Archive for category Science

Glass vs. Epoxy: Divot!

The WS2812 RGB LED atop the Bowl of Fire Floodlight

Reflector floodlight - purple phase

Reflector floodlight – purple phase

failed in the usual way after a bit over a year of constant use.

I’d done an unusually good job of epoxying the ersatz heatsink in place:

Reflector floodlight - finned LED holder

Reflector floodlight – finned LED holder

I wrapped the bulb in a towel with only the heatsink sticking out, whacked the side of the heatsink parallel to the glass with a plastic-face hammer, and it popped right off:

Epoxy vs glass - divot

Epoxy vs glass – divot

The missing piece of the epoxy ring turned out to be a divot ripped out of the glass, which I didn’t notice until I’d chipped the fragment off the aluminum, so no pictures.

Given the relative strengths of epoxy and glass, pulling a divot seems impossible, but folks doing 3D printing on glass platforms have been reporting exactly that failure for years. The prevailing theory seems to involve small scratches and defects in the glass surface, with subsequent weakening, and stresses applied to the epoxy perpendicular to the glass surface pulling the cracks apart.

Replacing the RGB LED will require drilling it out and probably a complete rewiring, because I seem to have made liberal use of epoxy inside the heatsink and brass tube.




Pure Matte Black the Hard Way

The best way to get a pure, non-reflective black uses optics, not pigments:

Matte black blade edges

Matte black blade edges

The shiny steel blades reflect light just fine, but the reflections have no way back out of the gap between adjacent edges: the angle of reflection always points away from you and the incoming light.

I always admire the blackness when I open that box.

Yes, I’m a member of the Society of the Easily Amused.


Monthly Science: Raising a Monarch Butterfly

A Monarch butterfly laid eggs in late July. On the 29th of July they looked like this:

Monarch Egg - focus stacked

Monarch Egg – focus stacked

By August 2, a pair of caterpillars had hatched and grew to 3 mm:

Monarch caterpillar - 3 mm - 2017-08-02

Monarch caterpillar – 3 mm – 2017-08-02

A day later, they were 4 mm long:

Monarch caterpillars - 4 mm - 2017-08-03

Monarch caterpillars – 4 mm – 2017-08-03

They really were sort of blue-ish with green hints:

Monarch caterpillar 1 - 4 mm - 2017-08-03

Monarch caterpillar 1 – 4 mm – 2017-08-03


Monarch caterpillar 2 - 4 mm - 2017-08-03

Monarch caterpillar 2 – 4 mm – 2017-08-03

By August 9, one had had more mature coloration:

Monarch caterpillar - 2017-08-09

Monarch caterpillar – 2017-08-09

The other caterpillar had vanished; we assume it got out of the aquarium and wandered off.

Apparently, the front end of the caterpillar (at the bottom of the picture) has a hard windshield reflecting the ring of LEDs around the camera lens. The caterpillar eats its skin after each molting, except for the windshield:

Monarch Windshield - 2017-08-09

Monarch Windshield – 2017-08-09

We kept fresh milkweed branches in a vase and the caterpillar ate almost continuously:

Monarch caterpillar - 2017-08-13

Monarch caterpillar – 2017-08-13

By August 15, the caterpillar was ready for the next stage in its life. At 10 in the morning it had attached itself to the screen covering the aquarium and assumed the position:

Monarch caterpillar - starting chrysalis - 2017-08-15

Monarch caterpillar – starting chrysalis – 2017-08-15

It transformed into a chrysalis by 5:30 PM:

Monarch Chrysalis - with skin

Monarch Chrysalis – with skin

The discarded skin remained loosely attached until I carefully removed it.

What look like small yellow spots are actually a striking metallic gold color.

Eleven days later, on August 26 at 9 AM, the chrysalis suddenly became transparent:

Monarch chrysalis - ready - left

Monarch chrysalis – ready – left


Monarch chrysalis - ready - right

Monarch chrysalis – ready – right

The shape of the butterfly becomes visible in reflected light:

Monarch chrysalis - ready - ventral detail

Monarch chrysalis – ready – ventral detail

The gold dots and line remained visible.

The magic happened at 3 PM:

Monarch chrysalis - emerging - unfolding

Monarch chrysalis – emerging – unfolding

The compacted wings emerge intense orange on the top and lighter orange on the bottom:

Monarch unfolding - left

Monarch unfolding – left

The butterfly took most of the day to unfurl and stiffen its wings into flat plates:

Monarch unfolding - dorsal

Monarch unfolding – dorsal


Monarch unfolding - right

Monarch unfolding – right

By 8 PM it began exploring the aquarium:

Monarch unfolded - right

Monarch unfolded – right

As adults, they sip nectar from flowers, but don’t feed for the first day, so we left it in the aquarium overnight.

At 10 AM on August 27, we transported it to the goldenrod in the garden, where it immediately began tanking operations:

Monarch on Milkweed - left

Monarch on Milkweed – left

A few minutes later, it began sun-warming operations:

Monarch on Milkweed - dorsal

Monarch on Milkweed – dorsal

Mary watched it while she was tending the garden and, an hour or so later, saw it take off and fly over the house in a generally southwest direction. It will cross half the continent under a geas prohibiting any other action, eventually overwinter in Mexico with far too few of its compadres, then die after producing the eggs for a generation beginning the northward journey next year.

Godspeed, little butterfly, godspeed …

In the spirit of “video or it didn’t happen”, there’s a 15 fps movie of the emergence taken at 5 s/image.


Mystery Eggs on Glass

An array of tiny eggs appeared on the outside of our bedroom window:

Insect eggs on glass - 2017-09-17

Insect eggs on glass – 2017-09-17

The patch measures 12 mm across and 14 mm tall. From across the room, it looks like a smudge, but it consists of hundreds of eggs, each on a tiny stalk glued to the glass:

IMG_20170919 vs 0917- Insect eggs on glass

IMG_20170919 vs 0917- Insect eggs on glass

The bottom image is two days later than the top one, both are scaled to about the same size and contrast. The critters look about the same, although I think the lines have more prominent ripples or bumps.

We have no idea what they’ll turn into, but they certainly look like they have two eyes and wings …


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60 kHz Tuning Fork Resonator: Maximum Overdrive

Datasheets loosely associated with the tuning fork resonators in hand suggest 1 μW maximum drive power, which works out to maybe 100 mVrms = 150 mVpk at about 10 kΩ ESR. If you inadvertently apply 500 mVpk = 375 mVrms, the resulting 14 μW does this:

Broken 60 kHz Tuning Fork Resonator - overview

Broken 60 kHz Tuning Fork Resonator – overview

I was applying a precisely tuned 60 kHz sine wave to the first pass at a crystal filter grafted onto the loop antenna preamp and wasn’t paying attention to the amplitude. For all I know, though, the poor thing died from a power-on transient. I’m pretty sure I didn’t break it during extraction, because it stopped being a resonator while in the circuit.

The missing tine fell out of the can:

Broken 60 kHz Tuning Fork Resonator - tine detail

Broken 60 kHz Tuning Fork Resonator – tine detail

Laser trim scars form a triangle near the tip, a T a bit further down, a slot just above the nicely etched gap.

A closer look at the fractured base:

Broken 60 kHz Tuning Fork Resonator - detail

Broken 60 kHz Tuning Fork Resonator – detail

The metalization appears black here and gold in person.

So, yeah, one down and 49 to go …



Monthly Image: Orb-Weaving Spider

Once again, the season of orb-weaving spiders has arrived, with this one building her web across a living room window:

Orb Weaving Spider - with insect

Orb Weaving Spider – with insect

I set the Sony HDR-AS30V atop a tripod, told it to take photos at 5 second intervals, then stitched the images into a Youtube video. It won’t go viral, but watching the spider construct her web over the course of two hours was fascinating.

She finishes the spiral at about 1 m video = 1.25 h real time, settles down for what might be a nap (it’s hard to tell with spiders), and has an insect join her for supper at 1:28, half an hour later. Spiders go from “inert” to “death incoming” almost instantly, even in real time running.

Another orb weaver set up shop in the adjacent window, but moved out the next day. Perhaps there’s a minimum spacing requirement?

Two more orb weavers guard windows in the kitchen and laundry room. We sometimes leave the lights on for them.

YouTube has other web-building videos with far more detail, of course.

The magic incantation to create the video from a directory of images in the form DSC01234.JPG:

sn=1 ; for f in *JPG ; do printf -v dn 'dsc%04d.jpg' "$(( sn++ ))" ; mv $f $dn ; done
ffmpeg -r 15 -i /mnt/video/2017-09-03/100MSDCF/dsc%04d.jpg -q 1 Orb-Weaving-2017-09-03.mp4


LF Crystal Tester: 60 kHz Resonator Frequency Distribution

Histogramming all 50-ish resonator frequencies shows reasonably good distributions:

Notably, there’s no obvious suckout in the middle, as with those eBay Hall-effect sensors.

60 kHz Resonant Frequencies - CX 24 pF - histogram

60 kHz Resonant Frequencies – CX 24 pF – histogram

I don’t know what to make of the difference between the parallel series-capacitor and basic serial resonant frequencies for each tuning fork:

60 kHz Resonant Frequencies - CX 24 pF - delta histogram

60 kHz Resonant Frequencies – CX 24 pF – delta histogram

Perhaps each resonator’s frequency depends on its (laser-trimmed) tine mass and follows a more-or-less normal distribution, but the parallel-serial difference series capacitor changes the frequency based on (well-controlled) etched dimensions producing quantized results from three different masks / wafers / lots, with the motional inductance and capacitance incompletely modeling the physics?

For reference, the resonators look like this:

Quartz resonator - detail

Quartz resonator – detail

Producing the histograms uses the LibreOffice frequency() array function, which requires remembering to whack Ctrl-Shift Enter to activate the function’s array-ness.

[Update: Faceplant about “parallel” resonance, which is actually the shifted resonant peak due to the 24 pF series cap. Apparently I typo-ed the second histogram subheading and ran with the error; the figures are now correct.]

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