Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The sediment and carbon filter cartridges in our house call for annual replacement and I wondered what was inside the big cartridge.
Much to my surprise, the white plastic cap unscrews easily after grabbing the filter in the bench vise and applying a strap wrench:
Whole house carbon filter – endcap
Water enters around the perimeter of the cap, flows through the media in the cylindrical cartridge, and emerges near the center at the other end. The filter is upside-down in the vise: the cap is on the bottom of the cartridge when it’s installed in the filter housing.
The brown stuff looks a lot like sand, but is probably KDF-85 media acting as a prefilter for the carbon:
Whole house carbon filter – prefilter
The white fiber pad separates the KDF-85 from the carbon granules filling the rest of the filter:
Whole house carbon filter – carbon
Atypically, I couldn’t think of anything to do with the empty cartridge, so I screwed the lid back on and lowered the whole mess into the trash can.
The kitchen came with matched Samsung appliances dating back to 2018 and, on a frigid winter day, we piled the contents of the freezer on the porch and gave it a deep cleaning. While the empty freezer was cooling down from its adventure, I wondered:
Where were the condenser coils were located?
Did they need cleaning?
How does one do that?
The manual is strangely silent about even the existence of the coils, so evidently cleaning them wasn’t of any importance to Samsung.
Rolling the refrigerator away from the wall just enough to get the phone camera down there suggests they exist and are in need of some attention:
Samsung refrigerator coils – first sight
Rolling the refrigerator out until the door handles met the countertop across the way let me climb over the counter and worm myself into the refrigerator-sized hole behind it, bringing along a screwdriver, the vacuum cleaner snout, and a few brushes.
Removing five screws released the back cover:
Samsung refrigerator coils – cover off
Looking into the intake end of those coils (on the right):
Samsung refrigerator coils – first intake view
So, yeah, I’m about to give them their first cleaning ever.
Five minutes of brushing fuzz, mostly into the vacuum, cleared a good bit of the exterior, but the interior needs more attention:
Samsung refrigerator coils – partial clean
Ten minutes later:
Samsung refrigerator coils – victory
Another five minutes:
Samsung refrigerator coils – intake cleaned
Making the coils cleanable and putting them where they could be cleaned were obviously not bullet-item goals for Samsung’s designers.
Although the coils are not perfectly clean, I don’t know how to get them any cleaner, despite knowing even a thin layer of fuzz kills the refrigerator’s much-touted energy efficiency. Perhaps blowing them off with compressed air, then cleaning a thin layer of dust off the entire kitchen, would help.
I think the refrigerator will be happier, at least for a while.
While tracking down an air leak in a living room window, I noticed one of the cellular blinds was missing an end cap, so I scanned a pair of surviving caps:
It is slightly tilted, but that doesn’t matter. You could devote more time to smoothing / reverse-engineering the shapes, but that doesn’t make much difference, either.
Inkscape exports the SVG coordinates with respect to the overall page origin in the lower left corner, so when OpenSCAD imports the SVG the paths end up far away from the origin. The trick is to put a 2 mm diameter circle at a known location, center the paths around it, then have OpenSCAD use the circle’s location to recenter the paths.
Because Inkscape uses the lower left corner of each shape as its origin, you must put the circle at (99,99) to have its center at (100,100). That is one of the many reasons you (well, I) can’t use Inkscape as a CAD program.
Import into OpenSCAD, recenter, and extrude the shapes:
CapCenter = [100,100];
PlateThick = 1.8; // thickness of visible end cap
HolderTall = 10.0 + PlateThick;
union() {
linear_extrude(height=PlateThick)
translate(-CapCenter)
import("Living Room shade end caps - Inkscape.svg",layer="Exterior");
linear_extrude(height=HolderTall)
translate(-CapCenter)
import("Living Room shade end caps - Inkscape.svg",layer="Retainer");
}
Which produces a solid model:
Living Room shade end caps – solid model
Save the model as 3mf, import into PrusaSlicer, and slice:
Living Room shade end caps – PrusaSlicer preview
Making the retainer shape a little wider would be a good idea to get better infill, but it’s a slip fit into the blind (surely why it fell out long ago) and need not withstand any stress.
Print as usual:
Living Room shade end cap – on platform
And then It Just Works™:
Living Room shade end cap – installed
It’s sitting atop a bookcase while I finish tinkering with its window.
All that seems like a lot of fiddling around, but it uses each program to its best advantage and it’s surprisingly easy after the first few models.
Because I must eventually diagnose and fix the HQ Sixteen’s Motor Stall Heisenbug, I printed out several views of the power supply PCB on glossy photo paper for best visibility.
The component side:
Power PCB – components
The solder side:
Power PCB – solder
The X-ray view:
Power PCB – overlaid
Considerable pondering and sketching produced an annotated view of the solder side:
HQ Sixteen – Power PCB – solder side – component labels – reduced
Here’s a tentative schematic drawn on the fly while extracting it from the PCB traces:
HQ Sixteen – Power PCB – rough schematic
!!CAUTION!! I have not verified the schematic against the actual hardware / PCB / components, as the Heisenbug has not reoccurred and I had no occasion to take the machine apart for checking. Do not assume any connections or components are correctly drawn.
Before I redraw the schematic in a more useful format, I must verify several nodes, because not everything in there makes sense.
In particular, the elaborate resistor string in the middle of the page seems to establish reference voltages for everything else, from the motor power supply turn-on delay to the RUN signal starting the motor.
The optoisolators definitely get the RUN command signal from the controller and feed the STALL motor status back to it. That’s assuming I understand enough to pin those labels on those connections.
!!CAUTION!!Read my caveats about the direct-from-the-AC-line non-isolated +160 VDC motor supply before connecting your instruments. The GND traces are not isolated from the AC line and are not at the normal “0 V” AC neutral potential.
But if this mess gets you further along with whatever you were doing, let me know how it all worked out for you.
A highly effective way to bait a rat trap for garden voles:
Rat trap – still baited
The trap is a Victor M205 (in a 12-pack as M326) with a big yellow plastic bait pedal. The bait is pieces of walnut, secured to the pedal with generous strands of hot melt glue. The trick involves mechanically capturing the walnut by slobbering glue over & around it, forcing the vole to pull & tug while gnawing the last bit of goodness.
Which generally ends badly:
Rat trap – gnawed bait
I do not begrudge the critters a fancy last meal; it’s gotta be better than their usual diet of carrots / radishes / turnips.
Voles have no qualms about eating the bait from a sprung trap with a dead compadre a few millimeters away:
Rat trap – empty bait
They will sometimes eat the walnuts and their dead compadre.
The plastic pedals work much better than the old-style metal pedals at holding the steel arm wire. The wire slides freely on the plastic, in contrast to the previous high-friction metal-on-metal latch.
Some of the traps were entirely too sensitive and required slightly bending the tip of the arm wire upward to increase the friction on the plastic plate. Always always always handle armed traps by the wooden edges beside the kill bar, so when it accidentally snaps your fingers are nowhere near the business end.
After I figured out how to properly bait the traps and we set out half a dozen traps in the most attractive crops, Mary’s garden produced 54 dead voles over the course of 90 days, sometimes in groups of three or four at a time. While this did not prevent all the crop damage, it definitely reduced the problem.
Next year we’ll start early and probably reach triple digits by midsummer.
The same technique with Victor M035 mouse traps (in 12-packs as M035-12) is brutally effective on house mice.
Mary is at least the third owner of a steel rack, originally intended to hold packages of retail stuff, which now holds (much of) her collection of quilting rulers:
Quilting Ruler Rack Base – overview
Obviously, it was never intended to hold heavy acrylic sheets, but it worked surprisingly well, right up to the point where too many of the rulers collected on two adjacent columns of pegs and overbalanced the whole affair atop her while she attempted to remove a ruler.
Subsequent accident recreation showed the rack toppled when the weight of the rulers on the two adjacent columns of hooks moved the center of mass outward, just inside the line between those feet, whereupon the slightest tug on a ruler pulled it over.
Measurements revealed the four legs do not sit on a square contact patch, are not parallel to the radii from the center point, and are not uniformly distant from the center. Rather than committing to a finished product, I made a cardboard prototype to verify a bigger base would solve the problem and I could capture all those feet.
You don’t have such a rack, so the exact dimensions don’t matter, but the LightBurn layout looks like this:
Quilting Ruler Rack Base
The disk is two cross-laid sheets for stiffness, with marks burned on the top to help align the feet more-or-less around the center point.
The oblong rings fit around the feet to capture them, so cut eight or twelve to make four stacks a bit taller than the wire diameter.
The H shape then glues atop the rings to hold the feet in place. They’re not removable, but a razor knife will eventually solve that problem.
I slobbered hot melt glue across the cardboard disks to hold them together, glued and aligned the rings where the feet dented the disks, stood the rack in the rings, and glued the H plates.
About an hour elapsed from the sound of the crash to the rack once again standing quietly beside the fabric cabinets.
We’ll run this for a while and eventually replace it with a plywood disk and screwed-in-place clamps for the feet, which will surely call for wood surface preparation / stain / seal treatment.
The Smell of Molten Projects in the Morning 
