Archive for category Science

Monthly Image: Cross-striped Cabbageworm

In the normal course of events, this critter would become an undistinguished brown moth:

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Right now, it’s a two-day-old cross-striped cabbageworm. Its kin are voracious consumers of Brassicacae out in the garden and Mary’s raising it as a show-n-tell exhibit for her Master Gardener compadres; she advised it to not start any long novels.

Taken hand-held with the Pixel XL through a clip-on 10x macro lens.


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Monarch Caterpillar Windshield

The Monarch Butterfly egg produced a teeny caterpillar:

Monarch caterpillar - 3 mm - 2017-08-02

Monarch caterpillar – 3 mm – 2017-08-02

Each time it molts, it eats all of its skin except for the transparent cap over the first body segment:

Monarch Windshield - 2017-08-09

Monarch Windshield – 2017-08-09

If the rest of the caterpillar were behind the windshield, it’d be feet-upward with its “face” at the top.

The picture comes from a focus-stacked set of microscope images captured with VLC; I turned the positioner’s elevation knob the smallest possible amount between each of 16 images along the 1 mm (-ish) height of the capsule. This magic incantation applies more weight to high-contrast and high-entropy regions:

align_image_stack -C -a monarch vlcsnap-2017-08-09-18h4*
enfuse --contrast-weight=0.8 --entropy-weight=0.8 -o Monarch_Windshield.jpg monarch00*
# empty line to reveal underscores in previous line

That came out pretty well.


Canon NB-5L Battery Status

My pocket camera has begun kvetching about a low battery rather more often than before, which suggests the batteries I’ve been using since 2014 have gone beyond their best-used-by date.

This came as no surprise:

Canon NB-5L - 2017-08-05

Canon NB-5L – 2017-08-05

I re-ran a couple of the batteries to make sure they hadn’t faded away from disuse, which didn’t materially change the results. The lightly used Canon OEM battery continues to lead the, ah, pack.

The camera’s lens capsule accumulated a fair bit of dust from many years in my pocket, which lowers its overall contrast and wrecks the high f/ images produced with the microscope adapter.

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Monarch Butterfly Egg

We watched a female Monarch Butterfly lay eggs on the stand of milkweed behind the house. She also found a lone plant in the vegetable garden that’s now standing in a vase on the kitchen table where we can keep an eye on the proceedings.

So far, so good:

Monarch Butterfly Egg on Milkweed Leaf - 2017-07-29

Monarch Butterfly Egg on Milkweed Leaf – 2017-07-29

I never knew Monarch eggs were so elaborate!

Captured with the VGA-resolution USB camera atop the zoom microscope, with VLC applying automagic gamma and level adjustment.

Focus-stacking the three best images helps the ribs toward the leaf, but not by much:

Monarch Egg - focus stacked

Monarch Egg – focus stacked

After picking out the images, all of which bear VLC’s auto-generated names like vlcsnap-2017-07-29-09h26m25s720.png, stack them thusly:

align_image_stack -C -a milkweed *png
enfuse -o Monarch.jpg milkweed000*

Tinkering with the options might improve things, but … maybe next time.

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Monthly Science: Final WS2812 Failures

My “exhibit” at the MHV LUG Mad Science Fair consisted of glowy and blinky LED goodness, with an array of vacuum tubes, bulbs, and the WS2812 and SK6812 test fixtures:

MHVLUG Science Fair - Chastain - highres_463020980

MHVLUG Science Fair – Chastain – highres_463020980

They look much better without a flash, honest. The cut-up cardboard box threw much needed shade; the auditorium has big incandescent can lights directly overhead.

Anyhow, what with one thing and another, the two LED test fixtures spent another few dark and cool days in the Basement Laboratory. When I finally plugged them in, the SK6812 RGBW LED array light up just fine, but three more WS2812 RGB LEDs went toes-up:

WS2812 LED test fixture - more failures

WS2812 LED test fixture – more failures

That brought the total to about 8 (one looks like it’s working)  out of 28: call it a 28% failure rate. While WS2812 LEDs don’t offer much in the way of reliability, running them continuously seems to minimize the carnage.

So I wired around the new deaders and took that picture.

Flushed with success and anxious to get this over with, I sealed the tester in a plastic bag and tossed it in the freezer for a few hours …

Which promptly killed most of the remaining WS2812 chips, to the extent even a protracted session on the Squidwrench Operating Table couldn’t fix it. When I though I had all the deaders bypassed, an LED early in the string would wig out and flip the panel back to pinball panic mode.

It’s not a 100% failure rate, but close enough: they’re dead to me.

As the remaining WS2812 LEDs on the various vacuum tubes and bulbs go bad, I’m replacing them with SK6812 RGBW LEDs.

For whatever it’s worth, freezing the SK6812 tester had no effect: all 25 LEDs lit up perfectly and run fine. Maybe some of those chips will die in a few days, but, to date, they’ve been utterly reliable.


Monthly Image: Mystery Lizard

We found this critter keeping a watchful eye on the construction at Adams Fairacre Farms during our most recent grocery trip:

Mystery frilled lizard - detail

Mystery frilled lizard – detail

I think it’s an undocumented alien that entered the US stowed away in a tropical plant, because it was affixed to the array of ceramic pots outside their (open) greenhouse windows:

Mystery frilled lizard

Mystery frilled lizard

To the best of my admittedly limited herpetological knowledge, none of our native lizards / geckos / whatever have such a distinctive dorsal frill / fin / ridge. I have no idea how to look the critter up, though.

We left it to seek its own destiny. Unless it’s a mated female (hard to tell with lizards), it’ll have a lonely life.

Perhaps it practices rishratha, which is entirely possible.


AD9850 Module: Oscillator Thermal Time Constant

With an LM75 atop the 125 MHz oscillator and the whole thing wrapped in foam:

LM75A Temperature Sensor - installed

LM75A Temperature Sensor – installed

Let it cool overnight in the Basement Laboratory, fire it up, record the temperature every 30 seconds, and get the slightly chunky blue curve:

125 MHz Oscillator - Heating Time Constant

125 MHz Oscillator – Heating Time Constant

Because we know this is one of those exponential-approach problems, the equation looks like:

Temp(t) = Tfinal + (Tinit - Tfinal) × e-t/τ

We can find the time constant by either going through the hassle of an RMS curve fit or just winging it by assuming:

  • The initial temperature, which is 22.5 °C = close to 22.7 °C ambient
  • The final temperature (call it 42 °C)
  • Any good data point will suffice

The point at 480 s is a nice, round 40 °C, so plug ’em in:

40.0 = 42.0 + (22.7 - 42.0) × e-480/τ

Turning the crank produces τ = 212 s, which looks about right.

Trying it again with the 36.125 °C point at 240 s pops out 200.0 °C.

Time for a third opinion!

Because we live in the future, the ever-so-smooth red curve comes from unleashing LibreOffice Calc’s Goal Seek to find a time constant that minimizes the RMS Error. After a moment, it suggests 199.4 s, which I’ll accept as definitive.

The spreadsheet looks like this:

T_init 22.5
T_final 42.0
Tau 199.4
Time s Temp °C Exp App Error²
0 22.250 22.500 0.063
30 25.500 25.224 0.076
60 28.000 27.567 0.187
90 30.125 29.583 0.294
120 31.750 31.317 0.187
150 33.250 32.810 0.194
180 34.375 34.093 0.079
210 35.375 35.198 0.031
240 36.125 36.148 0.001
270 36.813 36.965 0.023
300 37.500 37.668 0.028
330 38.125 38.273 0.022
360 38.500 38.794 0.086
390 39.000 39.242 0.058
420 39.500 39.627 0.016
450 39.750 39.959 0.043
480 40.000 40.244 0.059
510 40.250 40.489 0.057
540 40.500 40.700 0.040
570 40.750 40.882 0.017
600 41.000 41.038 0.001
RMS Error 0.273

The Exp App column is the exponential equation, assuming the three variables at the top, the Error² column is the squared error between the measurement and the equation, and the RMS Error cell contains the square root of the average of those squared errors.

The Goal Seeker couldn’t push RMS Error to zero and gave up with Tau = 199.4. That’s sensitive to the initial and final temperatures, but close enough to my back of the envelope to remind me not to screw around with extensive calculations when “two minutes” will suffice.

Basically, after five time constants = 1000 s = 15 minutes, the oscillator is stable enough to not worry about.