Buy extension cords, not wire

When you’re in the sticks, your supply options are limited. That’s why the other day I bought a couple of extension cords instead of the bulk wire that was right on the other side of the aisle at the hardware store. I needed some 16-gauge and 18-gauge wire because the 14 and 12 I had wouldn’t fit into the terminal block of the gadget I was building.

The 16-gauge 2-conductor bulk wire, aka lamp cord, was 69 cents a foot. So was the 18-gauge. So was pretty much every other %#% bit of bulk wire they had on the shelf. The 15-foot 16-gauge extension cord was $6.99, and 8-foot 18-gauge was 4.99. And I have some nice plus I can splice in somewhere if I need them.

It makes sense from the store’s point of view, because most of the time for them the cost isn’t so much the wire as the employee getting the spool down from the shelf, finding the wire cutters, measuring out the length, and probably engaging in a little conversation to make sure the customer isn’t going to appear in tomorrow’s newspaper. But for me, with cutters and crimpers and strippers galore, it’s way easier to do my own. Of course if I needed a longer wire run than the extension cords allowed, I might have to fall back on the bulk stuff. But if I needed a longer wire run and was planning on using lamp cord, that would probably be a sign I was doing something wrong.

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Solder first, Trim Headers Later

I had a bunch of Adafruit Metro Minis to solder up for a workshop I’m teaching, and –as usual — almost all the header strips were longer than they needed to be. I guess it’s much quicker to pack a few extra than to cut each strip to precisely the right length, and the offcuts will certainly find use.

But the cool thing is that the metro mini’s mounting holes are placed just right so that you can just jam the entire header strip onto the board and leave the excess hanging over the end. Then, after everything is soldered, go back and clip. Definitely faster, and almost certainly saved me from counting wrong on at least one strip. I don’t know if it was an intentional part of the design or accidental, but if it was accidental please do it again.


As you can see from the closeup, the mounting hole isn’t exactly in line with the headers, so there’s a little bit of a jam that holds the headers in place. Better yet. (Oh, and just by the way, I was originally planning to use Trinkets, but the short-duration USB thing is one more headache for students who aren’t that computer-savvy in the first place.)

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A really stupid feature set

In the process of getting solar panels, we talked ourselves into a heat pump with a couple of split heating/cooling units (gotta find something for all those nice renewable kilowatts to do). But it turns out that Mitsubishi designers are either not very smart or really, really want to sell upgrades.

In particular: there’s a button you can push to change from your current setting to a pre-stored alternate setting; there’s also a button for setting a timer to turn the unit on or off according to a schedule. But — unlike pretty much every conventional thermostat built since the energy crisis of the 1970s — there is no way to change the thermostat according to a schedule so that it’s, say, cooler at night than during the day. Some web searches suggest that we might be able to get a wifi-enabled add-on that would let us schedule our heating and cooling with an app. From anywhere in the world.

Oh, and all this is operated by a remote control that is not coded to any specific heating/cooling unit. So if you have two units (say, upstairs and downstairs) and it’s possible for a nice strong IR light to bounce off walls and through doors from the vicinity of one unit to the vicinity of the other…

Maybe when I build the IR-proof flaps that keep both units from doing everything in synchrony I’ll just add a controller that captures some of the signals and includes an RTC. (Even though the local rep has warned me that customers who tried to make their heating/cooling units change their thermostats according to a schedule have experienced unwanted Service Calls.)


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Lubricate your fans

(tl;dr: if you have a fan that cools your hot end or heat break, lubricate it. It may solve some problems.)

It’s a good thing I splurged on the dual extruder for my printrbot way back when. Not that I use it very often, but entirely by accident it saved me from going down a diagnostic rabbit hole.

I’ve been printing car bodies for a little mobile-robot workshop at the 11-year-old’s school, and I finished a roll of PET+, so I decided to do the rest of them in PLA. Cued up a roll, did some test extrusions, started the print. Jammed. Cranked up the temp, ran about a foot of filament to clean out any PET+ remnants, started again, jammed again.

For about an hour I went through the same cycle with different rolls of PLA, cold-pull, “cleaning filament” etcetera. When I did a series of text extrusions, things were fine, but when I tried to print, jam. I got ready to disassemble my hot end, but.

Just to procrastinate a little, I decided to deal with the fan on the second hot end, which had been stopping randomly for a few months — it’s always on, because that’s the way the printrbot does the fans on the all-metal hot ends, but I hadn’t actually been printing with it, so I didn’t worry too much. So I read up on fan lubrication, and while I was doing the one, I figured I might as well do the other fan, on the hot end that I do use. It hadn’t been stopping or making noise, but what the heck.

Guess what. I thought the fan on the primary hot end was running fine, but apparently it wasn’t. Because now both fans are running, and I just ran the same hour-long build that was jamming consistently, without a single hitch.

Note to self: consider building a cheapjack tachometer to see when the fan slows down.

Other note to self: consider printing up little caps for the lubricant well around the sleeve bearing, because apparently cheap 30mm fans don’t bother with those.

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Everything is parallel

Or at least multithreaded. I was prototyping some vaguely image-related ideas in Processing, and decided that I wanted to pick which image file I was going to mess with on the fly rather than hard-coding the filename and path into the program. Down the rabbit hole I went.

Processing has a function for using your operating system’s select-a-file dialog. But because of the way that I/O is handled, it can’t just return a value containing/pointing to the file you selected. You have to specify a callback that — oh, wait, the callback can’t return a value either, it has to modify a previously-defined global variable.  (The Processing language reference conveniently sidesteps this twist by providing an example that simply prints the selected file name to the console.)

So I put the file-selection magic in the setup function for my code, which runs before the main loop. The main loop ran, and then the selection dialog popped up. Huh? Oh, right, multithreading. The code in setup() returns as soon as it’s told the operating system what it wants and what callback to trigger. The fact that nothing substantive has been accomplished yet is irrelevant.

I have to admit to feeling just a tiny bit like a real programmer when I added a semaphore to the file-selection callback and the main loop. Now the main loop spins cheerfully at 30 frames a second doing nothing until I pick a file. Oh, and I want an output file too. Good thing my code doesn’t actually do anything.

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The autopilot conundrum

This morning I stopped by a local school where some of the kids had crowdfunded a 3D printer (a printrbot Play) to see if I could help them get it working. I seem to have become the town expert, which is a frightening thought.

The machine had never worked for them. One of the axes apparently jammed somehow either during shipping or initial setup (the kid who was mostly in charge of it described multiple episodes of that rattling noise that comes with a skipping stepper motor and his immediate response of pulling the power plug). And when I got to it, it wasn’t responding at all.

So we reinstalled drivers, swapped in a known-good USB cable, reinstalled Cura, tried Cura on my linux laptop. Nothing. The furthest we got was “Opening serial port …. Closing serial port.” And on the laptop, “lsusb” reported no change when the machine was plugged in. Eep. A blown board didn’t seem that likely, and yet.

So as a last resort we turned the Play on its side and I held the ground shield of a spare USB dongle against the firmware-update pins (we didn’t have a jumper handy) while the kid plugged in power and pressed the reset button. This time “lsusb” reported an Atmel DFU device, which means the printrboard is probably OK, it’s just that the stepper blowback or the constant unplugging and replugging borked its firmware. So tomorrow I drop off a jumper, and the kid finds the instructions for downloading and reflashing. All in a morning’s work.

Except that before we ran through all that diagnosis, these folks were pretty much convinced they’d flushed $400 (plus shipping and filament) down the toilet. When you make a machine that Just Works and can be operated by people with little to no expertise — which Cura also helps enable — it’s really great.

But when anything goes wrong, it’s like throwing a toddler into the deep end.  All the simplifications and pre-built configurations that make a combination like the Play and Cura suitable for schools mean that you’re not going to run into the usual teething problems of getting a printer going. Only the unusual ones, which may even be hard for a relative veteran to diagnose and fix. And that’s a recipe for trouble.

Not that I have any good solutions. Either newbies still have to learn a lot more, or mass-market printers have to become orders of magnitude more bullet- and fo0l-proof (which means more expensive and/or much slower to arrive). Or veteran volunteers need to be thicker on the ground.


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There’s a reason some things are surplus

The 11-year-old has been bugging me for a few years now that he wants to build a crystal radio set, and sourcing the parts individually is something of a pain. So when I saw a kit for cheap at a surplus site, I thought: Cool!

Perhaps not. After a couple of tries we got the antenna wire wound onto the cardboard tube (barely — about half an inch so spare on each side when all the turns are solidly butted against each other) only to find that the holes in the molded, foldable plastic sheet that serves as the frame aren’t quite big enough for the tube.

Sorted that. Turns out the tabs that are supposed to lock the frame together when you fold the sides up, don’t. Sorted that too.

Then the 11-year-old, who had been doing pretty well with the instructions, asked me to interpret a paragraph that apparently referred to the two pieces of extra wire in the kit, one of them as “the second wire” and the other as “the other wire”. We duly hooked them up to the places specified. After spending several minutes with the wire stripper trying to find that tiny little thread of metal inside the tough rubber insulator.

Nothing. Nada. Less than the crackling we got just touching the earphone wires to metal objects.

So the kid went back to playing retro video games while I reread the instructions and looked at the circuit to figure out what it thought it did. Turns out “second wire” and “other wire” are synonyms. Time to undo and redo some tiny bolts and washers. Then I read further in the little booklet and found the instructions for connecting one wire to a cold water tap (because we live in a parallel universe where no one invented PEX or nylon and so all water taps are connected to ground) and then holding the other wire in your hand while with your other hands you hold the kit and move the little tuning ball across the antenna.

Did that, actually got some 60-cycle hum. It’s a beginning, and the kid was not entirely disappointed.


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