USB Charger: Abosi Waveforms

For comparison with the Anonymous White Charger of Doom, I bought a trio of Abosi USB chargers:

Abosi charger - dataplate
Abosi charger – dataplate

The symbology indicates it’s UL, but not CE, listed. Consumer Reports has a guide to some of the symbols; I can’t find anything more comprehensive.

Applying the same 8 Ω + 100 µF load as before:

Abosi charger - 8 ohm 100 uF detail - 100 ma-div
Abosi charger – 8 ohm 100 uF detail – 100 ma-div

The voltage (yellow) and current (green, 100 mA/div) waveforms look downright tame compared to some of the other chargers!

I made a cursory attempt to crack the case open, but gave up before doing any permanent damage. Hey, that UL listing (and, presumably, the interior details) means they’re three times the price of those Anonymous chargers!

JPG Recovery From a Camera FAT Filesystem

You can do it by hand, as I used to, or use recoverjpeg:

dmesg | tail
cd /tmp
sudo dcfldd if=/dev/sde1 of=pix.bin bs=1M count=100
recoverjpeg pix.bin 
ristretto image00*

Nothing prizewinning, but better than no picture at all:

Garage Robin - recovered image
Garage Robin – recovered image

Note that you start by copying a reasonable chunk of the partition from the Memory Stick / (micro)SD Card first, to prevent a bad situation from getting worse.

Now I can remember the easy way the next time around this block …

Drill Press Vise Table Refresh

I built a small plywood work table for the drill press:

Drill press - scarred vise table
Drill press – scarred vise table

Obviously, that was a long time ago. It’s a plywood scrap with a small cleat screwed to its bottom, upon which one can position / clamp / hold / finagle smallish workpieces without worrying about drilling into the surface.

The most recent batch of aluminum backing plates prompted me to finally replace that relic:

Drill press - new vise table
Drill press – new vise table

The mill vise under the plywood grips the cleat and the whole affair rides on a Sears “Drill Press Milling Attachment Stock No 27585” which is basically a simple XY table with hand dials. It’s not rigid enough for actual milling (which you should never do on a drill press, anyway, because the end mill will pull itself out of the Jacobs chuck), but it’s good for tweaking the position before you drill something.

One should never hand-hold workpieces while drilling.

Don’t do as I do, do as I say. OK?

USB Current Probe Extender

Having gotten two answers from two USB meters, I figured it was time to get primal:

USB Current-Probe Extender - wiring
USB Current-Probe Extender – wiring

That’s a pair of USB breakout connectors and lengths of nice silicone wire (24 AWG power & 28 AWG data), with just enough slack for a Tek A6302 current probe:

USB Current-Probe Extender - in action
USB Current-Probe Extender – in action

So I can see the actual current waveform of a Glass Tile box running from a bench power supply:

Tiles 2x2 - bench supply - 50 mA-div
Tiles 2×2 – bench supply – 50 mA-div

The top trace is the firmware heartbeat from the Arduino Nano, the middle trace is the SK6812 LED data stream, and the bottom trace is the USB current at 50 mA/div. The current steps downward by about 10 mA (just after the data burst) when one of the tiles changes color and and LED shuts off.

The current probe reveals some mysteries, such as this waveform from a dirt-cheap USB charger:

Tiles 2x2 - anon white charger - 50 mA-div
Tiles 2×2 – anon white charger – 50 mA-div

I wonder why it’s ramming 100 mA current spikes into the circuit, too. At least now I can see what’s going on.

Monthly Image: Rt 376 Overgrowth Clearing

NYS DOT cleared the Japanese Knotweed from the shoulder along Rt 376 north of Maloney last year:

The last image in that gallery is from the end of April; you can see the weeds just starting to grow under the guide rail.

Japanese Knotweed, being basically a weed on crystal meth, becomes a lush hedge from a standing start in five weeks:

Knowing how NYS DOT’s Region 8 Dutchess South Residency’s brush trimming has(n’t) worked in previous years, this took us by surprise:

Rt 376 Marker 1095 - 2020-06-10
Rt 376 Marker 1095 – 2020-06-10

Because chopping Japanese Knotweed to the ground doesn’t actually discourage it, we hope they’re scheduled to return every couple of months …

Solid Modeling: Support Puzzle

I’ve been putting this type of support structure inside screw holes & suchlike for years:

Browning Hi-Power Magazine Block - solid model - Generic 1 - support detail
Browning Hi-Power Magazine Block – solid model – Generic 1 – support detail

It’s basically a group of small rectangles rotated around the hole’s axis and about one thread thickness shorter than the overhanging interior.

I’ve found that incorporating exactly the right support structure eliminates Slic3r’s weird growths, eases removal, and generally works better all around.

So doing this for the baseplate of the Glass Tile frame came naturally:

Glass Tile Frame - octagonal support
Glass Tile Frame – octagonal support

This OpenSCAD snippet plunks one of those asterisks in each of four screw holes:

  if (Support)
      for (i=[-1,1], j=[-1,1])
          for (a=[0:45:135])
                translate([0,0,(Screw[LENGTH] - ThreadThick)/2])
                  cube([Screw[OD] - 2*ThreadWidth,2*ThreadWidth,Screw[LENGTH] - ThreadThick],center=true);

The “cubes” overlap in the middle, with no completely coincident faces or common edges, so it’s 2-manifold. Slic3r, however, produces a weird time estimate whenever the model includes those structures:

Slic3r - NaN time estimate
Slic3r – NaN time estimate

NaN stands for Not A Number and means something horrible has happened in the G-Code generation. Fortunately, the G-Code worked perfectly and produced the desired result, but I’m always uneasy when Something Seems Wrong.

Messing around with the code produced a slightly different support structure:

Glass Tile Frame - quad support
Glass Tile Frame – quad support

The one thread thick square on the bottom helps glue the structure to the platform and four ribs work just as well as eight in the octagonal hole:

  Fin = [Screw[OD]/2 - 1.5*ThreadWidth,2*ThreadWidth,ScrewRecess - ThreadThick];
  if (Inserts && SupportInserts)
      for (i=[-1,1], j=[-1,1])
        translate([i*InsertOC.x/2,j*InsertOC.y/2,0]) {
          for (a=[0:90:360])
                translate([Fin.x/2 + ThreadWidth/2,0,(ScrewRecess - ThreadThick)/2])

Which changed the NaN time estimates into actual numbers.

One key difference may be the small hole in the middle. The four ribs (not two!) now overlap by one thread width around the hole, so they’re not quite coincident and Slic3r produces a tidy model:

Glass Tile Frame - quad support - Slic3r
Glass Tile Frame – quad support – Slic3r

The hole eliminates a smear of infill from the center, which may have something to do with the improvement.

In any event, I have an improved copypasta recipe for the next screw holes in need of support, even if I don’t understand why it’s better.

Glass Tiles: Matrix for SK6812 PCBs

Tweaking the glass tile frame for press-fit SK6812 PCBs in the bottom of the array cells:

Glass Tile Frame - cell array - openscad
Glass Tile Frame – cell array – openscad

Which looks like this with the LEDs and brass inserts installed:

Glass Tile - 2x2 array - interior
Glass Tile – 2×2 array – interior

The base holds an Arduino Nano with room for wiring under the cell array:

Glass Tile Frame - base - openscad
Glass Tile Frame – base – openscad

Which looks like this after it’s all wired up:

Glass Tile - 2x2 array - wiring
Glass Tile – 2×2 array – wiring

The weird colors showing through the inserts are from the LEDs. The red thing in the upper left is a silicone insulation snippet. Yes, that’s hot-melt glue holding the Arduino Nano in place and preventing the PCBs from getting frisky.

Soak a handful of glass tiles overnight in paint stripper:

Glass Tiles - paint stripper soak
Glass Tiles – paint stripper soak

Whereupon the adhesive slides right off with the gentle application of a razor scraper. Rinse carefully, dry thoroughly, and snap into place.

Tighten the four M3 SHCS and it’s all good:

Glass Tile - 2x2 array - operating
Glass Tile – 2×2 array – operating

So far, I’ve had two people tell me they don’t know what it is, but they want one:

Glass Tile - various versions
Glass Tile – various versions

The OpenSCAD Customizer lets you set the array size:

Glass Tile Frame - 3x3 - press-fit SK6812 LEDs
Glass Tile Frame – 3×3 – press-fit SK6812 LEDs

However, just because you can do something doesn’t mean you should:

Glass Tile Frame - 6x6 cell array - openscad
Glass Tile Frame – 6×6 cell array – openscad

Something like this might be interesting:

Glass Tile Frame - 2x6 cell array - openscad
Glass Tile Frame – 2×6 cell array – openscad

In round numbers, printing the frame takes about an hour per cell, so a 2×2 array takes three hours and 3×3 array runs around seven hours. A 6×6 frame is just not happening.

The OpenSCAD source code as a GitHub Gist: