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.
Who’d’a thunk it?
The dam at Red Oaks mill has accumulated several large trees over the past year that often serve as perches for birds surveying the pool.
We spotted these ice formations on a recent walk.
The bottom edge of the toothbrush is just inches over the roiling water.
Sometimes I get to do an easy one. This dust collector came with the house and sits on the fireplace; one of the little guys fell off when Mary went on a cleaning frenzy. As nearly as I can tell, he had a bad butt weld (using the exact term) with marginal penetration.
A dot of JB Weld, an uncomfortable overnight stay on the workbench, and he’s as almost good as new. I briefly thought about resistance-soldering him together, but came to my senses: epoxy to the rescue!
The balance point is sufficiently delicate that the additional weight of the epoxy pulls his side down a bit. I’ll call it art and leave it at that, although I should build a little circuit with a proximity sensor and an electromagnet to keep the thing in motion.
Yeah, that’s my Tau Beta Pi Bent in the background… along with the little glass bead I made in the Corning Museum of Glass a few summers ago.
Got a package from halfway around the world that, I thought, corresponded to a recent eBay order. Opened the envelope and pulled out a box containing … a Digital Media Player?
That’s odd. I don’t recall ordering one of those.
At this point, anybody who’s read Frank Herbert’s The White Plague should get the chills. Do you or don’t you open a mysterious package from far away that seems to offer something interesting?
Pandora might have something to say, too.
Well, open it I did, and found exactly what I’d ordered: a stash of female headers pins. Of course, one can’t tell what else might have come in the package, but so it goes.
Now I can hand Eks half a lifetime supply of the strips to replace the ones I mooched.
One other mildly surprising part of the package: it seems we’ve gotten to the point where magnetic closures are cheap enough to replace everything else, including intricate origami tucks. There’s a small steel plate pasted under the flap. Who knew?
Twas the Night…
By Mary Nisley
‘Twas the night before September, when outside the house
Many creatures were stirring, not just a mouse;
The garden was fenced all ‘round with care,
In hopes that deer would never come there;
My daughter was nestled all snug in her bed,
While replays of band practice ran through her head;
My husband was sleeping, and hoped for much more,
As I settled down for a short summer snore.
When out in the yard there arose such a clatter,
I sprang from the bed to see what was the matter.
Away to the window I flew like a flash,
But saw nothing on the deck; what was that crash?
Then off to the kitchen to flip on the lights,
To better reveal the outermost sights.
When, what to my wondering eyes should appear,
But an eight pointed buck: a powerful male deer!
His head, it was lowered; his mouth, it was red,
He looked mean and angry, a monster to dread.
When he moved I saw a most terrible sight,
His antler was tangled in the fence very tight.
I ran for my husband, to wake him from sleep,
He groggily blinked, then from the bed he did leap.
We dashed to the doorway, but the buck, he was gone,
One glimpse of my motion made him quite strong.
We surveyed the garden with the help of a light,
What destruction was done before the buck’s flight?
Alas! My poor garden, damage lay all around,
Two heavy steel fence posts he’d bent to the ground.
The ruin was total in two veggie beds:
Stalks twisted and broken, big leaves lay in shreds.
We pushed the posts upright, unsnarled all the net,
As we patched the fence up, we felt it was wet.
Shining flashlight on hands revealed blood on our fingers,
But it was not ours: could deer blood still linger?
Sunshine the next morning revealed all of the damage,
Plus an antler tip broken in the buck’s desperate rampage.
The rabbits and woodchuck say “Thanks Mr. Buck!
You’ve opened the garden, it’s our great luck!
We’re feasting on beet greens, parsley and chard,
To fatten for winter is no longer hard.”
We wish you happy holidays, filled with warmth and good cheer,
And may your next growing season have gardens without deer.
Folks: I couldn’t make this one up; that is exactly what happened. I believe the buck was grazing on fallen apples from my neighbor’s tree when, in the dark, his antlers tangled in my fence netting. They were velvety, still soft and growing, so when he broke a tip trying to escape, there was blood all over. At 2:00AM I was outside, stringing up twine and drenching it with deer repellent, hoping to keep the rest of his herd from testing my jury-rigged fence.
Acknowledgments: Thanks to Clement Clarke Moore and his “The Night Before Christmas” for the shape of this poem and for my lines 9-11. His words fit the situation so well that I couldn’t resist using them.
Ed says: It’s Christmas: we can take the day off from tech, right?
Doesn’t look like much, does it? It’s an ordinary blue LED that I used for the upper colon dot in a clock. Worked fine for a few dozen power-on hours, then it turned off a bit after 6:00 pm one day. Back on an hour later, more or less, then off again by the next morning, back on again, off again.
Might be a software error, as each colon LED is a separate TLC5916 display driver output. Might be a soldering problem, as my board doesn’t have plated-through holes. Might be (shudder) a burned-out transistor inside the TLC5916.
When it’s off, VCC appears on both sides, within a few tens of millivolts.
Resoldered the joints, after which it worked for a while. When it’s on, voltage measurements look normal: about 3.5 V drop across the diode and 1.5 V across the driver transistor.
No obvious code problems, but, then, code problems are never obvious.
Finally the thing stopped working for a few hours. I unsoldered it and there’s no continuity: it failed open. Peering deeply inside with a microscope shows nothing unusual: the flying gold wires look OK, the bonds look flat, and the chip has no burn marks.
Just a bad LED, I suppose. It’s surplus, of course, but that doesn’t mean much these days; there’s a lot of surplus going around.
Soldered in a replacement from the same batch and it’s all good.
So far, anyway.
This is truly embarassing: I managed to leave a steel rule (not a ruler in the shop) atop a sploosh of ferric chloride for far too long. I eventually noticed the corrosion creeping around the edges.
The bottom was hideous.
So I sprayed it down with TopSaver, applied fine sandpaper, applied a Scotchbrite pad, and it came out surprisingly well.
The ferric chloride, of course, came from a circuit board etching project. How you’re supposed to prevent that is to cover everything for about six feet around the spot marked X, but I don’t do that nearly as often as I should.
Mostly I lay a sheet of packing paper atop the workbench and whisk it into the trash when I’m done, but this time I’d left it in place because my resistance soldering gizmo wound up anchoring the far end. Soooo, a drop or two soaked into the paper and of course the ruler wound up exactly atop that spot.
The stuff is murder on stainless steel sinks, too…
I dropped in to mooch some female header strips from my buddy Eks (which is not nearly as obscene as it sounds) and got the story behind this innocent-seeming 2.2 megohm carbon-composition resistor.
It seems he was debugging a defunct tube-based audio amplifier. He’d probed everything and discovered that the grid bias on one of the tubes was totally wrong, which caused protracted headscratching over the associated circuitry.
Now, in semiconductor work, a 2.2 meg resistor is an open circuit compared to the other circuit impedances. In fact, you can use pretty nearly any resistor with green or blue in the third band as a standoff in Manhattan-style construction in place of those small insulated pads.
Megohm-value resistors are actually useful in tube circuitry; you’ll see plenty of green and blue bands sprinkled around those sockets. Although we didn’t get into details, I suspect this one was part of a grid-leak bias circuit that holds the grid voltage just a bit below the cathode; the bias comes from the few electrons that whack into the grid wires rather than passing through, so the total DC current is in the microamp range.
After more headscratching, Eks yanked this resistor, measured it, and found it was a completely open circuit. A 2.2 meg resistor isn’t all that much different from an open circuit (it’s hard to tell the difference with an in-circuit measurement) when used in a transistor circuit, but the difference separates correct function from failure for a tube amp.
Eks swapped in a new resisistor and the amp worked fine. Case closed!
The digital multimeter in my desk drawer tops out at 2000 kΩ, which shows you just how much demand there is for high-value resistors these days…
The Smell of Molten Projects in the Morning 