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2017 October 14

Shaving my head

Filed under: Uncategorized — gasstationwithoutpumps @ 12:51
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On Wednesday 25 October 2017, I’m going to get my head shaved (just the top, not my beard) as part of St. Baldrick’s fundraiser for pediatric cancer.  I missed the head shaving last year, as I was at the iGEM Jamboree in Boston, or I would have done it then.

The head-shaving event is being organized locally by the Treehouse Childhood Cancer Initiative at UCSC.  Cancer genomics has become a major research topic at UCSC, and pediatric cancers are a particular focus, so this fund raiser has particular significance for UCSC.  Last year they raised $29,488 with 28 shavees.  I don’t expect to raise anywhere close to $1000, personally, because I’m not willing to badger my friends and family to make donations, but I hope that a few people will be willing to contribute token amounts.

If you feel like giving to a good cause (or just want to see a picture of me with no hair on top, to be posted after the event), you can donate at

If you want to know why you should give to this charity, rather than the 100s of others asking you for money, St. Baldrick’s has a good list of reasons at  The reasons I found most compelling is that St. Baldrick’s is the biggest funder of pediatric cancer research other than the US government, and they are a pure research play: funding nothing but pediatric cancer research. This focus makes St. Baldrick’s a long-term social investment, rather than addressing immediate emergencies.

Charity Navigator rates St. Baldrick’s moderately—their transparency is excellent and their administrative expenses low, but their fundraising expenses are moderately high and they have already committed to spending most of what they have collected, so they have low reserves.  St. Baldrick’s explains that the financial thing is an accounting difference—their commitment to funding grants appears as a liability, even though there is no external debt involved and they bank the money before they make the commitment:

The link for donating again:


2017 October 10

Why the blog has been quiet lately

Filed under: Robotics — gasstationwithoutpumps @ 21:49

I’ve not been writing much for the blog lately, because my time has been consumed by two projects:

  • rewriting my book—I have to get at least all the parts needed for BME 51A done by the end of December.
  • Gabriel Elkaim’s Mechatronics class, which I’m sitting in on this quarter.

The Mechatronics course has the well-deserved reputation of being the most time-consuming course on campus.  I’m trying to do all the labs for the course without a partner, as it would not be fair for me to join a student team (both because I already know a lot of the electronics and debugging parts of the course, and because I may not have time at the end of the quarter to spend all my time in the lab as the students do).

I got the first lab (Lab 0) done without too much difficulty—most of the problems I had were with learning MPLABX and the Events and Services Framework that they use for programming the “roach” robots.  The students may have hand an advantage over me, as they had all (or almost all) used MPLABX in prior courses—I’ve never programmed a Pic32 processor before.  One irritant for me is that they were using a different bootloader, so software had to be downloaded with ds30, for which they only had a Windows version available.  That meant that I had to use the lab computers at least for the downloads.

I ended up with very different solutions to the “roach” programming than most students did, because I started with the idea of simulating bacterial swim-tumble chemotaxis to do the required negative phototaxis. My design was inherently probabilistic—a Markov model rather than deterministic state machine.  The flat state machine worked fairly well, but was needlessly complicated with four states, despite which it could sometimes get confused about whether a bumper was still pressed and continue pushing into a wall for a while. For my hierarchical state machine, I managed to separate the task into 3 different small state machines: one for left-motor reflexes, one for the right-motor reflexes, and one for the swim-tumble phototaxis.

One problem I had with Lab 0 (other than a general distaste for the MPLABX IDE) was that the roaches lacked any mechanical feedback other than the bumpers, but different roaches ran at very different speeds.  I had tuned the parameters on the first roach I worked with, which turned out to be one of the fastest ones in the lab.  When I went to get checked off, I ended up with one of the slowest roaches, and the mean tumble time was too low—the roach did not turn enough to make a big enough change in direction.  I had to change one time constant and retry checking off later—again with a very slow roach, but this time the random search did eventually manage to crawl into the dark area.

I’m considering trying to port their Events and Services Framework to Teensy boards, so that I can do almost all my work at home—I’m not that happy with the Uno32 boards.

Lab 1 is more straight-forward than Lab 0: analog design for a track-wire detector (inductive pickup of 25kHz signals) and a beacon detector (which I looked at this summer) to pick up 2kHz IR signals.  In class today, Gabriel challenged the students with the claim that a one-chip solution was possible.  This afternoon I did a 3-op-amp version of the track-wire detector (and I could reduce that to one op-amp with some small changes to the requirements).  I think I can use a similar approach for the IR beacon, but that will probably still take 4 op amps, as the initial signals are much smaller.  I might try to get that done tomorrow, if I get enough done on my book—I’m trying to alternate days of working on the book and playing with the mechatronics.

I’m not going to share my solutions on the blog, much as I’d like to, because the Mechatronics course uses the same design exercises each year, and I don’t want students copying what I did without understanding.  (There is enough of a problem with that in my own course—I don’t want to mess things up for someone else’s course.)

2017 October 8

Mail delivery problems

Filed under: Uncategorized — gasstationwithoutpumps @ 23:19
Tags: ,

For decades we had excellent service from the USPS, with prompt deliveries to our door 6 days a week.  USPS has the lowest prices for small items (I don’t know any commercial service that will deliver anything for under 50¢, as USPS still does for first-class mail), and the service used to be great.

In the past two years (since our long-time mailman retired), delivery has gotten a bit unreliable.  I hear from neighbors that the problem is occurring all over Santa Cruz—the USPS is understaffed locally, and they can’t cover all the routes, so they drop routes on a rotating basis, providing approximately 5 day a week service.

This is mildly annoying, but what irks me is not the reduced service so much as the way that they report it on their tracking service “Informed Delivery”.  Instead of something honest like “understaffed—route skipped”, they report the non-delivery as “receptacle blocked”, blatantly lying about the problem and blaming the customer for their failure.

Even in the past, when delivery was routinely good, I noticed a tendency of the Santa Cruz Post Office to push the boundaries of honesty.  For example, when you paid for 2-day delivery, they were very careful not to scan the packages when they were handed over the counter at the post office, but waited until the post office closed at the end of the day to scan the package, giving themselves an extra 24 hours to make their delivery promises.

I imagine that the USPS pay scales are set based on cost of living in some cheap part of the country and are not really living wage in Santa Cruz.  They have job ads out for “City Carrier Assistant” at $16.41 an hour, which just meets the City of Santa Cruz definition of a living wage (they require $16.21 an hour with benefits for anyone hired by a city contractor, or $17.68/hour without benefits).   These aren’t even permanent jobs: “This is a non-career position through which employees are hired to serve a 360-day term, with the possibility of reappointment to additional 360-day terms.”

The pay is a little better than entry-level jobs in retail (which everyone is having a hard time filling, because the pay scales are so low), but less than shift supervisors or assistant managers.  Anyone with skills (apprentice electrician, plumbing installer, automotive technician, …) can expect higher entry-level pay.

Incidentally, I don’t see $16.41/hour on the postal-workers’ union pay-scale chart—the closest I can find is Pay grade 4, Pay step GG at $16.4688/hour.  Does the less-than-a-year contract circumvent union protections also?  I’m beginning to see why there is a shortage of postal workers locally.

2017 September 27

Jig for drilling Lego bricks

Filed under: Circuits course — gasstationwithoutpumps @ 15:07
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For the pulse-monitor lab, I have students drill ⅛” holes through 1×2 black Lego bricks (see Lego as LED holder and Lego as LED holder revisited), to make holders for 3mm phototransistors and 3mm LEDs. I hauled my drill press up to campus in my bike trailer last year to have students drill their own bricks, but I was not happy with the plywood jig that I had put together at the last minute—it worked, but there was a tendency for the bricks to jack-knife when the drill press vice was closed, because I had a sliding piece to clamp the brick.

I redesigned the jig yesterday and came up with a much simpler and (I think) more reliable design:

This side view shows the jig cut out of a piece of polypropylene cutting board that had been retired from kitchen use as too beat up. The bottom edge is straight, and the top edge has a rectangular cutout exactly the width of a Lego brick. (The top edge is not flat, because it was cut from a part of the cutting board that had a handle.)

Here is a top view of the jig in the drill press vice. In classroom use, I’ll probably use some painters’ tape to hold the jig to the non-moving jaw of the vice.

To use the jig, open up the vice a little bit, snap the brick into place, and tighten the vice gently to hold the brick securely. The cutting board is just a little thinner than the height of the brick, so the clamping force of the vice is entirely on the brick.

I may add these photos to my book.

2017 September 23

My son returned to college yesterday

Filed under: Uncategorized — gasstationwithoutpumps @ 21:31
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I’ve been wandering around the house today, cleaning things up and generally being a bit adrift, in part because my son has returned to UCSB (where he will be a senior in computer science this year) on Friday.

His trip back was a little different from what was planned.  It started out as planned, with him catching the 7:55 a.m. Highway 17  Express bus to Diridon station in San Jose, where he planned to wait for the Coast Starlight down to Santa Barbara.  We noted before he left that the Coast Starlight was running about 3.5 hours behind schedule (a common occurrence—hence the nickname the Coast Starlate).  When he tried to check his luggage at Diridon station they recommended that he change to the 4790 Thruway bus to San Luis Obispo and take the 790 Pacific Surfliner the rest of the way, because the Coast Starlight was running so late.   He did that, though he much prefers the comfort of trains to buses, and it turned out to be a good move.  He could get out at Goleta, rather than Santa Barbara, cutting out about 10 miles of ground transport at that end.  He ended up getting to his new apartment in Isla Vista about the same time that the Coast Starlight left Salinas, so he saved over 6 hours (the Coast Starlight never made up the delay—by the time it got to Santa Barbara it was 4.5 hours late).  I don’t know whether he’ll take the Pacific Surfliner in future, or even try the Greyhound (which is even faster, as there is a direct bus between Santa Cruz and Santa Barbara)—it depends on his willingness to trade off comfort for speed, as the Coast Starlight is a very comfortable way to travel, even if it is ridiculously slow.

One thing I did today was to box up 52 pounds of stuff (mostly clothing, but also bedding, some electronics, and dishes) to ship to him in Isla Vista (via UPS ground, about $40).  He only took about 75 pounds of luggage with him, because of the Amtrak 50-pound limit on single items for checked luggage (though the Thruway bus+Pacific Surfliner switch meant that all his luggage ended up being carry-on).  Because he is living in an unfurnished apartment this year, he had already ordered furniture (a bed and mattress, anyway) from Amazon, and his roommate had been there to receive it, so he knew he had a bed waiting for him (though he probably had to assemble it).

You’d think that by the 4th year, I’d be used to having him go away to college, but the transition each fall is still a little unsettling—I’ll miss our technical conversations.  Oh well, within a couple of weeks I’ll have his bedroom set up as a workshop again, with the drill press and scroll saw back on the table, and the stuff he left scattered on the table packed away in boxes.

I’ll need the workshop this fall, as I need to make more lab setups for my course (I’ll have lab sections of 50 students, so we’ll need 25 lab stations, instead of just 12).  I’ll also be sitting in on the Mechatronics course at UCSC, which has always sounded like a lot of fun, but which will probably be close to a full-time job for a person to do alone instead of in a 3-person team. My sabbatical this fall will be spent on the Mechatronics course, continuing revisions to my book, and building the lab setups for winter and spring.

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