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

Epoxy Joint: Test to Destruction

Some years ago, I put the LED power supply for one of the Kenmore 158 machines atop a plastic project box with an adjustable boost supply inside:

Needle LEDs power supply – exterior

The LEDs connected through a coaxial power jack on the far side of the box, held in place with a generous blob of epoxy:

Needle LEDs power supply – interior

A closer look:

Kenmore 158 COB LED – power supply jack

I’m adding a light bar, similar to the one now going onto the Juki TL-2010Q, which needs a direct connection to the 12 VDC supply. Rather than add another coaxial jack, I ripped out the existing jack and installed a DE-9 connector (serial ports being a fading memory by now), giving me an opportunity to test the epoxy joint:

Kenmore 158 COB LED – power supply jack – epoxy bond

Which required grabbing the connector with a pair of pliers and twisting / bending / abusing until it popped free. I don’t know how much grip the scored lines added to the joint, but the connector definitely didn’t give up without a fight; it wasn’t going to fall off on its own.

To be fair, the epoxy had a better grip on the coaxial jack than on the plastic plate, perhaps because the bottom of the jack had all manner of nooks and pins intended for PCB mounting. Ya use what ya got, sez I.

The new connector looks exactly like it should and, because it’s held in place by a pair of screws, should last forever, too:

Kenmore 158 COB LED – power supply

More about all that, later …

2019-02-03
DSO150: USB Battery Charger

Continuing the process of silk-purse-izing the DSO150, a batch of USB 1S lithium battery charger modules arrived from halfway around the planet. I drilled & filed a suitable hole / slot / aperture in one of the few remaining spots in the case, then stuck the PCB to the bottom with good foam tape:

DSO150 – USB charger – internal layout

Because the charger includes cell protection circuitry, I replaced the original protected 18650 cell with a bare cell sporting solder tabs. The cell should go directly to the charger board, but the switch disconnects the + wire; I’m unwilling to believe the charger won’t slowly and inexorably discharge the cell if I don’t use the DSO150 for a few months. It could happen.

A label makes the hole look almost professional:

DSO150 – USB charger – Micro-B jack

Well, makes it look Good Enough™, I suppose.

The power switch gets a label, too:

DSO150 – USB charger – battery switch

Flipping the switch ON lights up the scope from the battery.

The charger (sensibly) will not route power from the USB port to the scope without a battery, so you must plug in a USB source with the switch ON, then flip the switch OFF. I don’t know why you’d want to do that, but there you go.

Now it’s a real portable instrument, with all the inconvenience of managing a built-in lithium cell.

2019-01-30
Vacuum Tube LEDs: Radome Prototype

Definitely not a vacuum tube:

Arduino Pro Mini – NP-BX1 cell – SK6812 – blue phase

It’s running the same firmware, though, with the Arduino Pro Mini and the LEDs drawing power from the (mostly) defunct lithium battery.

The LED holder is identical to the Pirhana holder, with a 10 mm diameter recess punched into it for the SK6812 PCB:

Astable Multivibrator Battery Holder – Neopixel PCB – Slic3r

Those embossed legends sit in debossed rectangles for improved legibility. If I repeat it often enough, I’m sure I’ll remember which is which.

The 3.6 V (and declining) power supply may not produce as much light from the SK6812 LEDs, but it’s entirely adequate for anything other than a well-lit room. The 28 AWG silicone wires require a bit of careful dressing to emerge from the holes in the radome holder:

SK6812 LED PCB – Pirhana holder wiring

The firmware cycles through all the usual colors:

Arduino Pro Mini – NP-BX1 cell – SK6812 – orange phase

A pair of tensilized 22 AWG copper wires support the Pro Mini between the rear struts. The whole affair looks a bit heavier than I expected, though, so I should reduce the spider to a single pair of legs with a third hole in the bottom of the LED recess for the data wire.

The OpenSCAD source code needs some refactoring and tweaking, but the Pirhana LED solid model version of the battery holder should give you the general idea.

2019-01-29
Vacuum Tube LEDs: Arduino Pro Mini vs. NP-BX1 Battery

A year or so ago, a certain Young Engineer suggested my Vacuum Tube Lights really needed battery power and rebuffed my feeble objections concerning low LED intensity (3.6-ish V, not plug-in 5 V USB) and short run time (because three constantly lit LEDs draw too much current). Having a spare NP-BX1 holder lying about, here’s a feasibility study:

Arduino Pro Mini – Neopixel – NP-BX1 battery

Not much to it, eh?

Hitching the DSO150 to a Tek current probe (which needs a 50 Ω load, thus the terminator on the BNC tee) seems a clear-cut case of a sow’s ear joining forces with a silk purse:

DSO150 – Arduino Pro Mini – Neopixel current

It was just sitting there, so why not?

Seen with a bit more detail on a better scope:

Ard Mini – NP-BX1 – SK6812 – 10 mA-div

Each vertical increment represents the current into a single LED (at 10 mA/div), with the PWM cycles ticking along at 1.3 kHz.

The current steps aren’t the same height, because the LEDs have different forward voltages. The taller step (at the top) probably comes from the red LED, with the other two being blue and green. The maximum current is only 40 mA, not the 60 mA you’d expect with a 5 V supply.

The PWM width, of course, determines the brightness of each LED. Eyeballometrically, the average current will be half of 40 mA for (just less than) half of each PWM cycle, so figuring each SK6812 module (there’s only one here) will draw 10 mA seems reasonable.

The “base load” from the Arduino looks like 2 mA, so there’s not much point in removing its power and status LEDs.

The NP-BX1 lithium cell has lost enough capacity to no longer power my Sony HDR-AS30V helmet camera for at least half of a typical ride. The camera draws around 1 A, so you can clearly see the defunct batteries:

Sony NP-BX1 – 2018-04-24

If the average voltage during discharge is 3.3. V, then a 10 mA load would be 33 mW and a defunct NP-BX1 battery with 2 W·h capacity (at 1 A) might provide 60 hours of continuous use. I’d expect more capacity at lower current, although it’s not clear the cells actually behave that way.

So a battery-powered Vacuum Tube Light might make sense, perhaps as romantic illumination for techie snuggling:

21HB5A – Guilloche platter

Ya never know …

2019-01-28
DMM Probes

After the Great DMM Probe Debacle, I picked up similar-but-different set of cheap probes and clip leads.

The needle-tip probes carry a 20 A current rating:

No-Name DMM probes – needle tip – 20 A

If you look out along the wire, though, you’ll find a 10 A rating:

No-Name DMM probes – needle tip – 10 A wires

Now, even though 20 AWG wire in silicone may carry a 17 A spec, the corresponding 200 °C temperature seems excessive for a test probe. Limiting the current to 10 A would reduce the power dissipation by two thirds, which should limit the temperature rise. Whether the wire actually contains 20 AWG of actual copper strands remains an open question.

The kit also had banana plug / test hooks with no particular rating, although the wire allegedly has 16 AWG conductors:

DMM Clip Leads – 16 AWG

The banana plug / alligator clip combo claims 30 A, also with 16 AWG conductors. Who knows? It could be true.

For comparison, the Siglent SDM3045 DMM came with these probes:

Siglent DMM probes – 10 A

The probes carry a 10 A rating and, although the wires aren’t branded, I’ll assume they have good-enough QC to ensure the copper matches the claims. The production values seem a bit higher, too, even if they bear a striking resemblance to the cheap probes.

And, for reference, the probes with the cold solder joint also claim 20 A:

No-Name DMM probes – 20 A

Wouldn’t trust any of ’em for more than a few amps, tops …

2019-01-25
Sony HDR-AS30V Helmet Camera: MicroSD Card Spacer

Sony tried, they really tried, to make their proprietary Memory Stick flash memory cards catch on, but the slot in their HDR-AS30V Action / Helmet camera accepts both Memory Stick Micro and MicroSD cards. The two cards have slightly different sizes, the AS30V’s dual-purpose slot allows MicroSD cards to sit misaligned with the contacts, and the camera frequently kvetches about having no card.

The only solution seemed to be starting the camera while watching the display to ensure the card worked, but it would sometimes joggle out of position during a ride.

I cut out a tiny polypropylene rectangle(-ish) spacer to fill the Memory Stick side of the slot, sized to fit between the spring fingers holding the MicroSD card against its contacts:

Sony HDR-AS30V Camera – MicroSD card and spacer

Not the best cutting job I’ve ever done, but it was an iterative process and that’s where I stopped. If this works and I have need for another / better spacer, I promise to do better.

The spacer’s somewhat mottled appearance comes from tapeless sticky (an adhesive layer on a peel-off backing: inverse tape!) applied to the top side, which will affix it to the slot. I’d rather glue the spacer to the MicroSD card, but then the card wouldn’t fit in the USB 3.0 adapter I use to transfer the files.

The chips along the left edge of silkscreen come from my fingernail, because pressing exactly there seems to be the best way to force the damn thing into the proper alignment.

So the slot + spacer looks like this:

Sony HDR-AS30V Camera – dual-card slot with spacer

The MicroSD card fits in the far side of the slot, facing toward you with contacts downward, thusly:

Sony HDR-AS30V Camera – MicroSD card with spacer

And then It Just Works™, at least on the very few rides we’ve gotten in during December and early January.

Incidentally, the blue and exceedingly thin latch finger holding the battery in place will snap, should you drop the camera on its non-lens end from any height. Conversely, should you drop it on the lens end, you can kiss the optics goodbye. Your choice.

2019-01-23
Tensilizing Copper Wire

The “bus bars” on the battery holders are 14 AWG copper wire:

Astable – NP-BX1 base – detail

Slightly stretching the wire straightens and work-hardens it, which I’d been doing by clamping one end in the bench vise, grabbing the other in a Vise-Grip, and whacking the Vise-Grip with a hammer. The results tended to be, mmm, hit-or-miss, with the wires often acquiring a slight bend due to an errant whack.

I finally fished out the slide hammer Mary made when we took a BOCES adult-ed machine shop class many many years ago:

Slide Hammer

The snout captured the head of a sheet metal screw you’d previously driven into a dented automobile fender. For my simple purposes, jamming the wire into the snout and tightening it firmly provides a Good Enough™ grip:

Slide Hammer Snout

Clamp the other end of the wire into the bench vise, pull gently on the hammer to take the slack out of the wire, and slap the weight until one end of the wire breaks.

With a bit of attention to detail, the wires come out perfectly straight and ready to become Art:

Straightened 14 AWG Copper Wires

The wires start out at 1.60 mm diameter (14 AWG should be 1.628, but you know how this stuff goes) and break around 1.55 mm. In principle, when the diameter drops 3%, the area will decrease by 6% and the length should increase by 6%, but in reality the 150 mm length stretches by only 1 mm = 1%, not 3 mm. My measurement-fu seems weak.

Highly recommended, particularly when your Favorite Wife made the tool.

The Harbor Freight version comes with a bunch of snouts suitable for car repair and is utterly unromantic.

2019-01-18