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2017 April 4

Second Santa Cruz Mini Maker Faire

Filed under: freshman design seminar,Robotics — gasstationwithoutpumps @ 10:37
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The Santa Cruz Mini Maker Faire ( is 2017 April 29, 10 a.m.–5 p.m. at Gateway School (126 Eucalyptus Ave in Santa Cruz, near Lighthouse Field).  I have been accepted as an exhibitor again, and I’ll have with me some of the freshmen from my freshman design seminar course.  This year was the most successful run of that course, with all three groups being able to demonstrate their projects.

Two of the groups collaborated to do an EMG-controlled arm.  One group did the electromyograph amplifier, the other built a MeArm from a kit and programmed a Teensy board to read the EMG output and use it to control the arm.  On their public demo during exam week, they had two working channels, to control the shoulder and gripper of the MeArm.  With a little practice, the operator was able to pick up a light object with the arm.  These groups will be joining me at the Maker Faire.

The third group build their own gripper out of medium-density fiberboard, using the scroll saw and drill press in the fab lab.  They were able to demonstrate the gripper, but did not have time to build the wrist that they had also planned.  I don’t know whether this group will be joining me at Maker Faire or not.

I’ll have a number of demos from the applied electronics course also—I still need to figure out what I’ll display and how I’ll lay things out on the table.

2017 January 19

Project ideas for freshman design seminar

Filed under: freshman design seminar — gasstationwithoutpumps @ 09:47
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I haven’t blogged much about the freshman design seminar lately.  So far, I’ve had the students take the training to use the drill press and scroll saw in the (rather limited) Baskin School of Engineering Fab Lab, and had them look for projects they might be interested in doing.  At one point, before the quarter started, I looked into using the Neptune software from Boston University (which I found out about at the iGEM Jamboree) for designing and building low-cost microfluidic systems, but the software was nowhere near ready for use by freshmen, and I did not have the time get all the pieces figured out and working with the somewhat different hardware tools we had available. So, as in previous years, I’ll be counting on the students to come up with a couple of projects that they are interested in and capable of making a good start on.  This is only a 2-unit class, so they only have 6 hours a week on it, 3 of which are in class.

I assigned them the task of finding interesting projects they would want to work on and providing links to web pages about the projects. I think that they may have been overly influenced by an example I brought up in class, but there seems to be a fairly large group interested in an EMG-controlled prosthesis.  That’s a bit ambitious for a 2-unit freshman course, but we could do an EMG, we could do some simple programming for servo motors (I think that more sophisticated motor control would take more time than we have), and we could probably get an already designed hand printed or laser-cut.

Here are some of the project ideas they’ve come up with, grouped by student, in their own words—I’ve not even fixed the typos:

Vernier has a simple (but kind of expensive) EKG sensor that records the electrical events happening within the heart. This sensor uses a digital control unit as well as an EKG sensor. Also, we would need some additional software help.
Vernier also has a project that is an LED color mixer that uses digital control unit. This will have the ability to shine red, blue, and green light, any of which can be shone individually or with other lights.

Similarly to the EKG sensor, Vernier has a blood pressure sensor that calculates blood pressure. Vernier uses a blood pressure sensor and digital control unit in order to carry out the experiment. This device has a cuff that is placed on the upper arm to in order to pressurize the arteries. The sensor monitors the pressure in units of mm Hg.
I thought this website was interesting as they have links to interesting DIY lab equipment such as the micro centrifuge.,_open-source_hardware
This website was has a large amount of open source hardware for science and also 3D printed equipment

From that website, I found
which was a DIY microscope

and also
for a DIY Bioprinter

[Later, from the same student:],_open-source_hardware
This website was has a large amount of open source experiments and DIYs

and I’d like to do an Arduino robotic arm project

-This would be my number one choice for a project to design. This post in particular doesn’t have a whole lot of specifics as to what parts were used, and how they built it, but it does have a brief explanation of how it works. [The student doesn’t say what the project is, but it seems to be an EMG-controlled RC car.]
-The  basics of an EMG and how they work. Materials and a quick blurb about cost vs learning. It would actually cost more to buy the components and build it ourselves than it would be to just buy a pre-built MyoWare. That being said, the learning experience is important.
-Again, pretty basic idea, but this site seems to have more about the coding and signaling from the EMG to the RC car
-Just the basic ideas behind an EMG and possible research applications

A free 3d printable prosthetic hand off of thingiverse.

This is a page detailing how to create a simple EMG.

Attached is also an extensive paper on making a myoelectric prosthetic hand. [attachment from email is not included here—there is a reason the assignment required links, not attachments]

How to build a CNC machine
Remote webcam — could be placed on robot
Wind turbine generator

This is a blood pressure diagnostic devise.
We can work on sensors, and it seems like a freshmen project.
Let me know what you think.  [Not a valid link, so I have no idea what the student is talking about.]
So I saw this, and I noticed the price. But if we could make the individual parts our self, and at the same time learn to implement human movement into a devise such as this it would be awesome. The correlation of movements are what interest me in this project.
Please let me know what you think. [The model arm to imitate a human arm is indeed pricey, as are all Pasco products.]

I’m interested in building nerve controlled prosthetic limb.(EMG)

This is a link that somewhat describes EMG with lots of article links at the bottom.

Homemade Electrocardiograph/ Will ONLY cost about $10/ Will take about 2-3 weeks/ Code available in a zip file. 

exiii HACKberry

3D Printed Bionic Arm/ costs about $200/ Open sourced/ Developed as a cheaper alternative to prosthetics/ Site has tutorials from assembling to programming. 
Response from a different student:
The Homemade ECG really seems like a cool project, but there was a warning about how it was dangerous because to try it someone has to attach the sensors to their chest. 

I like the HACKberry prostetic hand. We would need to choose a specific part out of it that we want to work on since it is a big project, I think. 

I would like to focus on learning how to program the hand to open and close. Also, I would love to learn how to design and construct it.

for this project, I want to work on making a functional mechanic hand.

I would like to make a foot-glove massager with an insert in between the big toe and the second toe using some of the concepts found at these links:

If it’s possible I’d like the glove to be able to massage the foot as if it was “kneading”/”squeezing” the foot.
The idea would be to help people (old or young) with bunions in their foot. You can read more about this foot problem here:

2016 December 30

Ultrasonic rangefinder with Analog Discovery 2

In Loudspeaker impedance with Analog Discovery 2, I looked at the impedance of  various loudspeakers including an ultrasonic transducer. Today I looked at shaping pulse bursts for driving an ultrasonic transmitter to get shorter received pulses with an ultrasonic receiver.  I’ve done this before using custom programs on a Teensy 3.1 board (see Ultrasonic rangefinders arrived), but I wanted to see what I could do using just the waveform generator on the Analog Discovery 2.

I measured the magnitude of the impedance of the transmitter (using either a 120kΩ resistor or a 1nF capacitor as a known impedance), then looked at the transmitter+receiver characteristics for frequencies around the resonances.  I’ve marked the peak received resonances on the impedance plot.

The impedance is approx 2.2nF, with 3 apparent resonances.

The impedance is approx 2.2nF, with 3 apparent resonances.

The primary resonance is around 40kHz, and is the frequency that the transmitter is designed to operate at.

The primary resonance is around 40kHz, and is the frequency that the transmitter is designed to operate at.

There is a secondary resonance around 54kHz, though it is considerably weaker than the 40kHz resonance.

There is a secondary resonance around 54kHz, though it is considerably weaker than the 40kHz resonance.

The third resonance, around 330kHz does not provide a very strong signal for the receiver.

The third resonance, around 330kHz does not provide a very strong signal for the receiver.

I tried two tests using the 40.445kHz resonance. In one, I used the simple waveform generator to produce a 40445Hz square wave, then used an 8ms wait and a 148.3µs run time, to produce bursts of 6 square waves. I set the idle output to the offset (0v) and used a 5V amplitude.

In the other test, I used the same wait and run times, but used the “custom” waveform to set up a signal that inverted the last 3 of the 6 periods (so that the half periods were +-+-+--+-+-+. This was fairly easy to set up by generating the 6 periods, then altering them by multiplying by a single period of a square wave. I could have created much more complicated bursts, but this pattern was enough to see the capabilities of the scope.

By triggering the scope on the signal sent to the transmitter (using channel 1), I could average 1000 sweeps to get a very low-noise view of the signal. (I can trigger on the waveform generator itself, freeing up one of the scope channels, but then I can’t average—I think that the averaging relies on interpolating get precise timing of the trigger.)  For plotting, I subtracted off the DC bias (fitted before time 0), as 60Hz interference caused a moderate offset to the signal even after averaging.

The bursts start out the same, but the simple 6-cycle burst results in the received waveform growing for 14 or 15 cycles, while the 3+,3- burst grows for 6–7 cycles and decays very quickly.

The bursts start out the same, but the simple 6-cycle burst results in the received waveform growing for 14 or 15 cycles, while the 3+,3- burst grows for 6–7 cycles and decays very quickly.

I tried some longer and shorter bursts, with the expected result that longer bursts resulted in stronger signals with a longer received burst width. Doing 8 cycles followed by 8 cancelling cycles seemed to produce a reasonable length burst with a fairly strong signal, but I did not explore variants much.

I still think it might be possible to use the phase information to get higher resolution than the approx 7.9mm wavelength, but identifying which pulse of the return waveform is which remains a problem, particularly if there is a complicated reflecting surface that superimposes several differently delayed pulses.

2016 November 5

Becoming a Maker: resources for a hobbyist engineer

Filed under: freshman design seminar,Uncategorized — gasstationwithoutpumps @ 22:42
Tags: , , , ,

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.


  • 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 (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.


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 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, 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, which includes the Digital Arts and New Media mechatronics work  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), 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  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  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 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.


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 ( 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 ( look like good value for the money for a conventional  digital oscilloscope, and the Analog Discovery 2 ( 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:

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, 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 (, 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 ( 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 ( 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 August 19

Redoing impedance test for tiny loudspeaker

Filed under: Data acquisition,freshman design seminar — gasstationwithoutpumps @ 18:21
Tags: , ,

In Ultrasonic rangefinder tests with tiny loudspeaker, I tested the 10mm CDM-10008 loudspeaker and found it ringing around 9.4kHz, but I reported

I don’t see any resonance around 9.4kHz in the impedance plot, though I admit not looking for narrow resonance peaks in that range.

Today I redid the impedance tests using a 10Ω sense resistor, so that I could use the same range for all voltage measurements, resulting in more correct impedance measurements.  I could definitely hear a resonance around 9.5kHz (and given my deafness at high frequencies, it must have been very loud indeed for me to hear it so clearly), so I looked for another peak in that neighborhood.  It is there and measurable, but not very prominent in the plot:

Because the second peak is on the sloping part of the plot and quite small, I had to model the loudspeaker with a j ω^α L semi-inductor to get a good fit.

Because the second peak is on the sloping part of the plot and quite small, I had to model the loudspeaker with a j ωα L semi-inductor to get a good fit.

I have not attempted to fit the data points past 200kHz, because I don’t believe that the multimeter I was using is really good at those frequencies.  The “corner frequency” I’m reporting around 100kHz is where the DC resistance is equal in magnitude to the impedance of the semi-inductor.

Given how small the peak is on the |Z| graph, but how loud the sound is around 9.5kHz, I probably need a different way of looking for resonances beyond the main one. I can’t rely on my ears for loudness at high frequencies, but perhaps I could use a microphone and record the amplitude it sees as a function of frequency.

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