Pruning Saw Sharpening

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
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
Pruning Saw sharpening – side view

Despite my crude technique, it cuts wood like a hot knife through butter.

Mystery Microscope Objective Illuminator

Rummaging through the Big Box o’ Optics in search of something else produced this doodad:

Microscope objective illuminator - overview
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
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
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
Microscope objective illuminator – lock screw

Releasing the screw let the fitting slide right out:

Microscope objective illuminator - lamp reflector
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
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
Microscope objective illuminator – RPi camera lashup

A closer look at the lashup reveals the utter crudity:

Microscope objective illuminator - RPi camera lashup - detail
Microscope objective illuminator – RPi camera lashup – detail

It’s better than I expected:

Microscope objective illuminator - RPi V1 camera image - unprocessed
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:

Microscope objective illuminator - RPi V1 camera image - auto-level adjust
Microscope objective illuminator – RPi V1 camera image – auto-level adjust

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.

All this is likely not worth the effort given the results of just perching a Pixel 3a atop the stereo zoom microscope:

Pixel 3a on stereo zoom microscope
Pixel 3a on stereo zoom microscope

But I just had to try it out.

Raspberry Pi HQ Camera Mount

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:

HQ Camera Backplate - OpenSCAD model
HQ Camera Backplate – OpenSCAD model

A quartet of 6 mm M2.5 nylon spacers mount the adapter to the camera PCB:

RPi HQ Camera - nylon standoffs
RPi HQ Camera – nylon standoffs

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
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
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.

The OpenSCAD source code as a GitHub Gist:

// Raspberry Pi HQ Camera Backplate
// Ed Nisley KE4ZNU 2020-09
//-- Extrusion parameters
/* [Hidden] */
ThreadThick = 0.25;
ThreadWidth = 0.40;
HoleWindage = 0.2;
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
function IntegerLessMultiple(Size,Unit) = Unit * floor(Size / Unit);
Protrusion = 0.1; // make holes end cleanly
inch = 25.4;
ID = 0;
OD = 1;
LENGTH = 2;
//- Basic dimensions
CamPCB = [39.0,39.0,1.5]; // Overall PCB size, plus a bit
CornerRound = 3.0; // ... has rounded corners
CamScrewOC = [30.0,30.0,0]; // ... mounting screw layout
CamScrew = [2.5,5.0,2.2]; // ... LENGTH = head thickness
Standoff = [2.5,5.5,6.0]; // nylon standoffs
Insert = [3.0,4.0,4.0];
WallThick = IntegerMultiple(2.0,ThreadWidth);
PlateThick = Insert[LENGTH];
CamBox = [CamPCB.x + 2*WallThick,
CamPCB.y + 2*WallThick,
Standoff.z + PlateThick + CamPCB.z + 1.0];
PiPlate = [90.0,60.0,PlateThick];
PiPlateOffset = [0.0,(PiPlate.y - CamBox.y)/2,0];
PiSlotOC = [0.0,40.0];
PiSlotOffset = [3.5,3.5];
NumSides = 2*3*4;
TextDepth = 2*ThreadThick;
//----------------------
// Useful routines
module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes
Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
FixDia = Dia / cos(180/Sides);
cylinder(r=(FixDia + HoleWindage)/2,h=Height,$fn=Sides);
}
//----------------------
// Build it
difference() {
union() {
hull() // camera enclosure
for (i=[-1,1], j=[-1,1])
translate([i*(CamBox.x/2 - CornerRound),j*(CamBox.y/2 - CornerRound),0])
cylinder(r=CornerRound,h=CamBox.z,$fn=NumSides);
translate(PiPlateOffset)
hull()
for (i=[-1,1], j=[-1,1]) // Pi case plate
translate([i*(PiPlate.x/2 - CornerRound),j*(PiPlate.y/2 - CornerRound),0])
cylinder(r=CornerRound,h=PiPlate.z,$fn=NumSides);
}
hull() // camera PCB space
for (i=[-1,1], j=[-1,1])
translate([i*(CamPCB.x/2 - CornerRound),j*(CamPCB.y/2 - CornerRound),PlateThick])
cylinder(r=CornerRound,h=CamBox.z,$fn=NumSides);
translate([0,-CamBox.y/2,PlateThick + CamBox.z/2])
cube([CamScrewOC.x - Standoff[OD],CamBox.y,CamBox.z],center=true);
for (i=[-1,1], j=[-1,1]) // camera screws with head recesses
translate([i*CamScrewOC.x/2,j*CamScrewOC.y/2,-Protrusion]) {
PolyCyl(CamScrew[ID],2*CamBox.z,6);
PolyCyl(CamScrew[OD],CamScrew[LENGTH] + Protrusion,6);
}
for (j=[-1,1]) // Pi case screw inserts
translate([0,j*PiSlotOC.y/2 + PiSlotOffset.y,-Protrusion] + PiPlateOffset)
PolyCyl(Insert[OD],2*PiPlate.z,6);
translate([-PiPlate.x/2 + (PiPlate.x - CamBox.x)/4,0,PlateThick - TextDepth/2] + PiPlateOffset)
cube([15.0,30.0,TextDepth + Protrusion],center=true);
}
translate([-PiPlate.x/2 + (PiPlate.x - CamBox.x)/4 + 3,0,PlateThick - TextDepth - Protrusion] + PiPlateOffset)
linear_extrude(height=TextDepth + Protrusion,convexity=2)
rotate(-90)
text("Ed Nisley",font="Arial:style=Bold",halign="center",valign="center",size=4,spacing=1.05);
translate([-PiPlate.x/2 + (PiPlate.x - CamBox.x)/4 - 3,0,PlateThick - TextDepth - Protrusion] + PiPlateOffset)
linear_extrude(height=TextDepth + Protrusion,convexity=2)
rotate(-90)
text("KE4ZNU",font="Arial:style=Bold",halign="center",valign="center",size=4,spacing=1.05);

Raspberry Pi Streaming Video Loopback

As part of spiffing my video presence for SquidWrench Zoom meetings, I put a knockoff RPi V1 camera into an Az-El mount, stuck it to a Raspberry Pi, installed the latest OS Formerly Known as Raspbian, did a little setup, and perched it on the I-beam over the workbench:

Raspberry Pi - workbench camera setup
Raspberry Pi – workbench camera setup

The toothbrush head has a convenient pair of neodymium magnets affixing the RPi’s power cable to the beam, thereby preventing the whole lashup from falling off. The Pi, being an old Model B V 1.1, lacks onboard WiFi and requires a USB WiFi dongle. The white button at the lower right of the heatsink properly shuts the OS down and starts it up again.

Zoom can show video only from video devices / cameras attached to the laptop, so the trick is to make video from the RPi look like it’s coming from a local laptop device.

Start by exporting video from the Raspberry Pi:

raspivid --nopreview -t 0 -rot 180 -awb sun --sharpness -50 --flicker 60hz -w 1920 -h 1080 -ae 48 -a 1032 -a 'RPi Cam1 %Y-%m-%d %X'  -b 1000000 -l -o tcp://0.0.0.0:5000

The -rot 180 -awb sun --sharpness -50 --flicker 60hz parameters make the picture look better. The bottom of the video image There is no way to predict which side of the video will be on the same side as the cable, if that’s any help figuring out which end is up, and the 6500 K LED tubes apparently fill the shop with “sun”.

The -l parameter causes raspivid to wait until it gets an incoming tcp connection on port 5000 from any other IP address, whereupon it begins capturing video and sending it out.

Then, on the laptop, create a V4L loopback device:

sudo modprobe v4l2loopback devices=1 video_nr=10 exclusive_caps=1 card_label="Workbench"

Zoom will then include a video source identified as “Workbench” in its list of cameras.

Now fetch video from the RPi and ram it into the loopback device:

ffmpeg -f h264 -i tcp://192.168.1.50:5000 -f v4l2 -pix_fmt yuv420p /dev/video10

VLC knows it as /dev/video10:

RPi - V4L loopback - screen grab
RPi – V4L loopback – screen grab

That’s the edge of the workbench over there on the left, looking distinctly like a cliff.

The RPi will happily stream video all day long to ffmpeg while you start / stop the display program pulling the bits from the video device. However, killing ffmpeg also kills raspivid, requiring a manual restart of both programs. This isn’t a dealbreaker for my simple needs, but it makes unattended streaming from, say, a yard camera somewhat tricky.

There appear to be an infinite number of variations on this theme, not all of which work, and some of which rest upon an unsteady ziggurat of sketchy / unmaintained software.

Addendum: If you have a couple of RPi cameras, it’s handy to run the matching ssh and ffmpeg sessions in screen / tmux / whatever terminal multiplexer you prefer. I find it easier to flip through those sessions with Ctrl-A N, rather than manage half a dozen tabs in a single terminal window. Your mileage may differ.

Bike Helmet Mirror: Brasswork Clamp

A bit of Quality Shop Time produced a slight improvement to the clamp holding the mirror to the stalk:

Helmet Mirror Ball Mount - mirror joint brasswork
Helmet Mirror Ball Mount – mirror joint brasswork

The general idea is to hold the wave washer (it’s mashed under the flat washer, honest) above those bumps on the plate holding the mirror and stalk balls. It’s a few millimeters from the end of a ¼ inch brass rod, drilled for the M3 screw, and reduced to 4.5 mm with a parting tool to clear the bumps.

While I was at it, I made two spare mirrors, just to have ’em around:

Helmet Mirror Ball Mount - new vs old
Helmet Mirror Ball Mount – new vs old

The new ball mount looks downright svelte compared to the old Az-El mount, doesn’t it?

I should replace the steel clamp plates with a stainless-steel doodad of some sort to eliminate the unsightly rust, but that’s definitely in the nature of fine tuning.

More AAA-to-AA Alkaline Adapters

Having a handful of not-dead-yet AAA alkalines and a bunch of LED blinkies built for AA alkalines, a pair of adapters seemed in order:

AAA-to-AA Alkaline Adapters - installed
AAA-to-AA Alkaline Adapters – installed

The blinkies need a somewhat wider base than they’d get from a pair of AAA alkalines, so it’s not quite as dumb as it may seem.

In any event, the positive terminal comes from a brass rod:

AAA-to-AA Alkaline Adapters - brass terminal
AAA-to-AA Alkaline Adapters – brass terminal

Nobody will ever see the fancy Hilbert Curve infill around the brass:

AAA-to-AA Alkaline Adapters - end view
AAA-to-AA Alkaline Adapters – end view

In this application, they’ll go from not-dead-yet to oh-it’s-dead faster than AA cells, so I can watch how the blinkies work with lower voltages.

Keyboard Tray Raising

Long ago and far away, I moved the keyboards off our desk surfaces to a more convenient location on a tray under the middle drawer. Mary’s desk recently gained a somewhat thinner keyboard with a thumbwheel volume control, so she wanted the tray moved up:

Keyboard Tray Relocation - in place
Keyboard Tray Relocation – in place

The supports on either side started out as 2×4 lumber with a slot cut (using the radial arm saw I no longer have) for the aluminum sheet:

Keyboard Tray Relocation - support view
Keyboard Tray Relocation – support view

For the record, a pair of screws hold each support to the drawer:

Keyboard Tray Relocation - support screw
Keyboard Tray Relocation – support screw

Not elegant. Works fine. Good enough!

Tiny Bandsaw™ wasn’t designed for ripsawing lumber, but the same Proxxon 10/14 TPI blade I use for aluminum worked better than I expected to lop a 1-¼ inch strip from the wood slats:

Keyboard Tray Relocation - bandsaw fixture
Keyboard Tray Relocation – bandsaw fixture

That’s a reenactment based on a true story. The wood scraps clamped on the bandsaw table leave enough clearance for the 2×4 slide to freely, yet not enough for the blade to wander off track.

You can tell how long ago I built the original trays: nary a trace of 3D printing!