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

  • Bike Helmet Earbud/Mic Connections

    I’m in the process of reworking the interface box between the amateur radio HTs on our bikes and our helmet-mounted earbud & mic lashup. Mary needed a new helmet before I got the new interface ready, soooo there’s an adapter cable in the middle.

    This time around, the helmet cable uses a male USB-A connector, rather than a female 6-pin Mini-DIN PS/2 keyboard connector. Either one is cheap & readily available as assembled cables, which gets me out of soldering teeny little connector pins. These days, though, USB cables are more common.

    The motivation for a non-latching, low-extraction-force connector at the helmet is that when (not if) you drop the bike, the helmet doesn’t tie your head to the bike and snap your spine. Falls on a recumbent are much less exciting than on an upright bike, but you still want the bike to go that-a-way while you go this-a-way. Been there, done that.

    The old helmet cable connector: female 6-pin mini-DIN. The wire color code is not standardized. Viewed from rear of female connector or the front of the male connector, with the key slot up:

     ear com - Gn   5  |_|  6  K - ear hot
 mic com - Or   3  key  4  Y - mic hot
        gnd - Bn  1   2  R - gnd

    The new helmet cable connector: male USB-A. Mercifully, they standardized the wire colors. Looking at the front of the male USB-A connector with the tab down and the contacts up, the pins are 4 3 2 1:

    • 1 – R – ear hot
    • 2 – W – mic hot
    • 3 – G – mic com
    • 4 – K – ear com

    The female USB-A connector is exactly the same.

    That arrangement should produce the proper twisted pairs in a USB 2.0 cable, but all the USB cables I’ve seen so far lay all four wires in a common twist inside the shield. Maybe it’s the cheap junk I buy, huh?

    It’s worthwhile to scribble some color in the background of the trident USB symbol so it’s easier to mate the connectors.

    Easy-align USB connectors
    Easy-align USB connectors

    Memo to Self: verify the connections & proper operation before shrinking the tubing!

  • NiMH Automatic Charger: Use the Real Battery Capacity

    Tenergy NiMH Charger
    Tenergy NiMH Charger

    This Tenergy automatic NiMH charger is typical of the breed: pick a charging current to match the cell / pack capacity, then stand back and let it determine full charge.

    The instruction sheet reads thusly:

    • For battery pack between 1100 mah and 2100 mah, please use the low level switch — charging rate: 0.9 A
    • For battery pack over 2100 mah, please use the high level switch — charging rate: 1.8 A

    Pop quiz: what charging current should you use for a battery pack made from nominal 2300 mAh cells?

    I thought so, too, but consider this graph (the full post is there):

    Tenergy RTU Pack A Tests - Aug 2009
    Tenergy RTU Pack A Tests – Aug 2009

    The actual capacity is more like 1600 mAh, not 2300 mAh. Do you set the charge current based on the wildly overoptimistic cell rating or the actual measured capacity?

    As you might expect: charge based on the actual measured capacity, because that’s what the battery can handle.

    The higher rate actually worked with new cells, but as the packs aged the charger would sometimes grossly overheat them. Bad for the packs, not to mention a bit scary.

    The lower rate worked perfectly, although it took me a while to figure that out.

    For what it’s worth, this is the charger I hacked a magnetic grapple onto the thermocouple. Much more convenient and considerably more durable than ptui tape.

    Memo to Self: One careful measurement is worth a dozen optimistic ratings.

  • Power Outlet Expander Failure

    Multi-Scorched Multi-Outlet Box
    Multi-Scorched Multi-Outlet Box

    This story begins years ago, as mentioned there. I’d retrieved the offending outlet expander / extension cord from my mother’s apartment and tossed it in my big box of Extension Cords.

    I recently plugged it in and was rewarded with a flash-bang inside the box. Taking it apart reveals two more blackened outlet compartments (in the lower right), but no more missing contact blades.

    It turns out that the black (hot) wire got caught between a stiffening rib on the back plate and the edge of the box supporting the brass plate connecting the white (neutral) wire to the contacts. Here’s reconstructed view after I cut off the extension cord.

    Crushed wire
    Crushed wire

    Flipping the wire over shows the spot where the copper conductor eventually poked through the insulation.

    Exposed conductor
    Exposed conductor

    It touched the sharp corner of the brass strip just to the left of the divider in this view. The notch in the divider channeled the jet of burning debris across the far wall of the right-hand compartment. The left-hand compartment is completely smudged.

    Short-circuit point and debris jets
    Short-circuit point and debris jets

    Looks like I get credit for this one… but even seeing how I did it, I’m not sure there’s any way to know none of the wires got crushed while reassembling the box.

    It’s safely in the trash and the cord is in my big box of Random Power Cords.

    Memo to Self: Make sure the box fits together smoothly?

  • NiMH Battery Pack Status

    Here’s the status of the AA NiMH packs I’ve been using with the radios on our bikes, plus three packs I made up last year and have been keeping on the desk to measure their long-term storage characteristics. Click for more detail.

    Bike Radio Pack Status - 2010-03
    Bike Radio Pack Status – 2010-03

    The “Tenergy 09 x” packs are new & unused with, frankly, disappointing capacity of about half their 2.6 Ah rating. That’s not much better than the used Tenergy packs (T9x and RTU x), which is either a Good Thing (they have good long-term stability) or a Bad Thing (they’re grossly over-rated to begin with).

    The two Duracell packs are far better than any of the Tenergy packs.

    The three 6-cell packs along the bottom are fading fast.

    The previous test runs are there, albeit with a 1 A discharge.

    This season I’ll use some Li-Ion packs that weigh twice as much with three times the capacity… plus a built-in charge gauge, pessimistic though it may be.

  • Opening a Quartz Crystal Can: Effects Thereof

    A comment on yesterday’s post about quartz crystal measurements prompted me to destroy a crystal in the name of science…

    The question is, what effect does exposing a crystal to the air have on its performance? I would have sworn it would never work right again, because it’s normally running in an inert atmosphere and maybe a partial vacuum. One measurement being worth a kilo-opinion, here’s what happened.

    I picked random crystal from the bottom of the crystal box, based on it having a solder seal that I could dismantle without deploying an abrasive cutoff wheel or writing some G-Code to slice the can off with a slitting saw. The crystal was labeled HCI-1800 18.000 MHz and probably older than most of the folks who will eventually read this… younger than some of us, though.

    The overall response, measured in the same fixture as shown yesterday (click the pix for more detail):

    HCI-1800 18 MHz - Baseline Overview
    HCI-1800 18 MHz – Baseline Overview

    The center frequency is 18.0050 MHz (at this rather broad span) and it has some ugly spurs out there to the right.

    A closeup of the series-resonant peak:

    HCI-1800 18 MHz - Baseline BW
    HCI-1800 18 MHz – Baseline BW

    The bandwidth is 1.50 kHz at 17.99950 MHz at this span.

    Naked HCI-1800 18.0 MHz Crystal
    Naked HCI-1800 18.0 MHz Crystal

    Then I applied a soldering iron around the seal and yanked the case off. I think that didn’t involve whacking the crystal with the case en passant, but I can’t be sure. In any event, it looks undamaged and seems to operate properly.

    A pair of spring clips attach to the electrodes and hold the quartz disk in position. They’re just the cutest little things and quite unlike the other holders I’ve seen. I think the solder blobs fasten the spring ends together and don’t bond to the electrodes, but what do I know?

    HCI-1800 Crystal Overview
    HCI-1800 Crystal Overview

    The quartz disk has a few small chips near the edge:

    HCI-1800 Crystal Edge Chips
    HCI-1800 Crystal Edge Chips

    I think those are Inherent Vice… simply because:

    1. They’re not in a position where I could have whacked the disk and
    2. I doubt I could whack it that delicately

    Anyhow, with the can off, here’s what the series resonant peak looks like:

    HCI-1800 18 MHz - Opened BW
    HCI-1800 18 MHz – Opened BW

    The resonant frequency is now 17.99968, 180 Hz higher, which may be due to instability in the HP8591 spectrum analyzer’s not-stabilized-for-ten-hours ovenized oscillator. The bandwidth is 1.55 kHz, 50 Hz wider, although I think that’s one resolution quantum of difference.

    Here are the two bandwidth traces overlaid.

    HCI-1800 18 MHz - Overlaid BW
    HCI-1800 18 MHz – Overlaid BW

    The peak has been centered in both, so you can’t tell they’re slightly different. The interesting point is the difference in the slope to the low-frequency side of the peak, which is slightly higher for the open-case condition. Seeing as how the missing case completely changes the usual stray capacitance situation, I’m not surprised.

    Anyhow, I admit to being surprised: there’s not that much difference after opening the case. I’ll put the naked crystal in a small container in a nominally safe place for a while, then retest it to see what’s happening.

    Memo to Self: A “safe place” is nowhere near the Electronics Workbench!

    Here are some other naked crystals:

    Naked Crystals
    Naked Crystals

    Notice the tarnished (presumably) silver electrodes on the crystal in the lower left. That one’s been sitting on my monitor and in other hazardous locations for a few years. I can’t find these anywhere right now, but if they turn up I’ll test them, too.

  • Crystal Properties

    Spent some Quality Shop Time measuring an assortment of crystals, some data from which will make up a Circuit Cellar column.

    And the raw numbers will come in handy one of these days, so here they are…

    12 MHz Asst HC-49/U Co+Cc/2 2Cc Fs BW Rs
    ECS 1 4.85 1.47 12.000162 787.5 40.1
    ECS 2 4.50 1.42 12.000150 725.0 40.1
    ECS 3 4.70 1.42 12.000325 1100.0 50.0 Rs out of range
    HC1 4 4.34 1.11 11.999000 600.0 36.0
    HC1 5 4.24 1.06 12.000137 537.5 36.9
    Sentry 6 5.14 0.96 12.000250 625.0 31.8 many spurs
    11.0592 MHz HC-49/U
    1 4.90 1.42 11.059275 562.5 9.3
    2 4.99 1.46 11.059112 575.0 14.7
    3 4.87 1.42 11.059275 512.5 9.6
    4 4.87 1.41 11.059125 550.0 10.0
    5 4.29 1.43 11.058935 750.0 18.1
    6 4.93 1.47 11.059000 537.5 10.7
    7 4.95 1.47 11.059200 525.0 8.1
    8 5.03 1.45 11.059037 575.0 11.1
    10 MHz HC-49/U spur +150 kHz
    1 2.57 1.36 9.997888 200.0 14.2
    2 2.61 1.30 9.997738 225.0 16.7
    3 2.75 1.30 9.997788 225.0 20.0
    4 2.67 1.30 9.997750 225.0 16.1
    5 2.75 1.26 9.997725 250.0 22.7
    6 2.69 1.27 9.997788 225.0 21.0
    7 2.69 1.26 9.997825 212.5 16.5 Circuit Cellar example
    8 2.69 1.22 9.997832 212.5 18.4
    9 2.72 1.24 9.997788 250.0 23.4
    10 2.68 1.20 9.997738 225.0 18.0
    18.43 MHz HC-49/US many spurs +10 +76 kHz
    1 3.86 1.33 18.432425 1.56 24.1
    2 3.79 1.22 18.432987 1.21 10.9
    3 3.93 1.39 18.432050 2.44 46.3
    4 3.97 1.40 18.431175 1.90 27.7
    5 3.89 1.33 18.431888 2.11 32.2
    6 3.92 1.39 18.430888 1.39 16.5
    7 3.99 1.35 18.431500 1.36 11.8
    8 3.97 1.35 18.431675 2.18 38.4
    9 3.95 1.31 18.430512 1.30 10.1
    10 4.04 1.50 18.431427 1.36 11.8

    The 18.43 MHz crystals are in the short /US cans with surprisingly high stray capacitance. Their bandwidths are in kHz and all over the map, as are the series resistances. Weird. Bad crystals? Bad technique?

    Capacitance measured with that fixture.

    Frequency & bandwidth from HP8591 spectrum analyzer with a fixture similar to the K8IQY design; the bandwidths seem to come in 12.5 Hz increments despite a (very narrow) 2 kHz span. The general process is there. Resistance measured from a cermet trimpot using a multimeter good for 0.1 Ω around 10 Ω.

    Crystal Test Fixture
    Crystal Test Fixture

    Useful equations, with column headings in boldface:

    • Lead-to-can capacitance for each lead: Cc = 2Cc / 2
    • Lead-to-lead capacitance: Co = Co+Cc/2 – Cc/2
    • Circuit Q: Q = Fs/BW
    • Circuit resistance: R = Rs + 25 (assuming 4:1 transformers)
    • Reactance XL = XC at series resonance: X = Q R
    • Motional inductance: Lm = X / (2 π Fs)
    • Motional capacitance: Cm = 1 / (2 π Fs X)
    • Parallel resonance Fp = Fs √(1 + (Cm / Co))

    More equations there.

    Memo to Self: Zero the capacitance fixture before critical measurements!

  • Generic Sony NP-FS11 Li-Ion Packs: Rebuild FTW!

    Herewith, the discharge test results for all the generic Sony NP-FS11 battery packs I have (click for a bigger image).

    Sony NP-FS11 Status - 2010-04
    Sony NP-FS11 Status – 2010-04

    The five mostly overlapping upper traces consist of:

    • Three packs (H, K, and L) rebuilt from the eBay junkers
    • F rebuilt from a deader in my collection
    • E is an older, no-name pack that just continues to work

    The rebuilt packs now have cells from batteryspace.com that are working fine: nominal capacity 600 mAh, actual around 1200 to 1400 for a parallel pair. It’s surprising to see a cell producing its rated capacity…

    The two lowest traces (G & I), plus the purple trace (J) are from the eBay source. The first two are obvious junk, but pack J is actually pretty good. The fact that it’s the best of six packs from that vendor tells you all you need to know about their QC.

    For those of you joining us via search engines, the rest of the story: