which is considered a major flaw in news reporting.  It is a similarly large flaw in scientific writing.

I recommend that the first paragraph of a scientific article give the specific research question being answered in the article, and that the rest of the introduction then be used for the contextualizing that question—why is it important? how does this study answer it? For engineering reports, the first paragraph should give the main engineering design goal and constraints, again using the rest of the introduction to say why that was important.

If the conclusions of the paper do not answer the question raised in the first paragraph of the introduction, then the question is not specific enough.


Make magazine

Filed under: Uncategorized — gasstationwithoutpumps @ 12:01
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It probably comes as no surprise to my readers that I’ve been a subscriber to Make magazine since 2007, and that I generally read it cover to cover, including many of the ads. I like the project descriptions and the attitude of the magazine—a combination of isn’t-this-cool? and you-can-do-it-too. I do sometimes get bothered by technical inaccuracies and sloppy editing in the magazine.

For example, in the latest issue (volume 50), I found four rather grating errors:

  • On page 25, where where Sean Cusak is giving characteristics of metals, they claim that stainless steel is “heavy” but steel is “medium”.  Carbon steels have a density of about 7850 kg/m3, while stainless steels are around 7480–8000 kg/m3 []. That does not strike me as substantially different.  My favorite stainless steel (316L) is 7990 kg/m3, only 2% denser than carbon steel. I don’t see that as a distinction between “medium” and “heavy”, particularly when they give copper (density 8960 kg/m3) as “medium”. Copper is heavier than stainless steel! If “weight” is supposed to mean something other than density, like mass/stiffness or mass/strength, copper fares much worse. I can’t believe that Cusak made such an obvious mistake—I suspect bad editing.
  • On page 53, Ben Krasnow writes “LEDs are still more expensive than T8, comparable or less energy-efficient in lumens per watt, and require a whole new fixture.”  That statement is about half true.  LEDs do require a different fixture than fluorescents, and LED fixtures are often more expensive than fluorescent ones (though the LED pucks I put in my kitchen cost very little for the fixtures—all the expense was the labor of patching and painting the ceiling and installing the pucks). But LEDs are now substantially more efficient than fluorescent lights, in part because they are more directional—half the light from fluorescent fixtures is lost in reflectors and diffusers. I get much more light from the 43.4W of LED lighting in my kitchen than from the previous 120W of fluorescent fixtures (granted, they were old T12 bulbs, but T8 would not have been much brighter). I think that Krasnow may be about 3 years out of date on LED lighting, and he should reexamine his information.
  • On page 81, where Charles Platt is describing making a capacitor from aluminum foil and plastic bags, it says “To check for short circuits, use a meter to measure the resistance between the 2 sheets of foil, which should be zero.”  That should say “should not be zero”.  You don’t want the two plates of the capacitor to be shorted together! This looks like a simple type-setting error that should have been caught by a technically literate copy editor (does Make have technically literate copy editors? does anyone?).
  • On page 86, in David Scheltema’s and Tyler Winegarner’s article on Pirate Radio Throwies, they say “Check local and federal laws first, of course” instead of saying, “Warning: these transmitters violate federal laws”. They don’t even point the reader to the relevant laws or where they can find out about them. “The FCC limit under Part 15 regulations is 250uV/m (48dBu) at 3 meters.” [] They also only suggest a bandpass filter “for a cleaner FM signal”, rather than insisting on one to avoid the interference inherent in using a square-wave carrier instead of a sine wave.  The bandpass filter is not given, only pointed to youtube video that has a simple RC filter (nowhere near enough to clean up the signal to legal levels, as pointed out in the youtube comments).  I believe that the readers of Make deserve (and need) better warnings before being encouraged to do illegal activities.

I usually find one or two such errors in each issue, so having (at least) four in this issue struck me as high. Is this just random variation, or are the Make editors getting sloppier?

As a stylistic matter, I found the “Over the Top” final-page item by James Burke particularly poorly written this time.  The picture would have been fine by itself, with a brief description, or with how-to instructions, but the badly written purple prose just detracted from it.

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