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.

Category: Oddities

Who’d’a thunk it?

Stainless Steel Rule vs Ferric Chloride: Oops

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.

Top corrosion

The bottom was hideous.

Bottom corrosion

So I sprayed it down with TopSaver, applied fine sandpaper, applied a Scotchbrite pad, and it came out surprisingly well.

After treatment

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…

2009-12-16
Debugging Tube Circuitry: Open Resistor

Open 2.2 meg resistor

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…

2009-12-14
Snail

Snail

Met this gadget outside a mall while my ladies were shopping for fabric. It’s certainly a distant relative of the snail I met near Adriance Library in Poughkeepsie some years ago with the same, then-new, camera.

It’s about a foot off the pavement on a brick wall. I fear it’s stuck, because the daytime temperatures are in the 50s and that’s pretty chilly for a cold-blooded critter.

But, on the whole, they’ve been around a lot longer than we have, so I left well enough alone.

2009-11-30
Alcohol Mist Flamethrower
Alcohol hand sanitizer pump spray

Our daughter snagged some tchotchkes from a high-school career fair, including one that she instantly recognized as a flamethrower: Antibacterial Hand Sanitizer Spray, 62% Ethyl Alcohol plus some other junk, in a handy pump-spray container. Heck, it even says

Warnings Flammable. Keep away from open flame. Keep out of reach of children.

I was so proud of her…

Flare3.gif

After homework, she stuck a candle atop the garbage can by the garage and fired off a few shots while I ran the camera. Here’s the best one, converted to a low-speed animated GIF.

We’re pretty sure that’s Sweet Babby Jeebus™ in the next-to-last frame of the flare. Maybe Madonna. Could go either way.

Much as with the “movies” I made for trebuchets and tree frogs, I used ffmpeg to shred the camera’s mpg movie into separate jpg images, some bash to select the frames, then convert to stitch them back together into a gif.

The general outline:
```
mkdir Frames
ffmpeg -i mov04990.mpg -f image2 Frames/frame-%03d.jpg
cd Frames
mkdir flare3
for f in `seq 760 780` ; do cp frame-${f}.jpg flare3 ; done
cd flare3
convert -delay 50 frame-* Flare3.gif
```
If my bash-fu was stronger, I could feed the proper file names directly into convert without the copy step.

Now, kids, don’t try this at home. At least not without responsible adult supervision…
2009-11-25
Buttonless Panic Button

Buttonless Panic Button

I can understand why it no longer has a button, but in which parallel universe does it make sense to put a clearly labeled Panic Button inside a high-school cafeteria, right next to the door?

Come on, now, really?

I managed to squelch the temptation to poke the remains of the switch stem with a pencil…

2009-11-18
Color Guard Night Practice: Rifles

Took these pix while chaperoning the Arlington High School Marching Band trip to The Dome at Syracuse University. They’re warming up, if that’s the proper word for standing around in skintight uniforms on a 45-degree evening at Skytop, in preparation for their show.

Many Strobed Rifle Tosses

The ISO 1000 setting on a Sony DSC-H5 produces absolutely terrible color noise, but sometimes it just doesn’t matter. These were taken under low-pressure sodium-vapor parking lot lights, with some mercury-vapor lighting in the background, so they’re basically monochromatic anyway.

Single Strobed Rifle Toss

The shutter is 1/8 second and the lights flicker at 120 Hz, so the rifles reflect 120/8 = 15 blinks as they spin. The similar included angles show that all the rifles spin at nearly the same rate: the Color Guard does very nicely synchronized tosses. They’re good!

Now, for one of my top-ten favorite pictures…

I moved around to put the mercury-vapor light behind her, which prevented flareout & added a crisp edge. The camera managed to get nearly the right exposure, even under considerable duress. This is a crop from a larger image.

She’s absolutely stationary with only her hands moving, exactly the way it’s supposed to be done.

Despite the slow shutter speeds, they’re both hand-held pictures. You simply don’t get to see my botches…

Oh, and by the way. The “rifles” are wooden dummies, carved out in a general rifle-stock shape, but without any metal parts or even a barrel. Frankly, I think the Color Guard should be trained up in marksmanship and carry actual rifles. Perhaps those would work well?

2009-11-10
Long Out of Warranty

Found this on the long-disused stage of the former Martha Lawrence School, now the St Francis Hospital Daycare Center, hosting the polling place where I was serving as an Election Inspector. It’s a bit hard to read, even in the larger version, but I thought a one-year warranty etched into a brass plate was interesting; it’s screwed right to the side of the dimmer panel.

Lighting Switchboard Warranty Placard

The warranty provisions require that the dimmer panel be properly maintained, regularly used, and kept clean. As you can easily see, it’s been a long while since anyone has put on a stage production.

I think the warranty ran out right around the time I was born, but I could be off by a decade or two either way.

Lighting Switchboard Dust Accumulation

2009-11-08