Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Blow out the contrast, flip right-to-left, then mask them en masse:
Small fragments – masked
Delete the images (inside their selection masks) to create a binary mask:
Small fragments – masks
Have LightBurn trace the binary images, wrap a rounded rectangle around the lot of them, duplicate the rectangle as a base plate, then fire the laser:
Smashed glass palette – fresh cut
They’re not secured in their sockets, but they won’t fall out unless I fat-finger the whole affair:
Smashed glass palette – loaded
The thing that takes getting used to: the whole process was about two hours of wall clock time from start to finish, with a leisurely breakfast and KP in the middle.
Lay some pieces atop an acetate sheet (to prevent scratching) on the scanner, grab the whole thing, then isolate an interesting chunk:
Smashed Glass – dark – piece 1
Next time: flip the image left-to-right to match the glass piece as seen from the top, because the scanner was looking at the bottom.
The weird purple background started as black, but blowing out the contrast while ignoring the color mis-correction makes the next step easier.
Trace around the perimeter with Scissors Select, clean up the result in Quick Mask mode, expand the selection by a few pixels to improve clearance, then turn it into a two-color image mask:
Smashed Glass – piece 1 – outline
Import the mask into Lightburn, trace it into vector paths (which is trivially easy and accurate given such a high-contrast image), then cut a chipboard prototype to make sure it fits:
Smashed Glass – piece 1 – acrylic mount
Clean up any misfits, test as needed, cut the inner shape and outer perimeter from 1.5 mm black acrylic, cut just the outer perimeter from 3 mm clear acrylic. Put the piece of black acrylic matching the glass shape into the scrap box.
Mix up a few milliliters of clear pourable epoxy, butter up the clear acrylic, lay the black acrylic on top, line up the edges, then gently place the shattered glass into the cutout:
Smashed Glass – piece 1 – acrylic top
Next time: apply gentle pressure, perhaps through a flexy sheet, to ensure the entire glass surface contacts the epoxy layer while squeezing out the bubbles. This will surely skate the glass across the acrylic, so don’t leave it unsupervised.
The relatively clear areas show where epoxy eased its way into the cracks between the granules; there is no correlation between the air bubbles and unfilled cracks. The epoxy had the viscosity of warm honey and I didn’t expect it to flow so easily, but it doesn’t affect the outcome.
Wait for a day, no matter how hard that may seem, for the epoxy to cure. Leave the small cup holding the remnants of the mixed epoxy nearby so you can test the cure without disturbing the Main Event.
The bottom looks pretty much like the top:
Smashed Glass – piece 1 – acrylic bottom
The shattered edge reflects off the bottom of the clear acrylic, as seen through the side:
At first we thought a mighty crunch in the morning meant the trash collection truck had dropped a garbage bin from a great height, but the sound of sirens and a myriad flashing lights revealed the true cause in our neighbor’s front yard:
NHR Crash – frontal view
The extent of the damage was more apparent from the road side:
The driver was walking around uninjured and the ambulance left quietly.
A day later, the trajectory became apparent:
NHR Crash – trajectory
The right side barely kissed the tree on the right, but the front wheel hooked the utility pole (that’s the new pole in the picture), snapped it off at ground level in addition to the usual break maybe ten feet up, and bounced a piece off the other tree:
NHR Crash – utility pole
I didn’t know you could shatter a cast aluminum alloy wheel, but the missing half of the outer face was lying amid the rather scrambled stone wall along driveway.
We’re reasonably sure we know the cause. Feel free to draw your own conclusions.
After the flatbed hauled away the car and everybody left, I harvested a few pounds of interesting debris from the lawn:
NHR Crash – tempered glass
It’s tempered glass from the driver-side windows, shattered into small chunks and barely hanging together in those sheets. Laminated windshield glass is entirely different stuff.
The smaller chunks glitter like jewels:
NHR Crash – tempered glass fragments
Obviously, the window had a bit of tint.
The smallest chunk, seen from its flat surface, shows the cuboid fragments:
NHR Crash – tempered glass fragment – front
A side view shows more complexity:
NHR Crash – tempered glass fragment – side
Tempering prevents a glass sheet from shattering into long knife-blade shards. Although the edges of the fragments are not keen, we are dealing with broken glass: they are sharp.
Broken tempered glass also sheds razor-edged flakes perfectly shaped to penetrate bike tires, although most roadside glass comes from ordinary beverage bottles. The tiniest flakes can make a mess of your eyes, so exercise at least some rudimentary shop safety practices.
Those slabs ought to be good for something, even if they fall apart at the slightest touch …
Once again, the discrete LM3909 circuitry can blink a blue LED while running a pair of alkaline cells all the way down to about 1 V, with one cell ending at 0.2 V and the other at 0.8 V. They started out discharged to 1.2 V each during their useful life, then blinked for a month; it’s as good a use for dead cells as I can think of.
With another pair of not-dead-yet cells providing 2.4 V, it started up again:
Blue LM3909 2.4V alkaline – 042
That’s a frame from a short video taken in subdued light, just to show it really does work.
The red LED is actually part of an RGB Piranha, just to see how it compares to an as-yet-unbuilt version with a single red LED in the same package.
The LED drops 1.9 V of the 2.75 V from the mostly used-up AA cells:
Astable Piranha Red – 2.75 alkaline – V LED
The original 33 Ω ballast resistor showed a peak current of 11 mA in a 30 ms pulse:
Astable Piranha Red – 2.75 alkaline – V 33 ohm
Replacing it with a 12 Ω resistor boosts the current all the way to 12 mA:
Astable Piranha Red – 2.75 alkaline – V 12 ohm
The 2N7000 gate sees a just bit more than 2 V, barely enough to get the poor thing conducting, which makes the ballast resistor mostly decorative. The MOSFET datasheet puts its 1 mA threshold somewhere between 0.8 and 3 V, so it could be worse.
Keep in mind the DSO150’s 1 MΩ input impedance sat in parallel with the 1 MΩ gate pulldown resistor forming the RC differentiator when I measured the gate voltage; I’ll leave the simulation as an exercise for the interested reader. The blinks were noticeably dimmer and perhaps a bit shorter, although eyeballometric calibration is notoriously hard.
The slightly revised schematic-layout doodle stacks the transistors along the negative bus bar:
Astable wiring layout – stacked 2N7000
Flipping the bottom transistor over to snuggle the two timing caps next to each other would eliminate the long jumper wire and probably look better.
Because a yellow / amber LED runs at a lower voltage than blue and green LEDs, it sits atop an astable multivibrator, rather than a discrete LM3909. The battery holder has a pair of carbon-zinc “Extra-Heavy Duty” AAA cells, so corrosion and leakage pose a foreseeable hazard.
The voltage across the 100 Ω LED ballast indicates a 9 mA peak LED current, which is somewhat dim in ordinary room light:
Astable AA – Amber – LED current 100 ohm
The corresponding LED voltage says the LED runs at 2.1 V for that much current:
Astable AA – Amber – LED V
Something around 39 Ω should make it more visible.
The Smell of Molten Projects in the Morning 