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.

Author: Ed

  • Raspberry Pi WiFi Adapters

    One might be forgiven for thinking these two USB Wifi adapters are essentially identical:

    USB Wifi adapters
    USB Wifi adapters

    Turns out the SunFounder RT5370 (on the top, with the stylin’ curved case) has better performance than the Wifi With Antenna (on the bottom, with full-frontal chunk goin’ on), by a not inconsiderable 5 to 10 dB. Boosting the received power level in the fringe areas of our house from -70 dBm to -63 dBm makes all the difference between not working and steady streaming.

    The built-in WiFi antenna on a Raspberry Pi 3 ticks along 10 dB lower, with -80 dBm (10 pW!) at the receiver making for poor communication: a Pi 3 works perfectly within reasonable line-of-sight of the router (even through our wood floor) and wakes up blind in fringe areas. Hacking an external antenna probably helps, but definitely isn’t a net win compared to ten bucks worth of USB adapter.

    The wavemon utility (it’s in the Raspbian repo) comes in handy for figuring that sort of thing.

    There is, of course, no way to determine anything important about the adapters from their product descriptions, which are essentially identical, right down to the price. Neither have any product identification on their cases. The back of the package for the SunFounder gadget gives some specs, none of which may mean anything (clicky for more dots):

    SunFounder RT5370 USB WiFi Adapter Specs
    SunFounder RT5370 USB WiFi Adapter Specs

    I ordered another SunFounder adapter, Just In Case it comes in handy, with the hope that both behave the same way.

  • Raspberry Pi 3 Reset Switch

    The (relatively) new Raspberry Pi 3 PCB layout puts the Run header in a different location than in the Pi 2, but a minute of filing gnaws a suitable opening:

    Raspberry Pi 3 - Reset Switch
    Raspberry Pi 3 – Reset Switch

    As before, a hot-melt glue blob holds the switch in place. I’d prefer a black case, if only to hide the blob, but clear-ish is what’s available right now.

    Remember those orderly shutdowns, even at the cost of a keypad button!

  • IBM 5100 APL: Nested Emulators

    A discussion about Raspberry Pi performance prompted this:

    IBM 5110 Emulator - Javascript on Raspberry Pi
    IBM 5110 Emulator – Javascript on Raspberry Pi

    From the inside out:

    Starting the show takes 17 seconds from clicking the Restart button (second from right, top row) to APL’s Clear WS prompt. I have no idea how that compares with a Genuine IBM 5100.

    I distinctly remember writing APL programs, but that’s about as far as my memory will take me. [sigh]

  • Cast Iron Pan Seasoning: Round 3

    After seasoning the pan after every meal for a few weeks, then not doing that for a few more weeks, its thick glaze began looking somewhat scuffed:

    Cast Iron Pan - scuffed
    Cast Iron Pan – scuffed

    You may recognize some of those scars from the previous picture:

    Wagner skillet - two weeks of use
    Wagner skillet – two weeks of use

    Perhaps the multi-layer seasoning was entirely too thick and prone to chipping; this time, I’ll try a thinner coating. Because it’s cast iron, the pan under the coating remains undamaged.

    A few hours in a bucket of sodium carbonate solution with a battery charger driving a few amps through it removed most of the glaze and a few minutes with a sponge sanding block cleaned off the rest. Applying flaxseed oil and heating it to 400 °F on a regular burner (under close supervision!) produced a nice coating:

    Cast Iron Pan - seasoned
    Cast Iron Pan – seasoned

    The single layer was way slick for veggies in the evening and handled the morning omelet with aplomb, so we’ll run with it until something interesting happens.

  • Rabbit Head

    Although we don’t think of this as a particularly tough neighborhood, this is the second severed head we’ve encountered in the last few years during our routine walks:

    Rabbit Head
    Rabbit Head

    We doubt a predator would do such a tidy job of parting the head from the body, then discarding it. The eyes surely went to a bird, though…

    It was across the Mighty Wappinger Creek, near the far end of Romca Rd. The Red Oaks Mill Civic Association is long gone and their building burned to the ground a few decades ago, but their name lives on.

  • Making and Mounting SD Card Backup Images

    The process of creating, configuring, and backing up a Raspberry Pi goes a little something like this:

    unzip /mnt/diskimages/ISOs/Raspberry\ Pi/2016-11-25-raspbian-jessie-lite.zip
sudo dcfldd statusinterval=16 bs=4M if=2016-11-25-raspbian-jessie-lite.img of=/dev/sdb
... Micro SD card to Pi, boot, perform various configuration tweaks ...
... card back to PC ...
sudo dcfldd statusinterval=16 bs=4M if=/dev/sdb of=Streamer5-2017-01-02.img
zip -1 Streamer5-2017-01-02.zip Streamer5-2017-01-02.img
rsync -ahuv --progress Streamer5-2017-01-02.zip /mnt/diskimages/ISOs/Raspberry\ Pi/

    The ZIP operation crushes an 8 GB image down to 1.6 GB, obviously depending on most of the image being filled with binary zeros or foxes or something trivial like that. You could work around that with fsarchiver, at the cost of handling each partition separately.

    You can pipe the incoming image through GZIP when you don’t need the image right away:

    sudo dcfldd statusinterval=16 bs=4M if=/dev/sdb | gzip -1c > Streamer5-2017-01-02.gz

    There’s an obvious gotcha when you try to write an image to a (slightly) smaller card than the one it came from. Writing a smaller image on a larger card works just fine.

    With a raw image in hand, you must know the disk partition offsets within the image to mount them in loopback mode:

    fdisk -l Streamer5-2017-01-02.img
Disk Streamer5-2017-01-02.img: 7.4 GiB, 7892631552 bytes, 15415296 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc280d360

Device                    Boot  Start      End  Sectors  Size Id Type
Streamer5-2017-01-02.img1        8192   137215   129024   63M  c W95 FAT32 (LBA)
Streamer5-2017-01-02.img2      137216 15415295 15278080  7.3G 83 Linux

    Knowing the offsets, the mounts go like this:

    sudo mount -o loop,offset=$(( 8192*512 )) Streamer5-2017-01-02.img /mnt/loop/
... snippage ...
sudo mount -o loop,offset=$(( 137216*512 )) Streamer5-2017-01-02.img /mnt/loop/

    Because a Jessie Lite system will fit neatly into a 2 GB SD Card, you can trim the disk image to eliminate most of the unused space:

    sudo losetup -f
/dev/loop0

sudo losetup /dev/loop0 Streamer5-2017-01-02.img

sudo partprobe /dev/loop0

sudo gparted /dev/loop0
... resize ext4 partition from 7 GB to 1.8 GB

sudo losetup -d /dev/loop0

fdisk -l Streamer5-2017-01-02.img
Disk Streamer5-2017-01-02.img: 7.4 GiB, 7892631552 bytes, 15415296 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc280d360

Device                    Boot  Start     End Sectors  Size Id Type
Streamer5-2017-01-02.img1        8192  137215  129024   63M  c W95 FAT32 (LBA)
Streamer5-2017-01-02.img2      137216 3833855 3696640  1.8G 83 Linux

truncate --size=$(( (3833855+1)*512 )) Streamer5-2017-01-02.img
... or, if you don't care about an exact fit, use ...
truncate --size=2G Streamer5-2017-01-02.img

    The partition and filesystem will plump up to fill the SD Card during the first boot on the Raspberry Pi.

    There exist automagic utilities for all that, but practicing simple stuff helps keep it all fresh…

  • Xubuntu 16.04 LTS Bringup

    Notes on updating my desktop Optiplex 980 from Xubuntu 14.04 LTS to 16.04 LTS, after being unable to compile OpenSCAD, Slic3r, and GNU Radio from source. Blowing three days on reconfiguration & tweakage after a clean install is the price one pays to get rid of a few years of cruft; the old version remains bootable and lootable on another partition, Just In Case.

    Install:

    • nfs-common
    • xfce4-goodies
    • xubuntu-restricted-extras
    • hp2xx
    • xsane, xscanimage
    • kate (which hauls in a big hunk of wayland, alas)
    • digikam
    • chromium-browser
    • devilspie2
    • dropbox (from site)
    • remmina

    Apply:

    The hacks required to ensure NFS mounts happen before signing in seem to be obsolete. Given that systemd now controls everything, I have NFI how to proceed if that’s not the case.

    The Xubuntu load progress display looks like it’s scaled up from 640×480.

    There seems no way to disable on-screen notifications without deep hackery; some of the collateral damage involves the death of the volume control applet in the indicator panel thingy, so I didn’t try very hard.

    The aforementioned volume control now fires up the Pulseaudio control dialog. That display explained why the audio came out of the 980’s crappy internal speaker, but switching it to the HDMI output produced only silence. After blowing away ~/.config/pulse and rebooting that sucker, it’s all good: Linux audio remains a slow-motion train wreck.

    The initial sign-on dialog appears on the portrait monitor, minus rotation, because the dialog box follows the mouse pointer: the initial mouse position sits one pixel beyond the landscape monitor. Blind-type the password, whack Enter, and it’s all good.

    FWIW, I’ve installed the XFCE flavor of Mint Linux on the laptops, but that’s basically Xubuntu with (some of) the ugly sanded off and really doesn’t buy much for somebody who pays no attention to eyecandy.