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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

Monthly Science: Audiograms
The audio test CD I used to measure my hearing for a Circuit Cellar project back in 2007 came to light, so I ran some tests:

Audiograms

I don’t have an absolute level calibration for any of those curves, so they can be shifted up or down by probably 10 dB without any loss of accuracy. The overall shape matters here, not the absolute level.

The brown curve shows my hearing as of nine years ago. I built and (of course) wrote about a rather chunky low-pass shelving filter that matched the 20-ish dB difference between my midrange and treble responses, then boosted the flattened result enough for me to hear what I was missing:

Board Top

Surprisingly, it worked fairly well. That, however, was then and this is now.

The two red curves show my current response, under slightly different conditions: the “buds” curve uses the same earbuds as the 2007 curve and the “phones” curve uses over-the-ear headphones. Perhaps:
- The previous (lack of) bass sensitivity came from the circuitry of the day
- My bass has mysteriously improved
- More likely, my midrange has gotten that much worse
The blue curve shows the response of a reference set of silver ears; the golden ears I used in 2007 were unavailable on short notice.

Given my limited bandwidth and the steep slope of that curve out toward the high end, simply fixing my (lack of) treble won’t suffice any longer: 50 dB is a lot of amplification. Compressing the bandwidth between, say, 200 Hz and 4 kHz to fit into 200 Hz to 2 kHz, then equalizing the result, might give me enough treble to get by, but it’d require re-learning how to hear.

That’s different from the straightforward frequency translation you get from a mixer. I don’t have enough audible bandwidth around 1 kHz to hear a 4 kHz slice of audio spectrum.

Back in 2007-ish, a real audiologist determined that I wasn’t “aid-able”. Maybe that’s changed.

The economics seem daunting. Michael Chorost gave a talk at Vassar lamenting the cost and terrible UX of his cochlear implants that reinforced my prejudices in that area. The discussion following my post on my Bose QC20 earphones includes useful links and rants.

The GNURadio project has enough signal-processing mojo for a nontrivial hearing aid, modulo having enough CPU power at audio frequencies. Battery power density remains the limiting factor, but I’m not nearly as fussy about appearances as most folks and some full-frontal cyborg wearables might be in order.
2016-05-01
Macrophotography Exposure Calculator

Back in high school, I designed and built a slide rule exposure calculator to improve my macro photographs:

Macrophotography Exposure Calculator – front

The base consists of three layers of thin cardboard glued together with Elmer’s Glue. The three slides have three layers of thinner white cardboard glued together, with offsets forming tongue-and-groove interlocks, topped with yellow paper for that true slide rule look:

Macrophotography Exposure Calculator – slide detail

Judging from the seams, I covered the hand-drawn scales with “invisible” matte-surface Scotch Tape. Worked well, if you ask me, and still looks pretty good:

Macrophotography Exposure Calculator – front – detail

The reverse side carries instructions under a layer of packing tape (which hasn’t survived the test of time nearly as well), for anyone needing help:

Macrophotography Exposure Calculator – rear

A closer look at the instructions:

Macrophotography Exposure Calculator – instructions

The slides still move, albeit stiffly, and it might be usable.

I vaguely recall extension tubes on an early SLR, but memory fades after that. Getting the exposure settings close to the right value evidently posed something of a challenge and, given the cost of 35 mm film + development, it made sense to be careful.

Fortunately, even today’s low-end cameras make macro photography, at least for my simple needs, easy enough, with the camera handling the exposure calculations all by itself:

SX230HS – macro lens – 15 x 20 mA ring light

I’m definitely not on the level of a professional insect photographer!

Randy’s observation to Amy in Neal Stephenson’s Cryptonomicon comes to mind:

“… One of the most frightening things about your true nerd, for many people, is not that he’s socially inept — everybody’s been there — but rather his complete lack of embarrassment about it.”

“Which is kind of pathetic.”

“It was pathetic when they were in high school,” Randy says. “Now it’s something else. Something very different from pathetic.”

“What, then?”

“I don’t know. There is no word for it. You’ll see.”

2016-04-27
Demolition Card GTA 5-10-9

So I found two copies of the US Army’s Demolition Card GTA 5-10-9 tucked under a row of completely unrelated books in the Basement Laboratory (clicky for more dots):

Demolition Card GTA 5-10-9 – 1

Demolition Card GTA 5-10-9 – 2

Demolition Card GTA 5-10-9 – 3

Demolition Card GTA 5-10-9 – 4

All four images wrapped up in a convenient PDF for your printing amusement:
Demolition Card GTA 5-10-9

One can only hope it’s slightly more useful than the Calculator Set, Nuclear, M28 — FSN 6665-897-8697 on another shelf. It dates back to the era when you could get ammonium nitrate that went blam when prompted; rumor has it that retail fertilizer now comes with built-in detonation inhibitors.

Essentially all adult human males have a story including the phrase “but for an (inch | second), I wouldn’t be here” … it’s a survivor bias thing.

2016-04-18
Filament Drive Gear Calculations
Some equations relevant to indentations produced by a filament drive gear:

Filament Drive Gear Indentations

For reference, the smaller indentations are 0.25 mm deep and 1.3 mm across the bottom.

Variables:
- d = filament (a.k.a. circle) diameter
- r = filament radius
- m = chord depth (inward from circle)
- c = chord length
- Θ = angle across chord from circle center, degrees
- A = chord area (a.k.a. indentation face area)
The length of the chord at the bottom of the indentation, perpendicular to the filament axis:

c = 2 sqrt(2mr - m²)

The chord angle:

Θ = 2 arcsin(c/2r)

The chord area, which would be the indentation face if it were perpendicular, which it isn’t:

A = (r² / 2) x ((πΘ / 180) - sin(Θ))

If you measured Θ in radians, the π/180 factor would Go Away.

Some doodles showing that reducing the indentation from 0.25 to 0.15 reduces the chord area by a factor of two:

Filament Drive Gear – indentation doodles

The implication being that you must maintain fairly constant force on the drive bearing against the filament to prevent stripping the indentations.
2016-04-07
M2 Platform Alignment Check

Five single-thread thinwall boxes scattered across the platform had an average height of 2.99 mm, with a range of +0.04 mm, -0.06 mm:

Thinwall open box – 1 thread walls

The wall widths work out to 0.39 mm, with a range of +0.2 mm, -0.01 mm.

Close enough, given that I can’t recall the last time I tweaked the platform height. I update the filament diameter setting in Slic3r every now & again as the printer gradually works through the spool, but, with one exception, this cyan PETG has been quite consistent and my tweaks didn’t really amount to much.

Frankly, given that any of the measurements may be off by ±0.02, the best I can hope for is an overall warm fuzzy feeling. When the printed results stop looking good, these results will (probably) provide some indication of whatever just changed.

The raw measurement data, such as it is:

Thinwall box measurements – 2016-04-01

2016-04-06
Sony HDR-AS30V Camera: Power Requirement

A recent ride got rained out after 27 minutes:

Rain Riding – 2016-03-25

We didn’t get much more than damp and planned the ride with a bail-out route home, so it was all good.

The camera ran from STK Battery A, which had gone flat 37 minutes into a recent ride, so I popped it in the battery tester and drained the rest of its charge:

Sony NP-BX1 – STK A 27 min vs full – 2016-03-25

The dotted section says it had 0.85 W·h remaining after 27 minutes. Hand-positioning a copy of that curve against the full charge and discharge curve says the camera required 2.8 W·h. Eyeballometrically averaging the voltage over the leading part of the curve as 3.8 V says the battery delivered 0.74 A·h = 2.8 W·h / 3.8 V, then dividing that by 27/60 says the camera draws 1.6 A. That’s less than the 2 A guesstimate from previous data, but I don’t trust any of this for more than about one significant figure.

Running the camera for 27 minutes requires 2.8 W·h, meaning 37 minutes should require 3.8 W·h. The curve says that’s the capacity at the 2.8 V test cutoff, suggesting the camera also has a 2.8 V cutoff.

Looking at the discharge curves from yesterday’s post:

Sony NP-BX1 – STK ABCD – 2015-11-03 vs 2016-03-24

If all that hangs together, the C and D batteries should run the camera for just slightly longer than the A battery, but that doesn’t seem to be the actual result: they’re much better than that.

More rides are indicated …

2016-04-02
Monthly Science: Five Months of Lithium Cell Wear

I’ve marched the four STK NP-BX1 lithium batteries through the Sony HDR-AS30V camera in constant rotation since last November. The A battery drained 35 minutes into an ordinary ride on a pleasant day, so charging and measuring the entire set seemed in order:

Sony NP-BX1 – STK ABCD – 2015-11-03 vs 2016-03-24

The dotted curves come from early November 2015, when the batteries were fresh & new, and the solid curves represent their current performance.

It’s been a mild winter, so we’ve done perhaps 75 rides during the last 150-ish days. That means each battery has experienced under 20 discharge cycles, which ought not make much difference.

The B battery started out weak and hasn’t gotten any better; I routinely change that one halfway into our longer rides.

The A battery started marginally weaker than C and D, but has definitely lost its edge: the voltage depression at the knee of the curve might account for the early shutdown.

Figuring that the camera dissipates 2.2 W, a battery that fails after 35 minutes has a capacity of 1.3 W·h. That suggests a cutoff voltage around 3.8 V, which makes absolutely no sense whatsoever, because the C and D batteries deliver at least 75 minutes = 2.8 W·h along similar voltage curves.

The B battery goes in the recycle heap and we’ll see how the A battery behaves on another ride…

2016-04-01