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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Progress is Bad

I’ve been working for a while on a wearable accelerometer/datalogger project, and I came up with a nice breadboard prototype using a spare Seeduino Stalker plus a bunch of other parts. But that’s kinda big to actually wear. Next up: a handy Micropython board: it’s small, it has a real-time clock, it’s way easy to code, but wait: the accelerometer returns all of five bits of resolution. It can tell upsidedown from right side up from sideways, but not much more.

So when I saw Adafruit’s lovely little Feather logging board it seemed perfect. Small, plenty of pins, LiPo battery socket and USB charging. (And unlike my Stalker, the micro-SD holder doesn’t fall open at inconvenient moments.)

What a terrible mistake learning experience.

When I wrote my code for the Stalker, I was using Arduino 1.06, because I hadn’t needed to upgrade (and the newer versions don’t work on my old mac anyway). But the Feather board uses the fancy new Board Manager magic in Arduino 1.6.x to install its pin descriptions and so forth. So off I went to install the newest version.

Now the lovely SDfat library I was using (fast, long file names) wouldn’t install, and even after I tried to install it by hand kept showing up as “invalid library”, because the Arduino folks have decided that there must be Order and Rules for how the files in libraries are arranged. And a properties file. (Which I understand in principle, but in practice “All that stuff you relied on that formerly worked is now broken” does not win friends.)

So I mucked around with that for a while, and complained in forum where a nice person said “Oh, yeah, the latest versions of the IDE aren’t so hot, downgrade to 1.6.5 and your library should work.” And (after a little more mucking) so it did.

New IDE capable of recognizing board, check. New configuration of SdFat library, check. But wait. All the real-time clock breakouts I have are 5-volt only, except for one that’s huge. Time to order a 3.3v RTC. Wait for it to arrive.

Put all the hardware parts together. Test compilation of old stalker program to see if the software parts will fit. Boom. Nothing works. Error messages claim files I know are there are missing. Messing with the include statements just produces more error messages. A search to figure out how I am messing up reveals that oops! the latest version of the core board descriptions file  installed by the magical Board Manager is not compatible with previous versions of the IDE. Tell the Board Manager to install the previous version instead. Hurrah! Everything compiles.

Doesn’t work, though. Feather just sits there when I try to get information from the serial port. All the power lights are on, but nobody is home. Maybe the new RTC really isn’t 3.3volt capable? Wouldn’t be the first time a seller stretched the truth on amazon. I get a regular arduino and try the clock there. Also nothing. Load up the I2c scanning sketch. Nerp.

Hmm, maybe I need pullup resistors? The nonexistent documentation was fuzzy on that point — some I2C devices have them built-in, some don’t. I break out the multimeter, and measure 4680 ohms between the clock line and Vcc, 4720 ohms between the data line and Vcc. Pullups are supposed to be 4.7K ohms. Just for the heck of it I measure between Vcc and ground: 400 ohms. Erm. That probably ain’t right, considering that realtime clocks are supposed to draw a few microamps.

Luckily, the boards were cheap so I’d ordered two of them. I popped the second one into the original circuit and golly if it didn’t come right up where it was supposed to.

Total time spent mucking around on something that should have been a simple swap of one microcontroller board for another: almost two weeks.


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A child of the 80s

Sometimes I wonder if the 11-year-old is too retro. His current hobby is playing an emulated version of Street Fighter 2 on his PC. And now that a vintage-gaming store has opened in the next town over, he pretty much wants to buy out their stock. (Lucky there’s still one standard-def TV in the house)

But he’s also kinda modern. So when we came across an ancient Atari-style joystick, he looked at it and said, “Hey dad, how about a Teensy in HID mode?”

We opened it up (which required drilling out one of the case screws that was apparently sealed with glue) and I soldered all the old connector clips to the circuit board, then clipped the wires short and soldered them to a spare Teensy 2.0. Anybody need a 9-pin Atari-style cable with only 6 sockets populated?

He mostly took it from there. I told him which pins I’d attached the wires to, and he fired up a copy of the Arduino IDE, found an example program that read a switch and bodged it to what he needed. Didn’t work. A day or two later he came to me and I thought about it,  realized how foolish I’d been, and said “Change all your pinmodes from INPUT to INPUT_PULLUP.” He did, and now the thing works.

Wonder what he’s going to do next.

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cleaning out the basement one bright idea at a time

When we were making new year’s resolutions last month, mine was to, y’know, build some of the cool kits and kit-like part collections I’ve acquired over the years.

First up: Solarbotics marble machine. Cute, simple, less than an hour build time if you don’t count waiting for the glue to dry.  Laser-cut frame, less than a dozen solder joints. I only managed to assemble two of the sections backwards, and just broke/lost one piece taking them apart, so I think it was a success. (And thanks, Solarbotics, for making some of the waste pieces from the gear-wheel supports exactly the same width as the tab that aligns the wheel layers.)

It’s a mostly glue-optional kit, because all of the tolerances on the laser-cut pieces are close enough that you have to hammer lightly on the bits to get them to go together, or somehow put all of your weight on one thumb. Which bodes well for it holding together longterm.

If I had been smarter, I would have done a test fit of the electronics and the structural bits before soldering, because some of the placements are not what they seem from looking at the instructions. The spacing of the pads on the circuit board (which is cleverly made part of the back of the solar cell) looks as if you can just tack down the component leads after trimming them to length, but no. The leads also need to be a bit longer than the nominal 3/8″ for some of the components to comfortably clear the body of the gearmotor, and the leads on the big capacitor need to be shorter to clear the marble race. But it all worked out.

The other thing I learned is just how pitifully weak northern sunlight is in the winter. I brought the completed marble machine to our front window to see how it moved; the instructions say it should pulse every 2-5 seconds, but nope. More like every 15-20. Maybe I’ll rethink that rooftop solar-panel installation I’ve been yearning for.

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more heated chamber


I think this is a pretty good indicator. Both prints using the same spool of ABS (which my friend Tyler at filabot dropped off for playing with because of the nonuniform color). Right without a chamber, left with chamber. The right one also suffers from cracking problems because it was about 7% under-extruded, but I don’t think that would have helped the warp much.

The left one might need a little less extrusion — you can see where the top layers of the bolt stuck to the bottom of the nut and broke away. (I think I’d like to be able to edit the g-code right there and insert a blast of fan cooling for just that layer.)

I’m using a honeycomb infill pattern for this, and I need fairly high infill, because otherwise some of the top shells just get cantilevered over empty space and slump down. But I worry that the strength of the hexagons contributes to warping. Does anyone else use, say, concentric infill for situations like this where strength is not an issue?

Oh, and thanks to Creative Tools for putting this one up.

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