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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The gift that never ends

This winter I had the idea of donating my old Cupcake CNC to the local library. Get it out of the basement, I thought. Put it where other people can use it. Find a home for all that extra 3mm filament that ain’t going in any of the printrbots.

What I didn’t realize was how many of the old machine’s quirks I had subsconsciously memorized, and just how finicky the toolchain has become in the years since I started using it. So I’ve been spending a lot of time at the library debugging, re-implementing, fixing, coaxing, undoing smart things that other people have tried to do…

Start with the tools: the only thing that will (apparently) talk to the cupcake is ReplicatorG. Because I’d have to build a machine-description file from scratch for any other host software, and bodging one together for ReplicatorG was painful enough. (Why yes, I did build my own custom geared extruder, and added a 3d-party stepper board to run it because, ages ago, I blew out one of the motor-driver chips on the extruder board that could otherwise be used for stepping.)

ReplicatorG means Skeinforge, with all of its interestingly-organized settings. And Print-O-matic, which gleefully ignores some but not all of those settings. (In particular, it ignores the temperature panel, which is probably a good thing to know before you start wondering why your hot end is extruding at ABS temperatures, no matter how many times you adjust the layer temperatures to be right for PLA.) At one point it seemed that the workflow would involve simply editing the g-code every time to get the right values.

So I got that stuff fixed, and darned if the kid I’d been teaching how to use the thing didn’t change some of the settings,  replug the USB adaptor cable into a whole different board and somehow cover the entire build surface with a thin, irregular layer of oozed PLA. Do you think perhaps I should write just a little bit in the way of documentation?

Today I go in to fix things again, and to substitute an unheated build platform covered in blue tape for the heated one. If all we’re printing is PLA it shouldn’t be a problem. Except, of course, rewriting the machine description file to compensate for the new distance between the platform and the endstop…

Oh, and did I mention that because this is a donated machine and not blessed by the IT department, it can’t thus far be connected to the library network?


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What time is it?

My next kit build is an Ice Tube clock from Adafruit. Which brings back lots of memories, because one of the first kits I built and wrote about was a nixie clock from Jeff Thomas, who was pretty much the founder of the modern nixie resurgence.

Times have changed since 2003. I’ve got a much better soldering iron, with a finer tip, and I wear serious magnifiers now. I’ve also built enough things that I’ve started to develop a sense of how kit instructions should go and PCBs should be laid out.

Or at least I thought I had. One the one hand, the “build a subsection and then test it before going on” methodology is helpful, especially for people who aren’t that great at soldering or placing components. On the other hand, it’s weird for anyone who’s used to just putting stuff in place, turning the board over and soldering everything. Some of the first things to go in were the tall stuff — sockets, big capacitors and such — which made sneaking the little resistors and caps and diodes in among them a little harder for the thick-fingered.

On the other hand, the step-by step testing came in handy when I soldered the piezo speaker where the inductor was supposed to go (but on the third hand, please more perspicuous positioning for the silk-screen labels — when you have a round outline that says “spkr” inside it, people can be forgiven for thinking that’s where the speaker goes, especially when the leads are a perfect fit.)

The vacuum fluorescent tube is just plain weird, with a bunch of thin, flexible uninsulated wires coming out. Having a set of evenly spaced holes around a circle was probably as good as any other way to connect it, although the holes could have been a touch bigger and made it less terrifying to pull the wires through. (The original nixie clock had this weird procedure where you put individual metal sockets onto the bottom of each tube, then aligned them inside oversize holes and filled in with solder. Tolerances have changed in 50 years.)

Anything with lots of fine leads is a pain. The chip carrier for the high-voltage tube driver had gotten mashed somewhere in the kitting/shipping/storage process, so it took a half our or so to straighten all the pins so they would fit their holes. More interesting because of course you can’t see the inner layers while you’re actually trying to insert the carrier. Maybe I need another level of magnifier.

Does it work? Yep, just fine. It won’t keep nearly as good time as its older cousin, because it uses a mere crystal instead of a surplus cellphone GPS unit, but that’s OK. The instructions for resetting the time are thoughtfully laser-etched onto the bottom of the case, instead of buried in a magnet-activated menu system that requires you to know your offset from GMT. I wonder whether, over the years, the VFD segments will start fading around the edges the way the nixie numerals have.

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I like Octoprint

So I was sitting upstairs where it’s warm, instead of down in the cold basement, and suddenly I had the idea to print something I’ve been noodling on for a while. Click. Click. Click. Move the Octoprint browser window so I could see it while I kept doing other stuff. 23 minutes and 16 seconds later, the part is done. Maybe when I go downstairs to fix lunch I’ll take the part off the bed.

Somewhat appropriately, it’s a piece to adapt the pi camera to a 2x tele-extender from a digital camera I had about 12 years ago. So the field of view on my remote Octoprint window will mostly show the print instead of mostly showing the frame of my printer and the surrounding basement.

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Who needs a laser cutter?

scrollbigscrollkerfWell, I do. Or at least I want one. But cutting out a bunch of parts on a scroll saw in the past few days has given me new appreciation of what can be done with simple tools. The kerf is not much bigger than a laser’s (plus, no soot stains).


I found myself comparing the workflow for this project if I’d had a laser cutter handy versus what I’m actually doing.

I’m making stamp pads for an animal-track unit at the 7-year-old’s school: wood blocks with craft-foam outlines (lifesize) of the tracks of various local creatures. I glued one set of tracks onto a piece of wood, cut out the blocks, then traced around those to make another three sets. Next: apply craft foam to the blocks, stick paper track templates to the foam, cut away everything that’s not track. A few hours work, most of it pretty mindless, the kind of thing you can do watching tv with the kids.

If I had a handy laser cutter, a lot would depend on whether I could get the track images in digital form or had a Glowforge with its magic camera. Otherwise, careful scanning or photography, followed by careful printing to make sure the sizes were right and there was no perspective skew. From there it would be pretty simple: Cut the wood (three times, to make up for only being able to cut 1/4-inch stock) and engrave the track marks on the top panel for a guide. Then cut the craft foam with the same file and stick all the little bits on, using the engraving as a guide. Finish gluing up the blocks. Not entirely sure which would be simpler; most of the work that’s eliminated by the laser is busywork, which could be either good or bad.

But I’m beginning to think about some kind of hybrid workflow for woodworking projects, where the laser does marking, engraving and maybe shallow cuts, followed by real blades. If I had a laser head mounted on something like a 4×8 Crawlbot I could mark everything for even the largest project in a single pass and then cut with a conventional blade.

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