Gas station without pumps

2017 January 8

Applying for Mini Maker Faire 2017

Filed under: Uncategorized — gasstationwithoutpumps @ 17:41
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I’m submitting an application for the Santa Cruz Mini Maker Faire 2017 (2017 April 29), since last year’s Mini-Maker Faire went well (see Santa Cruz Mini Maker Faire went well).  This year I’m getting my application in early, rather than dithering about it for months as I did last year.  I have less free time to prepare the display this year, but I have a better notion what I want to do, so it should not take long to get ready.

Last year's banner, which I can reuse this year. I might also make a shorter one that will fit on the front of the table.

Last year’s banner, which I can reuse this year. I might also make a shorter one that will fit on the front of the table.

The “non-public” description of my display is straightforward:

I’ll bring a tabletop full of electronics projects, as last year (see https://gasstationwithoutpumps.wordpress.com/2016/04/16/santa-cruz-mini-maker-faire-went-well/ ).

Laptops demonstrating free software to turn cheap microprocessor boards into data-acquisition systems suitable for home labs and science-fair projects.
Homemade LED desk lamp and stroboscope.

Several of the projects will be interactive (an optical pulse-rate monitor, oscillators that can be adjusted to change Lissajous figures on an oscilloscope, …).

A few changes from last year: a more reliable pulse-monitor design and a new USB oscilloscope.

The public blurb is similar to last year’s:

See your pulse on a home-made optical pulse monitor!
Record air pressure waveforms using free PteroDAQ data acquisition software!
Play with a bright custom-design LED stroboscope!
Control fancy Lissajous patterns on an oscilloscope!

I removed mention of an EKG, because I decided that it was too much trouble to tether myself with EKG leads all day.

My “Maker bio” is a bit boring, :

Kevin Karplus has been an engineering faculty member at UCSC since 1986, but has done hobbyist electronics on-and-off since the 1960s. For the past few years he has been working on a low-cost textbook to make hands-on analog electronics accessible to a wider range of students.  Several of the projects on display are from the textbook.

2016 November 12

Big patch mending

Filed under: Uncategorized — gasstationwithoutpumps @ 12:44
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Today’s post is a followup on my two most recent posts: Becoming a Maker: resources for a hobbyist engineer in which I talked a bit about becoming a maker and Overvaluing innovation in which I talked a little about the importance of maintenance. What I’m showing today is an example of the Maker repair ethos—fixing things rather than throwing them away (even when the labor cost of the repair is higher than replacement cost).

I had a flannel duvet cover that we’ve not been using, because it had gotten some bad holes in it:

The largest hole here is big enough to get a foot stuck in. The holes are probably the result of a combination of lots of washing of the flannel and sharp toenails.

The largest hole here is big enough to get a foot stuck in. The holes are probably the result of a combination of lots of washing of the flannel and sharp toenails.

The first thing to do was to sew the holes shut, so that they don’t get any bigger.

Because the holes are near the bottom of the duvet, a long way from any edge to the material, I sewed them shut by hand. The results did not have to be pretty, as I was going to cover them.

Because the holes are near the bottom of the duvet, a long way from any edge to the material, I sewed them shut by hand. The results did not have to be pretty, as I was going to cover them.

The next step was to make a patch.

I cut the patch out of the back of an old flannel shirt that had a worn-out collar. The material of the shirt was still good—only the collar had failed. (Collar failure is a common problem with flannel shirts—I wish they wouldn't put plastic collar stiffeners in flannel shirts.)

I cut the patch out of the back of an old flannel shirt that had a worn-out collar. The material of the shirt was still good—only the collar had failed. (Collar failure is a common problem with flannel shirts—I wish they wouldn’t put plastic collar stiffeners in flannel shirts.)

I hemmed one edge of the patch to the duvet cover with a backstitch, using a large cutting mat as a “darning egg” to keep the fabric smooth and flat.

I used a slightly lighter thread for the sewing than for the material, because it was the closest match we had, and because erring on the side of being too light generally is less visible.

After hemming one edge, I used whip stitch or blanket stitch to hold down the other three sides of the patch.

Whip stitch is the simplest way to attach two pieces of fabric when you only have access to one side.

Whip stitch is the simplest way to attach two pieces of fabric when you only have access to one side.

The blanket stitch is a somewhat decorative treatment for a patch edge, but I worry that it may snag too easily.

The blanket stitch is a somewhat decorative treatment for a patch edge, but I worry that it may snag too easily.

The patch was big, so it took me a while to do all the hand-sewing. I think that this is the biggest patch I’ve ever hand sewn.

Here is the final patch, with a tape measure to give an idea of the scale.

Here is the final patch, with a tape measure to give an idea of the scale.

I believe that this patch should give us another year or so of use out of this flannel duvet cover. If it fails again, I don’t plan to patch it again, as the fabric at that point will be so worn out that it won’t be worth the effort of salvaging.

2016 November 5

Becoming a Maker: resources for a hobbyist engineer

Filed under: freshman design seminar,Uncategorized — gasstationwithoutpumps @ 22:42
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Although I’m on sabbatical, I agreed to give a “coffee hour” workshop for WiSE (Women in Science and Engineering).  I had originally offered to repeat the “Speaking Loudly” workshop that I gave last year, but the organizer requested that I talk about becoming an engineering hobbyist.  We finally settled on the title “Becoming a Maker: resources for a hobbyist engineer”, to be presented Monday 14 Nov 2016 (2:45–3:45)—no location has been identified yet in Biomed 200.

This post is an attempt to collect my rather scattered thoughts on the topic.  It is a topic I’ve talked about before—the last day (sometimes the last week) of my electronics class is always selected by student requests, and one topic that was requested last spring was for resources to continue on in electronics as hobbyists.  This audience will be a bit different, I think—more like the students at the beginning of my electronics course than at the end of it, so I’ll probably have to find some lower-level tutorials.  The material should also be useful for my freshman design seminar.

I’d really appreciate suggestions for more resources to add to this list, or categories of resources I’ve omitted.

Basic categories of resources are suppliers, workspaces, tools, project idea sites, tutorials, hobbyist forums, and blogs.

Suppliers:

  • For electronics parts, I generally use DigiKey, but sometimes Mouser, Jameco (for wire and MeanWell power supplies), Parts Express (for loudspeaker “buyouts”), AliExpress (for cheap generic Chinese parts). Ebay has some of the same Chinese companies as AliExpress, and searching Ebay is sometimes a bit easier. Digikey generally has the best search capabilities of any of the electronics distributors, is very fast on delivery, and generally has very low shipping costs.  But they don’t carry everything, and their prices are not always the cheapest, so it is sometimes worthwhile to do some comparison shopping.  If Texas Instruments have the part you want, there are often free samples available on their web site if you just need one or two—worth checking for pricier parts.
  • For microcontroller boards, I use PJRC (Teensy boards), AliExpress (for very cheap development boards of standard processors), and occasionally DigiKey.
  • Microcontroller peripherals. When I was starting out, I bought a fair amount from Sparkfun and Adafruit Industries, and I still enjoy reading their advertising emails, but I don’t buy many of their products any more.  They do provide a lot of support for beginners, though, with blogs, tutorials, and online forums, so should definitely be included on my list. Sparkfun had an educator discount program, which offered 20% off, but they just changed this to a “flexible” discount program where you have to negotiate with their educator staff. I’ve never liked that sort of non-transparent pricing, where how much they like you determines how much things cost.
  • For printed-circuit boards, I’ve used a lot of different suppliers.  My current favorite is SmartPrototyping, but I’ve also had good experiences with Elecrow, SeeedStudio, IteadStudio, and OSH Park.  Note: all the Chinese companies have other services and sales besides just the PCB manufacturing—some of their components and pre-made boards are useful and cheap, though not as well-documented as those from Sparkfun or Adafruit. OSH Park is the only US company on that list.  When I first started I used Advanced Circuits (another US company that had what looked like a good price for student projects), but I did not end up liking their pricing model for small boards, which were all I was interested in.  The Chinese companies provided much better pricing if I was willing to wait, and OSH Park provided better pricing if the boards were tiny enough.  (OSH Park has an area-based pricing scheme that is great for tiny boards but rather expensive for large ones.)
  • I almost never buy anything that is “call-for-quote”—I figure that their pricing is so high that they are ashamed to put it up where people can see it.  (It feels like the old if-you-have-to-ask-you-can’t-afford-it model of exclusivity.)  The one exception is when you are ordering a very large quantity or need special services—getting quotes for contract manufacturing makes sense, as the pricing models often depend on things like how busy the factory is.  But standard prototyping should have standard prices, which is what makes the prototyping PCB assembly services (like SmartPrototyping, Elecrow, …) attractive.If you need small-scale production (1000s of parts), then you are better off getting bids through Alibaba (an article by Andrew Minalto explains how to avoid getting scammed). I’ve never gotten bids from contract manufacturers, but my son has so I asked him for his advice. Here’s what he sent me (lightly edited):

    You’ve created a PCB design, gotten some prototypes made and tested, and now you want to go to production, anywhere from a few hundred pieces to tens of thousands. Here’s how to get get quotes from a bunch of cheap Chinese manufacturers. You’ll create an account on alibaba.com (use an email you’re okay with a lot of overeager manufacturers having), and then you can post a buying request. Make sure to give all the relevant details about the PCB (thickness, finish, soldermask color, RoHS compliance, etc.), to note any special assembly instructions (bending leads, applying heat-shrink, etc.) and descriptions of unusual components, to request quotes both for your full order quantity and for samples, to request that they include the cost for DHL shipping in the quote, and to attach gerber files, the bill of materials, and an assembly drawing or placement file. Once you’ve posted the request, you’ll get responses over the next few days. These will mostly be through the Alibaba website, but some manufacturers might email you directly, and some might do both.

    On the “Quotations” tab for your request, there’ll be a list of manufacturers who’ve responded. For each one, you’ll see what looks like a quotation, with a picture, quantity, and price, but it’s probably copy-pasted and meaningless. You want to scroll to the messages, where you can see a probably copy-pasted message saying that they’re interested. If you reply to this or email them, they’ll typically get back to you with a quotation. You might need to prompt them to include shipping in the quote, or to quote for the quantity you actually requested. When you have multiple questions or notes for a manufacturer, put them in a bulleted list, as that makes it more likely they’ll actually respond to each point.

    Once you have a few quotes, you can negotiate, but often at least one of the quotes will be cheap enough that’s it’s not worth the time to haggle. Once you’ve found a few manufacturers that are easy to communicate with, understand your design, and have reasonable quotes, you can order samples. Samples are very unlikely to be free, but will be cheap relative to the full order.

    Once you’ve received samples and chosen a manufacturer, you can go ahead and order. There are a few different ways to pay: for small orders like the samples, PayPal is convenient, but for larger amounts manufacturers don’t like it because of the fees. They prefer bank transfers (TT), though you will assume the risk there, since these aren’t reversible. I haven’t had any issues using them, but Alibaba does provide an escrow service (Alibaba Secure Payment), if you’re nervous.

  • For mechanical parts, I often just go the hardware store—either Westside Hardware or the hardware store on River Street that has changed its name so many times I’ve lost track of their current name (Google Maps has “ProBuild”, but I don’t know it that is up-to-date). When I need some specific material or hardware that is either hard to get or expensive in the hardware stores, McMaster-Carr has been my best source.  They have a wide selection of hardware and materials, with prices that are ok for prototyping.  You have to know what you are looking for, though, as browsing their website is not easy.  There are also numerous specialized sites for specific hobbies (RC cars, model airplanes, model rockets, …) and some of the stuff is usefully repurposeable (like the mounting hardware for model-airplane propellers is good for mounting other rotating objects).
  • When I’m looking for enclosures, I often go to the crafts section of Palace Arts for the cheap wooden boxes sold for decoupage, or to the thrift stores in Santa Cruz for wooden bowls.  Santa Cruz has a number of good thrift stores—I’ve had the most success at the thrift store at the corner of Water and Poplar on the Eastside, but Salvation Army and Goodwill downtown are also worth checking.
  • For tools, I check Harbor Freight, Amazon, AliExpress, and Ebay and I do general Google searches.  The Harbor Freight tools are generally cheaply made, but usable.
  • Santa Cruz is not great for sewing stores—Hart’s Fabrics on Seabright, Judy’s Sewing and Vacuum Center, and Beverly’s Fabric and Crafts are about it. There are also some knitting shops (good places for finding yarn), but all the weaving stores have closed.

Workspaces:

Finding places to build stuff at UCSC is hard—the space crunch for instructional space and student space is severe. There aren’t the lightly used spaces that can be repurposed that many other colleges have. Part of the problem here is a decades-long focus by the system-wide UC administration on building research space with little or no attention to instructional space and student space.

There are a few spaces available:

  • The Baskin School of Engineering has a tiny Fab Lab space in Baskin Engineering 138: 538 square feet with a few benches, a drill press, a scroll saw, and a laser cutter.  Access to this space requires getting safety certification, see https://bels.soe.ucsc.edu/FabLab for details.
  • The Physical and Biological Sciences Division has an underutilized student machine shop in the basement of Baskin Engineering. There is some information at http://pbsbo.ucsc.edu/facilities/shops/machine/index.html, but they carefully do not include any prices—I’ve been told that their basic machine shop training is expensive and that the hourly rate to use the shop is also high.  The high prices and general lack of marketing for the shop probably both contribute to the low usage.
  • The Arts Division has the OpenLab Research group http://openlabresearch.com/, which includes the Digital Arts and New Media mechatronics work http://openlabresearch.com/ucsc-digital-arts-and-new-media-program-with-openlab.  I don’t know what space or equipment they have, nor how students can get access to it.

In the Santa Cruz community, there is also Idea Fab Labs in the Wrigley Building (2879 Mission St, Santa Cruz) https://santacruz.ideafablabs.com/, which has a good laser cutter, 3D printers, an electronics workbench, woodshop tools including a CNC Shopbot, a jewelry-making station, and a sewing/fabric arts station(more tools info at https://santacruz.ideafablabs.com/facility/).  They have lots of space and they have a weekly open house Mondays 5:30pm–8:30pm “where the public is invited to see our equipment, take tours, and get a feel for the facility.”  Their prices are generally a bit high (rent is expensive in Santa Cruz), but they have a student special price for UCSC and Cabrillo students that is quite reasonable (see https://santacruz.ideafablabs.com/techstudent/).  If you are working with wood, plastic, or fabric, they offer more capabilities than any of the UCSC spaces, but they don’t have tools for working with steel nor specialized tools like small CNC mills (used for PCB prototyping and microfluidics).

There are, of course, other places one can work.  The Bike Church at the Hub (703 Pacific Ave, Santa Cruz) has classes and open bicycle workshop hours http://bikechurch.santacruzhub.org/ if you want to work on repairing, modifying, or building bicycles. The Bike Coop on the UCSC campus also provides some space for bike repair.

For electronics work or jewelry, a desktop in an apartment or dorm may be all the space you need for working.

Tools:

What tools you need depends on what you want to do and how much space you have to do it in. I have been slowly acquiring tools for about 40 years, so I have a lot—but I often need to buy some new tools when I start a new project. Most of my projects are electronic, but I have found it useful to have a few woodshop tools as well (a drill press and a scroll saw, for example) to handle the mechanical parts of whatever I’m building.  A toolbox to keep your hand tools organized is very useful—what size you need depends on how many tools you have (I have a huge 42″ wide toolbox on wheels (see New bedroom furniture), and I still have a lot of tools that don’t fit in it).

For electronics, the basic tools include

  • breadboards for prototyping.  These are more like consumable items than tools, because the spring contacts do wear out after a while.  I usually have 3 or 4 with different projects on them, and I often need to decide which older project to sacrifice when I start a new one.
  • wire. You need the right size wire to use breadboards.  I’ve had the most success with 22-gauge solid hookup wire, but it is possible to use cheaper 24-gauge wire, if you don’t mind wires coming loose occasionally (I find that debugging loose wires is such a time sink that the slightly higher price of 22-gauge wire is well worth it).  I keep the wire I’ve cut and stripped for breadboarding in ziploc bags, sorted by color, so that I can quickly find what I need.  I also have skeins and spools of wire, for when I don’t have an already cut piece of the right size.
  • microcontroller board. A lot of hobbyists start with an Arduino microcontroller board, because there is a lot of hobbyist infrastructure (beginner tutorials, easy projects, boards for interfacing various peripheral devices, …).  Personally, I prefer the Teensy boards, which are more powerful, cheaper, easily interfaced to a breadboard, and use the same Arduino development environment.  My son and I have also developed software to use the Teensy boards as a fairly powerful data-acquisition system (PteroDAQ) that makes it easy to collect data.
  • Digital multimeter.  A $10 multimeter like the DT9205A is a useful debugging tool for electronics.
  • Soldering iron. If you want to make something permanent in electronics, soldering has been the go-to technology for as long as there has been electronics. (Soldering itself goes back at least 4000 years.)  I used to use a cheap $10 soldering iron, upgraded to a $25 soldering station, and eventually to a $100 temperature-controlled soldering station.  The better iron is nicer to work with, but you can use a cheap iron if that’s all you can afford.  For any iron be sure to keep the tip clean and tinned, and don’t leave the iron running when you are not actively using it—hot tips corrode quickly.
  • A board holder is nice to have if you do a lot of soldering.  My favorite is the Panavise Junior (model 201), but I recently bought a cheaper holder (https://www.amazon.com/gp/product/B00Q2TTQEE) that can hold larger boards and looks like it will be reasonably functional.
  • An oscilloscope is very nice to have, but will run you $300 or $400 for one that is useful.  The Rigol oscilloscopes (http://www.rigolna.com/products/digital-oscilloscopes/) look like good value for the money for a conventional  digital oscilloscope, and the Analog Discovery 2 (http://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/) looks like a a good value for a USB oscilloscope (paired with your laptop). I’ve not yet used either one, so this recommendation is entirely hearsay.
  • Various hand tools—I list the ones I recommend for beginners on the tools list for my electronics course: https://gasstationwithoutpumps.wordpress.com/tools-and-parts-list-for-applied-electronics-w2017-and-s2017/

Tutorial sites:

Many of the companies that sell to hobbyists have tutorials.  I know that Sparkfun, Adafruit, Jameco, and Arduino all do, and I’m sure that there are many others. If you like video tutorials, just doing video searches on Google can turn up a lot.

I’ve found that Wikipedia often provides very substantial tutorials on technical topics, if you are looking for theory, rather than how-to instructions.  When trying to figure out how to do something, I often use Google to look for answers.  It may take some time to find the right keywords for the search, and the first few sites I check are often not very useful—developing good search skills is very useful if you want to be able to teach yourself new skills of any sort.

For programming questions, stackexchange.com answers often come up in searches.  I’ve found them to be a very valuable resource, but there are a number of jerks there who dump on beginner questions—I recommend searching for answers there, but not asking questions there. (A number of women have complained about the hostile attitude of stackexchange—by not asking questions there, I have not exposed myself to the hostility.)

There are a lot of free resources on the web for learning electronics, but finding a good balance between theory and hands-on practice is difficult.  A lot of the textbook-like sites are heavy on theory but provide little help for solving your practical problems, and a lot of the hands-on sites omit the crucial information you need to do your own designs, expecting you to just copy what they have done without learning how to do the design yourself.

[Plug for my book Applied Electronics for Bioengineers—it isn’t free, but at $4 it is pretty good deal on an introduction to electronics for college students, and it has a number of entry-level design projects that are set up as design challenges, not as paint-by-numbers assignments.]

A lot of people like the Instructables site (http://www.instructables.com/), but I’ve generally found the presentations there to be a bit disappointing, providing just instructions for copying what they have done (and often doing things in awkward ways).  It may be mainly a matter of taste, though, so you should see whether the presentations are to your taste.

Idea sources:

Make magazine (https://makezine.com/) often has ideas for projects over a range of difficulty from kid-friendly to expert maker.  I tend to find the magazine inspiring, but I’ve never been tempted to make any of the projects they’ve written articles about.  Their more general articles on how to do things (tools and techniques) have been of more use to me.  Their material is generally well written, but the rate of technical errors is a bit high—I would not trust them as a sole source on anything.

Instructables has a lot of ideas for things to do, though separating the crap from the reasonable ideas is often difficult.

If you are interested in picking up fabric art skills, Santa Cruz has some active fiber-arts groups, like Santa Cruz Handweavers’ Guild (which I used to belong to), which supports spinners, braiders, felters, and dyers as well as weavers.  They can be an excellent resource for information and ideas.

Visiting stores that sell hand-made goods (pottery, handweaving, woodwork, jewelry, … ) can be a good way to see what other people are doing.  Some of it will seem way beyond anything you can do (that’s ok—hobbyists don’t have to be able to do everything as well as people who dedicate their lives to something), but some things will spark ideas for projects you can do.

Forums and blogs:

There are huge numbers of forums and blogs, and I’m not going to try to list them all.

Hackaday (https://hackaday.com/) is one of the biggest electronics maker blogs around, but I can’t keep up with their 10 posts a day so I’ll probably be dropping them from my feed reader. Because I can’t keep up with even one blog, I’ve not gone around looking for other blogs, which makes it hard for me to recommend any.  I know that Sparkfun, Make, Adafruit, Jameco, … have blogs, but I couldn’t say how good they are.  (Of course, I have my own blog, but it tends to be rather heavy on testing out projects for my courses—about 30% of the blog posts are on that.)

Almost everyone making things for the hobbyist market sponsors a forum for their customers.  These product forums are often good places to ask for help with technical details that can be hard to find in the documentation of the products.  The Arduino, Sparkfun, Adafruit, and PJRC forums are ones I have visited, though I’m not active on any of them. In some cases, the only place important features are documented are on these forums (PJRC, who make the Teensy boards, are particularly bad about documenting some things only on the forum).

 

2016 November 2

Halloween 2016

Filed under: Uncategorized — gasstationwithoutpumps @ 16:47
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Halloween was a bit of an impromptu arrangement this year. I was at the iGEM Jamboree all weekend, and my wife and I only got home from Boston a little before 7 p.m. on Halloween, so we did not have time to carve a pumpkin this year.  Instead, I decided to improvise a very fast pumpkin surrogate:

First, I found a cardboard box large enough to hold the LED stroboscope that I had made for the mini Maker Faire.

First, I found a cardboard box large enough to hold the LED stroboscope that I had made for the mini Maker Faire.

Then I cut out a stencil pattern from a piece of heavy paper.

Then I cut out a stencil pattern from a piece of heavy paper.

I made one mistake when cutting the stencil, cutting away the opaque center for the lower part of the B. I just used blue painter’s tape on the back of the paper to stick the piece back on, and recut the B.

Initially, I tried taping the stencil over the opening in the box, but the light was not diffuse enough—the individual LEDs were visible and the stencil pattern unclear. I then tried taping the stencil to the cutting mat and taping the cutting mat to the front of the box. It wasn’t very secure (painter’s tape is not very sticky—by design), but it worked for the evening.

The final result looked much better in the window than a 20-minute project had any right to.

The final result looked much better in the window than a 20-minute project had any right to.

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.

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