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2016 April 30

Sixteenth weight progress report

Filed under: Uncategorized — gasstationwithoutpumps @ 17:39
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This post is yet another weight progress report, continuing the previous one. I’m doing a little better this month, going above my target range for only 5 days:

Weight is still hovering around the upper end of my self-selected target range.

Weight is still hovering around the upper end of my self-selected target range.

April saw a gradual decrease in weight, followed by a large upward spike at the end of the month.

April saw a gradual decrease in weight, followed by a large upward spike at the end of the month.

The large upward spike corresponded to a 4-day trip to Illinois for a family wedding and a 90th birthday celebration for my dad.  His birthday was months ago, but travel to Colorado in mid-winter is a difficult, so we moved the celebration to the same weekend as his granddaughter’s wedding, so that we could get everyone to come.

My exercise for April was good (averaging 4.72 miles/day bicycling), despite the trip to Illinois and having had a bad cold for the last week (flying with a bad cold is no fun).

2016 April 20

AliExpress guarantee is bogus

Filed under: Uncategorized — gasstationwithoutpumps @ 07:43
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I have bought a number of things (mainly electronics) direct from China using AliExpress.  I was encouraged to do so by their “Buyer Protection”:

Full Refund if you don’t receive your order

You will get a full refund if your order does not arrive within the delivery time promised by the seller.


I have twice now needed to invoke that guarantee—both times items shipped by China Post that did not arrive.  I don’t know whether the problem is that shippers weren’t sending stuff, or stuff was getting “lost” in China Post.

The first time was a small order, and AliExpress followed through on their guarantee.

The second time was a larger order for my class (about $150 worth of resistor assortments), and the shipper sent me a tracking number that indicated that the shipment had been sent to Russia.  I opened the dispute with AliExpress after waiting a month for the delivery, and after a long wait they denied the claim saying that they were satisfied with the evidence.  I escalated the dispute, and the escalation was denied—in the denial I was sent a different tracking number claiming that the delivery had been made 2 months earlier.

I was not informed of messages from the seller, only of final decisions by AliExpress (for instance, the “corrected” tracking number was supposedly entered into the AliExpress system on 11 April, but I didn’t get informed of it until 20 April, when AliExpress denied my escalated claim).

The tracking claims that delivery was attempted on Feb 27 at 1:16pm and made on Feb 29, at 5:32pm.  I was home both times and no such delivery was made.  (Also our mailman never gets to our part of the route by early afternoon, and rarely even by 5:32pm—I believe that the tracking is fraudulent, which leads me to suspect China Post, rather than the shipper.)

Bottom-line:  the AliExpress guarantee is not worth much if no delivery is made.  In future, I will not order from AliExpress except when either

  • the item is so cheap I don’t really care if it isn’t delivered (there seems to be about a 20% risk).
  • the item is expensive enough that I’m willing to pay for a reliable delivery service like DHL rather than the free shipping through China Post.

2016 April 16

Santa Cruz Mini Maker Faire went well

The first Santa Cruz Mini Maker Faire seemed to go well.  I did not get to see much of it, since I was busy at my booth most of the day, though I did get a break for lunch while my assistant Henry manned the booth, and I made a quick tour of the exhibits during that break, to see what was there, though with no time to chat with other exhibitors.

I understand that about 1800 people bought tickets to the Mini Maker Faire, which probably means there were over 2000 people on-site, including volunteers and makers.  I hope the food vendors did OK—I ate at the Ate3One truck, since I never have before, but my opinion afterwards was that CruzNGourmet and Zameen have better food (both of those trucks are frequently on campus, and I’ve eat at each several times).

My day went pretty well, though I had one annoying problem, having to do with my pulse monitor display. When I set up the booth Friday evening, the pulse monitor was not working, and I thought that the phototransistor had somehow been broken in the rough ride in the bike trailer, so I brought the pulse monitor home, replaced the phototransistor and tested in thoroughly.  Everything worked great, so I packed it more carefully for transport in the morning.

When I got everything set up Saturday morning, I found I had no electricity, though the electricity had worked fine the night before.  After I finally tracked down a staff member with the authority to do anything about it, he suggested unplugging the other stuff plugged in and switching outlets.  I turned out that the only problem was that the outlets were so old and worn out that they no longer gripped plugs properly—taping the extension cord to the outlet box so that the weight of the cord didn’t pull out the plug fixed the power problem.

Once I had power, I tested the pulse monitor, and it failed again!  I used the oscilloscope to debug the problem, and found that the first stage transimpedance amplifier was saturating—there was too much light in the room, and even shading the pulse monitor didn’t help. By then, my assistant for the day (and my group tutor for the class on campus), Henry, had arrived and gotten the parking permit on his car, so I raced home on my bike to get resistors, capacitors, op amp chips, multimeters, hookup wire,and clip leads to try to rebuild the pulse monitor from scratch on the bread board.

When I got back to Gateway School, I tried a simple fix before rebuilding everything—I added a pair of clip leads to the board so that I could add a smaller resistor in parallel with the feedback resistor in the transimpedance amplifier, reducing the gain by a factor of about 30.  This reduced gain kept the first stage from saturating, and the pulse monitor worked fine.  Rather than rebuild the amplifier, I just left the pair of clip leads and the resistor in place all day—they caused no problem despite many people trying out the pulse monitor.

I think that I want to redesign the pulse monitor with a logarithmic first stage, so that it will be insensitive to ambient light over several decades of light.  That should be an easy fix, but I’ll have to test it to make sure it works. I don’t think I’ll have time this weekend or next to do that, but I’ll add it to my to-do list.

I’ll need to think about whether to include having a logarithmic response in the textbook—that is certainly more advanced than what I currently include (just a transimpedance amplifier), which is already pushing students a bit.  A transimpedance amplifier is a pretty common component in bioelectronics, so I really want to leave one in the course.  I’m not sure a logarithmic amplifier is important enough or simple enough to include at this level (I don’t currently cover the non-linearity of diodes).


Here is the booth display with my assistant, Henry. I was permitted to use painter's tape to attach the banner to the whiteboard.

Here is the booth display with my assistant, Henry. I was permitted to use painter’s tape to attach the banner to the whiteboard.

The magenta laptop on right (which my family refers to as the “Barbie laptop”) was a used Windows laptop that I bought for testing out PteroDAQ installation on Windows. It was set up with PteroDAQ running all day, recording a voltage from a pressure sensor and a frequency from a hysteresis oscillator (as a capacitance touch center).

Just to the left of that was a fairly bright stroboscope, using 20 of my constant-current LED boards. To its left is my laptop, displaying the current draft of my book. Behind (and above) the laptop is my desk lamp, which uses the same electronic hardware as the stroboscope, though with only 6 LED boards, not 20.

In front of the laptop is the pulse monitor, which includes a TFT display in an improvised foamcore stand. I used just a half block for the pulse sensor, relying on ambient light (sunlight and the desk lamp) for illuminating the finger.

To the left of the pulse monitor was a stack of business cards for my book and sheets of paper with my email address and URLs for this blog and the book.  I should have included the PteroDAQ URL as well, but I had forgotten to do so. I did tell a lot of people how to find PteroDAQ from the navigation bar of my blog, but putting it on the handout would have been better. Ah well, something to fix next year (if Gateway is crazy enough to do another Mini Maker Faire, which I hope they are).

I also had all my bare PC boards that I had designed and not populated, plus my two Hexmotor H-bridge boards, behind the business cards. One of the amplifier prototyping boards was displaying in the Panavise that I use for soldering.

On the far left of the table is my Kikusui oscilloscope and two function generators, set up to generate Lissajous figures.  I let kids play with the frequencies of the function generators, take their pulse with the pulse monitor, and play with the pressure sensor and the capacitive touch sensor.

My booth was not the most popular of the Faire by any means (certainly the R2 Makers Club in the next booth was more popular), but I was kept busy all day and I talked with a lot of people who seemed genuinely interested in what I was doing, both with the UCSC course and as a hobbyist.

2016 April 4

Banner blooper

Filed under: Uncategorized — gasstationwithoutpumps @ 22:48
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My table banner for the Santa Cruz Mini Maker Faire arrived today from Spoonflower, and it looked really good, until I tried to put it on the table.  I had foolishly ordered a design that was a yard of fabric 56″ wide. The 56″ wide part was reasonable, but the table is most likely only 25–27″ high, so the yard-high pattern is about 50% too big!

I should have thought of that before sending off the order!

Oh, well, perhaps I’ll have a wall behind me that I can blue-tape the banner to.  Or I can put the top foot of it on the table top, though that will make stuff on the table less accessible.

2016 March 31

Fifteenth weight progress report

Filed under: Uncategorized — gasstationwithoutpumps @ 22:12
Tags: , , , , , ,

This post is yet another weight progress report, continuing the previous one. I’m doing a little better this month, ging above my target range for only 6 days:

I've been fluctuating around the top of my target range, when I'd rather be in the middle of it (about 3–4 lbs less than my current weight).

I’ve been fluctuating around the top of my target range, when I’d rather be in the middle of it (about 3–4 lbs less than my current weight).


My exercise for March was a bit low (averaging just under 4.1 miles/day bicycling), but I was good about my raw-fruits-and-vegetables-for-lunch diet during the week, and did not indulge too much in sweets (except for the week of Spring break, when my son was home so we had ice cream and sorbetto in the freezer!).

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