Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Based on Tee’s unfortunate experience, I finally got around to labeling the Bafang batteries on our Tour Easy ‘bents:
Bafang battery labeling – charge jack
On the other side, each lock is now color-coded to its key:
Bafang battery labeling – lock and keys
It’s laser-safe polyurethane vinyl applied to the battery after vigorously wiping crud off the surface with denatured alcohol. Think of it as an outdoor testcase for PSA vinyl.
I’m sure there’s a master key out there for all e-bike locks, but we remove them so rarely the color coding should suffice.
Worst case, pick the lock with a piece of wire and a hex key.
I finally managed to whack the mini-lathe’s carriage stop handle with the chuck, prompting a quick repair:
Carriage Stop – handle epoxy clamping
I probably should have epoxied a rod into the recess under the handle, seated in a drilled hole into the hub, but let’s see how long this quick-n-dirty version lasts.
While I had the hood up epoxy was curing, I lasered a block of edge-lit acrylic to replace the credit card shims:
Carriage Stop – spacer
Which turned out to be one itsy too thick. Rather than sand / machine it down, the step over on the left grew a little brass shim:
Carriage Stop – spacer and shim
Both pieces depend on snippets of adhesive sheet to hold them in place, which seems reasonable because they’re always in compression. That also eliminates the hole and pin I originally thought would be necessary; living in the future is just grand.
The four corner holes hold locating pins in the layered acrylic base:
SJCAM M20 Battery Replacement – case layers
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:
SJCAM M20 Car-Mode Battery Hack – battery case
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:
SJCAM M20 Battery Replacement – charger wiring
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:
SJCAM M20 Battery Replacement – trial install
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:
SJCAM M20 Car-Mode Battery Hack – case doodle
I truly hope this entire effort is a waste of time.
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:
SJCAM M20 Battery Replacement – circuitry
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:
SJCAM M20 Battery Replacement – wrapper layout
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:
SJCAM M20 Battery Replacement – case wrapper top
The bottom view, showing the latch retaining the contact block:
SJCAM M20 Battery Replacement – case wrapper bottom
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:
SJCAM M20 Car-Mode Battery Hack – battery wrapper
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.
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.
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:
SJCAM M20 Car-Mode Battery Hack – circuit doodle
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:
SJCAM M20 Battery Replacement – circuitry
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:
SJCAM M20 Battery Replacement – camera cable exit
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:
SJCAM M20 Battery Replacement – charger wiring
More on the cases tomorrow.
Putting it all together, the lashup goes a little something like this:
SJCAM M20 Battery Replacement – trial install
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:
SJCAM M20 Car-Mode Battery Hack – test ride
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.
That’s made of rags from the box o’ wipes out of view on the right, laid out in no particular order, on a contrasting background to simplify the next step.
Tap the Trace button and fiddle with the sliders to get a nice solid outline, along with other junk off the edge of the cardboard:
Random fabric – LB trace
All of the traced vectors will be in a group:
Random fabric – LB shapes
Ungroup them, select the outline in the middle, invert the selection, and mass-delete the junk around the edges.
If you don’t move anything, the outline will be exactly over the shape on the platform. This will come in handy later.
Import all the shapes you want nested inside the outline, group them with the outline, and hand them to the Arrange → Nest Selected tool:
Random fabric – LB nesting setup
LightBurn saves the selected objects as an SVG file with the file name in the clipboard and fires up a browser tab at https://svgnest.com/. Upload the SVG and let the nesting algorithm chew away for a while:
Random fabric – LB nested
The weird triangles come from the Dot Mode perforations that ought not be there; inner shapes get subtracted from outer ones, which makes perfect sense. Your shapes will differ.
Download the nested shape SVG, load it back into LightBurn at the prompt generated after exporting the shapes, and LightBurn will apply the transforms to the original shapes. Put the outer shape on a tool layer and the inner shapes on whatever cutting layer you like, snap the outer shape (with the nested shapes inside) to the previously undisturbed outline of the stuff on the platform, and Fire The Laser!
Now there’s a pretty good chance I can do that again …
The Smell of Molten Projects in the Morning 