Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Category: Science
If you measure something often enough, it becomes science
Spotted in a soon-to-be-rebuilt rest area on I-87 north of Kingston NY, a chandelier stuffed with old-school CFL bulbs of various vintages:
NYS I-87 Rest Area – CFL chandelier
The yellowish dome on the far right might still house an incandescent bulb, but I can’t tell from here.
Judging from the high color temperature and even illumination, the chandelier next to it has 16 newish LED bulbs:
NYS I-87 Rest Area – LED chandelier
What’s of interest: both chandeliers have two dead bulbs and, perhaps, the center floodlight of the LED fixture had died, too. We don’t know how long they’ve been in place, other than that the LEDs are certainly more recent, but a 6% failure rate is nothing to brag about.
From what I’ve seen, the reliability of both CFL and LED bulbs is greatly overstated and certainly do not justify preemptive replacement of a working bulb of any vintage.
Each air conditioning unit has a pair of lightning rods atop it, with their aluminum grounding cables securely clamped to the steel frame underneath.
The rod reclining on its side caught my eye. Perhaps its fat cable wasn’t relaxed enough during installation, although I thought those wide bases would be firmly screwed to the unit’s steel top. Of course, that could be the only one without screws.
The building extends another three stories upward from that roof, but our experience suggests lightning strikes where it will.
The trail camera uses two parallel banks of four series AA cells to get enough oomph for its IR floodlight. I’m not convinced using bucked lithium AA cells in that configuration is a Good Idea, but it’s worth investigating.
These are labeled HW, rather than Fuvaly, because it seems one cannot swim twice in the same river:
HW bucked Li AA cells
In any event, they come close to their claimed 2.8 W·hr capacity:
HW bucked Li AA – 2023-05
The lower pair of traces (red & black) are single cells at 2.7-ish W·hr, the blue trace is a pair at 5.4 W·hr, and the green trace is a quartet at 9.8 W·hr. Surprisingly close, given some previous results in this field.
Recharging the cells after those tests shows they all take 3 hours ± a few minutes to soak up 730 mA·hr ± a few mA·hr, so they’re decently matched.
Measuring the terminal voltage with a 10 mA load after that charge lets me match a pair of quartets to 1 mV, which is obviously absurd:
HW bucked Li cells – initial charge 2023-05-05
The numbers in the upper left corner show the initial charge of four cells at a time required the same time within a minute and the same energy within 4%.
Sticking them in the trail camera must await using up the current set of alkaline AA cells.
Bonus: a lithium fire in a trail camera won’t burn down the house.
After all, pictures like this are definitely worth the hassle:
According to the manual, which I have hitherto had no reason to doubt, our non-turbo 2015 Subaru Forester has a 15.9 gallon fuel tank:
Subaru Forester – Fuel Capacity Chart
One screen shown on the dashboard’s Multi-Function Display gives the current mileage and estimated range:
Forester – MPG Range
Dividing those two numbers gives you 13.97 gallons, the current fuel level. As you’d expect, should the average miles per gallon change, the range will change accordingly.
The trip odometer says we have driven 72.8 miles since I filled the tank. Dividing that by the average mpg gives 2.3 gallons, so the tank could possibly hold 16.2 gallons, which, given all the averages involved, is reasonably close to the 15.9 gallons shown in the manual.
Being that type of guy, I have a spreadsheet tallying each fillup since the car was new:
8.1 gal average
7.5 gal median
13.9 gal maximum
Long ago, my father taught me to fill the tank when the needle got halfway down and I’ve been doing so ever since. As a result, we have only rarely seen the Low Fuel Warning Light:
Subaru Forester – Low Fuel Warning Light info
A concatenation of unavoidable events put us southbound on I-87 when that light went on. Given the estimated range of 70-ish miles, I planned to refuel at the New Baltimore Service Area, about a dozen miles ahead.
The engine shut down and all the dashboard warning lights lit up with the Service Area Ahead sign in view:
Out of Gas – Service Area Ahead
All the “facilities” are blank because they’re rebuilding the whole place, with the gas station remaining open.
So I slapped the shifter into neutral and we drifted slowly along the shoulder, under the bridge visible ahead, and eventually came to a halt at the beginning of the exit lane.
There was only one thing to do:
Out of Gas – Walking On
Some storytelling later:
Out of Gas – Walking Back
Just because I could:
Refueling – GPS Track
For what are, I trust, understandable reasons, I started the tracker after I began hiking and forgot to turn it off before driving away.
After figuring out the devilishly complex spring-loaded anti-spill spout on the gas can, we drove 1500 feet to the Service Area:
Out of Gas – Service Station
As usual, I filled the tank until the nozzle automatically shut off, for a total of 13.554 gallons in two transactions:
Pump Receipts
Now, it is possible the Forester fuel system has another 2.3 gallons tucked away somewhere, but if that reserve doesn’t make the wheels go around, it’s not doing me the least bit of good.
The fact that I’ve occasionally added just short of 14 gallons suggests the estimated remaining capacity depends strongly on the average mileage up to that point and I have come very very close to running out of gas on several occasions.
As far as I can tell, the usable fuel capacity is a scant 14 gallons and the Low Fuel Light goes on with, at most, a dozen more miles in the tank.
This is the second time in more than half a century of driving I’ve run out of gas.
My father was right and I shall henceforth mend my wayward behavior.
The next morning the dead section lit up again, albeit with a dim ring at its right end. I think one LED in that string failed open and darkened the whole string, then failed short under the voltage stress, and is now quietly simmering in there with slightly higher than usual current.
The lights over the workbench weren’t in the first wave of conversions, so they may be only four years old.
For sure, they have yet to approach their 50000 hour lifetime …
This was really a thinly veiled excuse for a deeper look at the QR code generator encoding the myriad parameters required to create the box and see what happens when you try to burn such a complex thing into chipboard.
Spoiler: chipboard has very low contrast and really does not work well with high-density QR codes.
Although the festi.info box generator can produce QR codes, I used qrencode (available in your Linux distro) on the command line to generate QR code image files with specific settings:
--size → size of the smallest square (“module”) in pixels
--dpi → DPI of the output image file
The default file type is PNG. The unusual 254 DPI makes each pixel exactly 0.1 mm wide and a peculiar 169.33 DPI = 0.15 mm came in handy for the first pattern.
The final parameter is the character string to encode, which you should definitely quote to prevent the shell from wrecking things while trying to help you.
A pattern with 4×4 pixel modules didn’t scan at all:
Chipboard QR code – 15pct 0.15mm 4×4 – overview
A closer look shows the modules have ragged edges due to laser timing variations during the engraving scans and gaps between successive scans because the spot size is less than the 0.15 mm scan interval:
Chipboard QR code – 15pct 0.15mm 4×4 – detail
Increasing the module to 6×6 pixels at a 0.1 mm scan interval :
Chipboard QR code – 15pct 0.10mm 6×6 – overview
A closer look shows the larger module reduces the relative size of the timing errors, while the decreased line spacing tidies up the blocks:
Chipboard QR code – 15pct 0.10mm 6×6 – detail
Reducing the power from 15% to 10% reduced the contrast to the point of illegibility:
Chipboard QR code – 10pct 0.10mm 6×6 – overview
A closer look shows the engraving barely punches through the surface and has somewhat more ragged edges due to the tube’s pulsating startup current at very low power:
Chipboard QR code – 10pct 0.10mm 6×6 – detail
I also tried 5×5 modules with similar results.
The laser spot size sets the engraving scan interval, which then determines the DPI value for the QR code image. With all that matched up, you can send the images directly to the laser in Passthrough mode, without having LightBurn resample the pixels and change the module’s shape.
Looked at from a different angle: given the laser spot size and the module size, the QR code image size is not under your control.
From another angle: given a QR code image size in, say, millimeters, and the engraving scan interval, the module size is not under your control.
All this is moot if you print QR codes on a high-resolution / high-contrast printer. It’s just the gritty nature of laser cuttery that limits what you can accomplish.
And, of course, using a material less awful than chipboard will definitely improve the results.
If you want a similar box of your own, here ya go:
The Smell of Molten Projects in the Morning 