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.

Tag: Repairs

If it used to work, it can work again

Craptastic Kitchen Scale Tinkering
The health plan I use pays $100 toward the year’s over-the-counter healthcare stuff, although with a caveat: you can only buy the stuff from a specific website. As you might expect, what’s available consists of no-name generic products with absurdly high sticker prices and, just to rub it in, the hundred bucks gets paid in quarterly use-it-or-lose it installments.

Seeing as how it was free, I got a kitchen scale:

SmartHeart 19-106 Kitchen Scale – top view

It has two catastrophically bad design features:
- Terrible battery life
- Overly sensitive controls
It runs from a pair of series-connected CR2032 non-rechargeable lithium coin cells. Which would be fine, except that the blue LED backlight stays on for 30 seconds after each button touch and draws about 10 mA.

The battery lifetime is best measured in days.

The four control “buttons” on either side of the backlit LCD are touchless sensors using copper foil stickers:

SmartHeart 19-106 Kitchen Scale – NP-BX1 retrofit

The alert reader will spot those the empty CR2032 coin cell contacts over on the left and a pair of NP-BX1 batteries in the middle.

I figured there was no need to keep feeding it coin cells while I played with it, so I conjured a holder from the vasty digital deep. Normally, that would be an OpenSCAD solid model suited for 3D printing, but in this case the lithium cells exactly filled the space between the PCB and the bottom of the case, so it became a 2D design neatly suited for laser cuttery.

Kitchen scale – NP-BX1 holder – LB layout

I planned to stick the orange cutout (in 1.5 mm acrylic) as a stabilizer around the pogo pins making contact with the cell terminals from the red cutout (in 3 mm acrylic), but just melting the pins into the acrylic seemed sufficient for the purpose. Strips of adhesive sheet saved from the margins of previous projects affix the holder (not the cells!) to the scale’s upper glass layer.

As far as I can tell, the scale is perfectly happy running on 7.4 V, rather than 6.0 V. The PCB has two terminals marked +3V and +6V, so it probably depends on which LEDs they use for backlights:

SmartHeart 19-106 Kitchen Scale – PCB detail

The alert reader will notice a peculiarity concerning the sensor pad connections along the top edge.

More on that second bad design decision later …
2023-03-20
Innovative Bumper Repair

Having seen bandage stickers on wounded cars, my first glance suggested a Frankenstein surgical version:

Zip-tied car bumper

They don’t make bumpers like they used to!

Which is, overall, a good thing, but crushable plastic definitely raises the repair cost for a glancing impact.

Fortunately, the scuff didn’t reach the headlight.

2023-03-17
Please Close The Gate Signs: MDF Weathering

With the new signs in place, the old ones paused briefly for a photo op on their way to the trash:

Please Close The Gate – weathered MDF

That’s eight months of weathering on MDF covered with indoor urethane sealant and it’s not as awful as I expected: the MDF didn’t actually disintegrate, it just collected some mold / mildew / crud.

A closer look:

Please Close The Gate – weathered MDF – detail

The black paint survived surprisingly well.

I hadn’t paid ~~much~~ any attention to the edges, so they got covered with random amounts of black paint and urethane. It seems that’s where the disintegration starts:

Please Close The Gate – weathered MDF – side view

MDF definitely isn’t the right material for an outdoor sign and I knew that going in, but it’s cheap and readily available, which makes up for a lot.

For comparison, they looked nice right after installation:

Please Close The Gate – fresh painted

Ya learn something new every year around here!

2023-03-09
Please Close The Gate Signs: Paint Masking FAIL
A warm day let me shoot the engraved signs for the Vassar Community Garden gates with rattlecan black:

Please Close The Gate – masking tape peeled

The full sheet of orange acrylic arrived with plastic protective film on both sides, which I planned to use for paint masking. Alas, one side also had a wrinkle running its length that ended up on two signs, so I replaced that film with blue masking tape.

As fate would have it, the first side of the first sign I peeled had masking tape and produced what you see above.

Things went bad in a hurry. The paint had no adhesion whatsoever to the plastic film and fell off in flakes as I peeled the film away:

Please Close The Gate – plastic peeled

I assumed the flakes would just fall off the signs, perhaps with a little persuasion, so I peeled and weeded all the signs before cleaning them up.

Although the paint was fully dry, when the molecularly smooth surface of each paint flake touched the molecularly smooth surface of the newly exposed acrylic, the two instantly and permanently fused together.

There were a lot of flakes:

Please Close The Gate – plastic peeled – detail

Removal techniques that did not work:
- Vacuuming with a brush
- Gentle rubbing with a soft cloth
- Firm rubbing after spraying with acrylic cleaner
- Scraping with a plastic razor blade
So I deployed a P220 grit sanding block and wrecked the glossy surface of both sides of all six signs. I briefly considered trying to recover the finish by sanding them all up through about 2000 grit, then came to my senses: my sanding arm is weak.

Careful examination of the last picture shows several places around edges of the circle where the plastic film melted into a blob that blocked the paint, rather than vaporizing. I used enough power to engrave only about 0.3 mm deep (because they’re engraved on both sides), but the transition wasn’t fast enough for a clean edge.

They don’t look as nice as I’d like, but they’re good enough for the purpose:

Please Close The Gate – installed

The acrylic sheet is more see-through than I expected, at least when backlit by bright sunlight.

Please Close The Gate – seethrough

Next: we discover what happens to UV-stabilized orange acrylic and black outdoor paint over the course of a year in garden sunshine.
2023-03-08
Bafang Triangle Plate Rework

The time has come to add a Bafang mid-drive motor to my Tour Easy recumbent, much like the one Mary has been using for the last two years. When I got to the point of installing the motor in the bottom bracket shell, this happened:

Bafang Triangle Plate – jammed screw

It turns out the triangle plate has slightly misplaced bolt holes:

Bafang Triangle Plate – misplaced bolt holes

If you look very carefully, you’ll see the holes sit just slightly above the midline of those ears. The additional fractional millimeter below the holes touches the motor end bell and prevents them from lining up with the tapped holes.

Normally, you’d just hit the plate with a file and be done with it, but it’s ferociously hardened steel: a file bounces right off.

I deployed a Dremel sanding drum above the ShopVac’s snout to catch the abrasive dust, eroded just enough steel to line up the holes, and everything now fits the way it should.

Done!

2023-03-03
Shower Faucet Handle Rebuild & Tightening

The shower faucet handles have been getting looser, but once a decade seems reasonable. This time around, however, the setscrews had dug themselves so far into the splined plastic fittings that they had run out of thread:

American Standard Shower Handle rebuild – gouged setscrew sockets

Wipe out the crud, clean out what’s left with alcohol to encourage stick-to-it-ivity, and fill the cavities with JB Kwikweld epoxy:

American Standard Shower Handle rebuild – epoxy fill

When it cures, file a flat across the sockets:

American Standard Shower Handle rebuild – flatted

Reinstall in reverse order with a dot of NeverSeez on the setscrews for good measure.

Just so you don’t have to look it up, this is what the cold water faucet innards looked like a decade ago:

Shower faucet valve stem

Ought to be good for another decade, right?

2023-02-21
Flypower Wall Wart: FAIL

The IR sensor on the under-cabinet LED lights I installed half a dozen years ago became increasingly flaky. Its wall wart power supply was on the hot side of uncomfortably warm, so I had an obvious culprit.

The data plate says it’s UL Listed, which is comforting:

Flypower LED wart – data plate

The open-circuit output of a 12 VDC power supply should not look like this:

FlyPower 12V 1A – no load

The horizontal scale is 100 ms/div, so those ramps seem much more languid than you might expect from a 60 Hz wall wart.

Adding a 16 Ω load to draw maybe 750 mA got its attention:

FlyPower 12V 1A – 16ohm load

The average may be 12 V with too-large dips at the expected 120 Hz, but looky at all the hash riding the output!

No wonder the IR sensor was having such a hard time. When the LEDs are off the voltage ramps between 16 and 5 V. When it eventually turns on the supply has impossible noise levels.

So I cracked the case and extracted the electronics:

Flypower LED wart – components

Those caps over there on the left rear don’t look healthy, do they?

Flypower LED wart – failed caps

No. No, they don’t and you shouldn’t be able to see the wiring inside the inductor between them, either.

Probing the Box o’ Wall Warts produced a similar-ish wart that only required harvesting and splicing the teeny coax plug from the failed adapter to put the LED strips back into normal operation.

The identical supply for the identical LED strips on the other side of the kitchen continues to work fine and feel only warm-ish, so I’ll let it be.

2023-02-15