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: Science

If you measure something often enough, it becomes science

Kenmore 158: First Needle LED Failure

The first white LED fixture built to illuminate one of Mary’s Kenmore 158 sewing machines has been in regular use for the last four years:

Kenmore 158 Sewing Machine – mixed LED lighting

We never found a good time to rip-and-replace the “prototype” with brighter SMD LEDs and one of the LEDs finally gave up.

They’re 10 mm white LEDs with five chips wired in parallel, which is obvious when you look into the remaining LED running at 1 mA:

10 mm white LED – chips

The center chip is just dimmer than the others, which means their QC doesn’t tightly control the forward voltage spec.

The wire bonds on the anode terminal of the failed LED look a bit sketchy:

10 mm white LED – wire bonds

Fortunately, I hadn’t removed the 120 VAC wiring for the original bulb and I have two OEM bulbs from other machines, so I just removed my LED gimcrackery, installed a good old incandescent bulb, and she’s back to sewing with a pleasantly warm machine.

The fixture holding the LEDs broke apart as I extracted it, but it’ll never be used again:

10 mm white LED – fixture

The LEDs are rated at 3.5 V and 200 mA (!), but were reasonably bright in series from a 6 V unregulated supply. Perhaps a power glitch killed the poor thing? We’ll never know.

LEDs are reputed to have lifetimes in the multiple tens of thousands of hours, but I’ve seen plenty of failed automotive LEDs and fancy new LED streetlights out there, not to mention many dead and dying traffic signals. Seeing as how they’re in (presumably) well-engineered fixtures with good power supplies and are at most only a few years old, there shouldn’t be any failures yet.

2018-05-23
Corroded Concrete

Nothing lasts forever, not even concrete:

Downspout Splash Block – Corroded Concrete

The downspouts are obviously more recent than the splash blocks, but the whole shopping center wasn’t more than a few decades old. Rain isn’t nearly as acid as it used to be, but it still eats away at concrete.

After about two decades, though, even high-quality concrete goes bad:

Rt 376 bridge deterioration – marker 1102 – 2018-05-07

That’s the upper surface of the Rt 376 bridge at Red Oaks Mill, with a fragment of the corroded lower edge still dangling over the Wappinger Creek:

Red Oaks Mill bridge – dangling concrete

Mostly, we manage to bike around the decayed infrastructure.

2018-05-19
Squidwrench Electronics Workshop: Session 2

Some ex post facto notes from the second SquidWrench Electronics Workshop. This turned out much more intense than the first session, with plenty of hands-on measurement and extemporized explanations.

Measure voltage across and current through 4.7 kΩ 5 W resistor from 0.5 V to 30 V. Note importance of writing down what you intend to measure, voltage values, units. Plot data, find slope, calculate 1/slope.

Introduce parallel resistors: 1/R = 1/R1 + 1/R2. Derive by adding branch currents, compute overall resistance, factor & reciprocal.

Review metric prefixes and units!

Introduce power equation (P = E I) and variations (P = I² R, P = E²/R)

Measure voltage across and current through incandescent bulb (6 V flashlight) at 0.1 through 6 V, note difference between voltage at power supply and voltage across bulb. Plot data, find slopes at 1 V and 5 V, calculate 1/slopes.

Measure voltage across ammeter with bulb at 6 V, compute meter internal resistance, measure meter resistance. Note on ammeter resistance trimming.

Measure voltage across and current through hulking power diode from 50 mV – 850 mV. Note large difference between power supply voltage and diode voltage above 750-ish mV. Note power supply current limit at 3 A. Plot, find slopes at 100 mV and 800 mV, calculate 1/slopes. Compare diode resistance with ammeter resistance.

Review prefixes and units!

The final whiteboard:

Whiteboard – Session 2

Hand-measured data & crude plots FTW!

2018-05-17
Squidwrench Electronics Workshop: Session 1
Some ex post facto notes from the first SquidWrench Electronics Workshop, in the expectation we’ll run the series from the start in a while. I should have taken pictures of my scribbles on the whiteboard.

Define:
- Voltage – symbol E (Electromotive Force or some French phrase), unit V = volt
- Current – symbol I (French “intensity” or some such), unit A = ampere
- Resistance – symbol R (“resistance”), unit Ω (capital Greek Omega) = ohm
Introduce Ohm’s Law & permutations, postpone calculations.

Measure the actual voltage of assorted cells & batteries. Identify chemistry, internal wiring:
- 1.2 = nickel-cadmium or nickel-metal-hydride
- 1.5 = carbon-zinc or alkaline
- 2 V = lead-acid
- 3.0 = primary lithium
- 3.6 – 3.7 = rechargeable lithium, several variations
- 4.8 = 4 x 1.2 V
- 7.2 = 6 x 1.2 V
- 7.4 = 2 x 3.6 V
- 9.6 = 8 x 1.2 V
- 10.8 = 3 x 3.6 V
- 12 = 6 x 2 V
Measure various resistors, favoring hulking finger-friendly sandstone blocks.

Introduce metric prefixes:
- Engineering notation uses only multiple-of-three exponents
- μ = micro = 10^-6
- m = milli = 10^-3
- k = kilo = 10³
- M = mega = 10⁶
Discuss resistor power dissipation vs. size vs. location, postpone power formula.

Clip-lead various resistors to various batteries, measure voltage & current.

Introduce fixed & variable power supplies, repeat resistor measurements.

Now compute permutations of Ohm’s Law using actual data!
2018-05-16
Monthly Science: As Seen On Radio

This showed up when I looked at our APRS tracks after a recent ride:

Balloon chase – KJ5HY-9

Poking around a bit showed the target:

Balloon chase – W2KGY-12

Contrary to what I thought, it didn’t come up the Hudson River from West Point:

Balloon chase – W2KGY-12 track – 2018-04-21 to 2018-04-24

Knowledge of the Universal Law of the Conservation of Perversity informs you a balloon will never land in the middle of a putting green:

Balloon chase – W2KGY-12 landing site

Apparently the launch is part of a regular class project at West Point. Good clean fun!

2018-05-01
Magnetic Field Visualization

Thinking about springs to apply downforce on plotting pen holders suggested magnets, so I extricated some neodymium bars from my collection of power toothbrush heads:

Magnets – single

A snippet of magnetic field visualization film shows a dipole pattern:

Magnets – single – field visualization

Snapping two of them together in line:

Magnets – in line

… produces a quadrupole:

Magnets – in line – field visualization

Now, if only I had some magnetic monopoles, this whole thing would be easier!

2018-04-21
Monthly Science: Hawk and Squirrel, with Turkeys

All of the local turkeys come together during snow storms, often lingering in the circle of pine trees in our back yard to get some protection from the wind. Mary spotted a Cooper’s Hawk in the midst of the turkey flock, with its wings spread around a recently captured meal:

Hawk with squirrel – wings spread

When she first saw it, the hawk had its back to us and looked like a cluster of dead pine branches; the recent back-to-back storms have cleared out quite a bit of deadwood.

When I quietly opened the back door for a better view, the hawk noticed and gave me the stinkeye from 100 feet away:

Hawk with squirrel – 2

The flock had moved out of the pine circle to surround the hawk and examine the situation, although they weren’t harassing it:

Hawk with squirrel – 3

We’ve counted 27 turkeys, more or less, on some days, well and truly outnumbering the hawk:

Hawk with squirrel – overview

Fortunately, turkeys feed mainly on insects and seeds, rather than tearing into carrion, so they’re not competing for the prize:

Hawk with squirrel – detail

Shortly after I gave up and went back inside, the hawk sank her (?) talons into the squirrel, lifted heavily into the air, circled around the pines, and flew off toward the Mighty Wappinger Creek out back.

A casual search suggests both the hawk and the squirrel weigh about 1 lb = 500 g: I’ll never complain about heavy grocery bags again!

2018-04-01