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

  • Casio EX-Z850 Shutter Failure

    After nine years, the shutter on my much–repaired Casio EX-Z850 camera has failed, producing images with horizontal white lines:

    Casio EX-Z850 Shutter Failure
    Casio EX-Z850 Shutter Failure

    That can also come from a sensor failure, but it takes perfectly good movies. That’s the differential diagnosis for shutter failure, because movies don’t use the shutter.

    The shutter still functions, in that peering into the lens shows the shutter closing as it takes a picture, so I suspect it’s gotten a bit sticky and slow over the years. None of the various shutter-priority speeds have any effect, which means that the shutter isn’t responding properly.

    A quick read of the service manual shows the Field Replaceable Unit for this situation is the entire lens assembly. Back in the day, a new lens assembly came with its own calibration constants on a floppy disk that you’d install with Casio’s service program (the latest version ran with Windows 98!) using a special USB communication mode triggered by a Vulcan Nerve Pinch on the camera. At this late date, none of that stuff remains available.

    While I could take the camera apart and crack the lens capsule open, I doubt that would make it better and, in this case, ending up with a crappy camera doesn’t count for much. Extracting the lens assembly requires dismantling the entire thing, which, frankly, doesn’t seem worth the effort…

    That image is number 7915: so it’s taken a bit over two images per day for the last nine years. I can’t swear the counter has never been reset, but that seems about right.

    Sic transit gloria mundi, etc.

  • Kenmore 362.75581890 Stove: Weak Oven Igniter

    The burner in our oven failed in December 2006, probably because the charred remains of an insect produced a hotspot:

    Burned Oven Tube Overview
    Burned Oven Tube Overview

    That replacement burner came with its own igniter that failed after 8.5 years, with symptoms of slow oven ignition and the occasional smell of propane.

    In normal operation, the igniter element glows yellow-hot for a minute or so before the valve opens, gas flows over the igniter, there’s a muffled whoomf, and the oven begins heating. The igniter remains powered as long as the oven is on, emitting a baleful yellow glare through the slots in the oven’s lower cover.

    It consists of a ceramic base holding a stout resistance heater that apparently suffers from increasing resistance as it ages, reducing the current to the point where it won’t activate the gas valve.

    I didn’t know that, either, but Google sees all, knows all, and tells most.

    The gas valve label says it requires 3.3 to 3.6 A from the heater to turn on the gas:

    Kenmore range oven gas valve - data plate
    Kenmore range oven gas valve – data plate

    But the old heater was good for barely 2.6 A (there’s a bit of parallax in this view):

    Kenmore range oven gas valve - weak igniter current
    Kenmore range oven gas valve – weak igniter current

    Igniters range from $18 to upwards of $60 on Amazon, so I picked the cheapest one, waited two days, installed it, and measured 3.5 A at First Light, down to a bit over 3.0 A at running temperature. That’s on the low side of the valve’s spec, but it seems happier with an extra half amp.

    We’ll see how long this igniter lasts; maybe next time I’ll double my spend…

  • APRS Electronics Case Power Contacts

    Mary reported hearing occasional beeps during a recent ride that indicated the Wouxun KG-UV3D radio on her bike was rebooting. It turned out that the nut soldered to the lug atop the screw contacting the radio’s battery contacts had turned itself slightly loose on the stud:

    HT-GPS Case - PCB and battery contacts - end view
    HT-GPS Case – PCB and battery contacts – end view

    Snugging it up against the PCB made everything happy again.

    However, while I had the APRS box off, I added strips of copper tape to enhance the connection to the radio:

    KG-UV3D APRS interface - power contacts
    KG-UV3D APRS interface – power contacts

    Mostly, those gadgets just keep working…

  • Verifying Yet Another Sony 64 GB MicroSD Card

    The replacement for the second failed Sony SR-64UY MicroSD card arrived:

    Sony SR-64UX 64 GB MicroSDXC card
    Sony SR-64UX 64 GB MicroSDXC card

    The previous cards were made in Korea, but this one came from Taiwan with a different serial number format:

    Sony SR-64UX 64 GB MicroSDXC card - back
    Sony SR-64UX 64 GB MicroSDXC card – back

    The tiny letters on the front identify it as an SR-64UX, but I haven’t been able to find any definitive Sony source describing the various cards; their catalog page listing cards for digital still cameras may be as good as it gets. This one seems to have a higher read speed, for whatever little good that may do.

    It stored and regurgitated the usual deluge of video files with no problem, which is only to be expected. This time around, I checked the MD5 sums, rather than unleashing diff on the huge files:

    cd /media/ed/9C33-6BBD/
for f in * ; do find /mnt/video/ -name $f | xargs md5sum $f ; done
11e31c9ba3befbef6dd3630bb68064d6 MAH00539.MP4
11e31c9ba3befbef6dd3630bb68064d6 /mnt/video/2015-07-05/MAH00539.MP4
... snippage ...

    It now sits in the fancy plastic display case that the HDR-AS30V camera came in until the previous replacement card fails.

  • Relics of the Empire: Electrometer Resistors

    From Russia, probably without love, routed through Bulgaria via eBay:

    Electrometer resistors - wrapped
    Electrometer resistors – wrapped

    They’re glass electrometer resistors from late in the Cold War:

    Russian 100 G electrometer resistor
    Russian 100 G electrometer resistor

    That one presents 100 GΩ between its lead wires, which would count as open in any other circuit I’ve ever built.

    The assortment arrived much richer than advertised, although I’d be even happier with a few more 10 GΩ and a few less 100 MΩ resistors. The 1000 GΩ = 1 TΩ resistor in the upper right seems absurd on the face of it, but there it sits.

    I have no way to measure these, other than to build an electrometer amp and see what happens…

  • Ionization Chamber: Resistor Noise Calculations

    Given the ionization chamber’s tiny currents and the huge resistors required to turn them into voltages, reviewing the thermal noise I generally ignore seems in order…

    The RMS noise voltage of an ordinary resistor:

    vn = √ (4 kB T R Δf)

    The constants:

    • kB – Boltzman’s Constant = 1.38×10-23 J/K
    • T – temperature in kelvin = 300 K (close enough)

    Mashing them together:

    vn = √ (16.6x10-21 R Δf)

    vn = 129x10-12 √ (R Δf)

    For a (generous) pulse current of 20 fA, a 10 GΩ resistor produces a mere 200 μV, so wrap a gain of 100 around the op amp to get 20 mV. An LMC6081 has a GBW just over 1 MHz, giving a 10 kHz bandwidth:

    vn = 129x10-12 √ (10x109 10x103) = 1.3 mV

    Which says the noise will be loud, but not deafening.

    A 100 GΩ resistor increases the voltage by a factor of 10, so you can decrease the gain by a factor of ten for the same 20 mV output, which increases the bandwidth by a factor of ten, which increases the noise by a factor of … ten.

    Ouch.

    With the same gain of 100 (and therefore 10 kHz bandwidth) after the 100 GΩ resistor, the output increases by a factor of ten to 200 mV, but the noise increases by only √10 to 4 mV.

    The LMC6081 has 22 nV/√Hz and 0.2 fA/√Hz input-referred noise, neither of which will rise above the grass from the resistor.

    With 10 kHz bandwidth, the pulse rise time is:

    tr = 0.34 / BW = 0.34 / 10 kHz = 34 μs

    The LMC6081 has a 1 V/μs slew rate that poses no limitation at all for these tiddly signals.

    That’s significantly better than the stacked Darlingtons and might be Good Enough for my simple needs.

  • Cheney C8600 Geiger Counter With CI-3BG GM Tube

    I haven’t built a kit in a long time, so when the Cheney C8600 Geiger Counter kit and a CI-3BG GM tube went on sale I had a pleasant interlude:

    Chaney C8600 Geiger Counter Kit - CI-3BG GM tube
    Chaney C8600 Geiger Counter Kit – CI-3BG GM tube

    It’s a good thing I have a pretty deep parts stock, as one of the caps didn’t fit into its holes at all.

    The Russian CI-3BG glass tube, according to the datasheet and discussion on MightyOhm, is sensitive to gamma and beta radiation, so it should serve as a simple cross-check on my ionization chamber results. It’s not clear the C8600 is applying the correct voltage to the CI-3BG tube, but it probably doesn’t make much difference; the supply is so feeble that there’s no way to actually measure the results.

    A closer look at the CI-3BG suggests the active volume lies inside that spiral-wrapped section between the white insulators:

    Russian CI-3BG Glass Geiger Tube - detail
    Russian CI-3BG Glass Geiger Tube – detail

    In round numbers, that section is 6 mm long and 3 mm OD. Figuring the ID at 2.5 mm, that’s a volume of 30 mm3 = 0.030 cm3. That’s maybe 1/7300 of the ionization chamber volume, so, (handwaving) assuming roughly equal sensitivity, the chamber should report three orders of magnitude more pulses than this little thing.

    It’s mildly sensitive to a radium-dial watch and perks up when a watch hand lines up along the spiral-wrapped volume. Given that the radium decay sequence spits out betas and no gammas, the (scaled) count may be a bit higher than the ionization chamber produces, but there are so many other imponderables that it might not matter in the least.

    Obviously, it needs a case of some sort…