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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 March 25

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

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.

2016 February 27

Applying for Mini Maker Faire round 3

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I’ just submitted my application for the Santa Cruz Mini Maker Faire, as mentioned in Santa Cruz Mini Maker Faire 2016Applying for Mini Maker Faire, and Applying for Mini Maker Faire round 2.

The banner will still be a yard of 56″-wide “Performance Piqué” fabric for about $18, but I’ve changed the design:



I’m still not happy with the design, but it is better than the previous one. I have time to work on it more before I have to order the banner, so I welcome suggestions. Should it be made simpler? busier? different colors? Should it include photos?  Are there other circuits I should include? Should I scale the circuits to have the same line widths? or make them have a wider variation in size? (Note: everything but the PteroDAQ logo is scalable graphics, so I can make things as big or small as I need to, and still get the 150dpi resolution needed for fabric printing.)

I’ve pretty much given up on writing an exciting one-paragraph blurb to go with the application and will go with something rather bland, just so I can get the application submitted.  Sometimes it is better to be done with a less perfect result than to keep fussing and miss a deadline.  Here is what I’ve submitted:

See your pulse on a home-made optical pulse monitor!
Record air pressure waveforms using Arduino or Teensy boards with free PteroDAQ data acquisition software!
Play with a bright LED stroboscope and desk lamp, made with custom-designed PC boards!
Use oscilloscope and function generators!
Watch demos of a home-made electrocardiogram (EKG)!

I did not submit a picture with the application, because I couldn’t think of a good one to submit—they wanted a URL for one that is on-line, which would probably mean something from this blog.  Ah, well, if they accept my application (which I assume they will), then I’ll be able to ask them what sort of picture they want and see if I can find something that is useful.

2016 February 26

Applying for Mini Maker Faire round 2

Filed under: Uncategorized — gasstationwithoutpumps @ 22:29
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I’m getting closer to applying for the Santa Cruz Mini Maker Faire, as mentioned in Santa Cruz Mini Maker Faire 2016 and Applying for Mini Maker Faire.

I have a title for the display:

Dr. K’s Applied Electronics

and an initial design for a table banner (to be printed as a yard of 56″-wide “Performance Piqué” fabric for about $18):


I have the design at high enough resolution for fabric printing, which is recommended to be a 150dpi.

I’m not real happy with this design—the book cover is boring and anemic, and the cover should probably have a dark border.  The PteroDAQ logo is better, but the colors of the logo and the book don’t fit well together.  The banner also doesn’t include Dr. K’s Applied Electronics, which is a nice name for a Maker Faire, but not one I’d currently want to put on the book.

Anyone have any ideas for improving the book cover or the banner?  

That leaves me with one main task: writing a one-paragraph blurb to go with the application, covering the things I plan to show:

  • The desk lamp and the strobe light (which use the same electronics hardware: only the firmware is changed to turn the dimmer into a strobe controller).  I can show both at once and have a few of the LED boards on display also. Maybe I should modify the firmware so that I can just move a jumper plug on the programming pins to switch between strobe and dimmer functions—I wonder if there is enough flash memory in the ATtiny 13A processor for that.  The strobe takes 364 bytes, and the dimmer takes 372 bytes, so even if no code can be shared (unlikely), they should be able to both fit in the 1kB flash.
  • An optical pulse monitor (with standalone display based on a 240×320 RGB ILI9341 TFT display I got from PJRC). I might want to make one that is more open than the wooden blocks I’ve been using, so that it is easier to see where you have to cover the hole to the phototransistor.  I might also want to try seeing if a green or yellow LED gives a better signal (I have a bright yellow LED that has a much narrower beam than any of my red LEDs). I’ve not tried using the display yet, but it sounds pretty easy to set up—I should have some time in the next week or two to try it out.
  • Function generators hooked up to an oscilloscope for Lissajous patterns?
  • A microphone and small amplifier hooked up to an oscilloscope? Note, I only have one analog oscilloscope, and it is a bit touchy to use—there was a reason for it being sold used on eBay! It also takes up a lot of table space—but it is the cliché icon of an electronics enthusiast or mad scientist. I could set up the Bitscope oscilloscope on my laptop, but it is not as iconic, and that would use up one of my 2 displays that could be used for PteroDAQ.
  • An EKG with PteroDAQ display? (It would need to be wired to me—too much trouble and expense to put electrodes on others)  I could also use the same standalone display design as for the optical pulse monitor, if I get that designed and built in time.  I don’t think I’ve got time to get the software working and build a case for a wearable EKG—I wonder if I can find a case that works with the TFT display.
  • Aquarium air pump, soft tubing, and pressure sensor hooked up to PteroDAQ?  (people can play with pinching the tubing to see the effect of pressure changes)   I usually use the pressure sensor with a blood pressure cuff or a breath mouthpiece, but the cuff is too much trouble to work with if there are many people, and I have no good way to clean the mouthpiece between users.
  • The PC boards I’ve designed.
  • Some of the tools a hobbyist needs (soldering iron, bread boards, wire strippers, …).
  • Laptop and iMAC for PteroDAQ displays.

I’ve decided against

  • Displaying the nerf-gun prototype (not pressurized) and the soda-bottle rocket launcher (again not pressurized).  These are a bit off the main theme of electronics and take up a too much space.
  • Having kids make LED “throwies” out of CR2032 batteries, LEDs, magnets, and electrical tape. I’d have to spend a lot on parts and spend all my time helping kids put together their throwies, not to mention the ecological disaster of using so many disposable batteries.

I will also want to hand out business cards that point people to this blog, PteroDAQ, and my book. I still have to design the cards. I haven’t decided whether they will be “professional” or “fun” designs, nor what graphics I want on them (other than not the book cover). Probably I’ll do one PteroDAQ-only card with the logo, the URL, and a brief description of PteroDAQ.  I’ll probably do another one for my book, with the book cover, the URL (or even a limited-time reduced price coupon), and a very brief blurb. I don’t know what to do about advertising this blog, if anything.

The bulleted list of things I want to show has to be alluded to in the “Project Description”, which “will also be used on [my] Maker sign”. So I need something simultaneously catchy and descriptive. Here are some key phrases:

  • See your pulse on a home-made optical pulse monitor!
  • Record air pressure waveforms using Arduino or Teensy boards with free PteroDAQ data acquisition software!
  • Bright LED stroboscope and desk lamp, with custom-designed PC boards!
  • Home-made electrocardiogram (EKG)!
  • Microphone amplifier!
  • Use oscilloscope and function generator!

Can anyone suggest some catchier things to put in the blurb?  I want to submit this weekend, if I can. (And before a writing teacher points it out, I’m aware that the list of key phrases is a mixture of noun phrases and imperative sentences, and so fails the “grammatically parallel” test.  I’ll probably fix things to be all imperative sentences, but I’m still trying to figure out the content, and not worried so much yet about copy editing.)

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