Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Measuring some low-value resistances with one of my DVMs produced weird results: dead shorts around 10 Ω.
Differential diagnosis:
Test lead tips clean
Wires firmly mounted in probes
Banana plugs OK
Short banana jumper across jacks reads 10+ Ω
Took the meter apart and what do we see? An ABC ceramic fuse in good old PCB clips:
DVM fuse holder
Spinning the fuse dropped the resistance by a few ohms. Adding a minute drop of DeoxIT to each end, rotating the fuse to scrub it in, and wiping off the excess put the total resistance back around 0.2 Ω where it should be.
While fiddling around with those SMD capacitors, it occurred to me that I really needed some SMD tweezers: small forceps with isolated jaws, connected to the capacitance meter’s terminals. In the nature of a proof-of-concept, I sacrificed a (surplus) Tektronix banana plug cable and an old plain-steel tweezer (stamped Made in Japan back in the day when that had the same quality connotations as does Made in Pakistan right about now) and lashed them together:
SMD tweezers – overview
I chopped off the tweezer joint with a bolt cutter, scuffed up the steel with a file, soldered the cable wires, cut a small wood block to fit, and epoxied the whole mess together:
SMD tweezers – epoxy joint
When the epoxy cured, a generous wrap of silicone tape hid most of the hackage. Two lengths of clear heatstink tubing insulate the handles from my sweaty fingers:
SMD tweezers – joint detail
Part of the reason for picking this victim was its cheap-and-bendy steel: more easily soldered than stainless, no regrets about filing the jaws to suit. They’re flattened on the bottom and filed to grip SMD chips along their length:
SMD tweezers – tip shape
That’s on the top panel of my indispensable AADE LC meter. The stray capacitance of that cable is around 50 pF, but the meter can null it to a fraction of a pF. At least as long as I don’t change my grip, that is, which isn’t too severe a restriction. [Update: got the link right this time.]
That gorgeous Tek cable turned out to be entirely too stiff and the natural curve doesn’t lie in the correct direction. The next version will probably use a length of RG-174 mini coax and a dual banana plug. I think I’d like angled jaws, too, so as to attack the chips from the top down.
But even this version works wonderfully well, as I sorted out a few hundred random SMD caps in two half-hour sessions that I’d been putting off for far too long. This is the last batch; I’ve learned the hard way that it pays to transfer batches of chips to their storage bins long before I think I should:
Sorting SMD caps
Yeah, it’s false economy, but it keeps me off the streets at night. OK?
Paralleling a 510 Ω resistor with each of the 180 Ω resistors on the LED ring light around the macro lens holder boosted the LED string current from 15 to 20 mA:
LED ring light – paralleled resistors
The complete botch job in the lower right is what you get when you don’t wipe the soldering iron tip first.
LED brightness being pretty nearly linearly proportional to current, the exposure gets another 0.4 EV that probably doesn’t matter in the least.
A hand-held picture of the pile of SMD resistors (which willingly produced four of the five resistors and required enhanced interrogation to extract the last one):
SX230HS – macro lens – 15 x 20 mA ring light
That’s pretty much overhead at f/8, so the depth of field is as good as it gets.
At some point we brought home a fruit fly starter kit that produced a zillion fruit flies in the worm compost bin; every time we opened the cover, half a zillion flies would emerge. After a bit of fiddling with the usual Internet recipes, I managed to produce something useful:
Fruit fly trap – overview
The trick involves making the liquid enticing enough to get the flies through the hole in the coffee filter top:
Frut fly trap – filter paper
I used about a cup of water, an ice cube of apple juice for sweetness (they are, after all, fruit flies), a tablespoon of vinegar for that delicious rotten aroma (they prefer damaged, easy to eat fruit), and a few drops of dishwashing detergent so when they hit the liquid they’re sunk.
The container must be tall enough to let them rise past the entrance opening on their way toward the light; I settled on the 2 pound ricotta cheese containers we have in abundance:
Fruit fly trap – results
That’s the catch after maybe a month at the end of the season, but it represents a week of activity back when we were breaking the infestation. I deployed four of those traps atop the compost bin to catch the half-zillion escaped flies and fired up the vacuum cleaner to extract the half-zillion remaining inside every time we opened the lid. After a few weeks of that, we’d managed to get ahead of their breeding cycle and the problem pretty much Went Away.
Picked up a Harbor Freight thickness gauge to measure Thing-O-Matic filaments and suchlike; it has a plastic piston and anvil, so it’s not well-suited to measure anything other than plastic parts. In fact, it’s all plastic and the various sliding surfaces produced a remarkable amount of friction.
Fortunately, the back cover pops off without too much of a struggle:
Harbor Freight Digital Thickness Gauge – cover removed
Dabs of silicone lube at all the contact points considerably improved its disposition.
The display offers 0.01 mm resolution, but I don’t believe that rightmost digit for an instant. The stated accuracy is ±0.1 mm, which is probably closer to the truth, and it agrees reasonably well with my considerably better quality digital caliper.
As part of making that PCB, the sanding disk on the side of Mr Belt Sander made a lot more noise than usual; it’s hard to tell, because I wear 30+ dB ear muffs. Turns out that the setscrew had worked loose enough to let the disk walk outward, chewing up the plastic dust collector cover and the aluminum table:
Belt sander disk dust catcher
The setscrew gouged the shaft enough to prevent the disk from sliding off the shaft, which was probably a Good Thing, but that also meant I had to jam a big flat-blade screwdriver inside the guts of the dust guard and twist to pry the disk off:
Belt sander disk shaft
A touch of the file on the shaft, a bit of cleanup inside the disk hole, a dab of Loctite, and it’s all good again.
The Smell of Molten Projects in the Morning 