Archive for category Electronics Workbench
While packing the vacuum tube LEDs for the HV Open Mad Science Fair, I noticed the knockoff Arduino Nano inside one had come unstuck from the base. It seems the double-stick foam tape I’d used had lost its sticky:
Replacing it with my now-standard black 3M outdoor rated tape ought to solve the problem forever more.
Before reassembling the light, I plugged the USB cable into the bench supply and watched the Nano reset erratically. Careful poking showed the USB cable was intermittent, so I carved it up:
As far as I can tell, the black wire (supply common) was cut mostly all the way through, with just a few strands remaining, before I peeled the insulation back.
A closer look at the solder joints doesn’t inspire much confidence in their QC:
If those pads tarnished along with their solder blobs, the overmolded plastic isn’t the right stuff for the job. If they started life like that … ick.
I must up my cable spend, although I have no confidence doing so will improve the quality.
I’ve finally had it beaten into my head: any public exhibition requires paper handouts, if only for younger folks who are too shy to ask questions. Paper may seem obsolete, but it serves as a physical reminder long after the sensory overload of a busy event fades away.
Hence, I made up cards describing my exhibits at the HV Open Mad Science Fair, each sporting a QR code aimed at far more background information than anybody should care about:
The QR codes come from one-liners:
qrencode https://softsolder.com/?s=dso150 -s 5 -d 300 -o dso150.png
So, go ahead, shoot ’em with your phone:
Memo to Self: put the cards in the Big Box o’ Stuff the night before.
Ping-Pong ball radomes tend to fall off their perches at the slightest touch:
Because I planned to take my collection along to HV Open’s Mad Science Fair, I finally used a Round Tuit for some adhesive action.
The general plan was to punch a ring from double-sided tape, thusly:
The OD required touching up the edge of a brass tube punch I’d made a while ago:
It worked exactly as expected:
Unfortunately, the 3D printed spider’s “spherical” socket has such a rough surface that the adhesive had too few contact points to hold the ball in place.
My fallback has become 3M outdoor-rated double-stick foam tape, so:
This leaves a small black ring visible between ball and socket. Recessing the foam tape by half its thickness should improve its ahem optics, although it’s probably not worth the effort with black PETG.
The battery pack on my ancient Dell E1405 laptop finally died, so I tore it apart to see what horrors might lurk within:
The case snaps apart without too much effort, although the delicate single-use latches won’t survive the operation. These certainly didn’t, which didn’t bother me at all, as I already had a replacement battery on order.
One of the cells (in the front) seems to have leaked ever so slightly inside its wrapper:
The three cells in that 3P section seem to have failed open: they pass no current at all.
The other pair of 3P slices, charged at 4.2 V with a 700 mA current limit until the current dropped under 10 mA, still have some life:
Perhaps recycling individual cells into LED glowies would be nice, as they have enough capacity remaining to run an Arduino for quite a while, and a 1S USB charger would make for a self-contained package.
There’ll be glowing glassware:
Some take-home art:
And, as always, a good time will be had by all!
As the basement’s fluorescent fixtures and lamps gradually die, I’ve been rewiring the fixtures for LED tubes, all bought from KEDSUM through Amazon. The first few batches looked like this:
The most recent two batches seem cheapnified:
The tubes show similar changes, going from a stylin’ version to a simple cylindrical cap:
The most recent carton label might lead you to think they’re counterfeits, but it could just be a simple typo:
There’s absolutely no way to tell what you’re going to get from any vendor on Amazon (or anywhere else, for that matter), so there’s no point in returning them, but I’d hoped buying “the same thing” from “the same seller” would produce a consistent result.
Well, I can fix that.
Start by prying the recessed top panel off the case:
Remove the circuit board to expose the tiny speaker, taking care not to rip the tiny wires out of the tiny connector:
You can’t measure a dead speaker, but it seems to be an 8 Ω unit.
The speaker sits in a rubber surround, with a foam rubber cushion against the PCB, tucked into a walled garden stiffening the case:
I don’t happen to have a tiny 8 Ω speaker, but I do have a bunch of small speakers, so I bulldozed those walls with a flush cutting pliers and a bit of cussing to make room:
Nibble an adapter ring to match the rim of the new speaker, thereby routing the sound out those little holes, and hot-melt glue it in place:
Hot-melt glue the new speaker in place atop the adapter, taking care to fill all the edges / cracks / crevices below it with an impenetrable wall of glop:
The sealing part turns out to be critical with these little speakers, because a leak from front to back will pretty much cancel all the sound from the cone.
Cut the wires off the old speaker, affix to the new one, replace the PCB, snap the case lid in place, and it sounds better than new.
Millions of transistors in those ICs, but Ooma can’t spec a good speaker? Maybe they should have used a bigger speaker to begin with; ya never know.