UptownMaker

Numeracy fail

2012-01-21T08:37:00.000-08:00

Side note- it's been a looong time since I wrote a blog post. Since then, I've had a second child, moved jobs (I'm now working at SparkFun- woot!), states (Colorado is state number six for me), and time zones. A lot of the more technical sort of blog post I'd write now goes up on the SparkFun website as tutorials, but I'm going to try to post more here.

Engineers and scientists (and other general nerd/geek types) like to talk about "numeracy", which is the ability of a person to grok math. It used to be that the primary "complaint" (if you will) was about people who play the lottery- "a tax on being bad at math". I'm not talking about valuation, here- being willing to pay five- to tenfold as much for a meal at a restaurant as it would cost to make at home, for instance. I'm talking about hard numbers- apples to apples.

Having a poor grasp on mathematics is getting to be a bigger handicap, though. I've notice recently when grocery shopping that the old principle of "buy more, save more" no longer applies- frequently, a bigger box of cereal, say, will cost MORE per ounce than a smaller box.

Or, containers will be cleverly redesigned to contain less but look the same, then the price is maintained. Next time you're at the store, check out the "half gallon" containers of orange juice. Many (most?) of them are 59 ounces, instead of 64. They don't look any different, of course, and there's no mention on them that 59 ounces is NOT a half gallon (and I'm not optimistic that many consumers know what a half gallon is, nor would be able to calculate price per ounce between a 59 ounce jug and a 64 ounce jug).

I noticed this BECAUSE I grok math. I do simple mental arithmetic many, many times a day as an electrical engineer- calculating expected currents, expected power consumption, approximate required resistance, etc etc. When I look at a package in the store, I can't help but calculate a price-per-ounce of the contents. It's usually right to within 5 percent or so- I round to make the math easier (metric would make it easier yet- is that why we haven't changed?). But I was noticing that there were discrepancies that could not be papered over by hurried mental math.

Keep an eye open- I've heard from a few others that they've noticed this but I'm curious how widespread this practice is.

One other place I've noticed crap numeracy is in science writing, and this is REALLY disturbing to me. Two variations on the same metric will be given in a book or article- say, the number of children who die of malaria every day and the number of people who die of malaria in a year. These values may be reported multiple times and usually won't be reported in close conjunction with one another (note that I don't think this is an attempt at dissembling by the author- it simply reflects the where and when in the work that each makes sense to be mentioned). The troubling thing is, the numbers reported are frequently mutually exclusive. For the above example, the number of deaths per year due to malaria may be reported as, say, 500,000. Quick mental math says that this implies slightly more than 1,000 people per day (remember, I'm an engineer- pi is "about 3" until I need a better answer). Elsewhere, a value of deaths of children will be given, and that number will be, say, 1,500 per day.

In my mind, alarm bells go off. I didn't calculate exactly how many people per day are claimed to be dying of malaria, nor exactly how many children per year are claimed to be dying, BUT my order-of-magnitude estimate tells me that the author is either not counting children as people or not paying attention to math. Frighteningly enough, neither was the editor nor anyone else who weighed in on the book. This kind of basic mathematical error casts doubts on everything else in the book- after all, someone who isn't capable of that kind of mental comparison is certainly unlikely to be able to judge the veracity of more complicated mathematics behind statistical predictions and observations that form the basis of most proposed solutions.

I'm not sure there's much we can do about this- I grok math because it's very much part of my daily life. I exercise those mental muscles constantly to a point where I apply them unconsciously to situations most people don't even relate to math. Maybe some kind of wide-scale gamification of mathematics? At any rate, I don't think it's something that can be addressed by education. Mathematics is fundamentally a foreign language to the human brain, and the only way to really learn a foreign language is to use it, over and over, until you are fluent.

Fun Google maps satellite image find

2011-07-01T12:21:00.000-07:00

I found this image on Google maps satellite images the other day.

It's a E-3 Sentry taking off from Tinker AFB near Oklahoma City. At first I thought it was a KC-135 (and that's what it went out on Twitter as) but then I noticed the rotodome on top.

It's neat because you can see the sequence of images as captured by the satellite. In the first "frame", it's just starting to pull away from the ground, and by the last frame it's well off the surface and past the end of the runway. You can also see the procession of the rotodome- the band of gray in the disk shows the rotation.

What is the propagation speed of a yawn?

2011-06-21T10:18:00.000-07:00

On the bus the other day, as I was rolling past waiting commuters on Marquette Ave in downtown Minneapolis, I saw a yawn traveling along through the crowd. Or at least, that was the appearance- it may have just been that people were randomly yawning as I passed. Regardless, that got me thinking: what is the propagation speed of a yawn through a given crowd?

We should be able to express that as an equation, if we choose our parameters wisely. First, let's define "speed", for the purposes of this exercise, as the time required for a yawn to travel a given distance through a crowd in any direction. The reason for that wording will become clear later.

So, that brings us to the equation:
V = d * q * (m / r) * f(C)
where
d is the average delay between when a person sees a yawn start and starts yawning themselves
m is some distance factor (it can be observed that someone closer is more likely to inspire a yawn than someone farther away- m will have to be determine experimentally)
r is the average distance between crowd members
f(C) is a function of the crowd shape, orientation of individual members to each other and crowd activity

f(C) can be thought of as a "crowd quality" metric, and it will be different for linear crowds (people waiting for the bus, but all facing the sreet), crowds where there is no orienting factor (people waiting for a concert, for instance, who may be facing any direction based on where their friends are), queues, or spectating crowds. It is also likely that by being similarly primed mentally will factor into f(C)- a room full of bored college students is more likely to propagate a yawn quickly than people waiting for a bus, all with different degrees of boredom and internal mental activity.

Now, let's consider directionality. If we pick two arbitrary points and attempt to measure the propagation time between them, we will get a false sense of the travel time because of the meandering of the yawn through the crowd. It is thus better to simply pick a "patient zero" and then watch for a yawn to occur in any person at a given radius away from that person. The resulting scalar value is the speed of a yawn, or perhaps the "speed of lassitude".

Why Dunbar's number matters

2011-06-01T10:41:00.000-07:00

So, I cast a fairly wide net in terms of things I passively track for potential food-for-thought. Blogs and tweeps, books, articles, etc- I try not to limit myself too much because I can skim pretty quickly across a fairly vast swath of content, even if it IS just a drop in the bucket.

This morning, the following tweet came through, from Tim Hurson:

To ourselves we are a complex of thoughts and feelings. To others we're just a bunch of behaviors.

Really not engineering related, of course, but it meshed well with something else I saw come through my twitter stream- a post about Dunbar's number, which is the supposedly optimal group size of human culture: the number of people that you can conceivably know about and care about. That group of about 150 individuals is your monkeysphere, and people outside of it are, to some extent, not really people in your mind.

I think there's a little more to that tweet than the 140 character limit allows. See, to people who consider you to be inside their monkeysphere, you are a collection of behaviors, and they have collected a series of behaviors to build a heuristic representing you and your expected reaction to future stresses.

To people who do NOT consider you to be inside of their monkeysphere, you are nothing more nor less than what you are doing at the moment. If you cut them off in traffic, you're a jerk. If you hold the door open, you're a nice guy.

The tricky part is, we all have people in our lives (co-workers, fellow bus commuters, hackerspace members) who consider us to be inside their monkeysphere, but we consider to be outside of our own, and vice-versa. This can cause major friction when someone behaves in an unacceptably familiar manner.

I guess my point is, the next time somebody irritates you or angers you, consider the Venn diagram of your respective monkeyspheres. If there is no overlap at all, there's a very good chance that the conflict is highly situational and not due to some intrinsic defect in either of your personalities. If there's a possibility of asymmetrical monkeysphere inclusion, ask yourself if you would change your judgment of their actions if you were closer to them, or if their actions would make sense if they were closer to you (or if they think they are closer to you than you think they are). And if you are within each other's monkeyspheres, then it's probably worth it to deal with the conflict as well as you can before it becomes a major problem.

UptownMaker goes to the Faire

2011-05-26T10:23:00.000-07:00

This past weekend I attended Maker Faire in San Mateo. It was an absolute gas (does anybody use that phrase anymore?)! I'm going to do a few quick posts highlighting my favorite sights- all my pictures and videos are on my Picasa site.

I'll start out with my favorite first: Miss Haley Who, swamp kirin wrangler.

This lovely fellow is a mechanical swamp kirin. He stands about nine feet tall and though he looks ferocious he's really quite gentle.

Haley Who, aka halo seabat, built this majestic creature as a gift for her little brother, Seth. It seems Seth was a bit heartbroken after their father explained that the few remaining wild swamp kirins in the east were best left unmolested in their natural habitats, and halo took pity on her brother, building him this mechanical version.

The pair of them wandered about the grounds, charming the pants off of just about everybody they met. Haley's disarming smile, the kirin's gentle gait and their tender interplay softened the overall image to the point where I never saw even the smallest of children exhibit any fear at all- mostly they wanted to touch the kirin, stroke its legs, even kiss it on the nose.

It felt magical, and I'm a happier person for knowing Haley and her kirin friend are out in the world.

USB CDC toy

2011-05-24T19:59:00.000-07:00

This was originally going to be my calling card for Maker Faire. It's a very simple implementation of Osamu Tamura's AVR-CDC project, realized without a board. I had planned to make it a small device that can be plugged into a USB port and observed on a terminal spitting out information about me. The Great Global Hackerspace Challenge project took a lot out of me, though, so I didn't get it done in time.

The blobby on the left is an I/O module- three input switches, three output LEDs, and a reset switch and power LED. It plugs onto the header that is currently being used for programming. The circuitry is pretty simple: 100nF bypass capacitor, the 5V in from the USB port goes to the positive supply pin through a 1N4001, and the USB D+/D- are connected to a couple of the I/O pins.

Some words about that 1N4001: it was chosen specifically for its high forward voltage. See, the USB input wants a 3.6V input or so, and the AVR doesn't want to run at the 16+MHz needed for this project below about 4V. Originally, following the schematic on the project home page, I was using a red LED as a voltage drop. The AVR never ran stably- the voltage (about 3.3V) was just too low. Now, it's running at about 4.2V, and the 68-ohm resistors between the AVR and the USB limit the current to just a few mA, and everybody's happy.

Right now, I'm up to my elbows in the source code of the original project, removing the serial I/O code and replacing it with easily used hooks for internal functions. Ultimately I'll bend it to be programmable through the Arduino interface- for now I'm working in AVRStudio5. Once I have it all done I'll release all the deets so anybody can make one. I may also make a PCB and sell kits for it through NoCube, and probably just the pre-programmed IC, as well.

Inductive power

2011-05-24T19:46:00.000-07:00

About two years ago I decided I was going to figure out a cheesy inductive power coupling circuit. I sat down one Sunday, started plugging some stuff together and this is what I ended up with:

This is the circuit I brought with me to the "bring-a-hack" dinner at Harry's Hofbrau that Jeri Ellsworth organized on Sunday night. You can see that the LED in the jar is lit- the jar is really just a gimmick and the little parasite works better outside the jar.

The circuit is very simple: the IC in the middle is a 12F683 that I programmed up to be a square wave generator (someday I'll blog that project, but for now, I'll just say that the oscillator frequency is jumper selectable and it can be set to either update constantly when powered or set and forget the output frequency and duty cycle) running at 50% duty cycle and (approximately) 71kHz. The square on the right is a bit of ~28ga magnet wire wrapped a few times around four screws. Power is delivered to it by a transistor- the coil gets driven by the full umph of the 9V while the PIC runs on the 5V regulator to the left.

Efficiency is TERRIBLE. Because I'm driving the transistor hard with a square wave I lose energy into the higher-order harmonics, and then I'm half-wave rectifying the output with the LED. If I made the drive waveform more sine-like and added some joule-thief circuitry to the parasite I'd see much better results. But then, this was never intended to be a huge project, just proof-of-concept.

One last thing, if you're thinking of doing this yourself: every hand-wound parasite is going to have a slightly different optimal frequency. The circuit as I made it was basically an LED, a 100nF capacitor and a coil all in parallel. Depending on the resonant frequency of the LC circuit, you'll see better results at different frequencies.

Do you see nouns or verbs?

2011-04-11T11:22:00.000-07:00

A friend of mine recently posted to Twitter a picture of an object that his 19-month-old identified as "K".

That got me to thinking- clearly, she knows what a "K" is, but it doesn't exist in the "privileged class" of objects that we arbitrarily refer to as "letters". Hence, she was able to spot a "K" someplace an adult would never even look for one.

At her age, she still sees nouns everywhere she looks. That doorstop LOOKS like a "K" so she identified it as such. As adults, we live in a world of verbs. We look at that object and see a doorstop- which is to say, we see what it DOES rather than what it IS.

There's an important distinction there, for makers and artists especially. We tend to be so wrapped up in the verb form of the world that we forget the noun. My personal experience with this has also been that even when I succeed in considering an alternative solution to a problem, I STILL verb-ify my solution, artificially limiting my pool of potential objects to a small pool.

I'm trying to break out of this habit but it's a difficult thing to unlearn. I'm paying more attention to what my daughter does with the things she picks up, how she investigates them for the intrinsic properties of form rather than the extrinsic properties of their intended uses.

I'm also trying to challenge myself to come up with descriptions of things that I salvage, descriptions of form rather than function.

It feels like writing left-handed.

Atmel's XMEGA- What's the deal with 'A' and 'D' families?

2011-02-15T07:58:00.000-08:00

Too busy to blog lately. I need to change that. Today I'll be doing lots of gateware builds on a project so I'll have some free-time.

I attended a seminar last week about the picoPower capabilities of Atmel's UC3, Atmega and Xmega processors, and it got me hankering to start working with the Xmegas. It did not, however, give me a good answer to a fundamental question: what the heck is the difference between the 'A' and 'D' family of Xmega parts?

Some Google searches failed to turn up a result, so being a good little creator of value, I thought I'd do the research and make a post about it. For more information about the Xmega in general, EMSL have a good starter article. In short, they are high-ish pin count, 3.3V microcontrollers that add some really nice features to those available in the Atmega parts.

They come in two flavors- 'A' and 'D', with 44, 64 and 100 pin count devices and QFN, BGA, and QFP package options. They also have scalable program memory sizes from 16k up to 256k. The big question I had was, why 'A' versus 'D'?

In short, it's peripheral availability. 'D' devices are lacking a few peripherals:

DMA controller
Battery backup system (providing dedicated battery backup supply option)
32-bit real-time counter
AES and DES cryptography engine
EBI (external bus interface- supports SRAM and SDRAM)
DAC (non-PWM digital-to-analog conversion)
JTAG support

That seems to be the real difference between the two families; obviously it's up to you to determine if this is a limiting factor.

Some of the things I'm most excited about involve the DMA controller, the DAC, and the EBI, so I'll probably be working with the 'A' parts. But that's just me...

Engineering definition: elegant

2011-01-19T08:06:00.000-08:00

Elegant (adj.): “I’m being an unnecessarily clever d!ck about this, and that’s going to open up a lorry-sized hole in my design that I won’t see because I’m being too smug about how clever this solution is. Oh, and it’ll be harder to fix, understand, build, troubleshoot, and use, but I saved $.000001 on each unit by committing untold future resources to solving the problems I don’t know I just made. It also took far longer to design than it would have had I done it in a more conventional manner, but that’s okay, because design time is free and per-unit cost is king.”

KISS is the alternative to "elegant", and frequently results in designs which are MORE elegant than trying to be clever produces.

The Power of the First Time

2011-01-12T10:43:00.000-08:00

No, not that first time (well, not exclusively).

Think about the first time you did something that scared the hell out of you. For me, the best example is the first time I set out to ride a rollercoaster and actually enjoy it. Before, the tiny number of times I'd been on coasters were all profanity-laced panic-attack-like attempts to assert my masculinity. This time, however, I decided to seize my fear and enjoy the ride. It worked- that summer, and the two years thereafter, I bought a season pass to the local theme park and racked up literally hundreds of out-and-back trips, and I made a couple of special trips to other theme parks to hit THEIR coasters, too. Something that had been previously unimaginable became a source of tremendous enjoyment to me.

What about the first time you used a tool you'd never used before? I was terrified of the vertical milling machine until the first project I used it for; now I can't imagine NOT having access to it.

Or the first time you used a skill? What spurred this post was my maker's notebook project. I'd considered doing something like that for a very long time, but never did. Now that I've done it, a whole new world of possibilities is opened up. I used some hot glue to repair an engineering notepad that had lost its cardboard backing this morning, basically using the same process I used for the maker's notebook. I'm starting to collect scrap paper (all those orphan printouts from around the printer, for starters) to make future pads. It's too easy NOT to do that, now that the skill is in my stable.

My point is, never underestimate the power of doing something once. Whether you're scared to do it, or think it'll take too long, or think it'll be too hard, you have nothing to lose by giving it a shot. If you succeed, even partially, the second, third, and fiftieth times will come almost without thought.

A Maker's Notebook

2011-01-10T20:13:00.000-08:00

I've long suffered from notebook envy. Not envy of any particular notebook; I just always wished I could be one of those people that carries a notebook around and jots down notes on everything- stuff they want to look up, buy, make, write about, talk about, whatever.
I never HAVE been one of those people, for a number of reasons. I'm scatterbrained, so even if I did have a pen and notebook, they'd have to be pocket-sized so I can not have to carry them around, or I'll lose them. I hate writing (I actually have a mild learning disability which affects my ability articulate ideas with a pen and paper), so I'm not likely to be writing draft blog posts or a novel in my notebook. I can't draw for crap, either, and I don't have much interest in developing that skill. I also never found a notebook I really liked- they're too big, or too rigid, or the paper is too thin, or they are lined/gridded wrong. I'm very Goldilocks on this.

I like the Maker's Notebook for a number of reasons: the pages are numbered and gridded, there's an elastic band to hold it shut, and there are pages of reference material in the back (although I think most of the reference material is stuff I'd never use). I don't like how big it is, the spacing of the gridlines (1/8" is too small for me), or the fact that it's hardcover.

I also don't like the idea of buying my maker's notebook. It seems...contrary to the whole spirit of the thing, I think.

So, what to do? Make my own, of course! I did a little research into what's involved in binding a book, and it turns out it's really quite easy. The process I followed is:

1. Draw up my pages (link goes to a ZIP file of the pages I made): I used Inkscape to make a template page, then I used a Python script to change the page numbers and create a new SVG file named according to the pages it contains. I only numbered the odd pages and didn't attempt to print on the back- I found that the printer I was using was too unreliable for my tastes (pages printed duplexed were off by a millimeter or two in both axes) to create two sided sheets. The pages are 85mm by 125mm, 5mm minor grids marked by "crosshairs" and 25mm major grids marked by lines- the last 10mm on the spine edge is unprinted to provide for margin.
2. Print them off (link goes to a PDF of the pages in one file): I printed the pages onto resume paper- I don't figure I'll be printing any resumes anytime soon so I might as well do SOMETHING with it. I didn't want the paper to be thin enough for the ink from my pen to bleed through (a problem I had with my last Moleskine notebook), and I was hoping to be able to write on both sides without even seeing the writing on the other side. I was partly successful- the ink doesn't bleed at all but it can be seen through the page.
3. Cut them out: I used a guillotine-type bypass paper cutter for mine, and cut the pages out one sheet at at a time. I used a flashlight to silhouette the cutting edge so I could line up the edges better. A slide-type cutter would probably work better.
4. Align the pages: Align the to-be-bound edges by rapping the stack edge-on on a table (think about the move you do when shuffling cards, between the fun flippity-flippity-flippity parts, to realign the cards. But more cautious.). Once you have a nice, well aligned stack (you'll only be able to get the binding edge REALLY straight), take a couple of binder clips and secure the stack by clamping them over the edge OPPOSITE the binding edge. Then, create a nice, solid edge on the binding edge by taking some pieces of stiff material (I used thin sheet aluminum but wooden or steel rulers, cut glass, paint stir sticks, or anything else of that ilk would work) and clamping them along the edge with another pair of binder clips. In the picture, the edge clamp pieces are a little short- they are sized for a different sheet but you see the idea. Make sure that the clips and clamping pieces are at least 2-5mm from the edge; less than that and you'll get glue on them, but more than that and the pages will not be tight enough (they'll want to spread as they absorb glue).
5. Smear the glue on the spine: I used fancy-shmancy bookbinding PVA, but regular old Elmer's Glue-All should work just fine, since that's pretty much the same thing. I've also seen websites recommend Gorilla Glue and hot glue as well, but I can't vouch for those first hand. It's nice to get something in a pot, though, like I used, because you can brush it on more readily with a tool, then. I used a foam paint brush and it worked perfectly. Start with a light coat and work it into the spine a little (by light coat, I mean, cover the entire spine, but not so thick you can't see the "grain" of the paper stack through the glue). Then, immediately, paint a slightly thicker layer over that (thick enough that you can't see the grain anymore, but not so thick it threatens to drip or run). Let this dry for a few hours; when you come back you'll likely find that you've got a few places (or maybe many places) where the glue has thinned, soaked in, or otherwise become transparent enough that you can see the grain again. Now put a thick dollop down, all along the spine- as much as you can get without drips forming. Go down the front, back, and ends, as well, by a millimeter or two or three. You want to form a nice "cap" over the bound edge, that captures all the pages and lends strength to the spine such that the pages fold easier than the glue cap does. Leave the binder clips and clamping pieces in place until the spine dries.
6. Cover it- once you've got a nice, thick spine coat of glue, you can put a cover on it. I used a piece of upholstery fabric from an old sample book, cut with pinking shears to prevent (or at least slow) fraying. Personal preference is key, here- I wanted the cover to be long enough that the back cover would flap over the front and be secured to the front, to keep the edge opposite the binding from becoming "frizzy". All I did to cover it was add a little more glue (a thin layer, but over the entire surface of the cap I'd created earlier) and wrap the cover around the bound pages (line it up nicely!). Be sparing with the amount of glue you use- as I smoothed the fabric over the spine, a lot of glue oozed down to the end and dripped out. I replaced the binder clips and clamping pieces along the spine, and the two clips along the open edge, just to make sure I got a nice crease.

Once the glue dries, you have a notebook! There are a few things I did wrong that I'll try and rectify with the next version:

The paper I used was too heavy. It could be a bit thinner and still be quite opaque; then it would fold easier, too.
I shouldn't have printed a line along the three visible edges I wanted to cut. The lines show up here and there which lend a slightly slap-dash look to the thing. Either printing a line that's offset by one of the paper cutter's grid units (so I can line it up with something else to cut) or just using the ends of the grid lines would have been better options.
The snaps I put on the cover are too thick. They lend an uneven feel to the surface, marring the sleekness of the closed notebook and embossing a circle on the first few pages. Better options escape me at the moment, though- both corners of the cover need to be fixed or the will inevitably fold up when stuffed into your back pocket. Elastic band, perhaps? Magnets?
The fabric I used is a few mm narrower than the book itself. Not a big deal, but a definite lack-of-planning issue.
The fabric is a little too floppy. I haven't decided if I like this or not. It's durable enough to protect the notebook but soft enough to easily be folded around the back. Next time I may use leather if I can find a source for usable size pieces on the cheap.
I rushed it with the reference information. The reference pages at the back have a few pinouts of transistors, the Atmega328P, standard resistor values, a tap/drill chart, ASCII characters, some conversion ratios and some tangent values. Most of them I just stole from around the web (that's why I didn't upload those pages); many are scaled bitmaps and screen caps, so the resolution is sub-par.
Time will tell if my "cross-hairs for minor/lines for major" solution is the right one. I may go to tiny little pips rather than cross-hairs, and I may abandon the major grid marks all together. I am, however, very happy with the 5mm spacing for the gridlines.

Despite all that, I'm very happy with my new notebook, and I'm reasonably sure that the combination of it being nearly exactly what I want and my having made it with my own hands is going to encourage me to use it. Now I just need to get a really nice pen to use with it!

Designing for the degenerate case

2010-12-30T11:22:00.000-08:00

In mathematics, a degenerate form is one that cannot be perturbed in some way without being rendered a member of a larger, more complex class. For example, a circle is a degenerate ellipse- change the constant multiplier of one of the terms and you push the form out of the class of circles into the larger class of ellipses.

Next time you're solving a problem, ask yourself: am I solving for a degenerate form? And, if the answer is yes, is that important? Let me give an example where the answer to both questions was "yes". I was tasked once with supporting some motion code which was intended to align a circuit board on a conveyor belt under a camera.

The code as written worked fine in the lab, but in the field, customers began to complain of erratic and unpredictable behavior- boards which would be incorrectly positioned at the start of inspection, pushed off the end of the conveyor, etc. It turns out that the code had originally been written to the degenerate case of a PCB that had no slots or notches and was less than 300mm long- even though the system was specified to handle ANY board of a length up to 450mm in length. The result was that it was relatively easy for a slot (or even a hole for a component lead in boards coming through before soldering) to allow enough light through to fail to activate the accurate positioning sensor, resulting in a misaligned board. Longer boards caused a problem too- they would be (only occasionally) detected as fault conditions because they would trip more than one sensor at once. Once I rewrote the code with the mental model of trying to align a picture frame with non-parallel leading and trailing edges (basically, the broadest possible class of objects that could come through the machine), a huge number of field issues resolved immediately.

Perhaps the most serious of these degenerate cases is the "normal" human. I have a number of "abnormalities" (if you will; I hope I don't offend anyone with my terminology but it's important, I feel, to consider denotation rather than connotation and to realize that "abnormal" is, in fact, a term with no qualitative meaning) of capability which have rendered my life, if not worse, at least harder than necessary. The most significant one is my colorblindness. I'm a deuteranope* - I have a great deal of trouble with red-yellow-green colors. I have a great deal of trouble with bicolor LED indicators- the colors of yellow, orange, red, green, and amber used in cheap indicator LEDs are all basically identical to me, differing only in intensity. The result is that I can get relative information from them (changes in state) but I can't get absolute information from them (is the light red or green?). If the encoded information is VERY important (for instance, stop/go signals at an intersection), and color is the ONLY way it is presented, or the only absolute way in which it is presented (for instance, some areas have stoplights that are horizontal, and green can be on the left or the right depending on the orientation of the intersection), the result can be disastrous. At best, it's an annoyance to roughly 10% of the population who lack "normal" color vision.**

The best way to avoid designing degenerate case flaws into a system is to explicitly write down what your expected use cases are. Get other people to look at them, and to look for holes in them. It's okay to discard their feedback, and it's not always important to expand your design to break free of a degenerate case (sometimes it's just too expensive to support every use case, and sometimes other restrictions rule out the need for supporting some use cases)(no need to encode the speedometer in a car such that a blind user can interpret it, for example), but you should consider them just the same. Fixing a design after the fact is far more expensive than doing it right the first time.

* I think I'm a deuteranope, anyway, based on discussions with a very smart coworker (who happens to be deuteranomolous). Most online colorblindness tests will only provide a better diagnosis than "yes, you're colorblind" if you enter SOMETHING in the field next to the Ishihara plate image, as the shape you see is what determines what type of colorblindness you have. I can't see ANYTHING in most of them, but "nothing" isn't an option. Ironically, these pages were probably designed by someone with normal color vision who completely failed to consider my case.

** So how to solve this problem? Use two LEDs instead of one with two colors, so the information is position encoded as well as color encoded. Use a blink code. Use colors which will be discernible to the largest number of potential users (relatively few people have a kind of colorblindness that causes them to confuse blue with any other color). Use significant differences in intensity to encode information.

5 comments on DIY projects that deserve a big, fat STFU

2010-12-28T09:43:00.000-08:00

Whenever you put a project out there in the community, be it on your blog, a community board, or as an article in another venue (or if it gets picked up by say, Hackaday or Make), you're bound to get some comments that are, shall we say, worth less than the calories they took to type. Worse still are the times you get these comments from someone to whom you are explaining (in meatspace) your current pet project- those times can be a SERIOUS buzz kill and I've lost the will to finish a couple of projects after comments like this.

"You know, Target sells something that [does that]/[does almost exactly that]." This is more common in meatspace than on the web, I think, because the web audience self-selects for people who understand that the joy is in the making, not the having. And, frequently, the "almost" is where the bugaboo lies- I want EXACTLY that, not ALMOST exactly that.
"Arduino is for losers." Or some variation thereon. Arduino, as a platform, is a lot like Python: best used when development time is the most precious commodity of all, more precious than CPU cycles, money, or cachet. People who get that, use it. People who don't get that spend a lot of time trolling comment threads but never actually make anything.
"Using a microcontroller/PC parallel port/Arduino for that was total overkill." Yes, I know, you could have built that project with four 7400 series logic chips, three capacitors, a resistor, a piece of perfboard, and an inflatable duck, but A. I didn't have those on hand, B. designing that circuit, wiring all that crap together and troubleshooting it would have taken more time than I wanted to spend on the project, and C. I made it and you didn't, so shut up.
"I/my cousin/Nikola Tesla/Jeri Ellsworth already did that better." That's great, really. If my "project" page is just a detailed description of my assembly of someone else's kit, I probably deserve to be chided (or at least ignored). But if not, then the odds are that I either did it ignorant of the prior art (which means my work should be judged on its own merit, not against someone else's) or I think I have something to add on the topic (in which case, you probably didn't read the post to see what I added before commenting, and shame on you for that) or you/your cousin/Nikola Tesla/Jeri Ellsworth didn't post it on the web or adequately document it (meaning, my documentation of the project adds to the richness of the human experience, or something).
"You have too much time on your hands." Another troll comment from someone who thinks they're hot stuff but never actually does anything. What, pray tell, SHOULD I be doing with the tiny little amount of spare time I carve out of parenting, working, housekeeping, commuting, and sleeping? I MIGHT tolerate this from someone who doesn't even OWN a television (because if you own one, I guarantee you spend more time watching it than you think), but since that's only something like 1.5% of the population and that 1.5% is too busy being productive to level such a shallow criticism, anything I'd suggest to this commenter would be inappropriate for a public venue.

I'll tell you who I feel bad for- the kids of these wastoids. "Pshaw. You call that a fingerpainting? Have you ever heard of perspective? Composition? Wiping your fingers between colors?"

So, as your mother should've taught you, if you don't have anything nice or constructive to say, STFU.

Last thought- this is a major reason hackerspaces are awesome. Most of these comments are easy in the faceless netvoid but you'd NEVER trot them out face-to-face. Plus, by their very nature, hackerspaces attract the people for whom the doing is the most important part; for them, results speak louder than words.

Draft proposal for SI units for bitching...

2010-12-27T09:22:00.000-08:00

... as proposed by Jeri Ellsworth: the "Jones", after EEVblog's Dave Jones.

As with all SI units, we must define it in terms of base units, so I propose this:

1 Jones = (# of complaints about a topic) * (sum of levels of annoyance caused by said complaints weighted by exposure frequency to causative events, in seconds between exposures) * (# of people likely to be exposed to your ranting)

Obviously, the level of annoyance varies from person to person; I imagine a level 1 annoyance ("mild eye rolling followed by repetition of action until desired result is achieved") for a more patient colleague might be a level 5 annoyance to me ("loud sigh with posture change and muttered profanity") and could rank to a level 100 for someone else ("widely distributed internet video rant with attendant behavioral change and increased probability of property damage to exact retribution on an inanimate object").

As a practical example I'll float my issues with OrCAD- there are five things which cause me pain every day with OrCAD, three level two issues ("eye rolling with quiet sigh") and one level 6 issue ("profanity audible but not comprehensible to workers in adjacent cubes") and one level 50 issue ("loud cursing and banging of mouse on desk"). Weighted, I'd say I get one level two event every 60 seconds of OrCAD usage (.033), one level 6 issue every 300 seconds (.02), and one level 50 issue every 3600 seconds (.014), for a total weighted annoyance of .067. At best, normally, about four people are exposed to my ranting; thus my irritation with OrCAD is about 5*.067*4 = 1.34 Jones.

The nature of this is such that it is similar to the Schmidt Sting Pain Index- individual preferences and tolerances will affect the outcome heavily, as does personal audience size (clearly, Dave has a much bigger audience than I do).

Regulators, mount up!

2010-12-21T11:14:00.004-08:00

On the heels of a few tweets regarding linear voltage regulators that I passed with a friend yesterday, I think I'll do a couple of posts on voltage regulation.

First, the general concept: voltage regulation is the creation of a stable, low-impedance DC voltage source from an unregulated DC voltage source. Examples of unregulated DC voltage sources are batteries, "wall wart" type AC/DC converters (even though many of these create very good voltages (these days, anyway), you should always assume that you (or someone else) will plug a different supply in), car cigarette lighter sockets, rectified and filtered transformer outputs, solar panels, fuel cells, dynamos, and fruit with pieces of zinc and copper in. In fact, pretty much anything other than a locally generated voltage from a well-designed regulator circuit should be treated as an unregulated source (for design purposes, at least).

This first post will concentrate on linear voltage regulators. Sometimes you'll hear these carelessly referred to as "LDOs", although the LDO (low dropout) regulator is really a subclass of linear voltage regulators, and not all linear regulators count as "low" dropout.

Pictured above is a typical linear regulation circuit. V1 is the unregulated source; D1 prevents a reverse-connected power supply from destroying the circuit, and should be a large enough power rating that it won't be in danger of damage when the circuit is energized (the 1N4001 is not a bad choice for this, although at higher currents it has a fairly high forward voltage drop). If the voltage drop from a diode is unacceptable, there are linear regulators available that have built-in reverse voltage protection (the LM2931 is a good example of this), and there is a trick that can be played with a PMOSFET which provides good coverage at the expense of increased cost (I'll not cover that here- maybe in a future post).

The capacitors are where the real work comes in, so to speak. Every different type of linear regulator will want to have different capacitors on the input and output- some will be happy with no, or minimal capacitance, while others will want a large "bucket" capacitor to provide current during surge periods. Some need a minimum amount of ESR (equivalent series resistance) to avoid oscillatory behavior while others are fine with a low ESR tantalum electrolytic or ceramic on the output. There are three things that need to be said here: first, ALWAYS check the datasheet for the part you're planning to use. The manufacturer will typically specify on the front page, in bold lettering, quotated, underlined, with a little drawing, what they expect in the way of capacitors and whether low ESR caps are expected/accepted. Second, the bucket capacitor on the input (C1 above) is much less important in most cases than a decoupling cap and output capacitors, UNLESS there's a significant distance between the unregulated supply and the regulator (i.e., a long wire running from a wall wart calls for an input cap, but a battery a couple of inches away likely doesn't). Third, you should derate the capacitor voltages by a factor of (at least) two- if you expect to see 12V on the input, use 25V or better capacitors. Ceramic capacitors are quite tolerant of at or near spec voltages, while aluminum electrolytics will suffer from prolonged near-spec voltages and tantalum electrolytics will freak out and die horribly with even small spikes above their rated voltage (seriously)(we're talking fire and brimstone freak outs, here).

So, now that you understand the circuitry, there are a couple of other key concepts to understand: quiescent current, dropout voltage, and power dissipation. Quiescent current is the current the regulator "wastes" in the business of doing its job. This is another look-it-up-on-the-datasheet value; the quiescent current will vary based on the cost of the regulator and the momentary load current (usually the Iq vs Iload spec is shown by a graph on the datasheet). Some regulators will have very low quiescent currents (<10uA); it rarely ranges above a few mA. The variation across load currents is usually not huge in absolute terms; for instance, the LM2931 mentioned above is from 1-10mA across its specified current range.

Dropout voltage is the minimum voltage difference between the input and the output. The dropout voltage will increase as the load current goes up, and as the temperature of the device increases (we'll talk more about this in the power dissipation section). If the input voltage is not greater than the output by at least the dropout voltage spec, the regulator will not perform as specified. Typically, the output voltage will begin to sag, and will remain at a level of approximately Vin - Vdo; as Vin sags further, so will Vout. Other characteristics will suffer too, such as noise rejection and surge current response. Cheap regulators like the ubiquitous 7805 may have a dropout voltage exceeding 1V for even fairly light loads; fancier regulators may have dropout voltages well below .1V for light loads.

Power dissipation is the big bugaboo with linear regulators, and the limiting factor in their use. The standard EE equation of P = I*V is applicable here; as the output current increases, the power dissipation of the linear regulator increases, as well. The actual equation should look more like this:
P = Iq*Vin + Iload*(Vin-Vout)

This leads us to a couple of observations: first, the greater the Vin/Vout delta, the more energy is wasted. This is an important data point, because, while running a 5V system off a 9V battery with a cheap 7805 regulator may seem like a no-brainer, you're going to waste a tremendous amount of the battery's capacity. An Arduino doing not too much pulls about 70mA; at that rate, you're going to deplete a 9V battery to 6V (which is probably about as low as you want to go before you start to eat into the margin of dropout voltage plus protection diode voltage) in something like 8 hours. Add an Xbee module and you're going to end up below half of that time.

Second, the greater the Vin/Vout delta, the hotter your regulator is going to get. With a fresh battery, the regulator on your Arduino is going to be dissipating close to 300mW, BEFORE you add additional load. Again, the datasheet will give you some idea of what you can get away with here: typically, there will be parameters for Vin max, Vin - Vout max (more important with adjustable regulators), Iout max and Pmax, and typically there will be multiple values for each depending on the selected package and whether or not the device is provided with a heatsink (either in the form of an actual chunk of metal or a solid connection to a large pour of copper). You'll need to comply with the most restrictive combination- if your 5V regulator specifies 20V maximum input, 100mA maximum output current, and 500mW maximum power dissipation, you obviously can't expect it to source 100mA with a 20V input level without melting. In fact, if that 500mW dissipation is depending on a big fat heatsink and forced air cooling, you might not even be able to reach that without destroying your part.

So, now, the question that started this all: If I'm running a 3.3V regulator and a 5V regulator off a 9V battery, am I better off dropping the 5V to 3.3V or conneting the 3.3V regulator directly to the 9V supply? The answer is, it depends.

Going from 5V to 3.3V is going to result in the 3.3V regulator dissipating less power (because the voltage delta is smaller); that may mean you can use a smaller regulator, or a regulator that can't tolerate the full 9V input supply. However, that power dissipation gets moved from the 3.3V part to the 5V part, so there's no free lunch in terms of reducing total power consumption. Maybe that's okay, because the 5V load is light, or because the 5V regulator can handle the greater power dissipation better than the 3.3V part could have. It may also enable you to use the output capacitors from the 5V regulator as input capacitors on the 3.3V supply, or obviate the need for input capacitors on the 3.3V supply at all.

Connecting them in parallel has the benefit of spreading the power dissipation between the two devices; it also means that a brownout on the 5V supply won't bring down the 3.3V supply (which could be good or bad).

The driving forces behind the decision, then, become your selection of the regulators to be used and the load on each regulator.

Lastly, I'll say that, despite the seemingly great amount of detail here, there's a lot I've left out. I didn't cover adjustable regulators at all (typically, they use a voltage divider to set the voltage at a pin, from which the output voltage is derived), or regulators with enable pins (generally used for power supply sequencing or disabling parts of the circuit when necessary), or multiple output regulators (pretty much the same as single output, but you'll need to sum the power dissipation of each output rail to calculate the total power dissipation of the package). Most of that stuff is refinements of the information here, and this is a good practical primer on the topic (or so I hope).

I've got a few more posts on the topic- switched capacitor supplies, inductive switching supplies, batteries, and maybe more on other types of unregulated supplies.

Voltage dividers

2010-12-15T20:01:00.000-08:00

A common problem in electrical engineering is the use of a resistor divider to create a circuit which derives a second (lower) voltage from a known voltage. This can be for a reference voltage to an ADC (as on the Arduino), to set the voltage on an adjustable regulator (where the regulator seeks to maintain an output voltage adequate to produce a set voltage at a feedback node), or to calculate the gain on an amplifier circuit, among other possibilities.

The canonical voltage divider circuit

Usually, we know Vin and Vout, but R1 and R2 are unknowns. We usually pick one of them (based on what's on hand, in the parts library, time of day, dog's birthday, roll of a 20-sided die, etc), then calculate the other. Almost always, that results in a value which is not readily available, so we pick the closest value, calculate the error, decide it's too much, and pick another resistor value and start over.

Error in the output voltage has a number of possible sources: input error (typically, we're pulling Vin off a supply rail, which means it's only as accurate as our supply; for a cheap 7805 shunt regulator that may be as much as 5%), bias current error of the sampling circuit (typically fairly minimal in most circuits, but if you want to use high-value resistors to minimize waste current for battery life issues, you may find that the minimal current drawn at the Vout node introduces significant error), variation of the selected resistor values from the ideal values, and error in the actual resistor values from their nominal value. Depending on what you want to use the output voltage for, even a fairly small error can be quite significant: many devices want power supplies to be within 5% or less, and every little bit of error reduces your design margin.

There are calculators all over the web that will do some of this work for you but they are usually only algebra cranks- they ask for three values and calculate the fourth; they rarely look for a "real" value that will work, and they don't usually tell you what kind of error you're introducing.

Since the values available are discrete and with a fixed tolerance, it's fairly easy to write a program that accepts Vin and Vout as parameters and returns an arbitrary number of solutions based on real values. Sure, it requires many thousands of calculations (for standard 1% resistors, there are 9,216 possible combinations if you consider only those within one multiplier (i.e., 1.00k<= R < 10.0k); if you expand the range (i.e., 100<=R < 100k), that number quintuples, but what are computers for if not for automating repetitive tasks?

Here's a program that uses Python (2.7) to solve for an arbitrary (default 5) number of solutions to the resistor divider problem. As arguments it accepts:

Vin
Vout
Series (standard 5% (E24) values, 1% (E96) values, or an arbitrary list from a file)
number of results desired
whether to include values one step above or below the nominal range

It returns a list to the command line which specifies:

multiplier for R1
multiplier for R2
absolute nominal error
worst case errors, +/- (given the tolerance of the parts specified)
parallel resistance of R1 and R2 (valuable if output impedance of circuit is important)

The worst case errors are only calculated for standard values- if you input a text file, both worst-case values will be the signed value calculated for the nominal value.

As an example, the TI TPS73201 regulator sets its output voltage based on a voltage divider- Vin is the desired output voltage, Vout is 1.204V, and by selecting appropriate resistor values, Vout can be set. Furthermore, the datasheet indicates that to minimize error, R1||R2 should be 19k.

A chart is provided in the datasheet for various common voltages; for 1.5V, the suggested resistors are 23.2k and 95.3k (both standard 1% E96 values). Running the script shows us 24 value combinations that have a better nominal error than that combination, BUT none of those combinations comes as close to the 19k parallel impedance requirement.

Maybe at some point I'll get this script executing in some fashion on a website; if I do, I'll link it. For now, download it and play with it yourself. Execute it from a command line; the -h switch will print a fairly comprehensive help list.

Fun with super-cheap LED flashlights

2010-12-13T16:33:00.000-08:00

Somehow I've become a prolific blogger lately. I wonder if this will last...

Today at work I had a serendipitous moment of seeing two desktop objects in an abnormal light: a small, scavenged lens cell and a super cheap (2 for $5) LED flashlight.

As part of my on-going inculcation into the mystical arts of optical engineering, one of my fellow engineers demonstrated to me the ease with which an illuminated object can be projected onto a surface, if the various distances are correct. His demonstration was with the image of the lit window that faces our cubes, but it occurred to me today that, by tweaking distances, I could probably get a similar image from my LED flashlight, writ large on a blank whiteboard.

Tah-dah! What's more, I found that, by moving the lens slightly along the optical path, I could bring different elements of the LEDs into focus. But lets start by analyzing this image.

First, you can see (though not very well) that the LED lenses are fouled quite badly. Most of the speckling on the middle three LEDs is NOT the whiteboard. More significant, however, is the fact that, of 12 LEDs, one is off entirely, one is barely on, and one is quite dim. This is owing to the sub-par circuit design of this flashlight (for $2.50, I don't expect much, but, hey, let's learn from it!): the LEDs are basically all in parallel with each other and with three AAA cells in series. The result of this is that the LED with the lowest forward voltage gets most of the current, until IT burns out, then the next lowest voltage, and so on down the line. The LED that is off either has a REALLY high forward voltage or is the first casualty of this chain of failure.

Interestingly, although it's not visible here, some of the LEDs seem to be flickering a bit- this may be a precursor to failure or simply a result of bad solder joints (which is another possible failure for the "off" unit). Rather than pads, the PCB (if you can call it that) which these LEDs are mounted to is essentially a couple of concentric rings of copper- resulting is an immense thermal mass which needs to be heated up to get a good solder joint. Most likely, this is being done by hand in a Chinese factory (believe it or not, hand assembly is economical in many Chinese assembly plants), which opens up many possibilities for cold joints and overheated diodes.

By sliding the lens a little further along the optical axis, I was able to bring some other features into focus. The middle three LEDs (particularly the lower left one) have clearly visible wire bonds to the center of the die. This isn't really bad or abnormal- I've seen similar things on very expensive LEDs as well. However, it's a pretty nifty little visible artifact of a part of the assembly process we normally don't think a lot about.

I'll also briefly mention the blue-ish color seems to be a hallmark of VERY cheap LEDs from China- I've ordered some "white" LEDs from the super-cheap vendors on Ebay before and they look almost more blue than white.

If you can't find it, you don't own it (part 4)

2010-12-12T14:10:00.000-08:00

Once you've got it all together, where do you use it?

My workspace is divided in half- an electronics bench with tools and a PC station. The PC desk is boring- two 19" monitors, speakers, printer, etc- I won't bore you with pics of that.

There are only a couple of things I really want to mention here as being special about my desk. First, the knife holders. These are the standard type of wall-mount magnetic knife mounts. Mounted vertically (because they were too long for horizontal) they hold my small tools- little screwdrivers, a wire stripper, a side cutter. I have duplicates of all of these tools in the mobile kit but it's nice to have them handy.

Secondly, the whiteboard. It's magnetic so I can stick stuff onto it, but it's really more useful as a whiteboard- I'm a big believer that whiteboards are the stuff engineering magic is made of. I have four of them in my cube at work, and one of the smartest facility design elements I've ever seen was in the "new" (this was probably over 10 years ago) EE building at the University of Richmond. Every hallway in the building had a little alcove directly across from each doorway where people who were walking along could stop, step out the line of traffic, and use a whiteboard in the alcove to explain a concept.

Third- drawers. And more drawers. And yet more drawers. To have any prayer of being productive, you need to categorize and segregate your goodies. The little wooden cabinets are narrow but long; the plastic drawers on top have several subdividers in each one, and the red cabinet in the lower left is big enough to accommodate quite large items (say, a 7" SMT component reel).

Finally, the monitor is (if I do say so myself) cleverly mounted:

I used a couple of long travel drawer slides from Ax-man to place it such that it can slide to the right, out of the way, exposing a shelf behind. I keep that shelf mostly empty so I can stash a project that I'm not done with but putting on temporary hiatus. This keeps the work surface from being cluttered with bits and pieces of stuff I'm not using at the moment, but which I'm not ready to put away. Also note the little baggie to the left of the monitor- it's a "tiny trash" bag, where I can deposit trimmed leads, stripped wire insulation, ruined screws and the like, thereby keeping that stuff from building up on the work surface. Clutter begets clutter.

The rest of my stuff is here- the shelves on the left are mostly domestic items- tool kits, screws, etc. Stuff any reasonable homeowner should have. Worth mentioning is that my junkbox cyclorama is just out of view in the lower left. The boxes on the shelf at the back are individually labeled subdivided containers; when I want to put a project in "cold storage" so to speak, either because I want to work on it much later or because I don't want to tear it apart but I'm done playing with it, I throw it in a box, label it, and shelve it. There is only one "random crap" box- EVERYTHING else is properly labeled, because boxes of random stuff might as well not exist when they get too big or too prolific in number.

Lastly, I'll say this: there is a reasonable amount of unused space on the shelves on the left, at the bottom. Unused in the sense that all the boxes that are stacked there are empty. This, I think, is the last critical element of keeping your space under control: provide for growth. If you can't immediately categorize an item (meaning, put it in a LABELED drawer or box), or create a NEW category for it (meaning, put a label on an empty box or drawer and throw it in there), the clutter will come back with a vengeance, and you'll never be able to find the parts you need.

If you can't find it, you don't own it (part 3)

2010-12-11T15:24:00.000-08:00

In part three, I'll show off my mechatronics tools and parts kit. Part four will be my workbench and parts storage; that'll probably follow pretty closely on the heels of this since I'm so totally snowbound I really can't do anything else.

It's bigger than it looks. I had a hard time with this box- it was one of those tool boxes that new homeowners who fancy themselves "handy" buy, which are inexpensive, totally lacking in adequate internal division, and end up full of things like rusty hacksaws, dull chisels, ruined putty knives and inexplicable sheet metal items with flanges and numbered mounting holes.

As always, mouse over for labels.

Mostly self explanatory; I'm going to mention a couple of things by name. First, the Pocket Ref on the left side. My copy predates Make but you can get it from the Maker Shed. If you don't own this, you should It has ALMOST everything you'll ever need to know- from the density and chemical composition of a huge range of substances to the masses, orbital periods, and average solar distance to each planet. In practical terms, it has density, hardness, and coefficient of thermal expansion on dozens of woods, metals, plastics, and glasses. It would, in fact, be pointless for me to continue to expound, so I'll say this: I have yet to be disappointed by this book when I tried to look something up.

JB Weld, if you don't know it, is a binary compound that works kind of like an epoxy- mix two pastes and they harden over time. Once it cures, it's really strong, drillable, machinable, etc.- and quite heat resistant, to boot. It's great stuff.

In the "main chamber" of the box is actual raw material. Salvaged gearboxes, motors, pulleys, and parts from optical drives take up most of the space, along with a hot glue gun and a bunch of sticks (I go through hot glue like potato chips). The small divided cases that attach to the lid are full of gears, sprockets, and fasteners, mostly compatible or nearly so with the Tamiya gearboxes that I've got in there.

Finally, on the left side, you can see an assortment of Sculpey III polymer clay. This stuff is BRILLIANT. When baked at 275°F (135°C) for about 20 minutes (depending on thickness) it sets up into, essentially, PVC. Furthermore, the curing temp is lower than the deformation temperature of most OTHER plastics, so you can use it to build out other parts (I've had great success using it to neck down the hub hole in a wheel or gear; pack it in, harden it, then re-drill a smaller hole). It's also low enough temperature that you can embed electronics inside your creations. It's not too expensive ($2 or so for a 2 oz. block, which is about the 2/3 the size of a deck of cards), and comes in a whole rainbow of colors.

So, that's effectively the end of my mobile workshop, except for one summary picture:

The little cart is from IKEA- I got it a couple of weeks ago for $9.50 in the As-is section because it didn't have the bag. The strap is an REI luggage strap meant to hold a smaller piece of luggage to a larger one, but it's tops for this. The wheels are a completely lost cause in a Minnesota winter, but it beats making three or four trips to get all my crap into the workshop.

I have a wheeled laptop bag, as well, which I keep my netbook and some assorted other stuff in, but it's too dull to warrant a post. Later tonight or tomorrow I will put up some pictures of my at-home workspace and storage system.

Coroplast snowshoes- it SOUNDED like a good idea...

2010-12-11T14:19:00.000-08:00

If necessity is the mother of invention, snow day boredom is the drunken dorm-mate who will ultimately get you picked up by the campus police.

If you're outside of the Minneapolis/St Paul metro area, you may only be cursorily aware of the current snow-tastrophe. We've gotten about 12 inches so far (300mm for you post-Imperialists) and are expecting another 4-6 (100-150mm). I managed to get my car safely embedded into a snowbank off of the snow emergency route I live on (read the rules regarding that here- it's harsh but necessary), and, after digging and pushing out a few more people on the walk home, I got bored.

My work has been throwing out shoebox sized coroplast boxes for a while now; and being, as I am, on the verge of collapsing into full-on hoarding behavior, I've been picking them up and carting them home. I've probably rescued about 800- there's a stack taller than I am at the Hack Factory. Anyway, I use these things for everything- as boxes for storing stuff, dividers in my toolkit, a platform to spread out my compost on, whatever. So, of course, faced with the reality of 18" (with drifts) of snow in my front yard, I decided to make snowshoes!

So, the basic construction is pretty simple- the beaver tail at the bottom of the picture folds up behind my boot, and the two pieces of knotted fabric strips tie around my ankle and over my toes. All the folds are held together by a few layers of packing tape- I'm not bringing diptheria serum to Nome, here, so I don't really care for long-term viability. I just wanted to walk around on top of the snow a bit. I've always wanted to try it.

So, without further ado, here's a video of me trying them out...It didn't work quite as well as I'd hoped.

So, my post-mortem:
First, they aren't rigid enough. They really just fold up around my foot and then I sink down to bedrock anyway.
Second, they are too big towards the instep. That's what all the goose-stepping was about- once I sank into the snow, the plastic very helpfully fanned back out, necessitating a wide stance and a longer-than-optimal pace length.
Third, the lack of a frame and a really strong shoe connection means that it's really more like trying to walk with a someone throwing a small sled under your foot with each step than on a snowshoe- I slipped and slid both foot on the plastic and plastic on the snow- that's why I fell at the end.

Did I do ANYTHING right? I think so...the packing tape seems to have held up well, and the pieces of fabric I used as ties were really nicely sturdy and big enough to easily be done and undone with gloves on. I think a piece of lathing or similar light but sturdy material across the toe and heel edges would've probably made them work reasonably well, but I don't have anything like that in the house and I really didn't feel like trying to slog out to the garage.

It was fun, anyway, and a good way to kill an hour on a snowy day.

Some thoughts on hackerspaces

2010-12-09T11:08:00.000-08:00

Of course, the world is replete with articles like this but I recently had cause to write down my thoughts on the issue and I feel like a little more on it couldn't hurt.

Why did I get involved in Twin Cities Maker back in 2009, before there was a space? Simple- I wanted to be part of a MEATSPACE community of people that likes to make stuff. It didn't exist, so when I found the group, there was no way I could NOT get involved. I think people who worry too much about virtual space replacing "real" interactions should look at hackerspaces as a dynamite counterexample. By definition, the people who are involved in these groups are the most likely to be tech savvy, the most likely to participate in online communities of informational interchange about their hobbies, the most likely to be creative basement hermits, AND YET, increasingly, they are seeking out face-to-face interaction as an adjunct to their online work.

The tools, the workshop space, the raw material bins: these things, alone, aren't enough. Oftentimes, I've given people a tour of the Hack Factory and, at the end, they'll say "that's great, but I have most of these tools in my garage. Why should I pay $50 a month to use them here?" (usually, the touree has an "I-can't-believe-you-haven't-thought-of-this" smirk when they say that). And I usually say to them, "if that's how you're going to look at it, the Hack Factory probably isn't the right place for you." They see an underfunded, understaffed, under-equipped TechShop, but a hackerspace collective requires a different mental model than a TechShop, in much the same way as a farmer's market is from a grocery store. Sure, the superficial trappings are similar (tools for use/food to purchase) but if you've shopped at a farmer's market, the difference is immediately apparent- people sitting, having coffee, chatting with the vendors and one another. In a word, community, which is the key to a hackerspace being successful- and it's what those people with the spiffy garage workshops don't understand.

TechShop is, in a way, a cargo cult realization of the concept- a belief that if you put a bunch of tools in a building and charge admission, people (and money) will show up. The Hack Factory is, in fact, a building wrapped around a community, and tools and materials have shown up- the community created the value of the space. I'm not knocking TechShop; in a place that's flush with technical types and cash (Silicon Valley), it's a great idea, and I have no doubt that a lot people who go to TechShop feel a sense of community there, as well. But in most places, the dedication of the individual to the community is more important than the willingness to pony up $100 a month, because you'll find more dedicated amateurs willing to pay $50 (and a parcel of their time) to support a community they believe in than you will to pay $100 for a little extra workshop space and some fancy tools.

Chris Anderson talks a lot (in his book, Free) about these dedicated amateurs, and the value of recognition to these people (us, I should say) as a compensation for their work, and why a lot of online communities attract people to do really high quality work for recognition rather than cash (Wikipedia). Hackerspaces attract the same sort of person that will spend hours writing and researching a Wikipedia article- they get a charge from the pride of producing a fine piece of work and knowing people appreciate it. The hackerspace, of course, puts it into meatspace, which (for some folks) increases the relative value to a point where people are not only willing to do the work for free, they are willing to PAY to support the community that enables that appreciation.

In the end, I suspect it's all about finding "your" people- people who understand the motivation behind making something that you could buy, buying something perfectly usable just for the parts inside, people who not only don't mock your three-story mobile toolkit, they think it's pretty cool. $50 a month seems like a bargain.

NDAs, Patents and Projects

2010-12-07T10:39:00.000-08:00

Some thoughts below on NDAs, patents, and people seeking project help from me when I'm wearing my freelance engineer hat. A lot of this comes from having followed the Piclist mailing list for about 10 years, as well as reading quite a bit of Don Lancaster's writings on the matter- as well as a healthy dose of professional dignity imparted to me by the conflation of engineering with other highly skilled professions such as law or medicine during college.

NDAs
Sometimes I'll get a feeler e-mail about someone who wants to work with me, and they start off right away by saying "if you're interested, let me know and I'll get an NDA out to you right away."

I don't mind working under an NDA (under certain conditions), but some things about being hit up by it right away like that scare me:

Once I sign this NDA, if I subsequently complete or publish a project which is remotely similar to this person's idea, there is a legal document which could cause grief for me. This is why music labels and publishing houses have rules about unsolicited material.
If the person e-mailing me is doing so as the classic "garage inventor", the assumption of an NDA feels to me like an assumption of asymmetry of relationship- they value their idea more heavily than my ability to make that idea a reality, and that spells trouble. The fact is, ideas AND engineering chops are both a dime a dozen. What's TRULY rare is the wherewithal to bring an idea to fruition in the right place at the right time.
I believe in open source hardware and software. An NDA is pretty much an acknowledgment from the get-go that this project will never see the light of day, EVEN IF there is no "secret sauce" in the project. If it's good enough to steal, it'll get stolen whether I post details on the net or not.

So, in the end, if the first e-mail is all about the NDA with zero or nearly zero technical detail, I usually assume I'm dealing with a prima donna type that I'm unlikely to be able to satisfy. It may be unfair, but my time is scarce and it seems like a good pre-filter.

Patents
Don Lancaster has a lot to say about patents (and being an engineer in general- if you're not familiar with his work it certainly a little browsing of his copious online archives certainly won't harm you any) so I'll not do more than touch on it. In short, all a patent does is give you license to sue someone if they rip off your project. If your project is good enough for a Chinese manufacturer to decide to rip it off, they'll make enough money to brush off your lawsuit. If not, you have nothing to fear because nobody will waste their time with your fiddling small change. The key is not to get overly self important about the matter- it's easy to waste a lot of time and money on patenting something.

Projects
Finally, how I actually view projects that make it through the filter to be considered:

Broadly, I divide commission projects into two groups- one-offs and product development. A one-off is something like that bathroom hassler that I posted a couple of weeks ago- probably something REALLY fun, where the client is not concerned with bringing something to production, the overall effort is like to be pretty small, etc. Those I usually negotiate terms on a by-project basis- I ask that they buy extra parts so I can keep some goodies at the end (I make them fully aware of the fact that some of the hardware is part of my payment), or get a little in-kind service (I've done projects for food, laser cutting, and soon, golf driving range access).

Product development is a bit different. For that I'm more likely to look for hourly rate plus development costs. Part of the reason for that is because the process is more in depth and difficult- a one-off is basically a jumped-up hobbyist project, whereas product development requires some real knowledge beyond just slapping something together. Another part is that, if things go well, they stand to benefit a lot from my work and so a steeper up-front cost is reasonable- it's an expense of doing business.

You'll find that a lot of people that come looking for help developing a product have no interest or ability to pay for it- but that's okay, because it's my day job to do that sort of stuff and the one-offs are more entertaining and enjoyable anyway.

The junkbox cyclorama

2010-12-06T17:26:00.000-08:00

Adafruit had a post a few weeks ago about building a cyclorama to take nice pictures of your work. I built one up for the office (we always have horrible pictures of things in our documentation), but for home I can't justify even the $50-75 one would cost me. So, I did what any good maker will do- hit the junk piles!

First, a word on sourcing: the local IKEA has a section right before the checkout called "As-is". (My wife and I frequent IKEA for some reason- we eat breakfast there about once every couple of weeks, and dinner there almost as often.) As-is is where IKEA goods too good for the trash but too bad to sell as new go- returns, scratch and dent, display models, etc. Every so often, they'll bundle up a bunch of crap and put it on a "mystery cart" or a "handyman's cart". The shelves just visible to the right above were a handyman's cart item; the lights all came from a mystery cart. I've actually bought far too many of both of those; my garage is stuffed with disused cabinet doors and partly assembled furniture along with piles of mystery cart lights. To be fair, I've also done a lot with the stuff I got out of them, but the piles of junk are probably not worth it.

At any rate, the backdrop lighting is provided by three "Kvart" lamps and the ambient lighting by a six-up "Glimt" light (link is to PDF of the assembly directions; apparently it has been discontinued).

There's a sample image; it's a little blurry around the edges (I don't have a tripod; I'll probably try to hack something together out of another Kvart desktop base) but I am quite happy with the quality of uniformity of the light.

Here we see some limitations; if the board angle is too steep, the picture shows hot spots from the individual bulbs. I may try to add some diffuser paper (well, office paper) over the lamps- that's going to be tricky because the bulbs are stupid hot halogens.

I'll probably also make a roof and side walls out of white foamcore (I have a bunch of THAT lying around, too, of course) in an effort to reign in some of the stray light I'm losing to the surroundings.

The backdrop is a blackout rollershade we had custom cut for a window without adequate measurement beforehand. I couldn't bring myself to throw it out and now I'm glad I didn't!

TFPC 33: Booklet printing

2010-11-30T13:26:00.000-08:00

33: Booklet printing

I don't know why I didn't see this feature on printers earlier but I love that I can print out a document designed to be folded in half and stapled in the middle.

Electronics tools you didn't know you needed

2010-11-29T20:25:00.000-08:00

Side trip from my regular posts on organizing your work space and taking it with you: tools that you didn't know you needed.

Most of the tools in the toolkit are obvious- the soldering iron, the tweezers, the "helping hand", etc. There are a few items that are in my toolbox (or are always close at hand) that I use constantly but somehow never make the lists I've seen for equipping a bench.

1. Cyanoacrylate adhesive- especially the brush-in-bottle "Krazy Glue" brand that I highlighted in my tool kit post. Useful for "dead-bug" assembly, reattaching lifted pads, and temporarily holding things in place while you work on them (I know many CNC machinists who use CA to hold their workpieces down while they are in process.
2. Hot glue gun- super useful for low-cost ruggedizing, strain relief, conformal coating and mounting PCBs. Nothing fancy- a standard low-temperature hobby gun will work fine. In fact, the high temp type take a little too long to cure for my taste, and tend to be too runny to boot. A few globs of hot glue will transfer the strain from the solder joint on a wire to, well, the glue gob; if you push a PCB against a surface and squirt a little glue through some available mounting holes, you get top-notch semi-permanent mounting, right where you need it.
3. X-acto knife- best tool ever for removing the outer jacket from a multiconductor cable. By bending the cable to a sharp 180° angle and lightly scoring the outer jacket, you can easily cut through only the jacket, leaving the conductors (or foil/braided shield) intact. Also useful in hacking (cutting traces and scraping off soldermask to create a new "pad") and rework (if the board is more important than the IC, the best way to remove a SMT IC is to cut the pins off at the package with an X-acto).
4. Scotchbrite pad/steel wool- cheap phenolic protoboards tend to be unplated, so the copper finish gets oxidized. You can pour a bucket of flux over the board before you start working OR you can rub it down with an abrasive pad of your choice. Scotchbrite and steel wool both work wonders. They can be used on old component leads, too, but that's a little harder.
5. Dental pick- good for lifting leads while you have the solder melted, if you need to rework a fine-pitch SMT IC. For larger scale stuff, good for maintaining pressure on a component while you melt away the solder, or for picking off questionable stuff on the board (is it a glob of solder or something else?)
6. Magnifier- I use a 3x for reading part markings and a 10x for doing board inspection.
7. Flashlight- pairs well with the previous item. It's also handy to be able to readily direct light under components without having to rotate the whole PCB.
8. Your nose- long a favorite tool of mine, this one would've been left off this list if not for being mentioned in Todd Harrison's excellent power supply troubleshooting blog posts. I daresay not many people who've spent any time working with electronics DON'T know what the magic smoke smells like; that smell will linger long after the heat is gone, and will often be present even if no damage is visible. Sniffing around on a board (UNPOWERED) can frequently alert you to a dead or damage component, or at least the region of the board that component is in.
9. Your fingers- a non-contact IR thermometer works well, too, but for sheer cheapness and immediate availability, nothing beats the fingertips for detecting unreasonably hot components.. NB NB NB GREAT CAUTION IS REQUIRED HERE. Do not probe circuits under power with your fingertips if there is a chance of them containing high voltages (above 24-30V).

TFPC 32: Internet symptom searching

2010-11-29T13:19:00.000-08:00

I was down- hard- yesterday with a bad bout of food poisoning, which brings me to the 32nd item I love about living in the future:

32. Symptoms of disease are easily available- Of course, this has it's downsides. While the SYMPTOMS are often widely available, as are the prognoses, sensitivity and specificity are often ignored, as are any kind of information about likely age groups, races, gender types, risk-enhancing behavior, etc etc.

In other words, it's better at ruling things OUT than ruling them IN- but it WAS comforting to know that the very serious food-borne illnesses generally don't have the symptoms I was suffering through.

TFPC 31- Online travel

2010-11-27T09:31:00.000-08:00

I've been obsessing over how I can plan a trip to Maker Faire next year using the train...online travel reservations are pretty spectacular, since I can try different departure dates and travel permutations and find a cheap option. I should write a Python script that spools out dates and returns prices...

TFPC Day 30- Web updates from anywhere

2010-11-25T10:52:00.000-08:00

Or at least, any PC. I need to figure out how to do this from my phone...

If you can't find it, you don't own it (part 2)

2010-11-24T20:38:00.000-08:00

In part 1, I covered my mobile electronics kit. This time around, I'll look at my mobile electronics toolkit.

While the mobile kit contains (almost) everything I need to do some breadboarding of circuits, more permanent hacks, installations, disassembly of finds and really fun stuff is all bound to require more advanced tooling than the cheesy $5 multimeter (that link shows it for $13, but it's available locally in the Twin Cities at AEI for less than $5, and with a bulk discount option)(yes, I have purchased multimeters in bulk) and adjustable wirestripper in the kit. After a few scrambling debacles where I realized I didn't have what I needed to finish the job, I decided that I'd best come up with a toolkit that I could use at home and on the road.

After some hemming and hawing at the local Home Depot, I bought a Stanley XL Tool Organizer, which is a nice fold-up unit- essentially, two of the more conventional see-through plastic lid boxes that fold up around a central spine that has a handle and six drawers. It was only $25 at the Home Depot; I bought the last one that was there and it's not on the website, so I'm wondering if it's been discontinued. Amazon has another one that's twice as expensive but has more drawers and clear sides rather than black- that's the one complaint I have about it is not being sure where things are all the time.

Here you can see how the drawers slide out; the "back" (relative to us; it's perfectly symmetrical) is folded down and the front is folded up. When the two halves are folded up the drawers are captive, but can be opened and closed with a bit of effort. I've not yet had one slide out on me while moving the toolkit around, so I consider it a pretty successful design.

The drawers have two different lengths- one short one at the top, to accommodate the handle in the center of the spine, and two longer ones on the bottom. The depth of the drawers makes it possible to store larger objects in the drawers than can be stored in the clamshell sides- at least, if you don't want to take a cutting tool to the dividers in the sides.

The image above has tooltips- hover over the image to see the active areas (may not work in feed viewers like Google Reader). Most of the stuff in the drawers was selected either because it wouldn't fit (comfortably) in the clamshells or because it fits so nicely here. It's also stuff that I find having access to without having to lay out the side is nice- the precision driver kit, wire strippers, and multimeter are among the most frequently used items in the tool kit. The butane heat gun is great for heat shrink; some day, when I have some extra cash, I may buy a combo butane heat gun/soldering iron. That's a long way off, though.

There are a couple of items of note in here- the digital caliper is a ridiculously useful piece of tooling and once you have one you'll wonder how you lived without it. There's a long-handled flat-blade screwdriver which is for prying apart seams in plastic cases more than anything else. The USB-serial adapter will probably eventually move to the computer kit. The solder sucker is a cheapo unit that I got from Marlin P Jones; I've seen it elsewhere as well and, surprisingly, it works substantially better than some that I've seen for five or ten times as much. Lastly, if you haven't seen the brush/can variety of cyanoacrylate adhesive, let me just take a moment to extol its virtues. The cap doesn't seem to glue itself on as easily, there's no tip to clog, and the brush is delicate enough to put glue right where you want it.

Nothing terribly unexpected on this side. I'll mention that, in addition to an Arduino, I usually have a "Thumbino" in here, which is an Arduino clone of my own design that is the size of a USB flash drive and plugs directly into a USB port for programming- no cable needed. Someday I'll sell them...if you're interested in buying one, let me know and I'll see what I can do.

There are a couple of things I'd like to add- I'd like to replace the sponge for the iron cleaner with a copper poof type tip cleaner. A small DC power supply would not be out of line, either here or in the electronics kit. A crimper and header connector kit wouldn't go amiss, either. So far, I haven't felt a lack of any tool as I've worked away from my home base- of course, I don't expect to be able to do fine-pitch SMT soldering on the road.

TFPC 29- RSS feeds of my favorite blogs

2010-11-24T19:27:00.001-08:00

Of course, it kills my productivity, but it's pretty much what I've always dreamed of- someone says, "here, I think this might be interesting to you" and I have all the reading I can manage.

TFPC 28- Project sharing on the internet

2010-11-23T19:47:00.000-08:00

28. Projects on the internet

Instructables, Makezine, forums, etc. I remember a time where you had one option for example projects involving microcontrollers: the PIC16F84. That persisted well into the 21st century- WAY beyond the point where the F84 was a viable product.

If you can't find it, you don't own it (part 1)

2010-11-22T20:58:00.000-08:00

Mr. Jalopy's famous side one, track one of the Maker's Bill of Rights is all well and good, but more basically, if you can't FIND it, you don't own it.

Owning an object has a cost, however minor, associated with it. You'll have to move it if you change residences, you have to keep your kid/cat/ferret/sugar glider away from things you don't want smashed/pissed on/drug under your couch/scent marked by a weird oily forehead gland, and clutter (IMO) occupies mental real estate we can usually ill-afford to waste. If you're going to pay these costs, you should take care to keep your gear well organized so these costs aren't wasted when it comes time to use something.

As a hackerspace-going maker, I find myself with an additional constraint- if I want to work on a project at the shop, I need to either bring what I need (tools and materials both) or be darn sure I know what and where stuff at the shop is. My solution is a robust, scalable, compact group of toolkits broken down by four disciplines:

Electronics- since I'm an electron jockey, this one was first. It's all the standard stuff- breadboards, jumper wires, voltage regulators, diodes, etc. One Arduino, of course, and a wire stripper, and a small, simple meter, but no real tools to speak of.
Electronics tools- this is the first "add-on". My electronics kit contains everything I'm likely to need to breadboard something up and get it working; this kit contains everything I'm likely to need to make a project permanent: soldering iron, pliers/dikes/screwdriver, more capable wire cutters, some spools of wire, a better meter, etc. Also, a few batteries and battery holders, a couple of Arduinos, some shields, and a few Xbee modules. Some cables, too.
Computer/custom project stuff- this is my rolling laptop case. It's a much less well defined kit, because I don't have a spare computer to throw at it right now, but ultimately I expect that it will contain a laptop, a nice assortment of cables (possibly drawing some out of the tools kit), a rich digital library, a nice notebook and several pens, a graphing calculator, and have assigned space for my o-scope and a small box which will be large enough to contain and protect projects in process.
Electromechanical parts and tools- enough parts and tools to make a fairly decent little robot (or six). Several Tamiya gearboxes and associated hardware, an X-acto knife kit, some drivers, belts, gears, motors salvaged from all manner of equipment, wheels, pulleys, etc. Sculpey, JB-Weld, and a hot glue gun round out the mix.

Below is a nice, tagged image showing the outside storage area of my electronics kit. If the box looks familiar, it's because it's the same one that the MakerShed electronics components packs are distributed in. They are sold locally for about $7 (frequently on sale for $5) at Menard's, a fairly stock home improvement warehouse common in the upper midwest.

Mouse over the buttons for descriptions (you may need to view on the blog site itself for that- Google Reader, at least, doesn't display them); click the image for a larger view. As you can see, there are some fairly esoteric parts in there (the QT110 touch sensor, pager motors, and the IR receivers spring to mind); I've still got some empty space even WITH those parts so why not? I feel like I have my bases pretty well covered here.

This, of course, is just the lid- it lifts up to reveal another set of larger and deeper storage compartments inside.

Inside, there is a nice assortment of 5% tolerance resistors (65 values) with each different value separately bagged, labeled, and stored in increasing order and segregated by decade for easy access (if you can't find it...). The Arduino clings to the underside of the lid; it's held in place by a few dabs of Sugru under some old PC motherboard standoffs. The largest subdivisions has a small, cheap meter, a few breadboards, a cheap wire stripper/cutter, and a largish HD44780 driven LCD (4x20, LED backlight). There's also a 3x magnifier, because there are a LOT of small numbers in this box, and a standard 5.5mm by 2.1mm barrel jack with wire pigtails that leads to the outside world.

There are a few other sensors in here, along with some batteries, some largish switches, discrete semiconductor devices, a bag of random LEDs, and some terminal blocks (see my bathroom hassler project for more details on the terminal blocks). Again, there are probably a few things in here that could go (SCRs? Really?) but for now and until I have a need for the space I'm going to keep them in.

I'm interested to hear what other people think I should have in here- maybe some logic ICs? I'd like to add some variable voltage regulators- I know I have some LM317 parts around here somewhere. A small variable voltage wall-powered supply would be nice, too. Some higher power transistors, too- the NMOS parts I have in there are pretty decent as are some of the PNP parts, but I have no PMOS or NPN TO-220 devices. Maybe some L293D motor drivers? What else am I forgetting?

Tomorrow (hopefully) I'll do a write up on my electronics toolkit.

TFPC 27- Geek culture

2010-11-22T19:47:00.000-08:00

27. Geek culture

Growing up geek was hard (I'm not going to claim it was as hard as growing up gay would be, naturally)- especially because my formative years were spent in a small school (less than 90 students from preschool through 7th grade) where a sizable number of the attendees were there as a school of last resort.

So it does me some good to see the embrace of geek-dom people like Wil Wheaton bring to the world, and to see that being a geek is no longer anathema. I'm sure it's still hard on teenagers and kids in small schools, but maybe it's getting better.

Hassling the bathroom going public

2010-11-21T21:20:00.000-08:00

Recently I was approached by an architecture/design firm to help with an electronic install at a client site. The client had requested a system that interacts with users in the bathroom- "interacts" meaning, hassles them when they come and go.

I spent some time debating how to do this; hacking an MP3 player would be easy, but keeping the devices synchronized is a pain- how do you play one sound, at random, then stop until the next input? The Adafruit Waveshield is nice and easy, but the sound quality is poor (22kHz 16-bit mono). Plus, the cost is kind of high for what you get- $30 for the Arduino and another $22 for the Waveshield.

Searches for a cost-positive MP3 shield failed me (there are some out there but they are really quite pricey) and the MP3 trigger somehow eluded my search.

It was around this time that Adafruit offered for sale the Chumby Hacker Boards. I decided that I'd do the project with that- it was a bit more expensive but it offered the benefit of playing many types of audio files natively, being programmable in Python (yay!) and being, well, cool. I partly defrayed the cost to the client by offering to do the job in return for enough parts to build a setup for myself (so I have a CHB of my own to play with) and pizza after the opening.
The electronics are fairly simple (outside of the CHB, of course)- I used a protoshield to interface with the CHB (on these beta release boards, Arduino-ish headers are in place; the final product is likely to have that removed as the compatability with Arduino shields is pretty low due to the 3.3V signal level and the lack of hardware SPI and PWM on the right pins of the header). For ease of installation, I hacked on a terminal block (Altech AK950 5-pos, purchased at Ax-Man for $0.50). The install of that is quite a good hack (IMO)- the AK950 is a 5mm spaced header which is close enough to .2" to line up well with the holes on the protoshield. I pushed some pins that I dug out of a .156" spaced header (also from Ax-Man) into the holes and soldered a right-angle .1" spaced snappable header to that. The right-angle pins drop through the board and Bob's your uncle. I used hot glue to secure the terminal block.

The cans and inductor on the lower half of the protoshield are a PCB I designed that has a step-up circuit on one side and a step-down circuit on the other. They use the same BOM (apart from the voltage set resistors), and can do step up from 3.3V to 12V or down from up to 30V to 5V. I got the board from Laen's awesome PCB batch buy.

For door detection I used a work-surplus (people who know me well are snickering at that; I'm infamous for the mountains of stuff I've scavenged from the trash at my office. My co-workers have in fact started bringing things to me instead of the trash bins, much to my wife's dismay.) infrared obstruction sensor. It's got an adjustable range and a nice, easily mounted package. Unfortunately, it runs on 12-30Vdc, hence the step-up supply (the CHB runs on 5Vdc input, and requires a pretty nicely regulated supply, at that). To manage the 12V->3.3V output conversion I used a transistor to make an OC circuit with a 3.3V pull-up resistor.

For additional state monitoring there's a PIR sensor (from Adafruit). Conveniently enough, that sensor runs off 3.0V-6.0V, and has an on-board regulator to 3.3V, which is the level of the return signal. That meant no signal conditioning needed there.

As you can see from the picture the sensor box is pretty simple- a black painted aluminum enclosure (bought at AEI in Golden Valley) with a hole drilled in it (the PIR lens is a scoosh too big for any step bit I had access to; I ended up using a boring bar on a vertical milling machine to widen out the hole). Inside the box is a voltage protection diode and a 5V regulator; the room was pre-wired with 4-conductor low-voltage burglar alarm wire, so I sent 12V to the box and regulated it down to 5V for the PIR. For the junction between the wire in the wall and the wire I pre-terminated with the 6-pin DIN connector (chosen because it was the only connector at AEI that they had two males and two females of), I duplicated my trick with the terminal blocks, only this time instead of hot glue I built a body up between the two out of Sculpey (one of these days I'll do a post just about that- it's amazingly useful stuff).

I coded up the state machine in Python (Python 2.6 has been built for the Chumby) and arranged for the program to run off a USB drive automatically on boot. The system has three events- enter, exit, and "loiter", and sounds in different folders on the USB drive will be played for each event, allowing users to change the sounds later if they wish.

It's been installed but it's not running yet; there are still some tweaks to be done to get the thing working reliably. Sometimes it loses track of what's going on- it stays in loiter when the room is empty, for instance. I need to tweak some timeouts on the motion sensor, I think.

If you're interested in seeing it in action, stop by Pizzeria Lola in South Minneapolis (55th and Xerxes) and ask if you can use the bathroom- I'll tweet when I have it up and running. They do a mean pie there, and the design of the place itself warrants a peak- particularly the spectacular copper-wrapped wood burning oven which is the centerpiece of the dining room.

TFPC 24, 25, 26 (Wireless Internet, YouTube, Injection Molding)

2010-11-21T20:13:00.000-08:00

24. Wireless internet

25. YouTube
A million monkeys with a million camcorders will generate more garbage than can possibly be imagined. Fortunately, there are a million OTHER monkeys pre-sorting it for me.

26. Injection molding
Okay, not new, but the last few years have seen an EXPLOSION of inexpensive goods come from China's vast injection molding farms. I'm not a big fan of cheap plastic crap, but there is some REAL gold hiding in that sludge. The inspiration for this was the ease and low cost of putting together some really awesome mobile making kits lately. Will post more anon, with pictures.

TFPC 23 (Awesome batteries)

2010-11-18T20:29:00.000-08:00

23. Batteries

Lithium based rechargeable batteries rock my world, even if they are much harder to hack.

TFPC 22 (Digital music)

2010-11-17T15:15:00.001-08:00

22. Digital music

Compressed digital music, in particular.

10,000 songs in your pocket. What's not to like?

TFPC 21 (Machine vision)

2010-11-16T12:07:00.000-08:00

21. Machine vision

There are a surprising number of machine vision applications out there these days- 2D barcodes, out-of-lane detection in cars, and manufacturing. This is a result of the dramatic increase in available computing power- as data transfer rates go up, image sensor integration gets cheaper and more complete, and processing cycles get cheaper, the number of applications will go up as well.

Which begs the question- why does the TSA need to people to look at my naked body on the scanner? Presumably, any thing a person would see could be seen by a computer; if the area of interest were cropped and presented to a human for follow-up, then a more thorough search could be ordered.

I suspect it's for the same reason voting machine companies have told us it's "impossible" to issue a paper receipt- failure of imagination coupled with hidebound ways of doing business. And money, of course. Lots and lots of money.

TFPC 20 (Twitter!)

2010-11-15T17:51:00.000-08:00

20. Twitter

What I don't like about Twitter is the incessant navel gazing (tweets of the "why hasn't he called?" ilk).

What I LOVE about Twitter is the ease with which it levels the playing filed for the sharing of ideas and information. People rich and famous to, well, me, can post something on Twitter, (potentially) gain a following, and disseminate information. Provided it can be shared in 140 characters or less.

The bandwidth restriction is something else to love, in the same way as it is for text messaging.

TFPC 17, 18, 19

2010-11-14T11:29:00.000-08:00

I suck at daily blogging.

17. Blogging (did you really not see this coming?)

Both creating and consuming. It's nice to see what's going on out there, what other people are doing, and to share your ideas and achievements yourself.

18. Tabbed browsing

Despite its attendant, the Wikipedia tab plague. It seems like such an obvious thing I'm amazed it took so long to come to fruition, although it probably only feels recent to me.

19. Super-easy free open-source software development

I am thinking in particular of Arduino, Python, and Processing (which I have yet to play with). Between the fact that these can be freely downloaded and used by anyone for anything and the massive culture of sharing tricks, tips, and how-to docs, you can pretty much figure out how to make a computer (either a PC or an embedded system) do what you want, quickly and easily. And cheaply.

TFPC 16

2010-11-11T17:30:00.000-08:00

16. Laser cutters

Cheap laser cutters (well, cheap is relative) can now cut any shape you can imagine out of some pretty useful materials. Acrylic, thin plywood (say, 1/4" or so), vinyl, and most other types of plastic can be sliced into intricate shapes for your home projects.

Wish I could afford one...

TFPC 15 and 16

2010-11-10T10:21:00.000-08:00

I'm struggling to keep up with this every day- it really is hard to carve 5 minutes out for it.

15. Ubiquitous cellular connection

Weak but it's true. I have no idea how I managed to see my friends before we could connect via cell phone. Although, for me, pre-cell phone days were college and high school, so I saw my friends around in person far more often.

16. E-commerce

I can buy pretty much anything, anytime. For someone with slightly esoteric hobbies (electronics still doesn't have enough clout to get really great local stores), that's a must.

TFPC 14 and 15

2010-11-08T20:18:00.000-08:00

14. Online banking

This one is actually a prime reason why I'm doing this. I was paying bills, transferring money and generally budgeting our lives when my wife pointed out how amazing it is that I can do that all online.

It's become so normal, so natural to me that I completely overlooked how incredible cool it is.

15. Hackerspaces

I think that about covers that.

The future's pretty cool 13

2010-11-06T16:21:00.000-07:00

13. USB

It seems like it's been here forever, but USB is a relative newcomer when stacked up against things like the parallel interface, serial ports, and PS/2, which are still (relatively) ubiquitous. We forget the bad old days, before hot swappable input devices were the rule, printers had cables that could actually bend with less than a one-foot radius, and adding more devices was a simple matter of plugging in a hub.

USB gets some flak from nerds for it's hub and star topology, inefficient use of bandwidth, and relative lack of hackability. It wasn't that long ago that the people were really worried about what the disappearance of serial ports and parallel ports from PCs meant for hacking; with the advent of product lines like FTDI's USB chips that emulate serial and parallel interfaces, I think all but the most die-hard serial fans will agree that we've come out ahead.

The future's pretty cool, 12

2010-11-05T20:11:00.000-07:00

12. Optical mice

I'd never thought of it before just now, but there are TEENAGERS out there who likely think "mouse balls" is a euphemism for some social disease.

Every once in a while, I come across a really old non-optical mouse somewhere in my company at some old, old workstation and I'm reminded anew why I love my optical mouse. Remember when the ball would hit a grain of crud and just...stop, in one axis? And you'd have to back it up and give it another run? Picking it up and jiggling it helped, too, sometimes. And let's not talk about the cleaning process...

If you want to have some real sadistic fun, find a friend who is old enough to have spent a lot of time working with a ball mouse but young enough that that time was highly formative (30-35, long term nerd), and put some scotch tape over the optical sensor on his/her mouse. The result will be a recalcitrant pointer that behaves a lot like a ball-mouse with a fouled roller.

Then watch as s/he instinctively does the mouse jiggle and back up and try again motion...

The future's pretty cool 11

2010-11-04T19:22:00.000-07:00

11. LCD monitors

I honestly never thought I'd see the day when a 19" LCD was not only affordable, but SO affordable that I would have TWO of them sitting side-by-side on my desk. When I started college my 17" CRT was larger than standard, and we marveled at the 19" that one of my friends brought back after the summer.

The future's pretty cool 10

2010-11-03T19:43:00.000-07:00

10. Digital watches

I still think they're a pretty neat idea.

The future's pretty cool 9

2010-11-02T18:39:00.000-07:00

9. Wikipedia

Any self-respecting information hound will nod in sympathy when you mention the Wikipedia tab plague (which reminds me- tabbed browsing may be number 10): you head to Wikipedia to look up, say, chi-squared tests for random variable distribution, and two hours later you're reading an article about the history of the Boxer Rebellion or the scuttling of the German fleet in Scapa Flowe at the end of WWI. You've completely forgotten why you pulled Wikipedia up in the first place, and you may have missed a meeting.

Maginot Line Engineering

2010-11-02T09:35:00.000-07:00

I tweeted on this a couple of weeks (months?) ago, but it's important enough a concept that I think it bears repeating because it applies to a lot of work that engineers (and, really, anyone) does.

For the less historically-inclined, the Maginot Line was a series of defensive fortifications between France and Germany built between the World Wars. France, tired of Germans tromping through their country every couple of decades, elected to try keeping them out by putting fortifications, guns, traps, and big, strongly worded signs in several languages all along the border with Germany.

And it worked- the Germans were utterly and completely repelled by the Maginot Line's defenses. Of course, they went AROUND them and attacked from the north, but by God, they didn't cross the Maginot Line!

In the engineering world, there can be a tendency to do the same thing. If one manufacturer's product has a defective lot, design them out! A particular technology (e.g, tantalum capacitors) fails you, don't use it again!

It seems like a simple fix, but I'm here to tell you: at best it is only breeding false confidence. At worst, it can actually CREATE a problem, because once a company has suffered through a problem (material contamination, process failure, what have you) that company is LESS likely to have that problem again than another company that hasn't yet made the same mistakes.

The lesson here is simple- learn from past mistakes and problems, but recognize when you're going too far. Ask yourself: am I spending too much time and effort on solving the problems of the last war? Because, I promise you, right now, someone somewhere out there is making something RIGHT NOW that is going to blow up in your product and give you a three-month headache.

The future's pretty cool 6-8

2010-11-01T10:31:00.000-07:00

Three-for-one today, because I pretty much didn't touch a computer all weekend. I need to figure out how to pre-post things.

6. High resolution dislpays

As Apple has famously pointed out, our eyes are capable of absorbing much greater detail than digital systems typically provide them with. "Normal" vision (ie., not SEVERELY color-blind, or capable of being corrected to 20/20 with reasonable glasses/contacts) allows for a tremendous data density in a small package, and displays are finally starting to catch up with that.

7. Gaming as a force for good

Some folks out there have finally recognized that the competitive spirit can be harnessed for good- from MMOs like WoW being used as economic microcosms and social fishtanks to competitions in neighborhoods to reduce power consumption.

8. The local food movement

This is a fave of mine, because it means that it's now possible to buy locally grown food direct from the farmer at prices comparable to the really cheap pre-packaged stuff. Net result: better food, lower prices.

The future's cool #5- SMT for everyone

2010-10-29T12:02:00.000-07:00

Okay, hardcore nerdery here. Sorry to the non-believers in the audience, but...

5. SMT technology for hobbyists.

Some will argue the point, looking back with nostalgia at the days when every IC was available in through-hole and sockets abounded, but I for one welcome our minuscule highly integrated overlords.

Ten years ago, when I bought my first parts from Digi-key, it was inconceivable to me that SMT parts could be usable on an at-home basis. Now, the proliferation of adapters (such as Capital Advanced Technologies' excellent "Surfboard" series), cheap hot-air and fine-point rework stations, excellent reflow tutorials, and extremely low-cost low quantity PCB fabrication services (like BatchPCB and the DorkbotPDX group buy), it's now completely and totally reasonable for a hobbyist to use SMT parts to realize extremely advanced designs in surprisingly small amounts of space.

All that's really needed is the right attitude.

Two for one: the future is awesome 3 and 4

2010-10-28T10:20:00.000-07:00

I missed yesterday (inauspicious, missing a goal two days in) but I'll make up by doing two today:

3. CPU cycles are so cheap as to be practically free

While excessive wasting of CPU cycles still bugs me (do I REALLY need something checking to see if updates for Acrobat/Flash/iTunes are available 24/7?), I LOVE the fact that CPU cycles are so cheap that we can waste them on GOOD stuff- operating system eye candy, virtual machines that let me write extremely simple code to do REALLY complex stuff that is highly portable (*cough* PYTHON *coughcough*), and data compression that lets high bandwidth analog come through even fairly narrow (by modern standards) pipes with great quality.

4. Text messaging

I LOVE text messaging. Not the "omg lol i cant bleve u sed that" kind (as a grammar snob that stuff annoys me, although from a technical standpoint, it shouldn't), but the simple fact that it is (arguably) as information dense a means of communication as I can imagine.

The 160 character limit (artificial in this world of essentially unlimited bandwidth that's too cheap to meter) as well as the clunky UI (a limit of the small input device) means that we've adapted to pack a lot of information into a short message. In my case, it tends to be "Pick up milk" or "Missed my bus"- messages that, transmitted by speech over the phone would involve lots of noise (chit-chat about how the day was, greetings, farewells, etc etc- stuff that can wait until I get home). The ratio of truly important data to time required to read/write it is astronomical; I can read a text message in less time than it takes to dial the phone.

The future's pretty cool, day 2

2010-10-26T18:52:00.000-07:00

2: I <3 nearly-free data storage!

The first hard drive I remember owning was 40MB on the Mac LC my parents got when I was in 6th grade.

Four years later we upgraded to a Performa with a 500MB drive.

Two years after that, we hit 1.2GB. Surely that will never fill up, I thought to myself. Of course, then I got to college right in the midst of the MP3 boom...

Now I have two 250GB drives in my PC, and I can add another two terabytes (an unimaginable 50,000 times larger than my first drive) for less than $100.

Relative to that first drive, that's too cheap to even calculate.

The future's pretty cool, day 1

2010-10-25T18:20:00.000-07:00

Public exercise:

I am going to attempt to provide an example of why living in the future is awesome every day for one year. I'll never come up with 365 totally unique reasons, but maybe, JUST MAYBE, it'll help me remember that my life in the future is not as bad as I sometimes think it is and maybe I should be more grateful.

And no, this is not going to be a "neat stuff you probably already saw" series of posts- if I provide a link to an item, it's because I want to provide an example of what I'm talking about.

Day 1: Cultural remixes

http://www.youtube.com/watch?v=wgzmZtwxYiE

I really can't say I like R. Kelly, but I love this video, and I love living in an era where that level of remix is possible.

Parsing the Current, part 2

2010-10-19T18:07:00.000-07:00

More data...and a pretty graph!

Okay, not pretty.

The three lines represent weekly tallies for total number of songs played, total unique artist names, and total unique tracks. Fun things this shows up:
1. Beginning in late 2007, the total number of songs per week trends up. I suspect that this represents a reduction in the amount of named programming in favor of either listing the tracks played during such programs or generally choosing to play songs instead of programs.
2. Dips in number of tracks at pledge drive time. Every six months or so (late May/early June and late October) there's a clear downward dip in the total number played, to the tune of about 15-20% or so. Hardly surprising, and they have to pay the bills. I still can't help but wondering if there's some kind of Laffer curve in pledge drives, where talking more decreases revenue because it alienates listeners, but talking less decreases revenue because you create less guilt.
3. The weekly diversity of tracks and artists clearly HAS been decreasing. There's a slow decline in diversity from early Q2 of 2006 on, with a sharp drop in track diversity in Q4 of 2007 and artist diversity in Q4 of 2008.
4. Really interesting are the three spikes in track diversity in Q2 '09, Q1 '10, and Q2 '10. After trying out a few theories about after-effects of the pledge drive, I remembered that they tend to do weekend countdown lists during Memorial Day weekends, which correspond to at least two of those blips. The third, in January 2010, is a mystery to me.

And now, some data: artist diversity across three semi-randomly* chosen weeks.
For the week beginning 23 Dec 2005 (2166 tracks):
1. Leela James (played 13 times, last on 2007-04-14 19:34:00)
2. Gang of Four (played 8 times, last on 2010-10-07 19:37:00)
3. Blackalicious (played 8 times, last on 2010-10-08 18:43:00)
4. Sun Kil Moon (played 7 times, last on 2010-10-12 13:40:00)
5. Matt Pond PA (played 7 times, last on 2010-10-09 04:34:00)
6. Teenage Fanclub (played 7 times, last on 2010-10-14 23:01:00)
7. David Bowie (played 7 times, last on 2010-10-14 22:46:00)
8. Diamond Nights (played 7 times, last on 2010-08-02 14:55:00)
9. Fiona Apple (played 7 times, last on 2010-10-13 19:11:00)
10. Spoon (played 7 times, last on 2010-10-14 17:12:00)

For the week beginning 6 Oct 2007 (2110 tracks):
1. Jose Gonzalez (played 14 times, last on 2010-09-26 22:52:00)
2. Spoon (played 13 times, last on 2010-10-14 17:12:00)
3. Band of Horses (played 13 times, last on 2010-10-14 07:19:00)
4. American Routes (played 12 times, last on 2007-11-11 08:32:00)
5. The Enemy (played 12 times, last on 2010-08-12 14:57:00)
6. Ryan Adams (played 12 times, last on 2010-10-08 18:00:00)
7. Steve Earle (played 12 times, last on 2010-10-13 15:55:00)
8. Radiohead (played 11 times, last on 2010-10-13 22:09:00)
9. Hot Hot Heat (played 11 times, last on 2010-10-11 14:22:00)
10. Sharon Jones and the Dap Kings (played 10 times, last on 2010-06-19 22:42:00)

Finally, for the week beginning 6 Oct 2010 (2286 total tracks) (get ready for a shocker!):
1. Cloud Cult (played 27 times)
2. Lissie (played 25 times)
3. LCD Soundsystem (played 23 times)
4. Robert Plant (played 23 times)
5. Of Montreal (played 22 times)
6. The Black Keys (played 19 times)
7. John Lennon (played 19 times)
8. Atmosphere (played 19 times)
9. Ray LaMontagne and The Pariah Dogs (played 19 times)
10. Mumford and Sons (played 19 times)

Holy cow! Back in 2005, the most popular artist for the week was Leela James, and she wasn't played quite two times a day. Fast forward to 2010, and you can guess that you'll hear FOUR Cloud Cult songs a day! Not only that, but some artists have gone "extinct"- Leela James went from being a top 10 to nothing in April of 2007. ("American Routes" is a radio program.)

Just as a measure, the 10 most popular tracks of the week in 2005 accounted for 78 0f 2166 tracks (3.6%), in 2007 it was 120 of 2110 (5.7%), and in 2010, 215 of 2286 (9.4%!). This meshes well with my observation that I hear the same songs over and over- I listen on the bus, mostly, for probably 2 hours a day, which I estimate to be about 20 songs a day or 100 a week. If 10% of those songs are coming from a list 10 songs long, I'm bound to hear the same songs several times over.

Again, I will reiterate that I really dig the Current. The DJs seem to REALLY love music, and their enthusiasm is infectious. I'm curious, however, as to how this Clear-Channel-esque playlist arose (anyone at MPR want to comment anonymously? :-)

I will also mention that at least one person I shared this data with responded along the lines of "I could have told you that" and indicated that he had dropped his membership because he no longer felt it was worth his support due to this drop in diversity (no, it's not me- I'm a sustainer and would be even if the Current goes away just for the news stations).

*I say "semi-randomly" because I know full well what a truly random choice would require; what I mean is that I chose them because the first one is at the beginning of my data set, the second is near the middle, and the third is near the end.

Data wrangling the Current

2010-10-18T11:53:00.001-07:00

Arguably, one of the better things about Minnesota is Minnesota Public Radio. MPR is a giant on the national public radio scene (producing shows like "The Splendid Table", "A Prairie Home Companion", and "Marketplace", although "Marketplace" is recorded out in CA).

One of their interesting recent endeavors has been a pop music format station, "The Current". It's at 89.3 in the metro Twin Cities region, and it is (for better or worse)(and let's not argue the point) pretty much the only radio station I listen to.

I've noticed over the last couple of years (I've been listening since January of 2006; they came online in January of 2005) that the diversity of music seems to be declining somewhat. Not in the sense that they play more mainstream stuff, but in the sense that they are playing fewer songs more often.

So, I decided I'd do a little data wrangling. See, one of the outstanding features of the Current is their religious devotion to citing the songs they play. The artist and title are ALWAYS given on the air, AND they have a complete web accessible playlist of (pretty much) every song they've played since 5:00 AM, Dec 22, 2005. I say "pretty much" because they occasionally have a program or "guest DJ" which is listed on the playlist rather than the songs played during that period.

I wrote a Python script which fetched every day's playlist data since it was first available, does some formatting (stripping leading and trailing whitespace, replacing a few meta-characters with their intended, removing entries with empty song/artist entries), and concatenates it into one long file.

This post is all about the first pass I've made over the data- it's really quite basic stuff. I'll try and post some more interesting things later; many friends on Twitter seem to be interested in this little project and have suggested some excellent metrics to investigate. So, without further ado, here's what I can tell you so far:

Total number of unique artists: 13438
Total number of unique songs: 50369
Top 10 songs by number of plays:
1. [323] My Girls- Animal Collective (2009-01-10 22:12:00)
2. [317] Dominos- The Big Pink (2009-08-03 18:36:00)
3. [309] Two Weeks- Grizzly Bear (2009-05-09 16:13:00)
4. [307] Kids- MGMT (2008-04-01 21:05:00)
5. [304] 2080- Yeasayer (2008-01-08 03:50:00)
6. [299] French Navy- Camera Obscura (2009-04-11 16:36:00)
7. [299] Ambling Alp- Yeasayer (2009-11-06 19:26:00)
8. [298] Home- Edward Sharpe and the Magnetic Zeros (2009-09-21 20:07:00)
9. [298] Time To Pretend- MGMT (2007-12-04 11:07:00)
10. [296] How You Like Me Now?- The Heavy (2009-10-26 23:35:00)

Top 10 artists by number of plays:
1. Wilco (played 2413 times)
2. Spoon (played 2370 times)
3. The Hold Steady (played 2153 times)
4. Beck (played 2074 times)
5. Atmosphere (played 2006 times)
6. Radiohead (played 1943 times)
7. The Flaming Lips (played 1915 times)
8. Prince (played 1866 times)
9. Cloud Cult (played 1791 times)
10. Arcade Fire (played 1790 times)

Commentary- first, this data is PRETTY good but not VERY good. Ferinstance, the 22nd most played band is "R.E.M.". But, if their database entry for, say, "Stand", has the band as "REM" or "R. E. M." or any of a hundred other possible variations, my program is not (as yet) sophisticated enough to notice. So R.E.M. might well deserve to be higher if one of their songs is reasonably popular.

Second, I think it's interesting (and it meshes well with why I started this project) that all of the top 10 songs in terms of popularity were first played since the end of 2007 (the oldest in the top 10 has a "birthday" of 4 Dec, 2007). In fact, 22 of the top 25 were released since the beginning of 2009. I think I need a better way of characterizing this metric, though- perhaps by number of times played in the first month after the song premieres.

Third, and but perhaps most importantly, I don't want to sound like I'm down on these guys. I still love the station (for the music they play and for the commercials they DON'T play). I hope this doesn't tweak anyone's nose or get anyone mad at me- more than anything, I like parsing data to assuage my own curiosity, and this whole thing is also an excuse for me to play around with using Python to collect and parse a lot of data.

I'll add a few other items to this list over the coming days- half-life of particular songs, time-of-day correlation, playlist diversity for one day/week/month versus a given other day/week/month, and maybe a few more. If you have ideas, let me know!

Python on the Chumby Hacker Board

2010-09-28T10:04:00.000-07:00

I picked up a couple of Chumby Hacker Board beta units from Adafruit for a project I'm working on, and of course I'm looking to use Python to write my app for the project. Turns out it's not all that tough.

I'll skip over the basics of getting your CHB talking to your PC over a serial connection- Adafruit covers that on their wiki page . I will, however, add a note to their method to say that, unless you're planning on doing a vast amount of Chumby hacking, you might be better served making an adapter to connect your FTDI cable to the CHB rather than rejiggering the connector. It's pretty easy- if the CHB header had two pins between RX and GND instead of one, you'd be able to plug it in directly, as the FTDI cable has the pins in the proper order.

By the way, I find putty a more palatable terminal program than HyperTerminal for this process, but that's just me.

Also, it may be a good idea to install the gcc environment on your board before installing Python. I'll not cover that, as Adafruit have a walkthrough of that as well.

I'm going to assume a level of novice Linux usage here- I'll try to put things in bold if I feel they warrant attention even from the more experienced Linux user.

Now that you're all set up and talking to the CHB, the first thing you need to do is acquire the Python package. There are directions for doing this on the Chumby wiki, but here it is in a nutshell:
1. Visit the above link and download the "python2.6-chumby.tgz" file at the bottom. If you are an over-achiever they have directions for building it from source, so you can use the latest and greatest version of Python, but 2.6 is probably just fine for most purposes.
2. Throw that file onto a USB flash drive. Plug that drive into your CHB.
3. Locate the mount point of your drive by typing "df" at the # prompt. As you can see above, this returns a list of the available filesystems. My drive is mounted at "/mnt/usb-306A-A6CF".
4. Copy the file from your flash drive to the local storage. The command for this is "cp / /mnt/storage/", where and are replaced by your particular drive ID and filename. In my case, I left the filename as standard, so I type "cp /mnt/usb-306A-A6CF/python2.6-chumby.tgz /mnt/storage/". Typing "ls /mnt/storage" will pull up the local storage directory contents. Note that the root filesystem is by default read-only, so you must copy it to /mnt/storage. That's what /mnt/storage is there for.
5. Change the working director to /mnt/storage- "cd /mnt/storage" does this. The rest of this tutorial assumes that your working directory is /mnt/storage.
5. Unzip the tgz. The command for this is "gzip -d python2.6-chumby.tgz". This will unpack the .tgz into a .tar archive.
6. Extract the tar file. It's a good idea to make a new directory to extract the contents into first- "mkdir python" will create a new directory called "python" in /mnt/storage. The command to extract the files is "tar -x -f python2.6-chumby.tar -C python"; this will create two subdirectories in the python directory, "bin" and "lib".
7. Add the /mnt/storage/python/bin directory to your path. This way, simply typing "python" at the # prompt will execute the Python interpreter, and your Python scripts can be executed as shell scripts.
7a. As mentioned above, the root filesystem is read-only. To make it writable, the command is "mount -o remount,rw /". The filesystem will be restored to read-only upon reboot.
7b. Back up the file /etc/profile. "cp /etc/profile /etc/old_profile".
7c. Edit /etc/profile. The savvy and swanky will do this using VI on the device itself; you're probably better off just pulling it off onto a flash drive, editing it on a more forgiving system, and copying it back. To do this, use the "cp" command to copy it to your flash drive ("cp /etc/profile /mnt/usb-306A-A6CF" for my flash drive path), edit it on your main PC in your text editor of choice, then reverse the process ("cp -f /mnt/usb-306A-A6CF/profile /etc/"; the -f switch forces the overwrite, and the trailing slash on "/etc/" indicates that you want to create the file in the directory without a name change).
8. Restart the CHB. Type "python" at the # prompt and you should see the Python shell start.

And that, as they say, is that.

One more note: If you want to make a script directly executable rather than running it as a parameter to python, add the line "#! /usr/bin/env python" to the top of the file. Use "chmod +x myscript.py" to add executable mode to the file's properties. The resulting file can be executed like any other shell script (by typing, for example, "./myscript.py").

Next up, I'll prepare a walkthrough of adapting "regutil" to a .dll, so you can modify the registers and access I/O from within your Python scripts.

OSHW and design tools

2010-07-14T07:04:00.000-07:00

Finally, there's some movement towards a unified concept of what "open source hardware" really is. Adafruit has posted their opinion on the matter for some time, and there have even been a couple of attempts to make an actual license to cover it.

What prompted this post is a developing sticking point in the issue: design tools. The discussion below references the "Definition of Free Cultural Works" linked to above.

In section 1, "Documenation", find the following passage:

The documentation must include design files in the preferred form for which a hardware developer would modify the design.

There's a lively Twitter debate (140 characters at a time isn't enough)(and I hate clogging the feeds of non-participants) between myself and Adam and Matt of Wayne and Layne about the implications of this statement regarding the tools which can be used to do the development as well as the file formats used to distribute the design.

As a burgeoning OSHW developer myself (along with fellow TCMaker member Pat), this is one of the first places my mind went. I was concerned (VERY concerned) that a part of the OSHW definition was going to be a mandate that designs be distributed in a format editable by a free program, or at least a format created by an open source program.

Why is this an issue for me? Because all my designs are built in Proteus, which is not free, nor open source.

I've tried Kicad, and I didn't care for it. It was unintuitive enough that I didn't feel it was worth working at learning. Same goes for Eagle (which, due to its pricepoint, is the darling of the hobbyist community). In fact, my first experience with Eagle, back in college in 2001, was what spurred me to find another solution. I've done schematic capture with OrCAD, which is expensive and uninspired but industry standard, and edited PCB designs with PADS, which is the poster child for an unintuitive UI. I've tinkered with several proprietary PCB house programs; they work okay but locking myself into a particular vendor is not an idea I relish.

That said, I think I can cautiously say that I've sniffed around enough to know what I like. Proteus has, so far, been far and away the winner.

But what does this mean as far as calling my work "open source"? Proteus isn't terribly expensive (the base price is $250, which will cover anything a hobbyist is likely to do), but it certainly isn't free, which means lots of hobbyists will find themselves effectively locked out of my designs (at least, as far as modifying them; there is a trial version that will allow them to view the files natively).

The debate started with the following tweets from @mbeckler:

I'm a bit troubled by the Open Source Hardware (OSHW) draft definition not mentioning closed vs open file formats and CAD tools.

and

If I have to purchase an expensive CAD tool to use your "open source" schematics or board layouts, it's not really Open, is it?

The problem, as I see it, is that subjective term "expensive". For some folks (okay, LOTS of folks), that $250 price tag on Proteus is completely unmanageable- having tried to learn Kicad and having watched Adam give a demonstration at the Hack Factory, with several crashes and a slightly clumsy web-based autorouter, I feel like the true price of that "free" package is more than I'm willing to pay. (EDIT: Per Adam's comment below, I'll stipulate that the demo wasn't under the ideal conditions. And that it was not his fault. However, my usability complaint based on my own experiment with it stands- it's not easy enough to use for me to move away from my perfectly good (albeit non-free and closed source) existing solution).

A key question to be addressed is WHY open your hardware designs? For me, it's to allow people to hack it and learn from it. To that end, while I will certainly provide the original design files, I feel that my primary responsibility as an OSHW community member has been acquitted if I provide the following information:

Schematic in a readily readable format (.png, .pdf, .svg, etc)
Board layout in a readily readable format (Gerber, .png, .pdf, .svg, etc)
Source code in a readily understandable format (plain text, well commented)
Solid assembly documentation
Solid theory documentation (how it works and why it's designed the way it is)

Obviously, of course, creation of derivative works is a major part of the open source ethos; some of No Cube's early products will be derivative from Arduino. Does that mean I have to bend over backwards to make sure that my design files can be modified by anyone who comes along? Does that, therefore, imply that my original design files need to be created in a free program? I think not, because no matter what program I choose, the possibility always exists that the creator of a derivative work will want to use a different tool. In fact, given the number of viable free options, even, I'd say it's basically a certainty that some subsequent creator will NOT want to use my tool.

In the end, so long as I provide thorough and approachable documentation of the design, the original design tool shouldn't matter, nor should the file format of the design documents. A good example is Adafruit- they would seem to be doing their design work in Eagle, but they provide documentation in other formats (although Eagle is still required to view their physical layout).

I'm definitely going to pay attention to this one and weigh in whenever I can; personally, I think strict requirements on the design tools for "valid" OSHW would be contrary to the core spirit of the open source ethic.

Make...stories?

2010-05-07T18:51:00.001-07:00

I'm reading Neil Gaiman's wonderful short fiction anthology, "Fragile Things", and one of his stories in there is his only personal ghost story, "The Flints of Memory Lane". It reminded me so starkly of MY only personal ghost story that I think I have to get it down. I've not told it, or even thought of it, in years, but perhaps I can do it justice...

The thing about seeing something vanish, really disappear, is how subtle it is.

I know, that sounds weird- some bleeding great big THING looming in front of you, gone, poof, like a fart in the wind (except it's your eyes and not your nose that are fooled), and you'd think subtle is the last word one would use to describe it, but there it is.

It's funny, actually- I don't really remember how old I was at the time. I can guess- somewhere between 14 and 17, because I was only out at the park for the six summers between when I was 14 and 20, and I clearly remember that I was in high school at the time, so that narrows it down a little. Everyone knew the park was haunted. People heard strange things, saw strange things, felt unseen eyes, etc. You know, the sort of things kids swear happened to their friend's friend late one night after everyone had gone.

"The park" was a bowl-shaped depression in the hills on the edge of town where the local small-town junior thespians put on a musical each summer. I was a techie- changing batteries in microphones, running a spotlight, climbing ridiculously tall poles during thunderstorms to wrap tarps around equipment that I valued more than my own health. At night, after the show, when everyone had gone home, my cousin and I were the Night Watch. We slept out there, peeking out the door of the costume shop every few hours to make certain no vandals or thieves were abusing the property.

Most nights, someone would hang out there until pretty late. This night, in particular, I remember a fairly large number of folks sitting around, chatting, huddling, flirting, as teenagers will on a cold prairie summer night. I probably felt more comfortable because of this; I suspect, aside from large amounts of alcohol, being in a crowd of people is the most effective courage-fortifier a person can find. That probably explains why I wandered out of the group and headed to the restroom on my own.

The restrooms were in a small cinder block building, shut with massive steel doors to keep out miscreants during the off season. At the peak of the building, pointed down and slightly out, were two floodlights, of the sort that leave you with big purple blotches in your vision if you looked at them, even in broad daylight. The others were either on the stage or in the backstage building; regardless, they were a few hundred feet away, on the other side of a greenbelt of trees growing around a coulee which was, of course, haunted.

The park was never intended to be an "all-hours" venue; the lights in the restroom were on a timer and were off well before I got there. Enough light bled in from the aforementioned eye-melters that standard restroom activities were manageable; not enough, however, that my eyes were not very well adjusted to the dark by the time I left.

Turning the corner out of the door to the restroom, I saw, standing stock-still about 10 yards away, right outside of the edge of the floodlit area, a man-shape. A BIG man-shape. Men of a certain age and disposition will remember a wrestler in the WWF with the stage name "The Undertaker". For a while, he was a main heel in the WWF- I always felt he was created to takeover for Andre the Giant. The man-shape facing me was bigger than The Undertaker in about the same degree as The Undertaker would've been bigger than me.

There's really only one option a well-evolved hominid brain has when presented with this sort of situation: complete and under catatonia. My joints seized. My eyelids, lacking a more desirable option such as emigration, tried to crawl behind my eyeballs in the hopes that, maybe, if they got out of the way, the eyes would start to report more favorable information. My higher brain functions became full of equations of the "a train leaves Chicago at 5 p.m. at 60mph and another train leaves New York at 7 p.m. at 50mph, where do they meet" sort, only these equations involved the levitation speed of the shrouded undead versus how fast I could run before my sneakers tore off.

I don't know how long I stood there, staring. Longer than two seconds, less than fifteen minutes. "It" stared back towards me (I can't say at me, because I didn't see a face, and moreover, I didn't have the feeling of being watched). I'm sure it was as scared of me as I was of it, or something equally reassuring that will let me sleep tonight. That's when the scariest, most nerve-jarring, mind-jangling event of my life happened.

The thing, this monstrous, black-cloaked, hulking THING, vanished. Gone. I bet you expected that he lunged towards me, or spread his cloak and reveal a portal to hell or something, and I fell down screaming and came to surrounded by the ashen faces of my friends with a distinct scent of sulfur in the air, didn't you?

See, and you expected that because of the simple fact that in all your life, in all the movies you've seen and books you've read and ghost stories you've heard, nobody who's ever seen something vanish has ever told you how it really is to see something vanish. No smoke, no "I flinched and he was gone", no "I looked back as I ran and nothing was there", no flashes of light or grand gestures: just a monstrous, don't-screw-with-me entity one second and empty grass and hillside the next.

The really, truly disconcerting thing, the part that makes this hard to think about too much, is that I didn't notice it disappear. THAT'S what makes it scary, scarier than anything it could have done (I say that now but a vision of my own death or being disemboweled probably would have been scarier). See, our brains spend most of our lives making up a map of how the world works. Things don't just...vanish. A movie ninja disappears in a puff of smoke or a leggy blonde disappears under David Copperfield's tablecloth and we're sort of...okay with that. Sleight-of-hand, ignore the man behind the curtain, etc.

But this, this was something different. It was sleight-of-mind, like BEING the leggy blonde disappearing under the cloth and discovering that it really IS magic fabric. When something disappears in front of you, and you realize that you don't know when it disappeared but you know it's been gone for a good while, well, that brings up some uncomfortable questions, questions about your the way your brain works and about the way the universe works and about whether either of them is actually working at all.

Like I said, subtle.

It's been a long time since this happened. I'm more skeptical now, less willing to believe that spirits and spooks and ethereal beings exist, let alone that they would have nothing better to do on a summer evening than scare the bejesus out of some kid leaving a cinder block shithouse in a public park. I've never had another, similar experience, and I've enjoyed excellent mental health since then, devoid of hallucinations, so I don't think it was insanity.

But maybe a little insanity is better than the alternative.

Qtouch libraries

2010-04-01T18:23:00.000-07:00

I'm so down with Atmel's Qtouch library. Basically, it lets you add capacitive touch detection to your projects- and it works through non-conductive surfaces. Think touch-sensitive sealed keypads, or the scroll wheel from the older generation of iPods.

Nobody- as near as I can tell- has this working with the Arduino environment yet. It should be doable, because you can do it in AVRStudio compiling code through WINAVR, which is just a distribution for AVR-GCC, which is what Arduino compiles its code with. I'm working on it, but here, in the meantime, is a walk-through of getting the Qtouch demos working with the '328P found on the Arduino board (under Windows- don't bug me about figuring out how to use it in Linux):

1. Download and install AVRStudio from Atmel- annoyingly, you have to fill in a long-ish form with the standard information about who you are and what you're doing. This is not, in and of itself, TOO annoying- but the fact that they make you do it for each download- even if you've registered before- is.
2. Download and install WINAVR from the SourceForge site- they do NOT make you register.
3. Download and install the Qtouch library from Atmel- you do NOT need to download and install Qtouch Studio- this is a frontend used for interfacing with some example projects that they have made and if you have the cha-ching to buy those you're probably not reading these instructions anyway.
4. Create a folder for your project- I don't care where you put it, but you'll want to have some files conveniently co-located to ease the paths in your include statements.
5. Move the following files from the Qtouch directory (default C:\Program Files\Atmel\Atmel_QTouch_Libraries_4.0) to the project directory (no need for subdirectories):

\include\touch_api.h
\AVR_Tiny_Mega_XMega\QTouch\common_files\touch_qt_config.h
\AVR_Tiny_Mega_XMega\QTouch\common_files\qt_asm_tiny_mega.S
\AVR_Tiny_Mega_XMega\QTouch\example_projects\avr5g1_qt_example\avr5g1_qt_example.aps
AVR_Tiny_Mega_XMega\QTouch\example_projects\avr5g1_qt_example\main_atmega324p.c

6. Fire up AVRStudio, and in the initial "Open Project" window, open the .aps file you just copied into your project directory. Expect some "project files not found" errors.
7. "Find" the project files that are "missing"- these will be listed in the project frame on the left side as files with a little red slash through them, and they will be the files you copied into your project directory.
8. Under the "Project" menu, choose "Configuration Options". You'll make the following changes:

In the "General" tab (selected from the icons on the left), you'll change the device listing to "atmega328p" from "atmega324p".
In the "Libraries" tab, you'll want to add the Qtouch library directory to the search path. By default, it's "C:\Program Files\Atmel\Atmel_QTouch_Libraries_4.0\AVR_Tiny_Mega_XMega\QTouch\library_files"
In "Custom Options", find the item in the list that says "-DSNSK1=A" and change the 'A' to 'C'. This is the one that took me some time to figure out, but it's related to which ports can be used for the SNS and SNSK functions. Ports B, C, and D can be used on the 328P, but A, B, C, and D can be used on the 324P. If you don't change that, you're trying to assign the role of SNSK to a non-existent port and you'll get an error in the assembler saying "Error: constant value required" in the qt_asm_tiny_mega.S file.

And that's it! Save your changes, hit "Build" and the example should compile up just fine. Some caveats at this point:

All you've done is prepare a template. You still need to assign pins to various functions, write code that checks the inputs and does something, and perhaps most importantly, make some kind of hardware capable of receiving the input. I haven't done ANY of these things yet.
You probably need a programmer to put this on your Arduino board, but I'm not sure. I think you can use AVR-DUDE to drop the generated file into memory using the bootloader but that's an exercise I've not tried yet.
There are a lot of things I don't know about this yet, but this is a jump-start for others because it took me a few hours to figure out all the necessary settings and changes to make to get the 328P compile working.

As I figure more stuff out, I'll continue to post- hopefully I'll figure out how to get all this working under Arduino, so more people can use it easily!

Omnidirectional wheels for bots

2010-03-23T06:16:00.000-07:00

Woot! had a neat WowWee RC vehicle on the other day, and I sent a link to a coworker thinking he might dig the locomotion system (he's a mechanical engineer, but an okay guy nonetheless). Five minutes later, he shows up at my desk with this:

He'd bought it years before, for no particular reason. He dug a bit and found a website that sells it, $9 a pop.

Yet another really cool item I'll never get to use in a project.

Viewing binary data as an image

2010-01-21T08:28:00.001-08:00

So, I have a stream of data from a FireWire device I need to interpret as an image. I'll not get into the how or why of this, but the problem is pretty simple: take a file which is 250,848 bytes long, with each byte representing the 8-bit grayscale intensity of a single pixel in a 536 x 458 pixel image, and reconstruct that image.

Turns out, finding an app to do this is a non-trivial problem. Sure, I could write something to do it (in the past, I've written a Scilab script that plots it, but that takes a lot of memory, runs slowly, and generally gives me few or no tools to deal with the "image" resulting, besides my eyes), but I KNOW this is a solved problem (my favorite term of late) and anything I came up with would likely be a south-pointing chariot.

In the end, I turned to my old friend, ImageJ. ImageJ is a powerful, free, Java-based image manipulation and analysis tool. It's no replacement for GIMP or Photoshop, but it provides a very simple interface to analyze images. Sure enough, ImageJ includes a provision to import "raw" image data- exactly what I needed.

Hopefully, someone, someday, will find this blog post on a Google search and it'll save them some time.

Did you see a sign on my door that says "Dead capacitor storage"?

2009-12-21T06:31:00.000-08:00

With apologies to Quentin Tarantino...

For a 10-year-old problem, the capacitor plague has been bizarrely present in my life recently.

It started a couple of weeks ago when a coworker offered me an LCD TV that was "flaky" as scrap (my scraphound predilections are by now legend among those who know me). Being the upstanding gent I am, I pointed out that it was probably bad caps, and I found and replaced the buggers for him.

A friend in Iowa sent me an e-mail, asking for help debugging a dead plasma he'd been gifted. He hasn't found bad caps yet but I'm fairly confident he will.

My PC was dead the other morning, when I got to work. Guess why?

A couple of months ago, I found a dead 17" LCD in the trash bin at the office. By now you should know how I fixed it.

A tweep I follow posted this article this morning.

This is fascinating for me in that it hits a number of points that people fail to understand about electronics:

They wear out, but certain components are more likely than others to wear out, and fortunately, those components are easy to fix.
There are two completely different realms for parts procurement. If you're dealing with quantities below, say, 1e6, you deal with the companies represented by distributors found in an Octopart or Findchips search. Above that, there is an entirely different group of manufacturers, and their components aren't cheaper because they grow on trees- they cut corners.
OEMs don't care about long life, just long-enough life. If they save $1 per motherboard by using caps with a MTTF of 2000 hours rather than 10000 hours, and that gets them past their warranty period, that's fine with them.
"High quality" electronics are not immune to this. ALL consumer goods (seriously, all of them) are dipping from the pool of cheap-o component makers. This is true from the $15 coffeemaker from Target up to a $2000 plasma TV, from brands like Coby all the way up to Dell servers.
If you're making a product pulling from the Digi-key sourced manufacturers, the quality of component you're getting will be much higher. Replacing a burst cap with one from DK with similar specs is going to get you a long way.

I'm wondering how many otherwise perfectly good consumer electronics items are in landfills because of this issue.

So, take heed- most likely, a failed cap lurks in that dead PC, somewhere. It's an easy fix that can bring lots of valuable electronics into your life.

Pulses on pushbutton

2009-11-16T15:00:00.001-08:00

A friend was asking after a circuit for making pulses from a pushbutton on push and release. Two ways immediately suggest themselves- using a PIC and using a differentiator.

The PIC is easy for me, at least- I have a small stock of 12F683s which are 8-pin devices. Add a bypass cap and you're in business- you could even reprogram it to change the delay, debounce the input, etc. Of course, not everyone has a PIC programmer, and I feel like it's a pretty trivial app for a PIC, so I'll not talk much more about it.

The differentiator circuit is a little more involved.
Apologies for the crappiness of the image- LTSpice doesn't generate great output images, for one, and this was part of a larger image (it started NPN based, and generated negative going pulses; that's where Q3, Q4, etc etc went).

V3 is the switch- in the application, it should be a 100-ohm pull-up to 5V and a switch that yanks C2 to ground when it's closed.

R4 pulls up the base of Q3 and Q4, keeping them turned off and providing a 0V output normally. In steady-state non-pushed, C2 will have about 0V across it. When the switch closes, the base of Q3 and the emitter of Q4 get yanked down (since the voltage across the cap can't change instantly). Q3 turns on, and the load sees a pulse that goes up to 5V. C2 charges to 5V (since one end is at 0V and the other is tied to 5V through R4), and as it charges, Q3 slowly turns off. Q4 has, as yet, never turned on, since the base has never been at a lower potential than the emitter. When you release the button, the (not shown in the drawing) 100-ohm resistor which is a pullup to 5V yanks the bottom of the capacitor up by 5V. Since the cap is already charged to 5V, the voltage across the capacitor is now 10V, which shoves the base of Q3 above the 5V rail by about 5V (turning it off even harder, for what it's worth)(which is not much) and, here's the magic part, shoves the emitter of Q4 5V above the 5V rail. Now, there's a 5V difference between the base and emitter, the transistor is biased, and it turns on, which again yanks the load up towards 5V. Again, C2 will discharge, and Q4 turns off as it does. The diode provides a clamp to the 5V rail, limiting the voltage on the output. It tends to pop up to 8V or so, although only briefly, so it may not be an issue.

This circuit is a real hack job- I know I could kill that >5V excursion if I spend a little more time on it. It's simple, though, and I like it.

The LTSpice file is available here.

EDIT: Adding a 270-ohm resistor between the base of Q3 and the emitter of Q4 keeps the excursion to a very reasonable .2V above 5V.

LTSpice

2009-11-10T08:16:00.000-08:00

For those in the electronics world, SPICE simulation can be a great way to answer the "will my circuit work as advertised" question without breadboarding. It's a great sanity check- if it don't work in SPICE, it won't* work on a breadboard.

LTSpice is Linear Technologies' own incarnation of SPICE. It's a nice little product, and comes with models for many of Linear's products (power supplies, op-amps, etc) along with many supporting components from other manufacturers (diodes, transistors, capacitors, inductors, etc) and generic parts (555s, LEDs, etc). Obviously, they provide it expecting people to download it, sim up a solution involving Linear parts and then sell eleventy-billion a year, thus providing a nice income stream for Linear (and it works- LTSpice makes it much more likely that I'll reach for a Linear part for power supply design than another manufacturer's parts).

But for the tinkerer, it means that there's a free, very powerful SPICE tool out there, which is well supported. Give it a look!

*for some values of "won't". For instance, there are times you might want to put a transistor in "backwards", or use just the collector-base junction as a noise source. In that case, the model probably won't hold up- but if you're doing things like that, chances are you don't mind not having a model for it anyway.

Breadboarding the Arduino- part 1

2009-11-07T09:57:00.000-08:00

A few weeks ago, I purchased 10 Atmega328P's from Mouser, naively thinking it would be easy enough to get them working on a breadboard as an Arduino sans the fancy (expensive) board. I was planning to use an FTDI USB to TTL serial data cable to bootload (I bought a 5V one, then realized that the two 3.3V ones I already had would work fine- lesson one of this saga). I also bought a some 16MHz crystals and the appropriate capacitors.

At this point, I want to extend my thanks to whomever it was that decided a 6-pin AVRISP compatible ICSP header would be a value-add to the Arduino. I know that 95% of the Arduino users out there will NEVER use it, but I am very grateful.

So, first hurdle- I figure I'll take one of the 328s and upgrade my Arduino (it was one of the, what, six? Duemilanove's that shipped with a 168 from the factory). Supposedly, the Arduino IDE has the capability of loading the bootloader onto a blank chip through an AVRISP, but I'll be buggered if I could get it to work. After a little bit of monkeying around with it, I gave up, admitted defeat and downloaded AVRStudio. I highly recommend this route if the IDE bootloader program (using AVRDUDE) doesn't work right away- the pain level of a ~100MB download is much lower than trying to debug AVRDUDE- at least, on my internet connection.

At any rate, I had no Atmega328 Arduino to snoop, and nobody, nowhere, had clearly and definitively stated what the configuration bits are supposed to be. So, for posterity, I do that here, now (note that they've changed since I first posted this):

Extended- 0xFD

High- 0xDA

Low- 0xC6

EDIT: Note that these settings ARE NOT the settings suggested in the "boards.txt" file in the hardware\arduino directory. My suggested low bits- 0xC6 instead of 0xFF- will allow more types of crystals or resonators to work, at the expense of a slightly increased power draw. If you're THAT WORRIED about power draw, you're probably already digging deep enough that you've figured all this out, already.

I made a few educated guesses and got values which more or less seemed to work, and then I grabbed the bootloader binary from its home deep in the catacombs of the Arduino application folder. Success! I could upload and run sketches with my new 328 enhanced Duemilanove. Flushed with my success, I immediately launched into the next portion of the project: getting a breadboarded 328 loading sketches through the FTDI cable and the IDE.

At this point, and exactly how I managed to do this remains unclear to me, I proceeded to brick all three of my remaining 328s (I know, I bought 10, but I sold 6 to friends). I know I somehow wrote inappropriate fuse bits to the config registers, but I don't quite know how I did that, let alone how I managed to do it to all three. I can only assume that, briefly, I was MONUMENTALLY stupid.

So, of course, I began a bit of yak shaving. First, I tried my JTAG-ICE mkII, but that only works on JTAG capable parts (which the 328 is not). I THOUGHT it might have HV capability (Microchip's equivalent, the ICD2, does), but alas, no. Finally, thanks to Jeff Keyzer's excellent tutorial on making an Arduino into a high-voltage programmer (only high-voltage programming can resurrect an Arduino under some circumstances; for instance, if the reset pin is disabled), I was able to bring the chips back from the purgatory I thought I'd condemned them to forever.

So, here I sit, at 2:30 in the morning, weeks after starting all of this, about to embark on the next step: getting the parts to work on a breadboard, through the IDE, with minimal "tricks" involved. I will mention that I've been at this point before- before I bricked the chips, I had put them in a bread board and started tinkering, but I just couldn't get the thing to work. We'll see if this turns out any better- with luck, the next post will be a post-mortem on why it failed before and what I did right this time.

Balloon boy- plausible?

2009-10-15T14:47:00.000-07:00

Quick and dirty math post-

The media reports the balloon was about 20' x 5'. Modeled in SketchUp as a 20' diameter sphere, shmooshed to a disc with a 5' vertical, that yields ~1000 cu. ft. of helium, or ~28,300L. As we all know, helium can lift 1.113g/L, for a total of about 31.5 kg of lift for that volume of gas. A quick Google search tells me the average 6-year-old boy weighs 46.2 pounds, or 21kg. That leaves 10.5 kg for the mass of the craft itself- about 23 pounds, or slightly less than the weight of three gallons of milk.

I guess it's plausible, but I'm skeptical. I think it will come out that he was never on board in the first place.

Essential Skills Redux

2009-07-15T16:15:00.000-07:00

Some general notes on the whole "Essential Skills" post.

A couple of commenters mentioned that it is a bit heavy on electronics. True; partly that's because I'm an electrical engineer, but it's also because, in my experience, it's also where many makers (aside: I will continue to use that term; I came to my personal peace with it during the discussion about what to name the Twin Cities Maker group) "fall down" and lose confidence or run aground. Electronics is a massive sphere, and my hope, by including those things on the list, was to encourage people to develop familiarity with the most basic, most useful aspects of it (at least, as far as general making is concerned), rather than feeling overwhelmed by the whole thing and steering clear of electronics projects altogether. Some of the coolest projects I've seen were banged together by people with little or no electronics experience, just the confidence to go forward and the willingness to make a few mistakes.

In the intro to the list for the BoingBoing crosslink, Cory Doctorow invoked Heinlein's "Specialization is for insects" mantra. I'll admit that I'd forgotten about that, but it was the spirit in which I was writing the list. Some people made suggestions later: rebuild an engine, wind a motor, weld, etc. I avoided things like that, because they tend to be too specialist. My goal for this list was to include nothing that required more specialized equipment than one was likely to find at, say, Wal-Mart. I think part of the maker "movement" is a sense that vast outlays of material and equipment cost are not and should not be required to do remarkable things. Welding, rebuilding an engine, using an engine lathe or a vertical milling machine, these are all admirable (and valuable) skills, but they are also out of reach for a vast swath of the making public. Most everyone, on the other hand, can find room (and money) for a tote box that contains a Dremel tool, an assortment of glues, a soldering kit and a multimeter.

Over the coming days (and weeks, no doubt), I'll make one post about each of the items on the list, and probably an updated list, too- I have no doubt some of the commenter's suggestions will make it on (and credit where credit is due, of course).

I hope some folks will check up occasionally and see what I have to say.

18 Essential Skills for a Maker

2009-07-13T09:09:00.000-07:00

@AntonOlsen recently posted an article on GeekDad enumerating 100 Essential Skills for Geeks. As he was inspired to do so by a list of "Essential Skills for Men", so I am inspired to make this list of essential skills for Makers.

His list was a little long (100 items), terse (essentially one line per item, but with links), and slightly biased (heavier on computers than I might have liked, but to be fair, that is the most common geek fetish). I'm going to go for a shorter list, with slightly more verbose entries, and try to cast a wider net. If I get interest from this list, I'll follow up with an article on each point going into more detail.

1. Calculate power consumption and estimate battery life- Most electrical projects will involve batteries of some sort. Having an idea of how long your project will run on a battery can save you a lot of trouble later- that wireless garden soil moisture monitor is probably not going to run very long on a 9V battery. Maybe solar is a better idea?
2. Spot valuable salvage- Not only knowing where to get it, but knowing it when you see it. Finding it isn't too hard- curbs, alleys, and the classic dumpster dive. Deciding whether to keep it is the real trick: can it be broken down? Are there useful things inside (gears, motors, electronics, hardware, salvageable wood, springs, etc.)? Is trying to salvage parts of it a wise thing to do (upholstered items left outside are a great way to get bedbugs into your home)?
3. Spot eminently hackable, cheap Chinese crap- The glut of crap from China occasionally brings some real gems with it. Woot.com recently sold some rotating LED-based "police lights" for $3, which connect to USB and can be turned on and off by pressing a key on the keyboard.
4. Find "prior art"- In the patent world, "prior art" is anything which suggests that the idea you are trying to patent (or have patented) was developed or described by someone else first. The existence of prior art can break a patent. In the Maker world, prior art is a springboard. Someone, somewhere on the internet did (or tried to do) what you are trying to do. They may even be selling bits of the project which may make showstopping technical challenges mere speedbumps.
5. Stitch a simple and serviceable seam- We're not talking about making your daughter's prom dress, here- just being able to neatly and durably reclose the seam on the Furby you just hacked into reciting the Vincent Price speech from "Thriller".
6. Understand the voltage/current ratings on a power supply- If a battery won't cut it, you should understand at least the rudiments of power supplies: how to get a cheap wall-wart AC adapter, what voltage you can use, and why it's okay to use a 500mA supply to replace a 250mA supply.
7. Know which glue to use, when- Elmer's white, spray mount, Uhu glue sticks, JB Weld, cyanoacrylate, and two-part epoxy all have their uses.
8. Know which tape to use, when- Duct, masking, Scotch, foam-two-sided, and (occasionally) electrical tape all have their uses.
9. Deal with recalcitrant fasteners- Sooner or later, you'll want to remove a screw or bolt that is stripped, broken, or uses a security bit. Owning a wide variety of driver bits is a start, but knowing how to drill out a fastener or cut a notch for a flat-edge screwdriver should be somewhere in your bag of tricks.
10. Use a Dremel- 'nuff said.
11. Find the parts you can't salvage- Locally or over the internet. You should know where local shops are that sell things like nuts and bolts by the pound, simple electronics (resistors, soldering tools, protoboard, etc.)(RadioShack is a poor choice for this, if it can be helped), fabric, paper, artist's supplies, wood, hobbyist tools and toys. You should also be familiar with Digikey.com, Mcmaster.com, Octopart.com, Smallparts.com, Adafruit.com, Sparkfun.com, and Jameco.com, just to name a few.
12. Identify electronics in the zone between too-hot and smoking by smell- When you smell the smoke, it's too late.
13. Strip, splice, and terminate wire- Trickier than it sounds. You should be able to splice wire using a crimp splice, a wire nut, and heat shrink + solder (note: electrical tape is NOT on that list). You should know how to use a wire stripper to strip stranded wire without cutting more than one or two strands. You should be able to attach a wire to your project in such a way that it will still be attached in two weeks, two months, or two years.
14. Create fairly neat holes of arbitrary size and shape in sheet metal, plastic, and wood- Nibblers, step-bits, tin-snips, chisels, awls, drill bits, and the appropriate Dremel bit all play crucuial roles here.
15. Use Ohm's law- V = I*R. Know it, use it, love it.
16. Tie useful knots- Bowline, taut-line hitch, slip, figure-eight, overhand, square, clove hitch, sheet bend. One or another of these knots will get you through most situations.
17. Solder.
18. Program a microcontroller- nothing fancy, just something along the lines of the Arduino. Just enough to make it spin a motor on a trigger or light an LED or sound an alarm.

Did I forget anything?

A Maker does gardens

2009-06-19T19:05:00.000-07:00

So, in keeping with our ethic of keeping our food as close to home as possible, Beth and I elected to put together a bit of a garden this year.

Rather than do it on the ground, as is more usual, I built some boxes up on stilts. Being the ever-resourceful scrap hound that I am, I found some really good sources for the material to make these boxes:

My work was clearing out a part of the factory and disposed of a demo dumpster FULL of various types of wood scrap. The bottoms of all the boxes came from some old shipping crates we no longer had a need for- they are rough-grade 1/2" plywood with a 2"x4" frame around the edge and one 2"x4" across the middle for extra support. 3'x4', pre-cut. Saved me a lot of effort and basically made the whole thing feasible.
The legs are largely made from scrap I found on the side of the road. Someone had done some concrete work and left the wood on the roadside for anyone to pick up. Warning: wood used for a concrete form takes on the fashion of concrete. It is insanely hard, will ruin your drill bits and saw blades, and is generally not worth the trouble.
Home Depot sells what they refer to as "cull lumber". It's typically on a cart at the back of the store, behind all the good wood. This is stuff that was damaged, warped, or otherwise undesirable. They pull it out, cut it into 4'-6' lengths, and sell it for half price or less. The price is nice if you don't need perfectly straight or pretty wood, and if you have a small car like ours, having it pre-cut (for free, instead of $0.25 per cut like they would normally charge) takes a lot of stress out of the transaction.
And, of course, Ikea. The picture to the left shows our bean box (hanging on the fence). The ladder above it is one side of a crib. Ikea sells "handyman's carts" periodically, which are basically all the bits and pieces of furniture that they don't think they can sell piecewise. For $15, you get one of their ginormous flatbed carts heaped above the level of the handles with things like this. The ladder structures in the picture below (against the garage) are bed base slats screwed together. The curvature of the slats holds the structure away from the wall so the cukes and zucchini can be more easily trained onto the ladder. I'm not sure what the structures on the middle two free-standing beds are, but they were $5 each and are almost exactly the width of the box, and have sturdy wire mesh with 4" spacing.

We may have gone a little crops-crazy. The left box above has six square feet of carrots, planted 16 to a square foot. The other half of the box is potatoes- Beth is trying a trick where you plant the potatoes and then keep covering the sprouts with an inch of soil everytime they pop up. The end result is supposedly a much thicker layer of potatoes beneath the surface. I'm afraid we're just going to end up with potatoes under six inches of soil, but it's worth the try. The right box is salad greens, chard, and turnips. I also tried replanting the roots from a bunch of lettuce from the Wedge and it took!
The right image shows the size of the raspberry patch- it was here when we moved in. The box has 10 winter squash plants- I'm hoping that we can train them to grow out in different directions from the box and just completely let them take over that side of the house. We got two types- queensland blue and Burgess' buttercup. They're both blue, pumpkiny squash that should store well. I'm hoping to get a dozen or so squash, and a cool room in the garage for them may be a future project.

The image to the right shows the main growing area. The fence in the background is overgrown with grapevines. No word yet on palatability but I'm hopeful. The box on the left has 12 tomato plants- 11 of them are small, yellow cherry tomatoes. The last one is the same as the three across the back of the next- Brandywine. We also have four San Marzanos, which make (supposedly) outstanding sauce. Against the wall, we've got cucumbers (of a large variety well suited for pickling) and zucchini. Most of the rest of those two boxes is full of onions (14 square feet, with four or five per), with three square feet of dill (OVERKILL) and one of leeks. At least four square feet are basil (I thought we planted six but it's only coming up in four), three of other assorted herbs (not coming along too well), and three are eggplant.
The tub on the ground has some bean plants and zucchini from the thinning out process- we'll have to figure out where to put those permanently, which means more construction. We also have a ground-level trough of strawberries and a small patch of rhubarb snuggled up on the other side of the steps.

All in all, we should have a lot of food, even if we only get half production out of this. Total cost was probably around $300. The largest single expenditures were screws and soil- we bought 2.5 yards of compost/soil mix for about $125, and that was a smidge too much.

Laser diodes and you

2009-05-18T14:15:00.000-07:00

I know some of the people who read this blog (or who will see links to this post on Twitter) are into laser diode projects, so I thought I'd throw out some of the lore I've acquired on the topic.

Laser diodes...

1. ...are current driven devices: Always drive them as such, being careful to limit the current through them to some relatively safe value. 30mA is not an unreasonable guess; as they age the current required for the same output power will increase.
2. ...aren't very laser-like: Don't expect a laser diode to put out a tidy little dot of light. That requires some optics. As the current pushed through a laser diode goes up, the efficiency of the device increases, and the divergence angle of the beam decreases. The beam tends to project an ellipsoidal shape on a perpendicular surface; the larger of the two dimensions will change more as the current goes up, while the smaller dimension won't change much at all. This is why laser pointers do not project a perfectly round dot of light.
3. ...are easily damaged by excessive current: Unlike LEDs and most other components, where excessive current draw kills by heat, laser diodes can be killed by exceeding, even momentarily, their maximum safe optical power output. Too many photons will damage the facets of the die, causing them to rapidly degenerate.
4. ...are easily damaged by static electricity: These are probably the most sensitive devices the average user will ever encounter. Static discharges of below 25V can kill or damage a laser diode.
5. ...can be readily damaged by heat during soldering: A laser diode overheated by 10-15°C and heated for too long by 2-3 seconds can be destroyed or have its lifespan significantly degraded. Always solder at the lowest possible temp, as quickly as possible, using lead-bearing solder if you can.
6. ...have a sharp "knee" in their output power curve: At some point, the laser diode passes the "lasing" threshold, above which the output increases linearly and very steeply with regard to increased input current. The device's efficiency in the datasheet will usually be given for this area, in terms of mW/mA.
7. ...usually have built-in feedback: Many laser diodes will have a built-in photodiode which will allow you to make an educated guess at how many mW of optical power are coming out of the diode. If you have access to the datasheet, there will be an efficiency value stated in there which describes the output current of the photodiode for a given bias voltage in mA/mW of optical power. This can be a very good thing to watch to make sure you don't blow the diode by overdriving it.
8. ...have a fast response time: Laser diodes are LED-like enough to be modulated at pretty high frequencies, providing a usable communications link for longer distances fairly easily.

So, that's all I can think of right now. In short, in most cases, you're better off buying a laser pointer or laser diode module and using that, since the optics and protection circuitry are taken care of and built right in. That's not always an option on a hobbyist budget, especially if your source for laser diodes is old optical drives.

Questions?

April maker challenge 21- RFID mouse

2009-04-30T14:02:00.000-07:00

I got started late on the AMC, so I'm a few behind. I have, however, managed to average one a day since the 10th. I'm offline at home until May 6 (moved- why do I NEVER remember to arrange things like that ahead of time?), so I'll post my last one now. I have a ton of others, so I'll trickle them out, because I enjoy this, but this'll be it for the daily do.

I'd like to include an RFID reader in a mouse. I think it's doable- some computer mice are pretty large, and by hacking ruthlessly at a hub and RFID reader, you should be able to do it easily enough.

Why, you might ask? Quite simply, it would be a good way to keep your PC secure. Workplace hijinks can occasionally cause heartburn, so I know several coworkers who lock their PC when away from their desks. I'd prefer to have it lock itself after 2 minutes of no action, then have it automagically unlock when I get back to my desk. Thus, an RFID reader that detects a tag I have in a ring I wear and unlocks the computer for me.

Next project- an RFID tag in a ring. :-)

April maker challenge 20- POV display

2009-04-28T14:26:00.000-07:00

The MiniPOV is an Adafruit toy that provides a discreet package for POV (persistence of vision) display. Normally, POV displays involve lights that are mounted to a moving arm or wheel. As the lights are swept across a person's field of vision, the slow response time of our vision receptors causes us to detect the changing light patterns as an image.

The MiniPOV depends on a person to provide the motion. Instead of being mounted to a moving object, the user holds it in his or her hand and sweeps it through an arc, providing the motion.

That's pretty cool, but it's also kinda small- it fits into an Altoid tin. I'd like to make a larger one- say, 12" long, with one LED every half- or quarter-inch. My deeply subversive application is to press this up against the window of my bus as it drives past all the suckers stuck in traffic on the highway, flashing a message to hopefully get them to consider some alternative to single-commuter driving.

April maker challenge 19- Inductive lamps

2009-04-28T14:21:00.000-07:00

I used to have one of those super fancy Phillips electric toothbrushes. One of the cool features of it was that it charged by sitting in a cradle that inductively coupled to the toothbrush handle, so the handle could be sealed water tight and yet still accept a charge.

I'm fascinated by this and by the potential associated therewith. I'd love to try using this for other applications. The easiest is a setup where a coil placed under a table passes power to a device sitting on the table, and the most obvious candidate would be a reading lamp or a centerpiece that has lights involved. The result is a cool centerpiece that lights up without the inconvenience of running a cord across the table.

April maker challenge 18- LED based "candles"

2009-04-28T14:12:00.000-07:00

This is a pretty common consumer product: a device approximately the size of a votive or maybe a tealight that behaves basically like a candle, in that it has a small LED that flickers and fades. The reason I want to make one rather than just buying it is that I have a special need- to be able to turn it on and off without contacting it. A few years ago I made some balsa and paper lanterns that can be hung from the ceiling on a string. A tealight in the bottom provides nice light, and the dozen or so that I made create a very warm atmosphere in a room where they are the sole illumination.

Of course, lighting all those candles is no fun. It requires hauling a chair around the room, getting up and down, and trying not to catch the paper on fire. Putting them out is similarly taxing, unless you let them burn down over four to five hours. Obviously an application ripe for electronify-ing, but an electronic light has the same problem: to turn it on, you need to get up on a chair, pull the light out of the lantern, turn it on, and drop it back in. I know, not SUCH a huge deal, but still more than one wants to do regularly.

So, my solution is a pretty simple one: make the lights magnetically switched. It's pretty simple to do- just put a reed relay in the system and drive the thing with a PIC. The PIC stays in sleep mode until you activate the relay, then it flickers the LED until you activate the reed relay again. Activation of the reed relay just requires waving a magnet on a stick near the lantern. A PIC in sleep mode can sit in a circuit with a couple of AA batteries for months without draining them.

April maker challenge 17- Tachometer glove

2009-04-28T14:01:00.000-07:00

Four, this time, because I know I'm going to go today and tomorrow without having another chance, since I'm moving tomorrow and I'm not going to have Internet access at home or work (eep).

Tachometer glove for race driving- I USED to have a zippy car (VW Jetta GLI), and I always had a hard time knowing where the tach was. I thought it might be nice to have feedback that didn't rely on vision (because taking your eyes off the road at certain times can be...dumb is the best word I can find) or sound (because open windows, music, road noise, and other things can distract you from the actual sound of your engine.

My idea was a pretty simple one- you put a pager motor on the back of a glove that fits snugly, so that the motor is held tightly against the bones to get maximum sensation. I'd guess a wireless link (Zigbee or Bluetooth or IR or whatever) would be most appropriate, and the motor would vibrate at a frequency either equal to or proportional to your engine RPM, providing simple physical feedback that is hard to obscure.

April maker challenge 16- portable collapsible squat bar for birth

2009-04-25T19:40:00.000-07:00

My wife is pregnant. She is very interested in pursuing natural childbirth practices, and one of those is the idea that squatting during childbirth is preferable to being flat on the back.

We have some concern that our chosen birthing "venue" (Fairview Riverside) may not have the necessary item for facilitating this position, and I desperately want to support my wife's birth plan, so I'm thinking about figuring out what exactly is required for this and trying to make it real and portable in the next six months. I'm guessing there are other women out there who might want this sort of thing as well.

April maker challenge 14 and 15- camping stove and micro-preamp

2009-04-24T09:56:00.000-07:00

I'm just going to give up trying to do one a day and go for two every two days. It seems more believable for me.

I have a small interest in camping, which I'd like to make into a larger interest in camping. One of my very favorite camp toys is the penny stove-an ultralight alcohol fueled stove made from two Heineken cans and a penny. Yes, they do have to be Heineken cans- the shape is important.

I have two of these little fellas and they work GREAT. A few mL of denatured alcohol into the stove is enough to boil a quart of water long enough to cook noodles, or make rice, or whatever. There are three other things I'd like to make in relation to these, though- a heat concentrator, a nice stand, and a larger burner version. In reverse order:

Heineken comes in 12 ounce cans or 24(?) ounce cans. I'd like to buy a couple of the big ones and make an uberstove. Just for kicks.

My current stands are two bent-up coat hangers. They require fairly level ground and are kind of wobbly. I'd like to make something more sturdy, possibly collapsible and possibly with a bit of leeway for unstable or unlevel surfaces.

The last I'm stealing from another AMC post: a heat concentrator. I'd like a highly portable and very easily used device that wraps around my stove, stand, and pot, which keeps the hot air coming up off the stove flowing along the sides of the pot instead of letting it disperse. I'm expecting this would make the penny stove much more efficient.

Next idea- micro-preamp. I have an interest in foley artistry (not that I've ever done anything about that interest) and I always have my MP3 player with me. My MP3 player has an input jack which apparently has a fairly high high input impedance. I also have a tiny little microphone which has a fairly high output impedance. I'd like to make a super-simple lo-fi amplifier that I could plug in to the MP3 player for when I find a really fun sound in the environment. I could then later collect these sounds, play with them, and possibly offer them to the world. Ideally, it would be powered by a button-cell battery and have an off switch to avoid draining it too badly (although that might be unnecessary if I design the circuit right). In fact, a REALLY fun trick would be an amplifier that could work on a charged capacitor rather than a button cell- must consider that.

April maker challenge 12 and 13- Jacob's Ladder and raised garden beds

2009-04-22T14:46:00.000-07:00

Two-fer today, to make up for yesterday. I wish I could get it together and post daily.

The first is a simple Jacob's ladder. I've always wanted one of these and it's an affront to my tinkering nature that more than 10 years after I started into electronics, I still haven't made one up.

The second is a raised garden bed for my vegetable garden. We'll be moving next week (eep!) and I have no interest in tilling up a large patch of yard in a rental property, and I'll need to buy some kind of soil to make it support plants anyway (there's little chance of success in the area I'll be living in without doing so, due to the advanced age of the neighborhood), so I'm thinking I'll build beds on legs, about two feet high and four feet by eight feet. I figure that'll make it easy to work them, and you should be able to reach the middle pretty easily. Good drainage, etc.

My company has a demo dumpster FULL of old shipping crates made of 1/2" plywood with a 2x4 frame. These should make wonderful box bottoms. There's other wood in there, too, that'll be perfect for the legs and sides. Free is good!

April maker challenge 11- IRduino

2009-04-20T17:48:00.000-07:00

I like the Arduino as a simple computing platform, but I've mentioned here before that I'd like to offload some of the more basic functions to a co-processor to let the Arduino have more CPU cycles for other stuff.

That's true for many, MANY tasks, and one of the ones I've been fascinated with since college is the capturing and parsing of data from an infrared remote control. Adding IR to your project is a SUPERB way to add very complex I/O.

I'm not sure if the Arduino has a library to read IR from remote controls, nor do I care, because it's likely to suck up an unacceptable number of CPU cycles. Thus, the IRduino: a shield with a small microprocessor (I'll probably use a PIC, since I know how to work those much better than AVRs) which decodes the signals from infrared remotes, packs it into three or four bytes (there are actually a LOT of possible codes out there, due to the number of encoding schemes). There would then be several options for sending this to the Arduino- a semaphore based scheme, a "dump-on-receipt" option, a "hold-until-request" option. Others, perhaps.

April maker challenge 10- Self-destructing USB drive

2009-04-20T06:30:00.000-07:00

So, since DHS can swipe your stuff at a security checkpoint for no good reason, I've been thinking I might like to make a self-destructing USB drive.

There are two possible tacks for this: one, a "snappable" drive where there's a small ampule that one would crush (a la cold war suicide pills) that connects an on-board 3V lithium battery backwards across a couple of pins, roasting some silicon and making the drive pretty much irrecoverable. I guess in the end, it would be difficult to completely wipe out the entire flash matrix, but it's a start. This has a disadvantage in that you need to KNOW someone is ABOUT to take your flash drive away in order to activate it.

The other method is a simple wire and switch method, where the drive is modified to reverse the 5V and ground unless the user does something to reverse that. The easy way is to put a switch on the drive which has to be flipped; that of course draws attention to the mechanism. A subtler method involves an internal reed relay that requires a magnet to be close to it in order to operate safely. That's less discoverable, but you're more apt to accidentally forget to do it and kill the drive yourself.

Of course, if one were to productize this, it would fail instantly, because DHS would become aware of it and all would be lost. You also need to make the hack relatively invisible; if it's not, you'll draw additional attention and make it MORE likely that the drive is confiscated.

This is, of course, the Sunday project. Another will follow later today.

April Maker challenge 9- mixer to food mill adapter

2009-04-18T19:40:00.000-07:00

In canning, when making sauce or jelly, the easiest way to go is to use a strainer to separate seeds and peels from the desired fruit meat. The drawback is you get crank arm eventually, because you have to turn the crank for sometimes up to a couple of hours at a stretch and, while it's not terribly physically demanding, the long throw of the crank means that your whole arm is involved which can really wear on the joints.

To that end, I've decided to make myself an adapter that will let me join my strainer to the PTO (or whatever it's actually called) on the front of my KitchenAid mixer. I bought a couple of universal joints at Ax-man that should do the trick nicely (necessary because the height of the mixer PTO and the height of the mill axis are not the same; I considered making a platform that the mixer can sit on and the mill could clamp to which would position the two machines to be coaxial but frankly, I'm not crazy about having to line them up THAT carefully every time, so two U-joints it is). This is going to take me a couple of hours in the machine shop probably, but since I had the mill already, buying the attachment for the mixer would have felt like a waste. Plus, I like the idea of being able to drive it by hand if necessary.

April maker challenge 8- Outdoor canning kitchen

2009-04-17T11:59:00.000-07:00

Canning in the house sucks. It involves putting a pot of water on to boil for hours at a time (some canned goods must be boiled for 30 minutes or more, and if you're doing it, you probably want to do enough to make it worth your time, so that means several rounds), tying up the whole kitchen, and release about a bazillion joules of heat-energy into your home. By the way, did I mention that this can only be done during the hottest months of the year? Yeah.

Beth and I are moving into a rental house in a couple of weeks, and I'd like to make an outdoor canning kitchen (I bet you though ALL my projects were electronics...). What I have in mind is a couple of those turkey deep fryer things, connected together through some kind of Y-valve, with a nice frame of some sort to add stability. A bench, too, probably. I can't build this stuff in because this is a rental, so it'll be an interesting challenge to see how I can do it.

Superhack power supply

2009-04-16T17:06:00.000-07:00

(click to enlarge)

I'm not going to count this in the April Maker challenge. I don't know why.

I hacked together a really hokey power supply for my tabletop foam cutter and as-yet-unbuilt acrylic bender (although strictly speaking, the portion of the foam cutter heating element that runs underneath the acrylic "table" has done a nice job of melting it). JTBarclay is using it for driving a 24V nigh-5W fan under a stir-plate, and Pat is building one for HIS foam cutter.

It does a fairly good job, although it has no check on the amount of current it draws from the unregulated DC supply, which is a MAJOR short coming. The IC is an 8-pin PIC that I've programmed with a PWM controller that reads a pot to determine the duty cycle (at least, in this configuration it does). Because of the way the design works, you can put a limit on the duty cycle by inserting a resistor between the potentiometer and the ground rail. Using a smaller potentiometer is wise if you were going to do that- you want to keep the overall resistance down. The larger the resistor, the lower the maximum duty cycle will be. If the resistor is equal to the value of the potentiometer, you'll be limited to a 50% duty cycle; if it is twice the pot's value, you'll be limited to 33%. The equation is Rpot / (Rpot + Rbias), where Rbias is the value of the added resistor.

April Maker challenge 6 and 7- Mini-lathe and RepscRap

2009-04-16T16:03:00.000-07:00

I keep falling behind, but I'll not be more than one day back, dammit!

Number 6- A mini-lathe. One of the most common things I use a lathe for is the drilling of a concentric hole (or reaming one out) in a circular object (gears and wheels, for instance). I don't need a super-accurate means to reduce a diameter or things like that, just a way to put a hole in the exact center of a gear when I'm trying to mate it to a particular shaft (of a potentiometer, or encoder, or what have you). I guess "lathe" is the wrong term, but it's the best I have.

Number 7- RepscRap. The RepRap, of course, is the open-source self-replicating 3d part printer. The RepscRap is an extension to that, a device which allows the reclamation of plastic material of appropriate composition by shredding it, melting it, and extruding it as a stick or rod the can be re-used in a RepRap. The material would be recaptured from junked electronics, pop bottles, or whatever uniform source of approrpriate material. Of course, I need to make a RepRap before this matters.

April maker challenge 4 and 5- Acrylic bender and tabletop foam cutter

2009-04-14T10:39:00.000-07:00

I'm a day behind so it's a two-for-one, but a quickie, because I'm behind in every possible metric my life could be measured in.

Number 4 is a tabletop hot-wire foam cutter. Imagine a scrollsaw or bandsaw, but instead of a saw blade, using a piece of hot wire. It excels in cutting intricate shapes out of pieces of expanded polystyrene foam, and can be used on other thin and low-density plastics as well.

Number 5 is an extension of this. By putting the hot wire at the edge of a table, along the corner, a piece of acrylic can be heated evenly along a line, which will allow it to be bent.

Both of these use the same power supply. That will be described as a future project.

April Maker challenge 3- Tamiya servo conversion

2009-04-12T07:52:00.000-07:00

Tamiya is a Japanese company that makes many hobby-type products- model kits, "experiment" sets, RC toys, and others. Deeply buried in their product line is a set of generic motor/gearbox combinations.

These range from very simple to very complex; I have a couple of their high-power ones, and one of the 6-speed ones as well. They are well constructed, fairly tightly toleranced, and loaded with features. The have a twin-axis gearbox, a worm drive gearbox, and a planetary gearbox, in addition to more "standard" types. Typical cost is between $10 and $20, depending on the model.

One of the most enjoyable items in the hobbyist robotics arsenal is the RC servo. However, most servo motors tend to be either pricey or weak, and they tend to be non-reconfigurable, meaning that you can't readily trade off speed for torque or vice-versa.

To that end, I'd like to make a small PCB that would let me take an input from a shaftless potentiometer attached to the output shaft of a Tamiya gearbox and turn the gearbox into a servo. Target cost would be $10 or less in parts, because that puts a Tamiya gearbox + this circuit in a price range to be MUCH better placed than a comparable servo.

April Maker challenge 2- servo driver IC

2009-04-11T09:40:00.000-07:00

Lately I've become obsessed with multiprocessing solutions for hobby level embedded systems. A PIC12F683 is a reasonably powerful 8-bit microcontroller in an 8-pin package, and it sells for right around $1 in qty 25. This can provide a powerful means for offloading certain functions of a circuit to another IC at minimal cost, allowing you to do heavier lifting in your main circuit than you otherwise might have. An example is servo-motor control with the Arduino. It's quite do-able, but you may find yourself in a project where you want to control a servo's rotational position based on user input from a potentiometer. In that case, using precious CPU cycles from the Arduino in the system just to read the pot and update the servo periodically is a drag. So why not take an 8-pin PIC and make a simple IC that reads digital inputs and converts the value to a servo angle?

It'd be easy enough- the servo output is a PWM signal but the duty cycle is low. The motor holds position expecting a pulse every 20ms, and the pulse is usually in the range of 1-2ms for 0° to 180°. That leaves you a minimum of 18ms to read the analog voltage(s) and calculate the next pulse length. At 8MHz (the maximum internal clock speed of the '683), each instruction is 500ns in length. If we do 8-bit math, we can have 256 variations representing 0° to 180°. Making the assumption that the pulse needs to be 1.5ms +/- .5ms, we have a 1ms dynamic range to express with 256 slices- about 4us per slice or 8 instruction cycles. I think that's probably enough time to do a pretty accurate timing routine for three channels, using three analog inputs, which is handy, because the '683 has 6 I/O pins, so that's three analog ins and three pulse outs.

April Maker challenge- project 1

2009-04-10T16:23:00.000-07:00

Over on the TCMaker web forum, a challenge was levied to all of us to come up with one project every day during the month of April. I'm behind, because I've been VERY busy preparing for and teaching my intro to electronics class through Studio Bricolage, but I'm going to try VERY hard to keep up with it for the rest of the month. Hence, the new blog.

Project 1: Airsoft pellet gun organ
Ax-man sells Airsoft pellet guns super cheap (~$10 for a pistol). I'm thinking it might be fun to try to make a pipe organ that articulates based on having the pellets fired down the pipes, which would then dump the pellets into a bin for immediate re-use.

It might get pricey, since I'm thinking I'd want the seven major notes, but I'm not sure how I'd go about tuning them or even what effect firing a pellet down a tube would have. Still, it might be cool to try out.