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Archive for August, 2014

Milkweed Tussock Moth

Although we no longer see Monarch butterflies, our milkweed patch attracts Milkweed Tussock Moth caterpillars:

Milkweed Tussock Caterpillar

Milkweed Tussock Caterpillar

This one apparently died on the patio step, half the house away from the milkweed patch, and the rear spines (on the right) have begun falling out. During the next week, I teleported two more from that step to the patch, under the assumption they’d be happier on a tasty leaf than on a slate slab.

They were all early instars, very short and quite fuzzy. Later instars will be much longer, with more distinct tussocks.

I wonder if you could shear them and use the “fur” for decoration? It wouldn’t spin into thread like wool, but someone, somewhere, has surely performed art with Tussock Caterpillar spines…

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Real Estate Sale Signage

Real Estate Agencies used to post property marker signs like this:

FSReEx-168

FSReEx-168

Even far off to the side, a bright background color catches your eye:

FSWeRe-107

FSWeRe-107

The signs sported primary colors, reasonably large type, and simple words, making them almost readable in those pictures and definitely legible from the driver’s seat. While not particularly handsome or stylin’, they got the message across: this house is for sale.

Then a strange thing happened.

Berkshire Hathaway somehow got into the real estate business and Borged several of the local agencies. BH being a Name Brand with a connotation of wealth & taste, their branding imposed a subtle touch on the new signage:

FSBkHath-113

FSBkHath-113

No, you can’t quite read that in real life, either, although the agent’s name and number on the header come close to the old standard.

One day, a old-school sign appeared along one of our usual routes:

FSHoLa-127

FSHoLa-127

Although white and green don’t pop out of the background, the sign has enough contrast that you can read what’s needed.

Then they became affiliated with Christie’s, the Big Name in the realm of high-end auctions. I have no idea what Christie’s has to do with real estate, but if Berkshire Hathaway can do it, it seems Christie’s thinks they can do it even better.

In any event, the Christie’s Corporate Standard evidently calls for very, very subtle signage:

FSShort-231

That sign might mark a high-end bed and breakfast, but certainly does not tell me that the place is for sale: none of the text approaches readability from the street, certainly not at normal travel speeds, and nothing about it even suggests that I should take action.

A few weeks later, two hang tags added a COMMERCIAL note (the property evidently has potential to become an office or retail space) and the agent’s name and phone number in minuscule type:

FSBase-128

FSBase-128

After a while, a very bright red do-it-yourself HOUSE FOR SALE placard suggested the property owner wasn’t entirely satisfied with the results to date:

FSSign-148

FSSign-148

The high-contrast black-on-white FOR SALE header definitely doesn’t match the rest of the sign, but its more legible information might motivate you to pause and puzzle out the rest. The red placard vanished a few days after the header appeared, leaving us with this peculiar mix:

FSHeader-153

FSHeader-153

None of the (numerous) Christie’s signs in the area have a header, so this may be a case of a squeaky wheel getting greased. I won’t be surprised to see a corporate image change, including larger type, as these fancy signs weather away.

Perhaps the correct conclusion to be drawn is that, in this Internet age, nobody buys a house based on the quaint custom of driving by a house-with-sign, thinking “Hey, that’s perfect for me!”, and calling the agent, so there’s no need for anything more than a pro-forma marker identifying a property that will be selected by filters applied to MLS / Zillow databases.

The most recent change simplifies the sign to the bare minimum:

FSMissing

FSMissing

Perhaps we’ve witnessed a falling-out over typography?

This began as a test of the Sony HDR-AS30V camera’s resolution, with the obvious conclusion it wasn’t intended as a camera suitable for recording text.

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ET227 Transistor DC Current Gain Variation

A Squidwrench Weekly Doings being useful for short-attention-span projects, I measured the DC current gain for all five ET227 transistors. The test conditions fall far below the ET227’s 1 kV / 100 A ratings, but they’re roughly what the sewing machine motor controller calls for.

The transistors don’t even begin to turn on until IB gets over about 50 mA, because there’s a 13 Ω shunt resistor (as measured, for either polarity) between the base and emitter terminal:

Fuji ET227 - equivalent circuit

Fuji ET227 – equivalent circuit

In the ET227’s normal use, that resistor dumps the Miller effect charge injected from the collector (with the intent of improving the switching time), but you must ram nearly 70 mA into the resistor to get 900 mV at the base, so the actual transistor base current isn’t all that high for low collector currents. But you measure gain by dividing goes-outa by goes-inta, so that’s what I’ll do.

The ET227 needs something like IB = 30 A to switch 100 A at the collector, so a few dozen mA into that resistor rounds off to zilch for its usual driver circuit. FWIW, with IB = 30 A, VBE tops out at 2 V: the resistor carries 150 mA and dissipates 300 mW.

Anyhow, randomly labeling the transistors from A (on the heatsink) through E, then hitching them up to a 1.8 A bench supply with a 33 Ω resistor to the base terminal provided some readings at single-digit collector voltages.

For IB = 72 mA:

IB IC hFE
A 72 490 6.8
B 73 540 7.4
C 74 480 6.5
D 75 440 5.9
E 76 520 6.8

For IB = 108 mA, with one bumped-knob outlier:

IB IC hFE
A 108 1220 11.3
B 101 1190 11.8
C 108 1280 11.9
D 108 1170 10.8
E 108 1320 12.2

Although the gain around 1 A comes out slightly higher than while running the motor, it’s in the same ballpark. This is not a high-gain device: it’ll need a driver after the optoisolator to squeeze enough current through the collector.

Eks tried to unload a huge old Tek transistor curve tracer on me that would be ideal for this sort of thing. I’m still not tempted…

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Revlon Tweezers: Bad Spot Welds

Mary bought a pair of Revlon tweezers a while ago, picking a Name Brand to avoid hassles with bottom-dollar crap:

Revlon tweezers - bad spot welds

Revlon tweezers – bad spot welds

Well, that didn’t work.

I contend that the only difference between Name Brands and the bottom-dollar crap I tend to buy is a bit of QC and a lot of price. I’ll agree that’s not strictly true, but it does fit a goodly chunk of the observed data.

Anyhow.

I milled a recess into the corner of some scrap plastic to locate the handle end, then arranged a step block to capture the business end:

Revlon tweezers - drilling setup

Revlon tweezers – drilling setup

That setup ensures the holes go into the corresponding spots on both pieces, because I couldn’t figure out how to clamp them together and drill them both at once. I drilled the other piece with its good side up to align the holes; doing it bad side up would offset the holes if they’re not exactly along the center line.

A closer look:

Revlon tweezers - drilling fixture

Revlon tweezers – drilling fixture

Talk about a precarious grip on the workpiece!

I filed the welds flat before drilling, so the pieces lay flat and didn’t distract the drill.

Then:

  • Center-drill
  • Drill 2-56 clearance
  • Scuff up mating surfaces with coarse sandpaper
  • Apply epoxy
  • Insert screws
  • Add Loctite
  • Tighten nuts to a snug fit
  • Align jaws
  • Tighten nuts
  • Fine-tune jaw alignment
  • Apply mild clamping force to hold jaws together
  • Wait overnight
  • Saw screws and file flush
  • Done!

The clamping step:

Revlon tweezers - epoxy curing

Revlon tweezers – epoxy curing

Those nicely aligned and ground-to-fit jaws were the reason Mary bought this thing in the first place.

The screw heads look OK, in a techie sort of way:

Revlon tweezers - fixed - front

Revlon tweezers – fixed – front

The backside won’t win any awards:

Revlon tweezers - fixed - rear

Revlon tweezers – fixed – rear

But it won’t come apart ever again!

There’s surely a Revlon warranty covering manufacturing defects, printed on the long-discarded packaging, that requires mailing the parts with the original receipt back to some random address at our own expense.

Ptui!

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Booklet Printing

Most technical papers intended for publication in Refereed Journals have huge margins. When I print them up as pamphlets for E-Z reading in the Comfy Chair, the text becomes an unreadably small block in the middle of the page.

Having tried various simple hacks that don’t work, the best solution so far involves a bit of PostScript magic…

pdfcrop --margins 36 whatever.pdf
pdftops -level3 -origpagesizes whatever-crop.pdf
ps2book.pl -f 1 whatever-crop.ps
ps2pdf whatever-crop_book.ps

Which will emit whatever-crop_book.pdf. Print the odd pages, reinsert the stack, print the even pages, then either fold or slice/bind as appropriate.

The --margins 36 puts a little whitespace around the text, which may be needed to get the text block out of the gutter if you’re binding the booklet. For those documents, --margins "36 0 18 0" may be more useful; note the blanks, not commas. This requires tuning for best picture, depending on the incoming PDF layout.

The -origpagesizes prevents the next step from assuming an incorrect page size. This is definitely necessary, at least in my experience so far.

The -f 1 enlarges the source text to fill the output page, which is the key step making the whole thing work for small incoming page sizes. However, there’s a weird interaction between this and the pdfcrop margins that I haven’t figured out yet; a zero-width incoming margin [may | may not] jam some line ends against the right edge of the output sheet.

That’s all derived from some booklet-printing hints in the Scribus wiki. A working link (as of today, anyhow) for the ps2book.pl script:

http://www.capca.ucalgary.ca/wdobler/utils/ps2book.xhtml

The R380 emits pages bassackwards for reading, but in the proper order for duplexing: the blank side of the first sheet is on the bottom of the stack, so it becomes the top of the flipped stack, ready to go back into the printer as the first sheet again.

Conversely, the HPLJ1200 produces output in normal reading order, with the blank side of the last sheet on top of the stack: flip and print the back sides in reverse order.

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FT82-43 Slit Toroid: Calibration

I’d have trouble faking this with a straight face:

FT82-43 - 56 turns - 24 AWG

FT82-43 – 56 turns – 24 AWG

That’s measured with the 56 turn winding connected directly to a bench power supply, cranking up the current, taking the reading, and turning the current back down again, so as to avoid cooking the poor thing inside its PLA armor:

FT82-43 toroid - mounted

FT82-43 toroid – mounted

The “49E” sensor came from one of the bags of eBay fallout. They saturate around 4.25 V; the outputs above 4 V lose their linearity due to the sensor, not ferrite saturation.

The original calculations guesstimates suggested 25 turns would produce full scale at 5 A, so 56 turns should top out at 2.2 A. Frankly, given all the imponderables in this lashup, a factor of two seems pretty close.

Offsetting the output by -1 A would yield a 2 A range that’s just about exactly right. Unfortunately, some fiddling about with neodymium magnets suggests that you (well, I) can’t stuff enough opposing field into the slit without saturating (some part of) the ferrite core, reducing the permeability, and blowing all the assumptions.

So that suggests a buck winding, obviously with more turns to allow less current for the same magnetizing force. Wrapping 110 turns reduces the buck current to 500 mA and assuming a bit over an inch/turn requires 10 feet, which is nearly 1 Ω of 30 AWG wire: the buck current dumps another 250 mW into (a somewhat larger version of) that PLA armor.

Or just throw away half of the Hall effect sensor range and use an op amp along the lines of the LED current sensor.

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NP-BX1 Lithium Batteries: 6 Month Status

The battery capacities after six months are, of course, lower:

Sony NP-BX1 - OEM Wasabi - 2014-08-17

Sony NP-BX1 – OEM Wasabi – 2014-08-17

I didn’t bring the HDR-AS30V camera along on the Hudson River ride, simply because each battery lasts about 1.5 hr in 1920×1080 @ 60 fps mode and I wasn’t up to replacing batteries during the ride, then charging all three every evening. Obviously, the camera wasn’t intended for that use case.

Somewhat surprisingly, the Wasabi batteries deliver the same continuous run time as the Sony battery: 1:30 vs 1:33. I used 250 mA for those discharge curves, but I think something around 500 mA would better match the camera load.

I’m sorely tempted to drill a hole in the camera’s case and wire in a honkin’ big prismatic lithium cell.

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