When you have one tester, you know the USB current. When you have two testers, you’re … uncertain.
The upper tester is completely anonymous, helpfully displaying USB Tester while starting up. The lower one is labeled “Keweisi” to distinguish it from the myriad others on eBay with identical hardware; its display doesn’t provide any identifying information.
The back sides reveal the current sense resistors:
Even the 25 mΩ resistor drops enough voltage that the charger’s blue LED dims appreciably during each current pulse. The 50 mΩ resistor seems somewhat worse in that regard, but eyeballs are notoriously uncalibrated optical sensors.
The upper line (from the anonymous tester) has a slope of 11.8 mA·h/minute of discharge time, the lower (from the Keweisi tester) works out to 8.5 mA·h/minute. There’s no way to reconcile the difference, so at some point I should measure the actual current and compare it with their displays.
Earlier testing suggested the camera uses 2.2 W = 600 mA at 3.7 V. Each minute of runtime consumes 10 mA·h of charge:
10 mA·h = 600 mA × 60 s / (3600 s/hour)
Which is in pretty good agreement with neither of the testers, but at least it’s in the right ballpark. If you boldly average the two slopes, it’s dead on at 10.1 mA·h/min; numerology can produce any answer you need if you try hard enough.
Actually, I’d believe the anonymous meter’s results are closer to the truth, because recharging a lithium battery requires 10% to 20% more energy than the battery delivered to the device, so 11.8 mA·h/min sounds about right.
Start with a single cell holding a glass tile over a WS2812 RGB LED:
A bit of OpenSCAD tinkering produces a simple 2×2 array with square interiors as a test piece:
The excessive stringing and the booger in the upper-left cell come from absurdly thin infill tucked into the too-thin walls; Slic3r doesn’t (seem to) have a “minimum infill width” setting and it’ll desperately try to fit infill between two nearly adjacent perimeter threads.
The little support spiders under the LED PCB recesses snapped right out, though, so I got that part right:
The perimeter threads around the LED aperture aren’t quite fused, because it was only one layer thick and that’s not enough.
A quick test with two LEDs showed the white PETG let far too much light bleed between the cells, which was no surprise from the single cell test piece.
Fortunately, it’s all parametric, so a bit more tinkering produced a slightly chunkier matrix with a base for an Arduino Nano and M3 threaded brass inserts for the screws holding it together:
Those two parts require about three hours of printing, much faster than I could produce them by milling pockets into aluminum or black acrylic slabs, and came out with minimal stringing.
A little cleanup, some epoxy work, and a few dabs of solder later:
An initial lamp test showed the white-ish glass tiles aren’t all quite the same color:
I thought it was an LED color variation, too, but the slightly blue tint in the lower left corner followed the tile.
The blurred horizontal strip across the middle is adhesive tape holding the tiles in place; I was reluctant to glue them in before being sure this whole thing would work. A peek into the future, though, shows it’s got potential:
After trimming off all the extraneous bits, the larger half of the connector (male pins) fits through the tubing and the smaller half (female sockets) barely fits through the bottom bushings.
It turns out half-inch copper pipe fittings (ID = 15.9 mm) almost exactly fit the tubing (OD = 15.7 mm):
A quick test showed the 45° (actually, it’s 135°, but we’re deep into plumbing nomenclature) positioned the lamp head too high and with too much reach:
So shorten the tube attached to the head and deburr the cut:
The 45° fitting is too high and a 90° fitting is obviously too low, so cut a 20° slice out of a 90° fitting:
Cut a snippet of brass tubing to fit, bash to fit, file to hide, buff everything to a high shine, silver-solder it in place, and buff everything again:
The 5/8 inch aluminum rods serve to stiffen the fitting, smooth out the torch heating, and generally keep things under control.
Wrap the obligatory Kapton tape around the butt ends of the tubes to fill the fitting’s oversize hole, put everything together, and it’s just about perfect:
I immobilized the fitting with black Gorilla tape, but it really needs something a bit more permanent. One of these days, maybe, a pair of setscrews will happen.
The additional reach required a little more counterweight on the far side for security, so I added the broken stub of a truck leaf spring. It should be secured firmly to the base plate, but no tool I own can put a dent in those three pounds of spring steel. Maybe it’ll merit a fancy enclosure wrapped around the base?
No surprise, as the car completely shattered the utility pole.
The glow draws 1.5 A from a bench supply at 1 V, just to show the filament isn’t lighting up evenly across those gaps. The bulb runs at 55 W from 12 V and would be, I’m sure, blindingly bright, although the heat concentrated in those few coils suggests it’d burn out fairly quickly.
By LED standards, though, you don’t get much light for your 1.5 W …
An underexposed version highlights the filament, just for pretty: