Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Despite carrying a glass-fronted gadget in my pocket for most of the past two decades, this is the first time I’ve done this:
Pixel 3a screen protector – as broken
Turns out you can’t trust a rolling seat on a slightly unlevel surface, as shifting your weight can let the thing roll out from under you with no warning. If you’re taking a picture at the same time, the phone reaches the impact point before your hand: even a nice case with bumpers all around won’t be quite enough protection.
I was tempted to leave it un-fixed as a constant reminder to not do that again, but the broken glass was rough to the touch and interfered with Android’s swipe-upward gestures.
Fortunately, the tempered-glass screen protector absorbed the energy without damage to the actual screen:
Pixel 3a screen protector – sidelit
A thin plastic layer holds the protector’s fragments together; I hadn’t known it was a two-layer structure.
Being that type of guy, I had a spare protector in a desk drawer and managed to apply it without trapping any bubbles or fuzz underneath.
It’s been hiding back there since the first (attempted) use showed it wasn’t a quadruped:
Erick Magna Holder – as-delivered stance
Grabbing the other end in the bench vise and whacking the top of the offending leg with a brass persuader pretty much lined it up. Closer inspection showed a problem with the push-to-detach lever:
Erick Magna Holder – rivet pivot
The rivet head and thin washers extend a bit beyond the circular arc, with the rivet holding the leg above whatever it’s supposed to stick to. I think the scarring on the rivet was an attempt to improve the situation, perhaps during a QC adjustment session, that didn’t quite work.
The hole through the leg is a touch under 4 mm and the Big Box o’ Random Small Screws disgorged a 6-32 screw with what might have been a 5/32 inch = 4 mm nominal = 3.8 mm actual shoulder of exactly the right length:
Erick Magna Holder – 6-32 screw clearance
The screw head flange cleared the floor, but wasn’t much of an improvement over the rivet. I eventually chucked it in the lathe and removed the flange & hex-head corners, an improvement you won’t see here.
Even with the frame whacked into alignment, all four feet didn’t contact the surface plate along their entire lengths. Absent a surface grinder, I deployed a big blue Sharpie and the largest file on hand:
Erick Magna Holder – filing base
Iterating Sharpie and file eventually knocked off enough of the high spots to make it Good Enough™ for the intended purpose, which is definitely notprecision metrology:
Erick Magna Holder – bottom filed
Those chunky cross-pieces are Old School alnico magnets, which is the only reason a simple lever can pry it off a steel plate.
Contemporary vacuum cleaner dust brush heads have bristles in some combination of [long | short] with [flexy | stiff]. The long + flexy combination results in the bristles jamming the inlet and the short + stiff combo seems unsuited for complex surfaces. Shaking the Amazonian dice brought a different combination:
Vacuum cleaner dust brush assortment – with adapters
That’s the new one on the bottom and, contrary to what you might think from the picture, it is not identical to the one just above it.
In particular, the black plastic housing came from a different mold (the seam lines are now top-and-bottom) and required a new adapter for the Kenmore Progressive vacuum cleaner’s complicated wand / hose inlet, with a 3/4 inch PVC pipe reinforcement inside.
Early reports indicate it works fine, so I’ll declare a temporary victory in the war on entropy.
As part of a recent homeowner project, I applied a file to dull pruning saw that, as far as I can recall, Came With The House™ and has been untouched for decades:
Pruning Saw sharpening – top view
Yeah, that’s a lot of steel filings; it was really really dull. Notice how they’re neatly lined up toward the blade?
It looks better from the side:
Pruning Saw sharpening – side view
Despite my crude technique, it cuts wood like a hot knife through butter.
Rummaging through the Big Box o’ Optics in search of something else produced this doodad:
Microscope objective illuminator – overview
It carries no brand name or identifier, suggesting it was shop-made for a very specific and completely unknown purpose. The 5× objective also came from the BBo’O, but wasn’t related in any way other than fitting the threads, so the original purpose probably didn’t include it.
The little bulb fit into a cute and obviously heat-stressed socket:
Microscope objective illuminator – bulb detail
The filament was, of course, broken, so I dismantled the socket and conjured a quick-n-dirty white LED that appears blue under the warm-white bench lighting:
Microscope objective illuminator – white LED
The socket fits into the housing on the left, which screws onto a fitting I would have sworn was glued / frozen in place. Eventually, I found a slotted grub screw hidden under a glob of dirt:
Microscope objective illuminator – lock screw
Releasing the screw let the fitting slide right out:
Microscope objective illuminator – lamp reflector
The glass reflector sits at 45° to direct the light coaxially down into the objective (or whatever optics it was originally intended for), with the other end of the widget having a clear view straight through. I cleaned the usual collection of fuzz & dirt off the glass, then centered and aligned the reflection with the objective.
Unfortunately, the objective lens lacks antireflection coatings:
Microscope objective illuminator – stray light
The LED tube is off to the right at 2 o’clock, with the bar across the reflector coming from stray light bouncing back from the far wall of the interior. The brilliant dot in the middle comes from light reflected off the various surfaces inside the objective.
An unimpeachable source tells me microscope objectives are designed to form a real image 180 mm up inside the ‘scope tube with the lens at the design height above the object. I have the luxury of being able to ignore all that, so I perched a lensless Raspberry Pi V1 camera on a short brass tube and affixed it to a three-axis positioner:
Microscope objective illuminator – RPi camera lashup
A closer look at the lashup reveals the utter crudity:
Microscope objective illuminator – RPi camera lashup – detail
It’s better than I expected:
Microscope objective illuminator – RPi V1 camera image – unprocessed
What you’re seeing is the real image formed by the objective lens directly on the RPi V1 camera’s sensor: in effect, the objective replaces the itsy-bitsy camera lens. It’s a screen capture from VLC using V4L2 loopback trickery.
Those are 0.1 inch squares printed on the paper, so the view is about 150×110 mil. Positioning the camera further from the objective would reduce both the view (increase the magnification) and the amount of light, so this may be about as good as it get.
The image started out with low contrast from all the stray light, but can be coerced into usability:
The weird violet-to-greenish color shading apparently comes from the lens shading correction matrix baked into the RPi image capture pipeline and can, with some difficulty, be fixed if you have a mind to do so.
As far as I can tell, Raspberry Pi cases are a solved problem, so 3D printing an intricate widget to stick a Pi on the back of an HQ camera seems unnecessary unless you really, really like solid modeling, which, admittedly, can be a thing. All you really need is a simple adapter between the camera PCB and the case of your choice:
The plate has recesses to put the screw heads below the surface. I used nylon screws, but it doesn’t really matter.
The case has all the right openings, slots in the bottom for a pair of screws, and costs six bucks. A pair of M3 brass inserts epoxied into the plate capture the screws:
RPi HQ Camera – case adapter plate – screws
Thick washers punched from an old credit card go under the screws to compensate for the case’s silicone bump feet. I suppose Doing the Right Thing would involve 3D printed spacers matching the cross-shaped case cutouts.
Not everyone agrees with my choice of retina-burn orange PETG:
RPi HQ Camera – 16 mm lens – case adapter plate
Yes, that’s a C-mount TV lens lurking in the background, about which more later.
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The Smell of Molten Projects in the Morning 