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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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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