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: Electronics Workbench

Electrical & Electronic gadgets

  • 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
    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
    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
    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
    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.

     

  • Silicone Insulated Wire

    Quite unlike the non-standard ribbon cable in the WWVB loop antenna, these 10 foot hanks of 24 AWG silicone insulated wire were exactly as described:

    24 AWG Silicone Wire
    24 AWG Silicone Wire

    The probes report a resistance of 270 mΩ (net of the 50 mΩ probe-to-probe resistance), as close as one could ask to the nominal 26 Ω/1000 ft spec for 24 AWG wire at the current Basement Laboratory temperature.

    They are exceedingly limp and flexy, due to many teensy conductors; not at all like PVC hookup wire.

    If you’re willing to buy 500 feet of each color, the cost-per-foot from a reputable supplier gets downright competitive, but I’m not in that market.

  • QRPme Pocket Pal II

    A QRPme Pocket Pal II could be a suitable project for a Squidwrench “advanced soldering” class:

    QRPme Pocket Pal II - front
    QRPme Pocket Pal II – front

    Yes, it comes with a tin case:

    QRPme Pocket Pal II - tin case
    QRPme Pocket Pal II – tin case

    You must fit your own insulating sheet under the PCB; polypropylene snipped from a retail package works fine.

    It’s intended as a “mint tin sized tester for all kinds of hamfest goodies”, but it seems like a nice source of small currents, voltages, and signals suitable for stimulating all manner of circuitry one might encounter in later sessions of a beginning electronics class.

    Before using it, of course, one must solder a handful of small through-hole parts into the PCB, a skill none of us were born with.

    For completeness, the back side, hot from the soldering iron:

    QRPme Pocket Pal II - rear
    QRPme Pocket Pal II – rear

    The kits (always buy two of anything like this) arrived minus a few parts, which I suspect was due to an avalanche of orders brought on by a favorable QST review. Fortunately, I (still) have a sufficient Heap o’ Parts to finish it off without resupply, although a hank of 9 V battery snaps will arrive in short order.

  • 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
    Whiteboard – Session 2

    Hand-measured data & crude plots FTW!

  • 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!

  • Sony NP-BX1 Battery Status

    The genuine Sony NP-BX1 that came with the AS30V camera suffers from voltage depression (green trace) and no longer survives a typical ride:

    Sony NP-BX1 - 2018-04-24
    Sony NP-BX1 – 2018-04-24

    The STK C battery (red trace) is also pretty much kaput, so the two of them go into the recycle bag.

    The very short blue trace is the Wasabi F battery after a ride, showing about 1 W·h remaining of the initial charge. After a full change, the upper blue trace shows it has a capacity in the same range as the others. Our rides are about an hour long, so the camera draws somewhat less than the 1 A test current, roughly what I’d estimated from other data.

    The cluster of traces along the top show the remaining Wasabi batteries are all pretty much alike, with the older F and G batteries no worse than the newer (and unused) H I J K batteries. I’m underwhelmed by the overall performance of the latter four, as I’d expect them to be better than their well-used predecessors.

    I’m still mulling an external 18650 cell grafted into a NP-BX1 carcass, but it’s stalled behind some other projects.

  • Relic of the Empire: Pay Phone Mount

    Spotted at the NSQG World of Quilts show in the WCSU O’Neill Center:

    Payphone mounting plate
    Payphone mounting plate

    I’m mildly surprised the (apparently recent) wall reupholstering didn’t cover it up. I’m certain many students don’t recognize it.

    The FCC says the US is down to 100 k pay phones from a peak of over two million; they don’t tally the number of bare wall mount plates, though.