Archive for category Science

Monthly Science: Weight

We’d been eating a “healthy” high-carb / low-fat diet, which produced the more-or-less expected 1 lb/yr weight gain over the course of three decades. Given that we eat about 106 Cal/yr, being off by a mere 0.3% seemed fixable, but we were always hungry while trying to cut out calories.

In April 2016, we decided our tummies had come between us, so we switched to a mostly ketogenic diet (clicky for more dots):

Weight Chart 2016 - Ed
Weight Chart 2016 – Ed

Having a Master Gardener in the family complicates dietary choices along the ketogenic axis, but Mary raised more green-and-leafy veggies, less squash-and-corn, and we keto-ized our meals reasonably well. Moderation in all things works fine for us, so losing 25 pounds at about 1 lb/week wasn’t particularly stressful.

Continuing through 2017, you can see how regular bike riding season affects winter bloat:

Weight Chart 2017 - Ed
Weight Chart 2017 – Ed

Our cycling vacation in July 2018 produced a blip, but the rest of the riding season worked as expected:

Weight Chart 2018 - Ed
Weight Chart 2018 – Ed

It’s straightforward to crash-diet two dozen pounds, but maintaining a more-or-less stable weight for the next two years suggests we’ve gotten the annual calorie count about right. FWIW, my bloodwork numbers sit in the Just Fine range, apart from the somewhat elevated cholesterol level typical of a keto-ized diet.

Starting in late 2018, however, a stressful situation of a non-bloggable nature (at least for a blog such as this) produced an unusually high number of road trips, motel stays, and generally poor dietary choices:

Weight Chart 2019-03 - Ed
Weight Chart 2019-03 – Ed

The situation now being over, our lives / exercise / diet will return to what passes for normal around here and my goal is to lose another 10% of my current body weight, ending at 150 pounds, by the end of the year. In round numbers, that requires losing half a pound = 1700 Cal/week, 250 Cal/day. Not power-noshing an ounce or two of nuts a day should do the trick.

If it makes you feel more science-y, you can use the NIH Body Weight Planner, but it produces about the same answer: knock off 300 Cal to lose weight, 250 Cal to maintain it, at essentially the same exercise level as before.

We’ve been recording our weights as dots on graph paper every Saturday evening for the last four decades, so I know for a fact I averaged 148 pounds when I wore a younger man’s clothes. I’ll re-post the 2019 chart, adding four dots every month, during the rest of the year.

This way, you can help keep me on track … [grin]



Another WS2812 Failure: Broken Glass

The WS2812 under the 5U4GB full-wave rectifier tube went into pinball panic mode:

Failed WS2812 - 5U4GB Rectifier
Failed WS2812 – 5U4GB Rectifier

It’s been running more-or-less continuously since late 2016, so call it

Because I’d be crazy to replace it with another likely-to-fail WS2812, I had to remove both of them before installing SK6812 RGBW LEDs and updating the Arduino Nano.

Unfortunately, I did a really good job of bonding the side light to the tube with epoxy:

Failed WS2812 - 5U4GB broken glass
Failed WS2812 – 5U4GB broken glass

The last tube manufacturing step involved flashing the getter onto the tube envelope, so as to remove the last vestige of air. Admitting air oxidizes the getter:

Failed WS2812 - 5U4GB getter oxidation
Failed WS2812 – 5U4GB getter oxidation

It was such a pretty tube, too …

5U4GB Full-wave vacuum rectifier - cyan red phase
5U4GB Full-wave vacuum rectifier – cyan red phase



RD JDS6600 Signal Generator: Warmup Time

An RD JDS6600 Signal Generator recently arrived from around the curve of the horizon, leading me to measure its warmup time:

RDS6600 Signal Generator - Warmup plot
RDS6600 Signal Generator – Warmup plot

Looks like it’s good to go after maybe 90 minutes and, after much longer, it settles to 10 MHz +36 Hz, for a correction factor of 0.9999964 on those days when you’re being really fussy.

The need for frequencies accurate to better than 4 ppm doesn’t happen very often around here, but it’s best to be prepared. It’s amazing what you can get for under $100 these days …

I measured the frequency by zero-beating against the Z3801 GPS Frequency Standard (purple trace in the middle):

RDS6600 Signal Generator vs. Z3801 GPS Frequency Standard
RDS6600 Signal Generator vs. Z3801 GPS Frequency Standard

Basically, trigger the scope on either trace, crank the JDS6600 frequency in 1 Hz, then 0.1 Hz steps, until the traces stop crawling past each other, and you’re done.

It’s worth noting you (well, I) must crank eleven 0.01 Hz steps to change the output frequency by about 0.1 Hz around 10 MHz, suggesting the actual frequency steps are on the order of 0.1 Hz, no matter what the display resolution may lead you to think.

The RDS6600 main PCB (Rev 15) sports a 24 MHz oscillator close to the Lattice FPGA:

RDS6600 Signal Generator - clock oscillator
RDS6600 Signal Generator – clock oscillator

The AD9850 step size worked out to 0.0291 Hz for the LF crystal tester. A 24 MHz clock would produce a 5.7 mHz step size, but that’s obviously no what’s going on. More study is indicated.

The bottom trace is the scope’s internal function generator, also set to 10 MHz. Zero-beating the JDS6600 against the scope’s output produces a similar result:

IMG_20190312_130925 - RDS6600 vs SDS2304X frequencies
IMG_20190312_130925 – RDS6600 vs SDS2304X frequencies

The scope’s function generator actually runs at (9.999964 MHz) × (0.9999964) = 9.999928 MHz, a whopping 72 ppm low. The on-screen frequency measurements don’t have enough resolution to show the offset, nor to zero-beat it with the Z3801 input, so it’s as good as it needs to be.

The Z3801’s double-oven oscillator takes a few days to settle from a cold start, so this wasn’t an impulsive measurement. Having the power drop midway through the process didn’t help, either, but it’s March in the Northeast and one gets occasional blizzards with no additional charge.


Monthly Science: Baking Powder Desiccant

Being that type of guy, I tucked a bag of silica gel desiccant and a humidity indicator card into a #10 can of baking powder, then recorded the bag weight whenever I refilled the kitchen container:

Baking Powder Can with Data
Baking Powder Can with Data

For reasons not relevant here, we pretty much stopped using baking powder a couple of years ago, so there’s a protracted silence between the last two data points:

That last point emptied the can and, after a few days in the 60% RH basement, the bag weighed 243 g. The slope of the line suggests it’s been near 240 g for a while, although the humidity card showed the air was reasonably dry in there.

At our current rate, we’ll open the next can in a year or so …

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Sapcicle Season

Once again, maple sap rises from the ground and falls from damaged branches:

And, sometimes, a tiny sweet treat during our walks …

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“5 W” G4 COB LED Specsmanship

A bag of G4 COB LEDs arrived from halfway around the planet:

G4 COB LEDs - 15 and 18 LED modules
G4 COB LEDs – 15 and 18 LED modules

Those are “5 W” and “4 W” cool white modules, respectively, with another set of 4 W warm white looking pretty much the same. There’s no provision for heatsinking, which makes the wattage seem suspect; halogen G4 bulbs run around 20 W, for whatever that’s worth.

The silicone overlay becomes nearly transparent when seen through an ordinary desktop document scanner:

Circular 12V COB 18 LED panel
Circular 12V COB 18 LED panel

Highlighting the PCB copper pours shows 18 LEDs arranged in three series groups of six LEDs in parallel:

Circular 12V COB 18 LED panel - copper layout
Circular 12V COB 18 LED panel – copper layout

The “smart IC” touted in the writeup turns out to be a bridge rectifier for AC or DC power:

G4 COB LED - 18 LED - components
G4 COB LED – 18 LED – components

The SMD resistors on all 15 modules measure 27.6 Ω, more or less, and seem randomly oriented face-up or face-down. I assume that one is face-down; maybe it’s just unlabeled on both sides.

Back of the envelope: there’s no way it will dissipate 5 W. The bridge drops 1.4 V = 2×0.7, the LEDs drop maybe 9 V, leaving the resistor with 1.6 V to pass all of 60 mA, so call it 700 mW.

Some measurements:

G4 COB LED measurements
G4 COB LED measurements

With 12 VDC applied to the pins, the bridge drops 1.6 V, the LEDs 8.2 V, and the resistor 2.2 V, with 80 mA through the whole affair dissipating just under 1 W.


Cranking the supply until the current hits 200 mA puts 15.7 V across the pins for a total dissipation of 3.1 W, burning 1.7 W in the LEDs and 1.1 W in the resistor.

Cranking the supply to 21.3 V drives 410 mA, dissipates just under 9 W total, produces a curl of rosin smoke from the PCB, and maybe delaminates the silicone around some of the LEDs.

OK, now I have a crash test dummy.

Given complete control over the application, I’ll strip everything off the PCB and bond it to a heatsink of some sort. With 6 LEDs in parallel, 120 mA (6 × 20 mA) total current might be reasonable and 200 mA (6 × 30 mA) probably won’t kill the things outright. Plus, I have spares.

An external 18 Ω resistor should suffice. Perhaps a pair of 6 Ω SMD resistors on the PCB, with fine-tuning through an external resistor. Call it 250 mW apiece: don’t use little bitty SMD resistors.



Epoxy Joint: Test to Destruction

Some years ago, I put the LED power supply for one of the Kenmore 158 machines atop a plastic project box with an adjustable boost supply inside:

Needle LEDs power supply - exterior
Needle LEDs power supply – exterior

The LEDs connected through a coaxial power jack on the far side of the box, held in place with a generous blob of epoxy:

Needle LEDs power supply - interior
Needle LEDs power supply – interior

A closer look:

Kenmore 158 COB LED - power supply jack
Kenmore 158 COB LED – power supply jack

I’m adding a light bar, similar to the one now going onto the Juki TL-2010Q, which needs a direct connection to the 12 VDC supply. Rather than add another coaxial jack, I ripped out the existing jack and installed a DE-9 connector (serial ports being a fading memory by now), giving me an opportunity to test the epoxy joint:

Kenmore 158 COB LED - power supply jack - epoxy bond
Kenmore 158 COB LED – power supply jack – epoxy bond

Which required grabbing the connector with a pair of pliers and twisting / bending / abusing until it popped free. I don’t know how much grip the scored lines added to the joint, but the connector definitely didn’t give up without a fight; it wasn’t going to fall off on its own.

To be fair, the epoxy had a better grip on the coaxial jack than on the plastic plate, perhaps because the bottom of the jack had all manner of nooks and pins intended for PCB mounting. Ya use what ya got, sez I.

The new connector looks exactly like it should and, because it’s held in place by a pair of screws, should last forever, too:

Kenmore 158 COB LED - power supply
Kenmore 158 COB LED – power supply

More about all that, later …