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

  • Tensilizing Copper Wire

    The “bus bars” on the battery holders are 14 AWG copper wire:

    Astable - NP-BX1 base - detail
    Astable – NP-BX1 base – detail

    Slightly stretching the wire straightens and work-hardens it, which I’d been doing by clamping one end in the bench vise, grabbing the other in a Vise-Grip, and whacking the Vise-Grip with a hammer. The results tended to be, mmm, hit-or-miss, with the wires often acquiring a slight bend due to an errant whack.

    I finally fished out the slide hammer Mary made when we took a BOCES adult-ed machine shop class many many years ago:

    Slide Hammer
    Slide Hammer

    The snout captured the head of a sheet metal screw you’d previously driven into a dented automobile fender. For my simple purposes, jamming the wire into the snout and tightening it firmly provides a Good Enough™ grip:

    Slide Hammer Snout
    Slide Hammer Snout

    Clamp the other end of the wire into the bench vise, pull gently on the hammer to take the slack out of the wire, and slap the weight until one end of the wire breaks.

    With a bit of attention to detail, the wires come out perfectly straight and ready to become Art:

    Straightened 14 AWG Copper Wires
    Straightened 14 AWG Copper Wires

    The wires start out at 1.60 mm diameter (14 AWG should be 1.628, but you know how this stuff goes) and break around 1.55 mm. In principle, when the diameter drops 3%, the area will decrease by 6% and the length should increase by 6%, but in reality the 150 mm length stretches by only 1 mm = 1%, not 3 mm. My measurement-fu seems weak.

    Highly recommended, particularly when your Favorite Wife made the tool.

    The Harbor Freight version comes with a bunch of snouts suitable for car repair and is utterly unromantic.

  • Monthly Image: Red Oaks Mill Dam Flow

    Some of our regular walks take us over the Rt 376 bridge downstream of the Red Oaks Mill dam and I try to take a picture whenever we cross.

    For reference, two years ago in December 2016:

    Red Oaks Mill Dam 2016-12-11
    Red Oaks Mill Dam 2016-12-11

    January 2018:

    Red Oaks Mill Dam - 2018-01-13
    Red Oaks Mill Dam – 2018-01-13

    April 2018:

    Red Oaks Mill Dam - 2018-04-08
    Red Oaks Mill Dam – 2018-04-08

    October 2018:

    Red Oaks Mill Dam - 2018-10-29
    Red Oaks Mill Dam – 2018-10-29

    November 2018:

    Red Oaks Mill Dam - 2018-11-18
    Red Oaks Mill Dam – 2018-11-18

    December 2018:

    Red Oaks Mill Dam - 2018-12-31
    Red Oaks Mill Dam – 2018-12-31

    The dam breast seem from the north (left in above pictures) in December 2018:

    Red Oaks Mill Dam - north view - 2018-12-30
    Red Oaks Mill Dam – north view – 2018-12-30

    Searching for the obvious keywords will produce far more pictures than the subject may deserve.

    Getting hydropower from the rubble would require considerable capital investment …

  • Red Fox Visitation

    A Red Fox came trotting around the garden on the day before Christmas, then nosed up to the back of the house:

    Red Fox visitation - 2018-12-24
    Red Fox visitation – 2018-12-24

    Presumably, it was in search of a snack. We wish it good hunting.

    A few hours later, the fox walked quickly across the back yard with half a dozen turkey toms close behind, perhaps urging it away from their hens. Everybody remained calm and collected, knowing their roles in this particular play.

    FWIW, Marist College fields Red Foxes athletic teams. The women’s teams are Lady Red Foxes, as “vixen” carries entirely inappropriate connotations.

  • Astable Multivibrator: 2N7000 MOSFET IDSS and Vthr Tests

    Building an astable multivibrator from MOSFETs for longer time constants and more reliable operation suggests I should know a bit more about their operation with minuscule currents and low voltages. I have a small stock of low-threshold ZVNL110A MOSFETs, but using something less obsolete seems in order.

    Dirt-cheap 2N7000 MOSFETs have a maximum IDSS around 1 µA at room temperature, which would be way too high in this situation; there wouldn’t be much difference between their ON and OFF states.

    The test setup is simplicity itself:

    2N7000 IDSS - calibration
    2N7000 IDSS – calibration

    The initial reading from a 4 V bench supply was 0.00 µA on the Siglent SDM3045, my best low-current meter, so I put a 10 MΩ resistor across the drain and source terminals:

    Astable - 2N7000 - IDSS cal
    Astable – 2N7000 – IDSS cal

    Close enough, particularly given the silver fourth band on that old carbon composition resistor and its no-doubt unclean surface.

    The rest of the 2N7000 MOSFETs have IDSS ≤ 10 nA, which you can’t distinguish from zero on that scale.

    The 2N7000 datasheet specs give a threshold voltage from 0.8 to 2.5 V for 1 mA drain current, bracketing a 2.1 V typical value, which would be too high for a nearly dead lithium cell.

    I calibrated the VGS(thr) current at 11 µA with a 348 kΩ resistor:

    2N7000 MOSFET Id cal
    2N7000 MOSFET Id cal

    Which produced 11.49 µA at 4 V, just as it should, so I plugged in a MOSFET and twiddled the trimpot for a nice round 10 µA:

    2N7000 MOSFET Vthr test
    2N7000 MOSFET Vthr test

    Most transistors conducted 10 µA with the gate at 1.42 V, with a few outliers spanning 50 mV on either side. Close enough and low enough!.

    Now, to conjure an astable.

  • Blog Summary: 2018

    Page views for 2018:

    Blog Post Summary - 2018-12-24
    Blog Post Summary – 2018-12-24

    At this late date, the RepRap site has a much better G-Code reference, at least for the weird and wonderful assortment of 3D printer commands.

    Given that I’m at best a secondary reference for Toyota Sienna ABS trouble codes, things must be getting grim out there in the minivan crowd.

    And, as always, houses (and especially plumbing) are trouble!

    As for everything else, well, it’s just me and my shop notes …

    WordPress reports 101 k ad impressions per month for 24.6 k “page views”, suggesting most folks see four ads per page. If you’re not using an ad blocker, start now!

    Those seem to be the most aggressive (and thus highly desirable to advertisers) video ads, because WordPress pays me a whopping 8¢ per kilo-impression; a few percent of the Youtube rate. The numbers are dropping, though, suggesting ads will never push me into the ranks of the thousandaires.

    Now you know.

  • Sonicare Essence: Final Battery Replacement

    After a bit over five years, the NiMH cells in my ancient Philips Sonicare Essence toothbrush finally gave out:

    Sonicare recharge dates - 2017-2018
    Sonicare recharge dates – 2017-2018

    Down near the end, the poor thing barely gave one brushing after an overnight charge.

    While I was dismantling the case, I charged the last two new-old-stock NiMH cells:

    Sonicare Essence - charging short cells
    Sonicare Essence – charging short cells

    They arrived the same five years ago as the deaders in the toothbrush, but haven’t been used in the interim and charged well enough. The NiteCore D4 charger arrived after they did and isn’t really intended for 2/3 AA cells, so I used short brass tubes to make up the difference. I should have used the 300 mA low-current charging option (press-and-hold the Mode button for a second), although it didn’t overcook them at 750 mA.

    The process went pretty much as before, with the new cells soldered in place atop the PCB:

    Sonicare Essence - batteries on PCB
    Sonicare Essence – batteries on PCB

    And the PCB tucked back into the case:

    Sonicare Essence - batteries installed
    Sonicare Essence – batteries installed

    I applied a solder bridge to the BLINKY pads, which seemed to disable the blinking and turn the LED on full with the toothbrush in the charger. Without waiting for a full charge cycle, I sucked the solder off the pads and restored the previous blinkiness.

    A few strips of Kapton tape and it’s back in operation:

    Sonicare Essence - retaped
    Sonicare Essence – retaped

    The first charge lasted for two weeks, so things are looking good again. When the stock of knockoff replacement brush heads wears out, it’ll be time to get a whole new toothbrush … even if the batteries aren’t completely dead yet.

  • Astable Multivibrator: SMT LED Ballast Resistor

    The original astable multivibrator ran from a dead CR123 primary lithium cell:

    CR123A Astable - front
    CR123A Astable – front

    With a terminal voltage falling from barely 3 V, the LED drew about 3 mA (1 mA/div), tops, without a ballast resistor:

    Astable - CR123A 2.8 V - 1 mA -green
    Astable – CR123A 2.8 V – 1 mA -green

    Hacking in a charged NP-BX1 secondary lithium cell boosted the supply to 4 V:

    NP-BX1 Holder - SMT pogo pins
    NP-BX1 Holder – SMT pogo pins

    Which, diodes being the way they are, raised the LED current to nearly 400 mA (100 mA/div):

    Astable - NP-BX1 4V - base V - 100mA-div
    Astable – NP-BX1 4V – base V – 100mA-div

    Somewhat to my surprise, a few weeks of abuse didn’t do any obvious damage to the LED, but I added a resistor while I was soldering up another holder:

    Astable - 51 ohm SMD ballast
    Astable – 51 ohm SMD ballast

    There’s not quite enough room for a 1/8 W axial resistor, so why not blob in a surface-mount resistor?

    Which cuts the current down to a mere 15 mA (10 mA/div) from a lithium battery at 4 V:

    Astable - NP-BX1 - 51 ohm ballast - 10ma-div
    Astable – NP-BX1 – 51 ohm ballast – 10ma-div

    It’s still blindingly bright, but now I don’t feel bad about it.