Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The step change in Week 22 shows when the replacement took over. After some poking around, Amazon Prime FTW.
The square-ish pulse starting in Week 26 marks a change from 55% RH to 60%RH and back again, to see how the front panel meter compares with the low end lab-grade hygrometer in the other side of the basement near the Hobo datalogger on the water inlet; they’re all off by a bit, but well within their expected tolerances. The 5% RH height of the step suggests a good match between their incremental calibrations.
It seems dehumidifiers last a few years, no matter which Brand Name you’ve decided to trust, so there’s not much point in developing a deep emotional attachment.
For the record, the old dehumidifier sported a GE label:
As it turns out, Electrolux bought Frigidaire a while ago, then absorbed GE’s appliances in 2014, so they’re all one big happy family now.
The various names notwithstanding, a recall notice suggests Gree Electric actually makes all the dehumidifiers badged with Brand Names you might think represent something significant.
Mary found a folding saw buried under a compost heap at Vassar Farms, where it had evidently been for quite a while. It cleaned up surprisingly well:
Folding saw – pivot shim
I made a crude brass shim to stabilize the crude blade in its crudely bent metal frame; the ugly hole came from freehand punching with the rebuilt leather punch tool. Probably spent as much time doing that as they did on the whole rest of the saw: it’s not a high-quality tool.
It could be an older version of the Harbor Freight Folding Saw, minus a fancy plastic-encased joint screw. I added a dot of Loctite to discourage this one from leaping to its doom.
As with the other pruning saws in my collection, that blade scares me just looking at it. I managed to avoid slicing myself open, although I did stab a finger with a sharp brass sliver…
As failures go, that one’s survivable; slightly larger epoxy dots should do the trick:
Silhouette temple – re-repair
The other temple worked loose inside the brass tube and rotated freely, so I yanked it out, bashed the tip slightly flatter, and epoxied it back in place, along with overcoating the epoxy dots on the lens to forestall another failure.
This has obviously blown right by the point of absurdity, but …
A semitrailer load of scrap metal pulled into an I-90 rest stop just after we arrived:
Metal scrap trailer – Cutting edge
Apparently, they dump the scrap into the trailer from a great height and, sometimes, a bar can gash the aluminum side wall. That slice obviously predates the current load, but you can see how it happened: dump a load atop a bar leaning against the side and you get a giant metal shear.
The trailer also had several puncture wounds:
Metal scrap trailer – Puncture wounds
I didn’t notice the circular feature at the bottom center until I looked at the picture, but it certainly reminded me of a bullet hole in glass plate. Close inspection of the original image suggests it’s a welded stress relief border around a drilled hole, perhaps with a boss on the inside of the trailer:
Lining the shield support box with copper foil tape turned out to be surprisingly easy:
Electrometer amp – shield – end view
The flat surface is two overlapping strips of 2 inch wide copper tape. I traced the exterior of the support box on the tape, cut neatly along the lines, slit the corners, bent the edges upward, peeled off the backing paper, stuck the tape into the box, pressed the edges into the corners, and didn’t cut myself once.
Applying 1 inch wide tape to the wall went just as smoothly, after I realized that I should cut it into strips just slightly longer than the hexagon’s sides.
The tape along the rim is adhesive copper mesh that’s springy enough to make contact all around the edge. I cut the 1 inch wide tape in half, which was just barely wide enough to reach::
Electrometer amp – shield – mesh soldering
Although you’re supposed to join the entire length of each seam for best RF-proofing, I tacked the corners and the middle of the long edge, then hoped for the best. The copper mesh seems to be plated on plastic threads that requires a fast hand to solder without melting, but I’m getting better at it. The adhesive is said to be conductive, but I loves me some good solder blob action.
The resistance from the flat bottom to the side panels and the fabric on the edge started out at a few ohms before soldering and dropped to 0.0 Ω after soldering, so I’ll call it a success. Didn’t even melt the outside of the PETG box, but I admit I didn’t take it apart to see what the copper-to-PETG surface looks like.
Covering the foil on the sides with 1 inch Kapton tape completed the decoration. I didn’t bother to cover the flat surface, because none of the circuitry should reach that far, and didn’t worry about covering the fabric tape for similar reasons. As madbodger pointed out, this violates the no-plastic-on-the-inside rule, but I’m still hoping for better results than having the entire plastic structure with all its charges on the inside.
A strip of horribly clashing orange plastic tape (which might be splicing tape for reel-to-reel recording tape) covers the outside edges of the fabric, prevents fraying, and gives the black electrical tape that holds the box down a solid grip:
Electrometer amp – shield – exterior
Yeah, like you’d notice mismatched colors around here.
Using black tape as an anchor seemed easier and better than messing with nesting pins & sockets. The copper fabric tape makes good contact with the rim of the PCB all the way around the perimeter and the black tape holds it firmly in place.
Early reports suggest the shield works pretty well…
Although I’d thought of a Mu-metal shield, copper foil tape should be easier and safer to shape into a simple shield. The general idea is to line the interior with copper tape, solder the joints together, cover with Kapton tape to reduce the likelihood of shorts, then stick it in place with some connector pin-and-socket combinations. Putting the tape on the outside would be much easier, but that would surround the circuitry with a layer of plastic that probably carries enough charge to throw things off.
Anyhow, the hexagonal circuit board model now sports a hexagonal cap to support the shield:
Victoreen 710-104 Ionization Chamber Fittings – Show with shield
The ad-hoc openings fit various switches, wires, & twiddlepots:
If white LED strips had existed in the early 1980s, the engineers responsible for the HP 7475A plotter would surely have done this:
HP 7475A Plotter – LED paper illumination
Not, that’s not stretched vertically: I bought a ream of B-size paper (11×17 inches) just for plotter demos.
Although the power supply does have a +12 V output, it comes from a TO220 transistor without a heatsink. The +5 V supply uses a robust TO3 transistor on a huge quad heatsink that can surely dissipate another watt or two without getting any sweatier.
I powered the LEDs from a dirt-cheap boost converter that provides a convenient brightness adjustment; it’s set to 10.5 V and that’s plenty bright enough. The converter attaches to pair of wires soldered across VR1, which is probably a crowbar that blows F3 (not shown) in the event the regulator fails hot:
HP 7475A – LED power tap – schematic
They don’t make power supplies like that any more.
The part locations (“O9” looks like a typo):
HP 7475A – LED power tap
The PCB has holes in exactly the right spot for a zip tie anchoring the wires exiting to the bottom:
HP 7475A Plotter – LED power tap – PCB top
This vertiginous view shows the inside of the case atop the chassis, with the boost converter affixed to the galvanized steel pan with foam tape and the LED wires stuck down with Gorilla Tape:
HP 7475A Plotter – LED strip and boost converter
Red silicone tape around a PCB-mount coax jack rounds out a true hack job.
Although I didn’t bring the plotter to the CNC Workshop, that venue’s dim light reminded me that you can never have enough light when you’re showing off your toys: the LED panels on the M2 and the LED light bars on the Model 158 sewing machine were the brightest spots to be seen.
The Smell of Molten Projects in the Morning 