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.
More craft stick markers followed the harvest home from Mary’s garden:
As before, all-caps names survive longer:
Although the name looks intact, the last few letters have cracks and would have fallen apart in a while.
Pretty much as expected, thin wood markers are not forever.
This dandelion weeder was no match for the rugged weeds among the decorative grasses Mary planted along the road out front:
You might expect the tang to extend well into the handle, but that’s not what you get in a cheap tool:
The Bucket o’ Rod-like Materials had a rake handle about the right diameter, so I sawed off a suitable length, set up the steady rest with a bushing, and turned the end to match the ferrule:
Pound the ferrule into place and drill the new handle to fit the tang:
The handle seemed a bit raw and, as it was already chucked in the lathe, got a synthetic string wrap with clear epoxy coating:
The pourable epoxy is reaching the end of its shelf life, but seemed entirely suitable for the purpose. I wrapped two layers of string around the dry handle, laid paper over the lathe bed, slathered epoxy over the whole affair, and let the lathe turn dead-slow for most of the day to even out the coat.
The next day: hammer the blade mostly straight again, smear JB QuikWeld on the tang and into the hole, gently hammer them together, chuck the blade, apply more epoxy to the ends, and let it turn:
A careful inspection reveals my casual disregard of the finer points of tool handle craftsmanship, but it came out surprisingly pretty:
The blade remains the finest butter-soft cheap steel and still doesn’t extend the length of the handle, but Quality Shop Time™ is not to be sniffed at.
And, hey, nary a trace of 3D printing or laser cutting!
Early one morning, a skunk dashed toward the garden:
If you look very closely, you’ll see a mouse watching from the end of a 4 inch drainpipe stashed along the garden fence:
The skunk went exploring near the garden gate (off to the right) while the mouse continued watching the proceedings:
When the skunk returned, the mouse decided discretion was the better part of valor and vanished into the pipe:
With the skunk gone about its business, the mouse returned to its duty:
Just another night at the office, out in the back yard …
Wearing my FitBIt Charge 5 tracker in the shower without activating its Water Lock feature occasionally produces odd results, but the most recent mishap ventured deep into the peculiar:
Its complete lack of buttons makes the thing completely waterproof, but also means it cannot continue when the touch / swipe interface gets horribly confused.
The recovery process requires snapping it onto its USB charging cable, then pressing the nearly invisible button embedded in the USB connector shell three times, with one second between each press: click hippopotamus click hippopotamus click.
Then it restarts / reboots and eventually all is well again.
Perhaps I can now recall the magic incantation without digging through the online help again, because I am certainly not going to suddenly remember to do the Water Lock dance before showering.
A little tweakage to the NP-BX1 battery holder for the astable multivibrator blinkies produced a simple version with the wire exit holes on the bottom:
The four corner holes hold locating pins in the layered acrylic base:
Those pins got cut slightly shorter to fit in the battery holder; in this photo they’re serving to align the layers and adhesive sheets while I stacked them up.
The geometry is straightforward, with the outer perimeter matching the 3D printed battery holder:
Cut one base and two wall layers from 3 mm (or a bit less) transparent acrylic, plus three adhesive sheets. I stuck adhesive on both sides of one wall layer, using the pins to align the adhesive, stuck the layer to the base, then topped it with the second wall layer, again using the alignment pins.
The motivation for transparent layered acrylic is being able to see the charge controller’s red and green status LEDs glowing inside the box. This probably isn’t required, but seemed like a Good Idea™ for the initial version.
With all that in hand, wire it up:
The USB charger PCB sits atop a layer of double-sided foam tape. After verifying that the circuitry worked, I globbed the wires in place with hot-melt glue to make it less rickety than the picture suggests.
The alert reader will have noticed the holes in the 3D printed NP-BX1 holder were drilled, not printed. In the unlikely event I need another case, the holes will automagically appear in the right place.
I haven’t yet peeled the protective paper off that top adhesive sheet to make a permanent assembly:
We use the car so infrequently that it’ll take a while to build up enough confidence to stick it together and stick it to the dashboard.
On the whole, it’s ugly but sufficient to the task.
A doodle with key dimensions, plus some ideas not surviving contact with reality:
I truly hope this entire effort is a waste of time.
Remove the spicy pillow from an M20 battery case and carve a notch in one side to see if this might work:
The circuit board is the charge controller for the evicted high-voltage lithium pouch cell, but I started by connecting an ordinary lithium cell with a Schottky diode to the PCB’s battery terminals.
This worked about as poorly as you’d expect, because the lower battery voltage minus the forward drop of the diode minus whatever happens in the PCB put the final voltage below the camera’s instant low-battery shutdown.
The terminals connecting to the camera in the rectangular bump are soldered to the back of the PCB, but the whole affair snaps out of the battery case. Unsoldering the PCB from the terminals, gingerly soldering directly to them, and adding a bulk storage capacitor produced a better result:
The cap stores just enough energy to keep the camera happy while writing to the Micro-SD card, although the LCD screen dims slightly during each pulse.
Cut a pad from a sheet of closed-cell foam that happened to be exactly the right thickness:
The elaborate thing below the case is a cardboard pad atop the sticky side of a PSA non-PVC vinyl sheet, laser-cut to fit:
The bottom view, showing the latch retaining the contact block:
Admittedly, that’s the last iteration of the wrapper, starting with a hand-trimmed Kapton tape version and three paper versions to get the dimensions right before trying vinyl. Looks good to me!
The final geometry has a 0.5 mm radius on all the corners:
The fillets reduced (but did not eliminate) mechanical oscillations while slinging the laser gantry around those corners. If I don’t point them out, maybe nobody will notice.
The PSA vinyl is marginally thicker than the original plastic wrapper, so the battery fits very snugly into the camera. On the other paw, getting the swollen battery out required a major effort; this one should not get tighter.
The last lithium cell (a.k.a. battery) for the longsuffering SJCAM M20 transformed itself into a spicy pillow:
SJCAM no longer sells those batteries and nobody else does, either, surely because the +4.35V marking shows they’re a special-formula high-voltage lithium mix that doesn’t work with ordinary chargers. Worse, you can’t substitute an ordinary (i.e. cheap) battery, because applying a high-voltage charger to a 4.2 V cell makes Bad Things™ happen.
Putting the M20 camera in Car Mode makes it begin recording when it sees 5 V on its USB input and shut down a few seconds after the USB input drops to 0 V. Without the internal battery, the camera’s clock doesn’t survive when the external power vanishes, which seems critical for a camera sitting on a dashboard.
Mashing all that together, I wondered if I could use one of the many leftover low-voltage NP-BX1 batteries from the Sony AS30V helmet camera without starting a dashboard fire, by preventing the camera from charging the battery, while still using it when the USB input is inactive (which, for our car, is pretty nearly all the time).
The circuitry, such as it is, uses a cheap 1S USB charge controller and a Schottky diode:
Power comes in on the left from a USB converter plugged into the Accessory Power Outlet in the center console and goes out to the camera’s USB jack, using a butchered cable soldered to the charge controller’s pads in the middle. The controller manages the NP-BX1 battery as usual, but a diode prevents the camera from trying to send charge current into the controller.
This should just barely work, as the diode reduces the battery voltage by a few hundred millivolts, so the camera will see the fully charged low-voltage battery as a mostly discharged high-voltage battery.
Suiting action to words:
It’s built inside the gutted remains of an M20 battery case. The 100µF tantalum cap provides local buffering to prevent the camera from browning out during bursts of file activity while recording. The wire emerges through holes gnawed in the battery case and the camera housing:
The charge controller on the other end of the wire lives in a layered laser-cut acrylic case attached to a modified version of the venerable 3D printed NP-BX1 battery holder:
More on the cases tomorrow.
Putting it all together, the lashup goes a little something like this:
The battery pack will eventually get stuck to the dashboard underneath the overhang, out of direct sunlight. Things get hot in there, but with a bit of luck the battery will survive.
The rakish tilt puts the hood along the bottom of the image, although raising the camera would reduce tilt and cut down on the skyline view:
The battery icon instantly switches from “charging” to “desperately low” when the USB power drops, which is about what I expected, but the camera continues to record for about ten seconds before shutting down normally.
The NP-BX1 battery in the holder comes from the batch of craptastic BatMax batteries with a depressed starting voltage. An actual new cell with a slightly higher voltage would keep the camera slightly happier during those last ten seconds, but … so far, so good.
Another possibility would be a trio of 1.5 V bucked lithium AA cells, with the diode to prevent charging and minus the charger.
The Smell of Molten Projects in the Morning 