Confirming the diagnosis, the cool white LEDs worked fine with the light turned on:
With nine spare SI2306 transistors in hand from the last time in this rodeo and minus the sticky adhesive foam covering the PCB, replacing the other driver transistor was no big deal, whereupon the lamp once again worked the way it should:
While I was in there, I spotted a dent in the input filter cap:
Most likely I squished a wire between the cap and the U-shaped steel strut joining the two halves of the pole. I relocated the replacement cap off the circuit board into an open space with a bit more room:
The fragile wires running to the lamp head got their own sheet of silicone tape (not shown here) to isolate them from the U-strut:
Tuck all the wires back inside, snap the housing together, and it should be good for another uhh half year or two.
It’s hard to be sure about such things, but I now have eight spare transistors …
The “live hinge” on my overnight eyeglass case shattered when it hit the floor (these things happen), which prompted me to finish a longstanding project of replacing the inadequate / worn out padding in my most-used cases to reduce rattles while in my pocket.
I’d long ago cut craft foam sheets to fit some of the cases, so I started by scanning a sample:
Admittedly, black foam on a white background isn’t much to look at, but it did fit one of the cases pretty well.
Rotate the image to make things simple, convert it into a monochrome bitmask, import it into LightBurn, fair some Bezier curves around it, duplicate and tweak for the other not-quite half of the case:
I ended up with several different versions for various cases, but you get the general idea:
They’re all cut from 2 mm EVAfoam sheets which, despite the “vinyl” in their name, do not contain chlorine and are suitable for laser cuttery.
Some of the deeper case halves required strips of adhesive sheet to secure the foam, but most sheets dry-fit in place.
The four control “buttons” on the SmartHeart kitchen scale are copper-foil tabs that sense the presence of your finger though about 5 mm of white plastic and glass:
The main failure mode seemed to come from the microcontroller locking up and refusing to recognize any of the buttons, most annoyingly the On/Tare button, while continuing to measure whatever weight was on the scale with whatever zero point it chose. Recovery involved waiting until the thing timed out and shut itself off.
The two buttons on the left select Kilocalories for any of the various foods arrayed around the display. Depending on how it jammed during startup, it might display the Kilocalorie value for, say, sugar, while ignoring all button presses. As the manual does not mention any way to return to weights after activating the Kilocalorie function, other than turning it off, it’s not clear recognizing the other buttons would be much help.
Because we have no use for those functions, I unsoldered the wires to those sensor pads and it no longer jams in that mode:
The alert reader will note the PCB legend says I have unsoldered the ON/OFF and UNIT wires. If one believes the silkscreen, the PCB dates back to 2015, so it now carries a reprogrammed microcontroller with functions that no longer match the silkscreen.
The overall soldering quality resembles mine on a bad day.
With those out of the way, the scale still jammed and refused to recognize the remaining two buttons. I wondered if it was somehow sensing ghost fingers over both sensors and waiting for one to vanish, so I added a shield ring around the power tab:
That reduced the sensitivity of both sensors to the point where they pretty much didn’t work, without reducing the number of jams.
So I tried increasing the sensitivity of the power tab by replacing it with a larger copper foil sheet:
That definitely got its attention, as it will now respond to a finger hovering half an inch over the glass, as well as a finger on the bottom of the case: it can now turn on and jam while I pick it up.
More tinkering is in order, but it’s at least less awful in its current state than it was originally, so I can fix a few other things of higher priority.
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:
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:
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.
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:
The alert reader will notice a peculiarity concerning the sensor pad connections along the top edge.
This was really a thinly veiled excuse for a deeper look at the QR code generator encoding the myriad parameters required to create the box and see what happens when you try to burn such a complex thing into chipboard.
Spoiler: chipboard has very low contrast and really does not work well with high-density QR codes.
Although the festi.info box generator can produce QR codes, I used qrencode (available in your Linux distro) on the command line to generate QR code image files with specific settings:
--size → size of the smallest square (“module”) in pixels
--dpi → DPI of the output image file
The default file type is PNG. The unusual 254 DPI makes each pixel exactly 0.1 mm wide and a peculiar 169.33 DPI = 0.15 mm came in handy for the first pattern.
The final parameter is the character string to encode, which you should definitely quote to prevent the shell from wrecking things while trying to help you.
A pattern with 4×4 pixel modules didn’t scan at all:
A closer look shows the modules have ragged edges due to laser timing variations during the engraving scans and gaps between successive scans because the spot size is less than the 0.15 mm scan interval:
Increasing the module to 6×6 pixels at a 0.1 mm scan interval :
A closer look shows the larger module reduces the relative size of the timing errors, while the decreased line spacing tidies up the blocks:
Reducing the power from 15% to 10% reduced the contrast to the point of illegibility:
A closer look shows the engraving barely punches through the surface and has somewhat more ragged edges due to the tube’s pulsating startup current at very low power:
I also tried 5×5 modules with similar results.
The laser spot size sets the engraving scan interval, which then determines the DPI value for the QR code image. With all that matched up, you can send the images directly to the laser in Passthrough mode, without having LightBurn resample the pixels and change the module’s shape.
Looked at from a different angle: given the laser spot size and the module size, the QR code image size is not under your control.
From another angle: given a QR code image size in, say, millimeters, and the engraving scan interval, the module size is not under your control.
All this is moot if you print QR codes on a high-resolution / high-contrast printer. It’s just the gritty nature of laser cuttery that limits what you can accomplish.
And, of course, using a material less awful than chipboard will definitely improve the results.
If you want a similar box of your own, here ya go:
A recent Squidwrench meeting provided the opportunity to make a couple of racks for an assortment of Refresh Tears / Liquigel bottles:
I used chipboard to find out if the cross plates would stiffen the floppy 1.1 mm sheets enough for this light duty. Indeed, the overall structure becomes a nice rigid box, even though the feet and corners can’t withstand much abuse.
The finger joints use the default settings, which produce a lot of fingers along the edges. This turns out to be a Good Thing, as it gave the yellow wood glue plenty of opportunities to bond the sheets together.
Combining the default 5° slope with nine bottles along each level wastes a tremendous amount of vertical space. The adjacent racks hold three much larger cans per level, so roughly the same space doesn’t look like much. In retrospect, a 3° slope should work for smaller bottles.
And, yes, the squash on the lower shelf store nicely and become yummy meals all winter long.