Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Littelfuse Mini Auto Fuse Puller-tester – as opened
Somewhat to my surprise, the other side of the PCB has components:
Littelfuse Mini Auto Fuse Puller-tester – circuitry
It looks like a transistor switch to minimize the current through the fuse and protect the LED from over / reverse voltage, should you apply it to a live circuit.
A pair of new cells had it working just fine, not that I expect to need it in real life.
The first white LED fixture built to illuminate one of Mary’s Kenmore 158 sewing machines has been in regular use for the last four years:
Kenmore 158 Sewing Machine – mixed LED lighting
We never found a good time to rip-and-replace the “prototype” with brighter SMD LEDs and one of the LEDs finally gave up.
They’re 10 mm white LEDs with five chips wired in parallel, which is obvious when you look into the remaining LED running at 1 mA:
10 mm white LED – chips
The center chip is just dimmer than the others, which means their QC doesn’t tightly control the forward voltage spec.
The wire bonds on the anode terminal of the failed LED look a bit sketchy:
10 mm white LED – wire bonds
Fortunately, I hadn’t removed the 120 VAC wiring for the original bulb and I have two OEM bulbs from other machines, so I just removed my LED gimcrackery, installed a good old incandescent bulb, and she’s back to sewing with a pleasantly warm machine.
The fixture holding the LEDs broke apart as I extracted it, but it’ll never be used again:
10 mm white LED – fixture
The LEDs are rated at 3.5 V and 200 mA (!), but were reasonably bright in series from a 6 V unregulated supply. Perhaps a power glitch killed the poor thing? We’ll never know.
LEDs are reputed to have lifetimes in the multiple tens of thousands of hours, but I’ve seen plenty of failed automotive LEDs and fancy new LED streetlights out there, not to mention many dead and dying traffic signals. Seeing as how they’re in (presumably) well-engineered fixtures with good power supplies and are at most only a few years old, there shouldn’t be any failures yet.
The probes report a resistance of 270 mΩ (net of the 50 mΩ probe-to-probe resistance), as close as one could ask to the nominal 26 Ω/1000 ft spec for 24 AWG wire at the current Basement Laboratory temperature.
They are exceedingly limp and flexy, due to many teensy conductors; not at all like PVC hookup wire.
If you’re willing to buy 500 feet of each color, the cost-per-foot from a reputable supplier gets downright competitive, but I’m not in that market.
A QRPme Pocket Pal II could be a suitable project for a Squidwrench “advanced soldering” class:
QRPme Pocket Pal II – front
Yes, it comes with a tin case:
QRPme Pocket Pal II – tin case
You must fit your own insulating sheet under the PCB; polypropylene snipped from a retail package works fine.
It’s intended as a “mint tin sized tester for all kinds of hamfest goodies”, but it seems like a nice source of small currents, voltages, and signals suitable for stimulating all manner of circuitry one might encounter in later sessions of a beginningelectronics class.
Before using it, of course, one must solder a handful of small through-hole parts into the PCB, a skill none of us were born with.
For completeness, the back side, hot from the soldering iron:
QRPme Pocket Pal II – rear
The kits (always buy two of anything like this) arrived minus a few parts, which I suspect was due to an avalanche of orders brought on by a favorable QST review. Fortunately, I (still) have a sufficient Heap o’ Parts to finish it off without resupply, although a hank of 9 V battery snaps will arrive in short order.
This cheerful assortment came from a friend with an assortment of happy chickens:
Multicolored chicken eggs
The lonely Medium white egg, obviously strictly from commercial, serves as a size and color reference. Most of the others weighed in the Large to Extra-Large range.
Even though none of the chickens had the digital upgrade, the morning omelet tasted just fine!
The downspouts are obviously more recent than the splash blocks, but the whole shopping center wasn’t more than a few decades old. Rain isn’t nearly as acid as it used to be, but it still eats away at concrete.
After about two decades, though, even high-quality concrete goes bad:
The back tire on my bike was flat when I rolled it out for a ride (the day after replacing the front shifter cable), which ought not be possible with a Michelin Protek Max tube inside. On the other paw, we’ve had zero flats in the not quite two years since installing the things, which says they’re doing very well, and I’ll take a flat in the garage over a flat on the road any day.
With the bike up on the stand, I didn’t spot the expected large glass chip or sharp wire, but I did find three smaller gashes:
Bike tire tread gashes – composite – 2017-05-13
… from which I extracted two small glass shards. Perhaps a wee puncture spent four days parked at the top of the wheel, with the ProTek’s internal goop drained away and unable to plug the slow leak.
Having spun the tire a few times while looking for trouble, I pumped it back up to 80 psi. After delaying the ride for half an hour, the tire pressure remained constant, and we enjoyed a fine ride around the block.
Because I’m writing this in the future, I know it’ll hold pressure just fine, which means I can declare victory and move on.
The tube & tire weigh more than some frames, but they’re worth it!
The Smell of Molten Projects in the Morning 