The Smell of Molten Projects in the Morning
Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
If you measure something often enough, it becomes science
The Hobo datalogger buried in the dirt under the patio kvetched about a low battery, which produced this surprising result:
Cells from the same lot have been doing just fine in the other dataloggers, so I hope this is a one-off weak cell and not the harbinger of another run of dead cells.
I replaced a dead 75 W halogen PAR30 bulb over the kitchen sink with a Satco S9415 LED bulb that was, at the time, advertised as “75 W equivalent”:
It’s noticeably less bright than the surviving halogen bulb, which is what you’d expect when 950 lm goes head-to-head with 1100+ lm (based on casual searching), but with a similar color temperature and beam pattern, so it’s Good Enough. I should have bought two and converted the halogens into glass sculptures.
The difference between the 22.8 year Life and the 3 Year Warranty always seems amusing. The warranty requires returning the bulb, so that’s about useless …
A bag of the Sakura Micron pens I was adapting for the HP 7475A plotter, before the generous donation of New Old Stock plotter pens arrived, come in a variety of useful widths:
This relentlessly organized doodle happened while reading some tech docs on the Comfy Couch:
The first two lines obviously belong in their own group, but, hey, it’s a doodle.
The two Uni-Ball Kuru Toga pencils, in 0.5 and 0.7 mm, have diamond-impregnated lead that’s supposed to be much more break-resistant than usual. I fear that they’ll land point-downward and wreck the rotating sleeve surrounding the lead, so I’ve managed zero drops so far. Even I hesitated at the 0.3 mm version.
Just for fun, I measured the J5 V2 flashlight’s current, by the simple expedient of unscrewing the cap and bridging the battery-to-case-threads gap with a multimeter:
The results:
As nearly as I can tell, they’re connecting the 18650 cell directly across the LED for High and PWM-ing it down to 50% and 25%. The PWM frequency is low enough to be visible during eye saccades and flashlight motions.
The flashlight knows how to do all five modes without its tail cap, so the controller + FET must live behind the LED. I can’t tell if the switch in the tail cap is just a dumb pushbutton (with, it seems, a surprising & ill-controlled resistance) or doing something clever with resistive levels (because the resistance varies with each push); at some point this thing will fail in an amusing manner and I’ll take it apart to find out.
The High setting dissipates 11 W (!) that pushes the flashlight well beyond uncomfortably warm within five minutes, so that’s not a useful long-term setting. The little alien egg beside the LED melted into a puddle during those five minutes; at least it won’t be moving anywhere else.
Setting it to Low = 25% PWM duty cycle = 0.7 A (average, sorta-kinda), a freshly charged 18650 cell lasts for about five hours down to 3.6 V, which is pretty close to the cell’s 3.4 A·h rating (kinda-sorta, ignoring the decreasing cell voltage, etc). That suggests Medium would last maybe two hours, tops, and there’s not enough heatsinking to discover how long High would last.
After 8.5 hours the cell was down to 3.2 V and the LED was, as you’d expect, rather dim. You could click to High for more light, of course, trading off runtime for brightness.
The square LED emitter array produces a square light pattern that’s not aligned with the flats on the body, so if you happened to be thinking of clamping a holder onto those flats, be prepared for some custom rotation to align the pattern with the outside world. That obviously doesn’t matter in a hand-held flashlight, but a bike headlight might look weird.
The zoom slider goes from a focused square (at full extension) to a well-filled round disk (at minimum length) with a diameter about five times the square’s side. I think the smooth zoom motion comes from grease-on-O-ring viscosity rather than precision machining.
The original back of the envelope data:
These emerged from a hidden corner of a basement shelf, where they’ve been sitting undisturbed for far too long:
I’ve known for a while that the PETE plastic used for nearly all bottles isn’t completely waterproof, but never had occasion to measure the results.
The laser-etched date code on the bottles says they “expired” in late August 2012, so, assuming one year of shelf life, they’ve been quietly evaporating for five years.
Sampling a few bottles shows a nearly uniform weight of 459 g. A drained bottles weighs 13 g, so let’s say the bottles now contain 445 g of water. They should start out with 500 g, although I’d be mildly surprised if it wasn’t a bit over that to prevent some dork from complaining about getting only 498 g.
Rounding in all the right directions, losing 60 g during five years works out to a tidy 1 g/month in a basement room at 60% RH.
The surface area of those wonderfully convoluted bottles might be 300 cm², so they lose 3 mg/cm²·month.
They’re near enough to 0.10 mm thick, which I’m sure is a compromise between reducing weight (and, thus, plastic cost) and incurring messy failures during normal handling. The evaporation rate surely varies as an inverse exponential of thickness, but I’m not going there.
I’m certain water bottlers know those numbers to several decimal places and can plot them versus all the interesting variables.
Memo to Self: don’t lose track of the water bottles!
After two weeks of more-or-less daily use, without any further seasoning:
The seasoning in between the scuffs & scrapes remains in fine shape. Running the Scotchbrite pad around the perimeter obviously wears the coating, but, on the whole, nothing sticks anywhere.
I’ve started re-seasoning it after each use, which isn’t a big deal, and we’ll see how the scratches level out.
The lovely gray-black patina on the nubbly outside surface from the original moderate-woo oven seasoning requires no further attention.
Although I’m not the type of guy who thinks twinkly LEDs will enhance his apparel, one of Mary’s quilting thread sources had a closeout deal on their “wearable electronics”, including a large cone of stainless steel thread / yarn:
… CR2032 lithium cells & holders, plus assorted LEDs on small PCBs.
The usual advice for connecting the thread seems to involve knotting it through the PCB holes, then sewing it to the backing fabric. Alas, I’m bad with knots and the stainless steel yarn isn’t all that cohesive:
The holder has an even smaller hole, but Mary gave me a needle threader that helped:
Some advice found on The InterTubes suggests using copper crimp beads (perhaps with solder) to prevent the thread from completely unraveling and keep the thread loop tight around the PCB hole:
Beadworkers use crimping pliers that leave a tidy dent; I mashed the beads with a needlenose pliers and called it good.
The LEDs seem to be white LEDs with filters or, perhaps, blue / violet LEDs with different phosphors: their forward voltages look more blue than red or green. Everybody in this field depends on the minor miracle that lithium cell voltages match blue LED forward drops closely enough that you can get away without a ballast resistor.; the cell’s 20-ish Ω internal resistance doesn’t hurt in the least. An interesting white paper (SWRA349) from TI explores the effect of current on cell capacity and how to size a parallel capacitor that reduces the peak battery current.
The black gunk is Wire Glue, which costs about five bucks for a lifetime supply in a small jar (or nigh onto 15 bucks via Amazon Prime) and is basically carbon powder in a water-based binder. Apply a dab to the connection and the water evaporates to leave the carbon + binder behind.
That works better on joints that don’t move, which is precisely what you don’t have in a wearable electronic situation. You can see the crumbling Wire Glue after the trip back from a Squidwrench meeting:
I also picked up a Permatext Rear Window Defogger repair kit (09117, if you’re looking) that seems to be a staggeringly expensive way to get a tenacious high-current conductive adhesive. More on that later.
The yarn runs 3.5 Ω/ft, much lower than Adafruit’s three-ply yarn (10 Ω /ft), and suggests itself for flexible connections, EMI gaskets, and suchlike.
Those LEDs are taped to the kitchen window, where they cast a cool light over the table, with the battery holders sitting on the sash. I’d just replaced some data logger CR2032 cells, so they’re running from nearly dead lithium batteries.
For future reference: 2.77 V and falling, pushing less than 2 mA through the LEDs.
The Smell of Molten Projects in the Morning 