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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.

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).

 

2013 February 14

Tinkering lab

Filed under: Circuits course — gasstationwithoutpumps @ 22:33
Tags: , , , , ,

Today’s lab was a “tinkering lab”, using the oscillator board they made in the hysteresis lab as a component to make a light-controlled sound generator.  They did not have a specific goal, other than to use the oscillator board, to produce sound on the loud speaker, and to be able to control/change the sound by shadowing a phototransistor.

I had them try to predict the effect of adding resistors or capacitors between each pair of points on the oscillator board (+5v, GND, Cap, and OUT), and to test how many of their predictions were right.  A lot of students turned out to have such weak mental models of the oscillators that they couldn’t figure out what would happen in even the simple cases. Few of them were able to do the prelab exercise of predicting what would happen if the added components in various places. Most of them eventually remembered or figured out again how the oscillators worked, and so were able to modify them in reasonable ways, but a lot of lab time was wasted doing what was supposed to be prelab work.

A few of the students were trying to figure out what to do without even a schematic in front of them, and when they drew a schematic it did not correspond to what they told me they were trying to do.  They worry me a bit, as by this point of the quarter the students should be able to copy schematics accurately and wire from them, even if they are sometimes a bit hazy on how the circuits work.

I’m also finding that several of the students seem to be incapable of learning from written material—students with no understanding of FETs as switches seemed to understand it fairly well after I explained it—using almost the same words as I used in the lab handout.  I’m not sure I understand why the explanation given verbally seemed to work, while the same one given in writing seemed to fail.  I find it difficult to believe that they really can’t learn from written materials, so there must be a different explanation.  Too much in the handout, so that they shutdown while reading it?  Not having read the handout? (possible with some of the students, but unlikely with the ones I observed the problem in)

I rely heavily on written material to communicate both design goals and details about the parts they are using, so I really need to figure out what is going wrong with the written channel for information.  Is there a way I could write the lab handouts that would be more digestible for the students? If the difficulty absorbing information from written sources is a real one, I may have to do more lecturing, though that seems like the wrong thing to do, as engineers have to be able to read spec sheets and learn from written sources.

Only a few of the students did the systematic exploration of what components in different places and predicting/observing the effect.  I may need to reduce the emphasis on that next year, and focus their attention more on potentially useful interventions (one pair wasted a lot of time looking at the least interesting pair: connecting extra components between power and ground).

Everyone eventually managed to get loud sounds out of the loudspeaker, and to control the sounds by shadowing the phototransistor, but I think that some just copied what others had done, without completely understanding what they were doing.  I think that they all ended up with essentially the same design I had, with the phototransistor shorting out the capacitor in bright light.  Everyone did eventually get the right pFET driver for the loudspeaker, though one group worked through the other three circuits first, and found why they were less desirable. We’ll see in the lab reports whether all the groups can accurately draw their schematics and explain how their devices work.

Overall, I’m moderately pleased with how the lab went.  Students deepened their understanding of RC time constants and the hysteresis oscillator circuit, and they got a feel for “cut-and-try” engineering. But I think I need to rewrite this lab for next year, with a little more direction in which pairs of terminals are worth exploring and how to think about the effect on the oscillator.

2013 February 7

Thirteenth day of circuit class and first op-amp lab

If you’re wondering what happened to the 12th day of circuits class, that was discussed in Quiz too long and too hard. On Wednesday, I did some do-now problems to check on some basics and to provide a hook for the day’s topics.  I asked for the voltage gain (Vout/Vin) for the following circuits:

First question: a voltage divider they are familiar with, and which almost everyone got right.

First question: a voltage divider they are familiar with, and which almost everyone got right.

do-now-2-2013-feb-6

A different voltage divider circuit, stressing the fact that voltage is between two points. Only about half the class got this, because I had not given enough examples of voltages other than to ground. Students who had the correct answer had two different ways of getting there: starting from Ohm’s Law, or simple proportional reasoning. I pointed out that a third way would be to compute the voltages of the two voltmeter leads using the voltage divider formula.

do-now-3-2013-feb-6

A reminder of the one op-amp circuit they’d seen (last Friday). Only about half the class remembered this one, so I did another derivation of it using a finite-gain amplifier instead of an ∞-gain op amp, showing what happens as gain goes to infinity. I think that I should do more of that, since many of the students are uncomfortable with infinity.

do-now-4-2103-feb-6

A hook for the main material of the day: non-inverting amplifiers. Only one student correctly guessed the gain of this circuit (one of the top students in the class—I think he “cheats” by reading the assignments when they are assigned to be read—I wish more students would do that).

After reviewing the unity-gain buffer, but before getting into the non-inverting amplifiers, I made a digression into what would happen if we swapped the two inputs to the unity-gain buffer.  Doing the algebra for the gain computation with a finite-gain amplifier and taking the limit, we again get a solution where the output voltage is equal to the input voltage.  I then stepped them through what would happen if there was a small perturbation in the input, which does not result in the amplifier settling down to the new value, but keeps getting bigger until the output slams into one of the power rails.  I used this to discuss positive feedback and the difference between a stable and an unstable design, but did not give them any tools for analyzing stability other than hand-simulating what happens if you add a small perturbation to the input.

Finally I got to the non-inverting amplifier, and stepped them through the reasoning behind the gain computation.  I think most of them followed it, though some are still disturbed that the voltage divider in the circuit has “Vout” and “Vin” labels reversed from how they are used to thinking of voltage dividers.  I have to wean the students away from the notion that formulas contain sacred variable names, and into thinking about them as having slots that get filled according to context.  That is, I have to have them attach semantics to the formulas, rather than relying on name-based pattern matching.

I was originally going to do inverting amplifiers as well, but I think I’ll leave those until next week.  I also decided not to have the students try to do a single-supply design for their first op-amp lab, but to use a dual-supply design, which is a little simpler conceptually.  I’ll have to rewrite the lab handout for next year, as I had originally planned to do a single-power-supply design.  I realize now that is too ambitious for the first op-amp assignment.  There was a mention in the lab handout of a DC-blocking capacitor on the output, but that is not needed in the dual-supply design, so just confused a couple of the students.

After the non-inverting op amp, I introduced them to the notion of block diagrams, and together we developed the following block diagram:

Block diagram for audio amp

Block diagram for audio amp

We didn’t do it all at once, of course, and it took some prompting to get the various parts all there. We started easily enough with the microphone and the loudspeaker, then added the amplifier. I had to prompt them a bit to remember that the microphone was best thought of as having a current output, but that the amplifiers we knew how to design were voltage amplifiers. Since their second lab converted the microphone current to a voltage, they got the I-to-V converter pretty quickly. We tried to guesstimate the gain needed by saying we wanted the loudspeaker to swing rail to rail (±3V) on a loud input, and I asked the students what they had measured on lab 2 as the AC voltage swing. A couple of students had something in their lab notebooks. I pointed out (again) the value of keeping good lab notebooks, since you never know what detail you might need later on. We used one of the estimates to pick a gain of about 50 for the amplifier.

I then pointed out a problem: the I-to-V converter they used in Lab 2 had a 1V DC offset, and if they put that into the amplifier, they would pin the output at the upper power rail, since it couldn’t go to 50V. After a bit of reminder that DC was a frequency of 0Hz, they came up with the need for a high-pass filter, and could even remember the voltage divider circuit to get it. But figuring out the corner frequency stumped them, because none of them remembered the frequencies of human hearing. Eventually someone came up with 20Hz to 20kHz, which goes a bit higher than humans hear, but is a typical stereo specification. We only cared about the low-frequency end anyway. I pointed out that knowing what sort of signal one was dealing with was an essential part of the design process, and one of the first questions they should ask when doing a design. They eventually settled on 10Hz as a reasonable corner frequency, though anything between 1Hz and 30Hz would probably do, given that their speakers have very poor bass response anyway (they are very fine 10W speakers for about $1 each, but they are still small speakers).

I think that I’ll continue to have the development of the block diagram as an in-class discussion (not try to put it into the lab handouts), so that the students can develop it themselves with guidance from me, rather than being handed it.  This decomposition of a design problem into smaller easily solved problems is one of the essential parts of engineering, and most of the bioengineering students have not had much experience with it.

I ordered them to pair up right away and come to lab with designs already done and ready to implement and debug. I think that too many of them have been under-prepared for labs, having just looked over the lab handouts the night before. From now on, I’m going to make sure they do some serious work on each lab before they touch wire to breadboard on it. (This will be particularly important on the last two labs, where they’ll be soldering the instrumentation amplifiers—unsoldering components is no fun at all.)

Today’s lab went great! Everyone got a working audio amplifier (generally with a gain of 40× or 50×), and could see the gain on a dual-trace oscilloscope (superimposing the signals at the mic and the output with different volts/division setting, which was particularly satisfying for showing the gain of 50).  They also observed clipping of the output with loud input signals, and the inability of the op amp to drive the 8Ω load of the loudspeaker all the way (it has only a ±23mA output capability).  I reassured them that we would design an amplifier later in the quarter capable of delivering loud sounds.

A few students came in with non-functional designs, but they were all quite close, and a few minutes of discussion at the whiteboard about how the resistors for the non-inverting amplifiers needed to be designed got them back on the right track when the circuits they built failed. I refused to look at designs until they had wired them up—I’m making “Try it and see!” the mantra for the class.  Perhaps we should put it on the t-shirts.

Some students also had a little trouble converting their schematics to wires on the board, but a little debugging and tracing wires was enough for me to point out discrepancies between what they showed me in the schematic and what I saw on the breadboard.  This was enough to get them back on track without my having to touch their boards.

I thought that this lab would be one of the toughest ones so far, but it turned out be the smoothest sailing.  Everyone finished on time with working circuits demoed!  Perhaps the op amps are not as hard as I expected for them, perhaps the design assignment the day before left them more prepared, perhaps they’re beginning to get the hang of things now after a somewhat rocky start.  Whatever the reason, I was really proud of what they managed to do today.  This is only lab 5 for them, and they are already doing more in the lab than the EE 101 students achieve by the end of the quarter!

Next week they’ll do a “tinkering” lab without a clearly specified objective, but with some strong constraints. In the course of the lab, they’ll learn about phototransistors (though not all the characteristics of them) and FETs as switches.  The lab is very thrifty, making use of the hysteresis oscillator board that they soldered up for the capacitance-touch sensor as a component without modifying what is on the board. They’ll also learn about a different style of engineering: tinkering, where one plays around with stuff to see what can be done.  I don’t think that most of them have had much opportunity to tinker in the past, and it is an excellent way to develop the mental models that allow one to reason about circuits without tedious calculations.  (Some calculations may still be needed, of course.)  Some of them may get frustrated with the  somewhat undirected nature of the play, I’ll undoubtedly get a headache from loud squealing of loudspeakers at high frequencies, and someone may burn a finger on an overheating FET, but I think that next week’s lab may be the most fun one of the quarter, and it should prepare them well for the class-D power amplifier later in the quarter.

Tomorrow I’ll start on group-work quiz corrections (the last student is taking the quiz in the morning), and have them try to finish the quiz corrections over the weekend. If the quiz corrections are problematic still, we’ll use Monday for more group work on them and possibly some Socratic lectures (they’ve had all the material they need—they just need some guidance on how to apply it).

More likely, on Monday we’ll do some work on gnuplot, so that students who need to redo one of the labs that involve model fitting will have a better handle on what they are doing.  If we do that, I’ll ask students to bring in their laptops, so that they can do some interactive work on gnuplot scripting.  I thought that the first script I gave them would be sufficient example, but I didn’t realize at the time the difficulty they would have in generalizing the example, so I’ll step them through a worked example, with them gradually building a script that does what they need. I hope to be able to address the scope-of-variables problem that I think is tripping some of them up, as well as detecting other conceptual stumbling blocks.

Although I started this week very depressed about the quiz results and having sleepless nights worrying about how to modify my teaching to get the concepts across, I’m now feeling very positive about the class.  The op amp lab went great, and I see ways that I think have a very good chance of getting the students comfortable with the material.  In about two weeks, I’ll give them another quiz (similar to the one that was so painful for everyone on Monday, with perhaps a couple of op amp questions), with the reasonable expectation that they’ll be able to nail it.

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