The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Author: Ed

  • X10 Appliance Module Local Control: Disablement Thereof

    After we rearranged the living room, we had a few floor lights in different locations that called for more X10 Appliance Controllers. I’m not a big fan of automated housing, because X10 communication is unreliable with a bullet, but it’s convenient to turn off all the lamps from the bedroom.

    Anyhow, the old RCA HC25 X10 Appliance Modules I pulled out of the Big Box o’ X10 Stuff suffered from the usual conflict between compact fluorescent lamps and the “local control” misfeature that’s supposed to let you turn the appliance on by simply flipping the switch. The problem is that a CFL ballast draws a nonlinear trickle of current that the module misinterprets as a switch flip, thus occasionally turning the lamp on shortly after you turn it off.

    This has been true since the first compact fluorescent bulbs appeared. The circuitry inside X10 modules hasn’t changed much, at least up until I bought the last round of switches quite some time ago. That’s either a Bad Thing (still a problem) or a Good Thing (everybody knows about it).

    The solution (everybody knows about it, just use the obvious keywords) is to cut a jumper on the module’s circuit board that’s obviously placed there for this very reason. In this view, it’s just below the lower-right corner of the fat blue capacitor. If you need confirmation, it’s connected to pin 7 of the only IC on the board.

    Snip the wire, move the cut end a little bit, and button the module up again.

    Local control jumper cut
    Local control jumper cut

    Oh, yeah. No user serviceable parts inside is a challenge around here…

  • Seating Knob Heads and Suchlike

    The Thing-O-Matic instructions suggest crushing the knob heads onto socket-head cap screws using pliers. That’s a desperation move for when you have no alternative.

    Instead, if you have a drill press (and you should!), do it this way: lightly grab the cap screw threads in the chuck and squash it into the head.

    Seating knob head on SHCS
    Seating knob head on SHCS

    The same trick works for pressing pulleys and drive splines onto motor shafts.

    Seating extruder drive on motor shaft
    Seating extruder drive on motor shaft

    You shouldn’t use your drill press as a heavy-duty arbor press, but for pressing small circular things onto shafts, it’s hard to beat.

  • Installing OpenSCAD on Arch Linux

    This was more tedious than it ought to be, but OpenSCAD now runs on my desktop box and uses OpenGL 2.2, courtesy of a not too obsolete nVidia GeForce 9400 dual-head card.

    OpenSCAD has a slew of pre-reqs, most of which were already installed. However, the openscad and cgal non-packages live in the Arch AUR collection, so they required manual twiddling to install.

    The pre-reqs:

    • cgal, which in turn requires cmake via pacman
    • opencsg

    The recommended PKGBUILD patch is easy enough to do by hand.

    The final build step takes ten minutes using both cores, but the final result uses OpenCSG the way it should.

    Oddly, the OpenSCAD rendering process for the few objects I’ve checked takes longer than on the laptop. Weird.

    This does not get the most recent build from the developers, but it’s close enough for my simple needs right now. The mailing list archive is invaluable.

    Then there was the laptop saga. Maybe the reason the laptop is faster is that it’s not actually using OpenCSG at all.

  • ATX Power Supply Dual +12 V Outputs: Fakery Thereof

    I wondered if the Thing-O-Matic would benefit from having its two high-current heaters on a separate +12 V supply than the DC Extruder, after finding that the heaters dragged the +12 V output down by nearly half a volt.

    A bit of rummaging turned up a suitable ATX supply with a data plate that might justifiably lead one to believe that the supply provides separate +12 V outputs:

    Turbolink ATX-CW420W power supply data plate
    Turbolink ATX-CW420W power supply data plate

    There’s no indication which of the four connectors might use +12V1 and +12V2, but, being that sort of guy, I applied an ohmmeter to the various yellow wires and found they were all exactly 0.0 Ω apart.

    Huh.

    So I opened the Warranty Void If Seal Removed top cover and found this situation:

    ATX with fake dual 12 V supplies
    ATX with fake dual 12 V supplies

    Nota bene:

    • All the yellow wires terminate in the same solder blob below the PCB
    • Two incoming wires got neatly spliced together in mid-air, despite having free holes in the PCB

    This may not come as much of a shock: they lie…

    Perhaps if you spend more money on your supply, it’ll actually live up to the data plate specs. Then, again, perhaps you’ll just be spending more money.

    And, if you swap in a fancy supply for the MBI-stock one, it might not make much difference at all. I suspect the various power levels and current capacities have pretty much the same degree of integrity…

  • Thing-O-Matic: Arduino Mega Heatsinking

    The Thing-O-Matic Motherboard rides atop an Arduino Mega (with the auto-reset option disabled), drawing most of its power from the hulking ATX connector at one end. The Mega draws power from the ATX +12 V supply and produces +5 V through its on-board regulator.

    As I noted there, that regulator runs surprisingly hot when fed from +12 V, even without any additional current flowing to the Mega’s pins. The solution here required another search through the parts heap, which eventually disgorged a small heatsink that was, I think, intended for a 16-pin DIP, although I obviously added the hole for some other, long-forgotten purpose.

    Motherboard regulator heatsink
    Motherboard regulator heatsink

    A bit of fin-bending to clear the (unused) power entry jack, a dab of JB Kwik epoxy, and a clamp to keep it in place while the epoxy cures:

    Clamping the Motherboard regulator heatsink
    Clamping the Motherboard regulator heatsink

    You won’t have such a heatsink, but any similarly shaped chunk of metal, even without fins, should suffice. Nothing critical about it, as long as it clears the Motherboard that will be plugged atop the Mega; you’re just increasing the surface area for heat dissipation.

    The Motherboard and Mega sit in the large opening across the Thing-O-Matic’s baseplate from the ATX supply’s fan intake, where they get plenty of cooling air. Do a before-and-after test with a fingertip on the regulator to feel the improvement for yourself.

    This is, admittedly, just a feel-good tweak, but a cool regulator is a happy regulator. Spread the joy…

  • Thing-O-Matic / MK5 Extruder: Cartridge Heater Doodles

    During the conversation following my original post on the MakerBot support forum, CodeRage suggested using cartridge heaters. I asked Eks about that and he said something along the lines of “Damn straight! We used ’em all over the place! Just do it!”

    CodeRage plans to retrofit his MK5 head with a pair of 230 V 150 W heaters running at 120 V to get a total of 75 W. I have qualms about running line voltage around the extruder head, but it’s certainly a better solution than toasting power resistors.

    The trouble with 1/2-inch models is that they don’t fit conveniently on the Thermal Core. I’d make an adapter block with a hole for the heater and two holes for the existing cap screws, but the screws don’t quite pass around a half-inch cartridge heater.

    He suggested 1/8-inch heaters from Sun Electric Heater Company, which look like just the ticket except that they’re nigh onto 40 bucks a pop. Ouch.

    High Temp Industries [Edit: new link 2013-12-27] has 1/4-inch heaters for under $20 that will fit in the space available. If I understand the configuration options, you can even get 12 V 30 W heaters (the same power as the existing resistors) with a 1000 °F (call it 500 °C) temperature rating.

    So I think what’s needed is to get some of those heaters, machine blocks to hold them on each side of the Core, and see how that works. The heaters will fit between the resistor screw holes and the Core is just about exactly 1 inch long. What’s not to like?

    This might work… except for the fact that HTI has a $150 minimum order, which is somewhat off-putting even for me. Anybody up for a group buy of ten cartridge heaters?

    Note that if you swap in some cartridge heaters, you really should do the separate +12 V supply Extruder Controller hack described there.

    [Update: Zach @ MBI has ordered a stack of cartridge heaters for their internal testing (he promises to send me some), plans a retrofit kit, and may become a retail source for the heaters. He reports the lead time to get heaters in bulk is something over two weeks, which is a lot longer than I expected.

    In light of that, I will hold the “group order” until I have a better handle on what’s needed to retrofit cartridge heaters into the existing MK5 head, how they’ll actually work, and what PID loop retuning may be required. Once I know more about all that, we can proceed.

    Having MBI handle the ordering & shipping makes sense to me!]

  • Thing-O-Matic / MK5 Extruder: Resistor Wrapup

    Extruder resistor wiring
    Extruder resistor wiring

    As nearly as I can tell, using a pair of 10 W power resistors as 30 W heating elements in the Thing-O-Matic’s MK5 Extruder Thermal Core isn’t going to work, at least if you want even minimal reliability.

    The fundamental problem is that the resistor specification limits the dissipation to a few watts, tops, near 250 °C, where they must run in order to melt any of the plastic filaments.

    The Thermal Core requires 20-30 W to maintain 225 °C, so each resistor must dissipate an average of 10-15 W at that temperature. That’s half of the MK5 extruder’s original design point and still nearly a factor of 10 beyond the resistor rating.

    The original design runs at less than 50% duty cycle to maintain 225 °C, which agrees with my measurements:

    • 50% of 60 W = 30 W
    • 33% of 60 W = 20 W

    If you want to run at lower power, it’s a drop-in replacement. Change the original 5 Ω resistors to 2.5 Ω resistors (from Digikey / Mouser / wherever), change the wiring to put them in series (not parallel!), and see how long they last. They’ll certainly fare better than at 30 W, but I wouldn’t expect more than a few hours of lifetime. The specs give them 1000 hours at rated power, which this certainly is not.

    A series connection means that when one resistor fails, the heat goes off. The original parallel connection left one resistor carrying the load and, at 30 W, it can actually get the Core up to operating temperature and keep it there. Many folks have been baffled by that, but the diagnosis is simple. Measure the resistance of the parallel resistors at the Extruder Controller end of the wires:

    • 5 Ω → one resistor has failed
    • An open circuit (infinite resistance) → both are dead

    The problem with the lower power dissipation, whether from a failed resistor in the original design or my suggested change, is that the extruder head has a thermal time constant of 10-11 minutes. Lower power means a longer cold-start time; 30 W should get it up to 225 °C in about 20-30 minutes depending on the insulation. That’s not really a problem if you’re printing a series of objects, but might be objectionable for quick printing sessions.

    However, when a resistor fails, the heat goes off, the plastic stiffens up, the DC extruder motor stalls, and the essentially unlimited motor current kills the A3977 driver on the extruder board. My incandescent lamp workaround may alleviate that problem: when the light goes on, check for a failed resistor.

    I picked up a stock of 2-to-3 Ω power resistors and will do some further experimenting with power levels, insulation, and suchlike. This is a short-term fix to get my Thing-O-Matic running, but there’s a better long-term way to go: cartridge heaters on a modified Thermal Core, which I’ll discuss shortly.

    If you arrived by search engine, jump there for my earliest guesstimates, go there to the beginning of the Thing-O-Matic hardware hackage posts, then read until you get back here. The story will, perforce, continue…