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.

Category: Machine Shop

Mechanical widgetry

RCA Alarm Clock Dimming

Mary prefers dim digits on the bedroom alarm clock, far below what the usual DIM switch setting provides. I’d slipped a two-stop neutral density filter in front of our old clock’s VFD tube, but the new one has nice green LED digits that ought to have a tweakable current-setting resistor behind the switch. Indeed, a bit of surgery revealed the switch & resistors:

RCA clock – DIM switch and resistors

It turns out that the 220 Ω resistors set the DIM current, with the 100 Ω resistors in parallel to set the BRIGHT current. Weirdly, the display operates in two halves: one resistor for the lower and middle segments, the other for the top segments. The resistor numbers give a hint of what the schematic might look like:

RCA clock – LED current-set resistors

The current control isn’t all that good, because the brightness varies with the number of active segments. With 470 Ω resistors (yes, from that assortment) in place, the variation became much more obvious; the LEDs are operating far down on their exponential I-vs-V curve. We defined the result to be Good Enough for the purpose.

Four short screws hold the circuit board in place, but one of them arrived loosely held in a pre-stripped hole. I cut eight lengths of black Skirt filament, anointed them with solvent adhesive, dropped two apiece into each screw hole, and ran the screws back in place. I likely won’t be back in there, so it should be a lifetime fix:

RCA clock – ABS filament in screw hole

Done!

As with all the trade names you remember from back in the Old Days, the present incarnation of “RCA” has nothing whatosever to do with the original Radio Corporation of America:

RCA clock – data plate

2011-12-13
Brita Pitcher Lid Hinge

This pitiful excuse for a hinge actually lasted far longer than I expected:

Brita pitcher lid hinge pins

Also much to my surprise, the plastic solvent-bonded to itself, although I doubt either of those pins will survive another four years.

The yellow discoloration seems to be most prominent on the inside of the lid, which suggests the water is nastier than they’d have you believe. The disinfection additive has switched from chlorine to chloramine and back to chlorine over the last few years, which may have something to do with it.

2011-12-11
SMD Measurement Tweezers

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?

2011-12-08
Tux Cookie Cutter: It Works!

Sean reports that the first field test of the Tux Cookie Cutter went well:

Tux Cookies

I obviously need a few samples for QC purposes…

2011-12-07
Fruit Fly Traps

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.

2011-12-05
Harbor Freight Digital Thickness Gauge: Lubrication Thereof

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.

2011-12-04
Belt Sander Disk Tightening

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.

2011-12-03