This is a draft list of parts for the Winter 2013 offering of Applied Circuits. There are five sections: things for students to buy on their own, things to buy (or make) for the lab, pressure sensors, tool kit for students, and consumable parts for students. The pressure sensors are separate, because I’ve not yet decided whether it is better to make them a per-student or per-lab-setup item. Note: I’ve not yet included taxes or shipping in most of the price estimates yet, which will drive up the prices. I’ve tried to avoid suppliers that lie about their prices by quoting low prices and having high shipping fees.
Students buy on their own
Currently we have only one thing for students to order on their own:
| Item | possible source | approx price |
|---|---|---|
| Arduino (recommend Uno Rev 3, but Leonardo or Duemilenova ok) | http://arduino.cc/en/Main/Buy | $25–30 |
The Arduino should be a standard one with female headers, though we won’t be using “shields” that need to plug it, we will be using wire to connect to breadboards and other PC boards. I just saw a bundle that has the Uno Rev 3, USB cable, breadboard, and jumper wires for $36: http://www.amazon.com/Starter-Kit-Newsite-Uno-Breadboard/dp/B0051QHPJM/ Unfortunately, we’ll probably have to put a breadboard in the tool kit, since most students will not buy this bundle.
For the lab
We will generally need 12 copies of each item for the lab, one per station—these are a one-time expense. There are also some consumables (plastic cups, for example) that I haven’t enumerated yet, but the prices there will be tiny.
| Quantity | Item | possible source | ≈price each | price |
|---|---|---|---|---|
| 3 | thermos | thrift store? Amazon? | < $6 | $18 |
| 1 | tea kettle (for boiling water) | www.amazon.com/Proctor-Silex-K2070Y-Electric-Kettle/dp/B00023XCWS/ | $11 | $11 |
| 12 | stainless steel electrode pairs | make at home | < $1 | donate |
| 12 | secondary containment tubs (dishwashing tubs) | http://www.amazon.com/Rubbermaid-2951-AR-BISQUE-11-4-Bisque/dp/B0000DINAX/ | $6.55 | $78.60 |
| 12 | plastic ruler | http://www.discountofficeitems.com/office-supplies/general-supplies/scissors-rulers-paper-trimmers/rulers-yardsticks/universal-acrylic-plastic-ruler-clear/p53260.html | $0.51 | $6.12 |
| TOTAL | $113.72 |
I’m not sure a plastic ruler is really what we need for the silver electrodes. I may need to design a laser cut piece of acrylic for holding the silver wires of a fixed length at a fixed distance for electroplating and characterizing the electrode pair.
Pressure sensor
We have to decide whether to have each student assemble a pressure sensor (soldering to a breakout board with a bypass capacitor) or make up 12 of them ourselves for shared lab use (a cost of about $164).
| Quantity | Item | possible source | price each | price |
|---|---|---|---|---|
| 1 | MPX2053DP pressure sensor | http://www.digikey.com/product-detail/en/MPX2053DP/MPX2053DP-ND/684660 | $11.526 | $11.53 |
| 1 | pressure sensor breakout board | custom, iteadstudio.com | ≈$1 | $1 |
| 1 | 0.1″ pitch screw terminals 4-long | http://www.digikey.com/product-detail/en/282834-4/A98335-ND/1153265 | $0.5812 | $0.59 |
| 2 | M3 × 16mm machine screw | http://www.amazon.com/Machine-Screws-16MM-Pack-100/dp/B009TE0F5S/ | $0.13 | $0.26 |
| 2 | M3 nuts | http://www.digikey.com/product-detail/en/MHNZ%20003/H762-ND/274973 | $0.0384 | $0.08 |
| 1 | 4.7µF capacitor | http://www.digikey.com/product-detail/en/FK18X5R1A475K/445-8404-ND/2815334 | $0.16 | $0.16 |
| TOTAL | $13.62 |
Tool kit
I’m assuming that we will provide soldering irons and solder suckers for the labs that require soldering.
| Item | possible source | ≈ price |
|---|---|---|
| wire strippers | https://www.sparkfun.com/products/8696 | $4.46 |
| diagonal cutter | https://www.sparkfun.com/products/8794 | $1.76 |
| needlenose pliers | https://www.sparkfun.com/products/8793 | $1.76 |
| jeweler’s screwdriver set | http://www.utopiatools.com/7Pc-Jeweler-s-Screwdriver-Set.html | $2.63 |
| thermometer | https://www.arborsci.com/student-thermometer | $3.25 |
| breadboard (23 long) | http://www.goldmine-elec-products.com/prodinfo.asp?number=G19128 | $3.95 |
| breadboard (30 long) | www.amazon.com/microtivity-IB400-400-point-Experiment-Breadboard/dp/B0084A7PI8/ $5.40 | — |
| TOTAL | $17.81 |
I’m not sure which of the breadboards is the better deal. We may need the slightly longer one, and it has more bus lines for power, but the shorter one looks like a better deal, if it is big enough.
Consumable parts
I’m undecided about which loudspeaker to get for the students. I have the pair of loudspeakers in cabinets, which cost $1, but shipping raises the price to $3.79, which is not bad for a pair of speakers in cabinets. Characterizing them is a bit messy, as they have two resonances (probably one from the loudspeaker mass-and-spring, the other from the Helmholz resonance of the cabinet). The beefy 8Ω loudspeaker from Parts Express (which I estimate at $1.52 including shipping) may be a better bet than the slightly cheaper one from Digikey, as it has a lower resonant frequency and will be harder for the students to burn out. It is a buyout sale, though, so may not exist in future years.
I don’t know whether our students will need to buy wire and solder, or whether the lab can provide what they need. I’ve guessed here that they need to buy hook up wire, but that we can provide solder. I may have to adjust things if that is wrong. (With lead/tin solder costing $25/lb and lead-free solder costing $75/pound, we may not be able to provide it—it looks like little 18g tubes cost $4, if we need to sell small amounts.)
I’ve still not figured out what transistors we need, because I haven’t got the power amp lab detailed yet. The NPN and PNP transistors are placeholders—I have to figure out whether we want to use bipolar or FET transistors, and what specs we need.
There are lots of sources for cheaper LEDs, but I wanted to use ones we could get data sheets for.
I don’t know whether we’ll need the header pins—I use the double-ended ones a lot with female-female jumper wires, and to make oscilloscope probe points on a breadboard. I’m not sure the students will need the regular ones, except to put probe points on their instrumentation amp protoboards. It might be useful to have the students have a few flexible jumper wires (male-male, male-female, or female-female) for connecting their breadboards to the Arduino, rather than using solid hookup wire.
Gas station without pumps 
Have you decided on lead or lead-free solder? Do you have fume extraction available? We use these, one per solder position. Another thing to keep in mind as far as lead toxicity goes is that solder suckers tend to spray powdered lead when they are cleaned out. Solder wick avoids that problem, although not nearly as easy for removing through-hole parts.
I would definitely have them do a practice solder assignment before they work on anything they will want to use again — it is surprisingly difficult to learn to co-ordinate both hands. A piece of cast-off circuit board may be good practice — any garbage piece of electronics (old enough to have through-hole components) can probably be cut into squares for students to desolder. Perf-board is not bad either. Alternately, the first soldering assignment I give is to ask students to make a sculpture out of 5-8 resistors (or other cheap components). This gets them practicing the hand-eye co-ordination skills. It also gives me an excuse to have them practice solving circuits, since they inevitably come up with some ungodly series-parallel combination where finding Rtotal taxes their math skills (and spatial/visualization skills too, since nothing is laid out in the orderly grid they are used to).
As for breadboards, I would tend toward the larger one. Inevitably there are students catching up on last week’s lab or getting started on next week’s, and it’s helpful to have a bit of room to allow more than one circuit at a time. Also, the more spread out the circuit is, the easier it is for students to visualize and troubleshoot.
Nice choice of wire strippers — I may recommend these to my students as well. 30 AWG is surprisingly hard to find in local shops.
Comment by Mylène — 2012 November 21 @ 13:48 |
No we haven’t decided. I generally solder with lead-based solders, because I have a lot of it around, some of which I bought a long time ago. The price difference is not as large as it used to be, so I could go either way. We don’t have fume extraction in the lab, but I’m not sure how a big a deal that is for the small amounts we’ll be doing. The soldering irons will just be brought into the lab for the two or three labs they’ll be needed—they’re not a permanent part of the lab setup.
I’ve used solder wick in the past, and found it very frustrating to work with. A good solder sucker is much easier for clearing out holes.
I’ll have to give some serious thought to a soldering exercise. Perhaps I could combine it with the hysteresis lab, which has a very tiny circuit and cheap parts.
Comment by gasstationwithoutpumps — 2012 November 21 @ 15:50 |
I start my students with lead-based solder as well, mostly because it is much easier to make a good joint and much easier to tell whether the joint is good (lead-free solder joints always seem to look cold).
One thing that makes solder wick work much better is liberal use of flux — I use RA type flux and corresponding flux remover.
Comment by Mylène — 2012 November 22 @ 06:26 |
I was planning to use rosin core solder with no additional flux. I understand that additional flux is important for surface-mount devices, but I was planning to stay away from SMD, and just have them do through-hole soldering. I think that your students, who are planning to be electronics technicians, need a lot more soldering skill than my students, who are planning to be bioengineers. I’m happy with them having fairly rudimentary hobbyist-level skills.
Comment by gasstationwithoutpumps — 2012 November 23 @ 07:43 |
More thoughts on the parts list:
If I get electrolytic blocking capacitors from Digikey, they’ll cost about 22¢ for 470µF, or 30¢ for 1000µF. If I get an assortment from ITEAD, the students will get 120 capacitors of (10 each of 12 sizes, up to 470µF) for $6—a bit too much if they only need one electrolytic during the quarter. If we re-sort the capacitors, they can get 1 each of 12 sizes for 60¢, which may be worthwhile, so that student designs aren’t overly constrained by the available parts. (Picking the size for them ahead of time is not a pedagogically good idea.)
I need to get some anti-static tubes for DIPs to distribute the parts to the students. Jameco has them for 22¢ each.
I’m planning to switch to MCP6004 quad op amps, which are 36¢ instead of 28¢, but which again constrain student design less, since they can do a 3-op-amp solution to a problem, not just a 2-op-amp solution. I’ve redesigned the instrumentation amp prototyping board to have 1 INA126P instrumentation amp and 1 MCP6004 quad op amp chip, 2 4-pin screw connectors (for sensor interface and for output interface), spaces for 9 resistors, 1 trimpot, and 2 bypass capacitors. (Other capacitors can be installed by using the prototyping part of the board.) It still all fits in the 50mm×50mm limit for the $1/board cost from ITEAD—I’m trying to decide if I should order 100 boards for $75 instead (I’ll probably need only 40–50 boards for the class this year.)
I’ve picked a couple of FETs to use instead of the bipolar transistors:
NTD5867NL nFET for about 39¢ each and NTD2955 pFET for about 50¢ each. FETs are more expensive than bipolars, and these are much beefier than the students really need, but that should keep them from blowing them up with excessive current (which they will have when they get the biasing wrong).
I’ve designed a first soldering project using the hysteresis oscillator. I can squeeze 4 of them onto the 50mm×50mm ITEAD board, and if I can cut them apart with the board shears, that would make the boards only 25¢ each. I’m thinking about a possible redesign to 50mm×25mm for a 50¢ board that would be easier to cut with the shears. (The 25mm×25mm layout has only a 0.1″ gutter, and I’m not sure I have that good an aim with the shears—I’d rather have a 0.3″ gutter.)
Comment by gasstationwithoutpumps — 2012 November 24 @ 21:32 |
Letting the students choose the values of the electrolytic capacitors seems like a good idea — even if only to let them test a variety of sizes and note for themselves when it does and doesn’t make a lot of difference. I also agree about the beefy transistors being good protection against biasing mistakes. As for the instrumentation amp boards, in your shoes I’d be tempted to go with the smaller order of slightly more-expensive-per-part boards — I imagine that a semester of use will turn up all kinds of little things you might want to change.
Comment by Mylene — 2012 November 25 @ 17:28 |
Since this is already the second design, before the class has even been taught once, I also expect that I’ll want to do a redesign. It would be helpful if I knew exactly how many students to expect. Currently there are 16 registered, so I need at least 32 boards, but lots of students register late, and the course hasn’t been advertised in the engineering undergrad newsletter yet. If the number grows to 25, I’ll need 50 boards. If it grow past that, I’ll need more. The break-even point for ordering 100 boards rather than the number I need is around 40 students, which I don’t expect to get to this year (though I might in future years).
Comment by gasstationwithoutpumps — 2012 November 26 @ 09:28 |
We won’t need to buy dishwashing tubs, as the lab support people already have secondary containment tubs available.
The plastic rulers are gone—I have designed and tested custom acrylic wire holders. I still have to cut out a dozen of them on the laser cutter.
I’m wondering whether I should add a micrometer to the student tool kit. For $9, it is not a bad price, and they can use it both for measuring the electrodes and for the thickness of the insulator in the capacitive touch sensor.
After consulting with my co-instructor, I think I’ll aim for one lab section in the initial board order. If we get more students, I’ll have to do a rush order for more boards, which will cost a little more. (Maybe I can charge the late-adding students a buck extra to cover the extra shipping.) That is, I’ll order 50 of the instrumentation amp boards and 20 (which doubles to 40) of the hysteresis oscillator boards. I only need another 10 of the pressure-sensor boards.
Comment by gasstationwithoutpumps — 2012 November 26 @ 16:57 |
Do you have a strong preference for the micrometer over a vernier caliper? If not, there are some similarly-priced calipers on Amazon, including some with digital readouts if that is preferable. In class, I use the analog ones because I expect my students to learn to read the vernier scale, but for myself, I use a digital unit similar to this one. I find calipers more versatile than a micrometer, especially for awkward shapes like pin spacing. It’s nice to have the capability for internal, external, and depth measurements. The internal diameter measuring tabs fit handily into through-holes to determine hole spacing.
Comment by Mylène — 2012 November 28 @ 12:21 |
I don’t like digital calipers (yet another tool whose battery will die between uses). I use both calipers and micrometers. I find the calipers are good for larger measurements, like inside diameter of tubing, but are not very accurate for small things, like wire gauge and thickness of plastic wrap or tape. The measurement I was thinking of was on the small end, where the finer resolution of a micrometer would be useful. I’m not sure that it is important enough to justify adding either calipers or micrometer to the purchased tool kit, though, for this course.
Comment by gasstationwithoutpumps — 2012 November 28 @ 12:48 |
I see your point — I hadn’t thought of your need to measure thickness of plastic wrap.
Comment by Mylène — 2012 November 29 @ 07:49 |
Another possible breadboard that looks like a better buy: http://www.meerkatsystems.net/html/10000023.html (63 rows plus 4 buses for $4.70 each, $5.50 each including shipping for 20).
Comment by gasstationwithoutpumps — 2012 December 15 @ 06:34 |
Better thermometer price http://www.labandscience.com/index.php?main_page=product_info&products_id=435:2026696b86d56de5070bff6b2694cd1e ($2.60 each including shipping and no-roll triangles for 20)
Comment by gasstationwithoutpumps — 2012 December 15 @ 07:00 |
In order to handle the alligator clips, we’ll probably need to include a screwdriver—I usually use my Swiss Army knife, but I can’t count on students having any tools these days. A set like http://www.eforcity.com/81178.html?efprcggbadtf121214=sc+gb+81178 for $4.40 including shipping is probably reasonable.
Also, the students don’t need to buy wire, as that is available in the lab.
Comment by gasstationwithoutpumps — 2012 December 15 @ 18:31 |
Better price for screwdriver set (should handle both tiny screw terminals and alligator clips): http://www.utopiatools.com/Econo-Mini-Screwdriver-Set.html $1.20
Comment by gasstationwithoutpumps — 2012 December 17 @ 07:24 |