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

  • Amazon EK3211 Kitchen Scale

    An unfortunate incident put enough water inside our kitchen scale to, ummm, render it inoperative. After a day of drying proved unavailing, I had nothing to lose by disassembling it.

    The central label on the back conceals two screws holding the platform to the aluminum beam:

    Amazon EK3211 Scale - platform underside
    Amazon EK3211 Scale – platform underside

    The metal plate twist-locks into the plastic platform. The hot-melt glue holding it in position suggests my construction techniques aren’t all that far off the mark.

    The beam cantilevers from a metal structure spreading the load across the plastic base:

    Amazon EK3211 Scale - interior overview
    Amazon EK3211 Scale – interior overview

    These are “after” pictures. Suffice it to say the interior was wet, including water droplets between the LCD panel and its plastic cover. Everything came apart easily, including the LCD with its attached zebra connector, and dried out thoroughly over the next day; I parked the panel atop my monitor for some gentle heating.

    After reassembly, it still didn’t work, which turned out to be due to both wires from the battery snapping off at their PCB solder joints. I didn’t think I’d handled it that roughly, but ya never know.

    With the wires soldered in place, the scale lit right up again:

    Amazon EK3211 Scale - display PCB switches
    Amazon EK3211 Scale – display PCB switches

    The display flashed CAL at one point during the proceedings, although the rather thin manual had nothing to say about recalibration and the PCB didn’t have any obvious test points / jumpers / labels to that effect.

    Two days of relentless spelunking produced my test weights:

    Amazon EK3211 Scale - test weights
    Amazon EK3211 Scale – test weights

    Given the provenance of those weights, a 0.2% error might not be the scale’s fault, even if it cost barely 10 bucks.

  • Bosch Laser Rangefinder Corrosion

    A few days after using my Bosch GLR225 Laser Rangefinder, it wouldn’t light up.

    This came as no surprise:

     

    Bosch GLR225 battery contact - corrosion
    Bosch GLR225 battery contact – corrosion

    Some vinegar, a bit of scrubbing, some rinsing, and it’s all good:

    Bosch GLR225 battery contact - cleaned
    Bosch GLR225 battery contact – cleaned

    The OEM batteries seem to have survived nigh onto four years, so I guess I can’t complain.

    Mutter & similar remarks.

  • Raspberry Pi: White OLED Display

    The white OLED displays measure 1.3 inches diagonally:

    RPi OLED Display - white on black
    RPi OLED Display – white on black

    They’re plug-compatible with their 0.96 inch blue and yellow-blue siblings.

    All of them are absurdly cute and surprisingly readable at close range, at least if you’re as nearsighted as I am.

    Some preliminary fiddling suggests a Primary Red filter will make the white displays more dark-room friendly than the yellow-blue ones. Setting the “contrast” to 1 (rather than the default 255) doesn’t (seem to) make much difference, surely attributable to human vision’s logarithmic brightness sensitivity.

    I must conjure some sort of case atop a bendy wire mount for E-Z visibility.

  • Kensington Expert Mouse Cable Replacement

    My posts about troubles with the Kensington Expert Mouse scroll ring remain disturbingly popular. My most recent warranty replacement has been running fine for several years, so I suspect they had a bad lot of IR detectors go their production line and into the field.

    In any event, a recent email asked about where to get the little connector inside the mouse to replace a worn-out USB cable:

    Kensington Expert Mouse - internal USB connector
    Kensington Expert Mouse – internal USB connector

    Maybe you’d be lucky enough to find an identical connector inside an old mouse in a junk box, but that’s not the way to bet.

    Given that you need not only the proper plastic shell, but also the pins and the crimper for a proper repair, I suggested just chopping the wires an inch from the connector and splicing the new cable onto the wires.

    Not an elegant solution, but it works for me …

  • 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.

     

  • Crystal Parameter Measurement Musings

    In order to probe a crystal’s response with decent resolution, I need a gadget to step a decent-quality sine wave by 0.01 Hz across the 10-to-100 kHz range and a logarithmic front end with a decent dynamic range. That’s prompted by looking at crystal responses through the SA’s 30 Hz resolution bandwidth:

    Quartz Resonator 32.765 kHz - 34.6 pF
    Quartz Resonator 32.765 kHz – 34.6 pF

    Mashing a cheap AD9850/AD9851 DDS board against an Arduino Pro Mini, adding a knob, and topping with a small display might be useful. A Raspberry Pi could dump the response data directly into a file via WiFi, which may be more complication that seems warranted.

    The DDS boards come with absurdly high-speed clock generators of dubious stability; a slower clock might be better. A local 10 MHz oscillator, calibrated against the 10 MHz output of the HP 3801 GPS stabilized receiver would be useful. If the local oscillator is stable enough, a calibration adjustment might suffice: dial for 10 MHz out, then zero-beat with the GPS reference, so that the indicated frequency would be dead on to a fraction of 1 Hz.

    The HP 8591 spectrum analyzer has a better-quality RF front end than I can possibly build (or imagine!), but, at these low frequencies, a simple RF peak detector and log amp based on the ADL5303 or ADL5306 should get close enough. One can get AD8302 / AD8310 chips on boards from the usual low-budget suppliers; a fully connectorized AD8310 board may be a good starting point, as it’s not much more than the single-connector version.

    With frequencies from 10 kHz to 100 kHz coming from a local oscillator, one might argue for a synchronous detector, formerly known as a lock-in amplifier. A Tayloe Detector might be a quick-and-dirty way to sweep a tracking-filter-and-detector over the frequency range. Because it’s a tracking generator, the filter bandwidth need not be very tight.

    At some point, of course, you just digitize the incoming signal and apply DSP, but the whole point of this is to poke around in the analog domain. This must not turn into an elaborate software project, too.

     

  • 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!