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

  • Monthly Science: CR2023 Lithium Cells vs. Wearable LEDs

    Those wearable LEDs spent the last five months sitting on the kitchen window sash, quietly discharging their CR2032 lithium cells:

    Wearable LED with CR2023 cell
    Wearable LED with CR2023 cell

    Occasional voltage measurements produced an interesting graph:

    CR2032 vs Wearable LEDs
    CR2032 vs Wearable LEDs

    CR2023 primary lithium cells start out around 3.3 V, so these were pretty much dead (from their previous lives in dataloggers) when I slipped them into their holders. The LEDs seem to be blue LEDs, with threshold voltages around 3.6 V, with colored phosphors / filters, so they started out dim and got dimmer. The green(-ish) LED obviously fell over a cliff and went dark in late January; I have no way to measure long-term microamp currents, alas.

    The reddish LED is still going, mmm, strong.

    If you need a rather dim light for a surprisingly long time, these things will do the trick.

    I should gimmick up another astable multivibrator to blink one LED.

    The original data:

    CR2032 vs Wearable LEDs - data
    CR2032 vs Wearable LEDs – data

  • Eneloop AAA Cells: First Charge

    With an AAA-to-AA adapter in hand, the Eneloop AAA cells looked like this:

    Eneloop AAA - as received - Ah scale - 2017-04-20
    Eneloop AAA – as received – Ah scale – 2017-04-20

    The glitch comes from a not-quite-seated cell, showing that a poor connection matters.

    The package touts “up to 800 mA·h, 750 mA·h min”, with asterisks and superscripts leading to “Based on IEC 61951-2(7.3.2)“, access to which requires coughing up 281 bucks. So it goes.

    A full charge made them happier:

    Eneloop AAA - first charge - Ah scale - 2017-04-22
    Eneloop AAA – first charge – Ah scale – 2017-04-22

    The as-delivered 530 mA·h capacity represents 73% of the 725 mA·h after the first charge, so I suppose they’re more-or-less within the “Maintains up to 70% charge after 10 years of storage” claim. The 16-10 date code suggests they’re hot off the factory charger, so they must ship with somewhat less than a full charge.

    Comparing the capacity in W·h makes more sense, because most devices (other than the Planet Bike blinky light these will go into, of course) use a boost converter to get a fixed voltage from the declining terminal voltage.

    They arrived bearing just over 600 mW·h:

    Eneloop AAA - as received - Wh scale - 2017-04-20
    Eneloop AAA – as received – Wh scale – 2017-04-20

    After charging, that went a bit over 850 mW·h :

    Eneloop AAA - first charge - Wh scale - 2017-04-22
    Eneloop AAA – first charge – Wh scale – 2017-04-22

    Call it 71% of full capacity on arrival. Close enough.

    The Planet Bike blinky will be somewhat dimmer with two NiMH cells delivering 2.3-ish V, compared with the initial 3-ish V from a pair of alkaline cells. I generally burn the alkalines down to 1.1 V apiece, so perhaps they’ll be Good Enough.

    Now, if I were gutsy, I’d install a rechargeable lithium AAA cell, with a dummy pass-through adapter in the other cell socket, and run the blinky at 3.7 V. At least for a few moments, anyhow …

  • Monthly Image: Turkey Mating

    Early spring brings out large turkey flocks and provides a window into their otherwise rather private lives.

    Despite all the strutting and posturing by the males, the ladies call the shots. When we see a hen go hull-down like this, we know what’s about to happen:

    Turkey mating - invitation
    Turkey mating – invitation

    Getting into the right position seems remarkably awkward and requires some cooperation:

    Turkey mating - mounting
    Turkey mating – mounting

    When her head and tail pop up, you know the thing is going right:

    Turkey mating - the moment
    Turkey mating – the moment

    And a back massage always feels so fine:

    Turkey mating - massage
    Turkey mating – massage

    Then he’s back to strutting & posturing:

    Turkey mating - aftermath
    Turkey mating – aftermath

    We hope they’ll show us their chicks …

    Taken with the DSC-H5, hand-held through two panes of 1955-era window glass: ya get what ya get.

  • Cheap WS2812 LEDs: Test Fixture Failure 2

    A second WS2812 RGB LED in the test fixture failed:

    WS2812 LED - test fixture failure 2
    WS2812 LED – test fixture failure 2

    The red pixel in the second row from the top sends pinball panic to the six downstream LEDs (left and upward). Of course, it’s not consistently bad and sometimes behaves perfectly. The dark row below it contains perfectly good LEDs: they’re in a dark-blue part of the cycle.

    The first WS2812 failed after about a week. This one lasted 7 weeks = 50-ish days.

    The encapsulation seal went bad on this one and, for whatever it’s worth, the remainder still pass the Sharpie test. Perhaps the LEDs fail only after heat (or time-at-temperature) breaks the seal. Assuming, equally of course, the seal left the factory in good order, which seems a completely unwarranted assumption.

  • Monthly Science: Sonicare Recharge Intervals

    After replacing the NiMH cells in my Sonicare toothbrush in July 2012, they delivered about 21 days = 21 brushings between charges. After a year, I laid a sheet of Geek Scratch Paper on the windowsill (*) and noted pretty nearly every recharge:

    Sonicare recharge - 2013-10 - 2017-01
    Sonicare recharge – 2013-10 – 2017-01

    Anyhow, the original cells crapped out after 2-½ years, when these still delivered 13 days. After 4-½ years, they’re lasting 12 days between charges.

    Color me surprised, because they’re 600 mA·h NiMH cells. The originals were 2000 mA·h cells, which you’d expect would last longer, but noooo.

    No reason to change them yet, which is good news.

    FWIW, I recently bought some cheap brush heads from the usual low-end eBay seller. The OEM brushes have colored bristles which fade to tell you when to change brushes, although I run ’em quite a bit longer than that. The cheap replacements have never-fading colored bristles and, I suspect, all the bristles are much too stiff. The dental hygienist says I’m doing great, so it’s all good.

    Sonicare brush heads - cheap vs OEM
    Sonicare brush heads – cheap vs OEM

    High truth: at best, you get what you pay for.

    (*) Being that type of guy has some advantages, if you’re that guy. Otherwise, it’s a nasty character flaw.

     

  • Quartz Resonator Test Fixture: 32 kHz Quartz Tuning Fork

    Soldering a 32.768 kHz quartz tuning fork resonator into the test fixture:

    Quartz crystal resonance test fixture
    Quartz crystal resonance test fixture

    The HP 8591 tracking generator doesn’t go below 100 kHz, so I used the FG085 DDS function generator as a source. I trust the 8591’s calibration more than the FG805’s, but right now I’m more interested in the differences between successive frequencies and the DDS can step in 1 Hz increments.

    The output appears on the 8591, with a big hump comes from the analyzer’s 30 Hz IF filter response sweeping across what’s essentially a single-frequency input. The hump is not the crystal’s response spectrum!

    With the jumper installed to short the 33 pF cap, the output peaks at 32.764:

    Removing the jumper to put the cap in the circuit, the response peaks at 32.765 kHz:

    The marker delta shows the difference between the two peaks, ignoring their 1 Hz difference:

    Quartz Resonator 32.764-5 no-34.6 pF delta
    Quartz Resonator 32.764-5 no-34.6 pF delta

    So I’d say the cap really does change the resonator series resonance by just about exactly 1 Hz.

    With the jumper installed to remove the cap from the circuit, setting the reference marker at the 32.764 kHz peak, and measuring the relative response at 32.765 kHz :

    Quartz Resonator 32.764-5 no cap delta
    Quartz Resonator 32.764-5 no cap delta

    So the response peak is much much narrower than 1 Hz: being off-peak by 1 Hz knocks 13-ish dB from the response.

    What’s painfully obvious: my instrumentation is totally inadequate for crystal measurements at these frequencies!

  • Quartz Resonator Test Fixture: 3.58 MHz Crystal Test

    Just to see if the resonator test fixture produced meaningful results, I plugged a 3.57954 MHz color burst crystal into the socket:

    Quartz test fixture - 3.57954 MHz crystal
    Quartz test fixture – 3.57954 MHz crystal

    This is a staged recreation based on actual events; pay no attention to the Colpitts oscillators growing in the background.

    Attaching goesinta and goesouta cables to the HP 8591 spectrum analyzer & tracking generator showed it worked just fine:

    Quartz 3.57954 MHz - no cap
    Quartz 3.57954 MHz – no cap

    The reference level is -40 dBm, not the usual 0 dBm, due to the loss in those resistive pads. Unsurprisingly, the parallel resonance valley looks pretty ragged at -120 dBm = 1 nW = 7 µV.

    Remove the jumper to put the capacitor in series:

    Quartz 3.57954 MHz - 36.4pF
    Quartz 3.57954 MHz – 36.4pF

    The marker delta resolution surely isn’t 1 Hz, but 750 Hz should get us in the right ballpark.

    Substituting a 72 Ω resistor, found by binary search rather than twiddling a pot:

    Quartz 3.57954 MHz - 72ohm
    Quartz 3.57954 MHz – 72ohm

    Which gives us all the measurements:

    • Fs = 3.57824 MHz
    • Fc = Fs + 750 Hz = 3.57899 MHz
    • Rm = 72 Ω
    • C0 = 3.83 pF
    • Cpar = 3.70 pF

    Turn the crank and the crystal motional parameters pop out:

    • Lm = 117 mH
    • Cm = 17 fF
    • Rm = 72 Ω
    • Q = 36 k

    Looks like a pretty good crystal to me!