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.

Tag: Improvements

Making the world a better place, one piece at a time

SJCAM M20 Camera: Battery Case Salvage

Remove the spicy pillow from an M20 battery case and carve a notch in one side to see if this might work:

SJCAM M20 Battery Replacement – battery interior

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.

2023-08-01
SJCAM M20 Camera: Car Mode Battery Hack

The last lithium cell (a.k.a. battery) for the longsuffering SJCAM M20 transformed itself into a spicy pillow:

SJCAM M20 – spicy pillow lithium battery

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:

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.

2023-07-31
Onion Maggot Fly vs. Sticky Traps: Season 3 Round 1
Six sticky traps have been out in Mary’s Vassar Farm onion bed from mid-April through mid-July, collecting onion maggot flies, other flying insects, and a bunch of shredded leaf mulch. Having just replaced all the sticky sheets, these are the results so far:
PXL_20230711_215255180 – VCCG Onion Maggot Trap F
PXL_20230711_215229538 – VCCG Onion Maggot Trap E
PXL_20230711_215159950 – VCCG Onion Maggot Trap D
PXL_20230711_215129817 – VCCG Onion Maggot Trap C
PXL_20230711_215041012 – VCCG Onion Maggot Trap B
PXL_20230711_215002214 – VCCG Onion Maggot Trap A
Each image is the front and back of a single sticky sheet flipped over left-to-right; I did not keep track of the original trap locations.

If you need the original camera images to get enough pixels for itemizing the smaller dots, let me know.
2023-07-21
Mini-Lathe Chuck Stops: Better Next Time
The story so far:
Daubing urethane adhesive into each pocket, sliding a tiny magnet atop the goo, and flipping them over onto a sheet of plastic atop the surface plate to let them cure went about the way you’d expect. Given the state of my fingertips, however, I was not about to fiddle with the phone / camera / anything, but it really did happen.

The final result:

Lathe Chuck Stops – on-lathe storage

The alert reader will notice the slight gap under the left leg of the first orange stop, which provides a good introduction for a few things that should happen differently the next time I do something like this.

To my credit, I got all but one of the 54=3×6×3 magnets into their pockets in the same orientation. That’s gotta count for something and, hey, that orange stop sticks to the chuck just fine.

That one also suffered from my failure to switch the Axis UI to metric units before touching off the Z axis at 0.1 mm, thereby putting the Z=0.0 level 2.53 mm below the surface. Fortunately, the 3 mm MDF baseplate prevented that error from creating three pockets in the tooling plate, although it did produce holes instead of pockets in the stop.

I dropped the magnets into the thru-cut stop on the surface plate and dabbed some adhesive atop the magnets to bond them into their holes. This worked fine and led me to suspect the easiest way to make these stops would be to just laser-cut the holes and skip the whole CNC thing.

The disadvantage of cutting the holes through is that adhesive will inevitably ooze out around the magnet and mess up the bottom surface of the stop. Sticking both the stop and the magnets onto kapton tape seems like it should seal well, but liquid always finds a way.

In any event, the two-part urethane adhesive (JB Plastic Bonder) expands slightly as it cures, which is great for gap filling and not so good for precision bonding. With the pockets in the other 17 stops arranged open-side down, the magnets held themselves firmly to the plastic sheet atop the surface plate and the expanding urethane pushed the acrylic stop upward, leaving the magnets standing slightly proud of the stop’s surface:

Lathe Chuck Stops – protruding magnet

Not by much, mind you, but not what I wanted, having painstakingly cut the pockets 2.2 mm deep for a 2.0 mm magnet.

Next time, dot some slow-cure clear pouring epoxy in each pocket, put the stop on the surface plate with the pocket facing up, then drop the magnet in place. The magnet pulls itself into the pocket, the epoxy doesn’t expand, any overflow will fill in over the magnet, and anything sticking out can be sanded off.

The fixtures worked well and aligned perfectly on the Sherline’s tooling plate. The 0.1 mm outset around the stops in the chipboard probably wasn’t needed, although the total repeatability seemed to be around 0.2 mm and pocket position errors are visible only on the smallest (red) stops:

Lathe Chuck Stops – misaligned pocket

All in all, this turned out pretty well. Next time will be even better!

And, perhaps, making the stops with 3D printing would be even better than that, at the cost of the usual gnarly surface finish.
2023-07-17
Mini-lathe Chuck Stops

Having occasionally been in need of a lathe chuck stop, I finally cleared that project off the heap:

Lathe Chuck Stops – demo setup

These are definitely not up to commercial standards, but also don’t cost fifty bucks each. A trio of 4×2 mm neodymium disk magnets stick the stop to the chuck (and to each other) with enough force to hold it there, but not enough to make removing it a hassle.

I imported the Z axis orthogonal view of the chuck jaws from the ball fixture for the running lights:

Lathe Chuck Jaws – solid model axial

Trace the right-side jaw, clean it up, put the tip a known distance from the origin, make a circular array, and draw a comfort circle the size of the chuck OD.

The stop geometry comes from a hull wrapped around a circle a few millimeters larger than the 4 mm magnet (out 20 mm from the center) and a circle at the center sized so the hull clears the jaws:

Lathe Chuck Stops – LB layout

Then a small circle at the center allows me to drop the stop atop a known coordinate and rotate it around the circle, because the XY coordinate center is not at the geometric center.

I cut out a few chipboard samples to verify the sizes, a few more from scrap acrylic to set up the pocketing operation, then half a dozen of each in cheerful kindergarten colors:

Lathe Chuck Stops – on-lathe storage

The 5 mm stop is obviously too fragile for commercial success, but I figured it’ll survive long enough around here. Worst case, I can make another handful as needed.

Although I have laser-engraved pockets in plywood, a few experiments in acrylic confirmed the surface finish is terrible and the depth control is iffy, at best. Given that I need a 2.2 mm deep pocket in 3 mm acrylic, a CNC mill seems the right way to poke the pockets:

Lathe Chuck Stops – pocketing setup

More on that tomorrow.

The LightBurn SVG layout as a GitHub Gist:

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view raw Lathe Chuck Stops – LB layout.svg hosted with ❤ by GitHub

2023-07-12
Danger Zone Refrigerator Magnets

Laser cutting the Danger Zone coasters with the proper kerf offset for a good fit produced a pile of waste pieces from the other side of the kerf that seemed too nice to throw out. A bit of rummaging in the Basement Shop Warehouse Wing produced a battered magnetic sign that fell off the side of another truck and some casual searching suggested the material was laser-cuttable, whereupon this happened:

Laser-cutting magnetic sheet

The trick is to cover the label side of the sign with adhesive sheet and the refrigerator side with blue painter’s tape, thereby simplifying the inevitable cleanup. Cutting through the adhesive produced poor results, perhaps due to molten adhesive or the sign material (which is almost certainly non-laser-safe PVC, alas) flowing into the cut and contaminating the process. Cutting through the blue tape worked reasonably well, albeit with a disconcerting shower of sparks.

The cutting pattern is the shape outline inset by about 0.5 mm.

Peel off the blue tape, remove the adhesive cover layer, align the outermost shape, press it down, add the rest, then admire the results:

SCP Cognitohazard – refrigerator magnets

The obvious difference in the “filament” size comes from two different kerf offsets, both on the order of 0.15 mm. It makes a big difference in narrow objects!

The Autonomous Object coaster created its own pile of scrap and you can see the gaps created by the mismatched kerf offsets:

SCP Autonomous Object refrigerator magnet

Not works of art, but they came out nicely given where they started.

2023-06-27
Laser Water Chiller: Alarm Wiring

I recently replaced the hack-o-matic icemaker + fountain pump cooler with a LightObject Q600 water chiller, an entirely uneventful process. The Q600 has a back panel “aviation connector” with an alarm output for water flow (more precisely, lack thereof) or over / under temperature: pins 1 and 3 are closed during normal conditions and open during alarms (and when the power is off).

I finally wired the chiller into the OMTech 60 W laser’s internal water flow switch circuit, so that should either flow sensor have a problem with the water or the chiller detects an out of bounds temperature, the laser won’t fire.

You may recall the laser’s HV power supply arrived with its Water Protect input jumpered to ground, which I then wired to the lid interlock switch to (presumably) reduce the likelihood the replacement power supply will fail hot. The laser’s water flow switch goes to the Ruida controller’s WP input, where it behaves as it should.

Pin 2 of the chiller’s alarm connector is not connected to anything, so I added a safety ground wire for no good reason:

Laser Water Chiller – safety ground wire

The dent in the evaporator tube (upper left) is worrisome.

While I had the side panel off, I jammed a strip of closed-cell foam around the base of the compressor to silence a truly spectacular rattle:

Laser Water Chiller – compressor vibration suppression

I think the three mounting screws (yes, of these two: one up, one down, for no reason I can see) are looser than they should be, but I’m reluctant to tip the whole thing over with a tank full of water to get at the nuts / bolt heads on the bottom.

The connectors have a twist-lock notch that you must release after removing the screw (on the far side) holding the shell to the body:

Laser Water Chiller – connector shell keyway

I repurposed a USB cable from the Big Box o’ Cables, wrapped with enough silicone tape to fill the cable clamp:

Laser Water Chiller – connector closeout

In retrospect, I should have paired the red + green and black + white wires, but nobody will ever notice. The drain wire carries the safety ground from pin 2 to the shielding, not that it matters. Both ends of the cable have identical connectors.

The laser cabinet has a convenient hole, albeit just a bit larger than required, which now has a simple adapter plate with the proper flats:

Laser Chiller Alarm Connector Plate

The blue ring is the same size as the hole, so as to ease lining it up, and the red perimeter surrounds the connector with strips of good double-sided foam tape for maximum sticktivity. Done in clear acrylic from the scrap pile, the platform’s internal lights give it that subtle blue-white hi-tech glow:

Laser Water Chiller – laser connector installed

The doubled-up cable ties on the water hose barb connectors are a Good Idea™ due to the somewhat higher pressure of the chiller’s water pump. The bottom of that recess had traces of water on it and, of course, having a hose pop off its barb is a Bad Thing™.

The new connector is wired in series with the internal flow switch, using a trio of grossly overqualified silicone-filled splices:

Laser Water Chiller – laser flow switch splices

I did not connect the safety ground from the chiller to the laser’s frame, because they do not share a common breaker circuit and I have better things to do than chase ground loops.

For whatever it’s worth, the gray cable that came with the laser might also be a repurposed USB cable, too: it has two fat wires and two thin wires, although it’s not wearing USB livery.

The laser is happy when the chiller is running and unhappy when it’s off, so life is good.

2023-06-23