Improvements – Page 143 – The Smell of Molten Projects in the Morning

Raspberry Pi WiFi Adapters

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

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

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

2017-01-11

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:

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!

2017-01-10

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.

2017-01-08

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…

2017-01-06

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:

tweak GRUB_GFXMODE=1280x720 to make the initial menu less imposing
XFCE wide border hack, increase window title contrast in themerc
copy ssh keys
kensington & wacom button swaps in /usr/share/X11/xorg.conf.d/
firefox: media.autoplay.enabled=false, click_to_play=true
fix still-broken dropbox indicator
discard extraneous fonts, install custom fonts
copy autostart script

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.

2017-01-05

Raspberry Pi Streaming Radio Player: Ignoring a Missing Volume Knob

The Dell AC511 USB SoundBars have volume control knobs, which this udev rule turns into the /dev/input/volume device:

ATTRS{name}=="Dell Dell AC511 USB SoundBar", SYMLINK+="input/volume"

I recently wanted to use an ordinary USB “sound card” that did not, of course, have a volume knob:

This hack skips the configuration that makes the knob’s events visible to the Python program:

import os.path

... snippage ...

# if volume control knob exists, then set up its events

VolumeDevice = '/dev/input/volume'

vp = select.poll()
if os.path.exists(VolumeDevice):
  v = InputDevice(VolumeDevice)
  v.grab()
  vp.register(v.fileno(),select.POLLIN + select.POLLPRI + select.POLLERR)

It turns out that if you never register a device with the event polling interface, then the interface never reports any events and the rest of the code remains blissfully undisturbed: the non-existent knob doesn’t do anything, while the volume control buttons on the keypad continue to function as usual.

The end result of this fiddling puts a Raspberry Pi 2 Model B to work as a streaming player on my Electronics Workbench, untethering the laptop from those powered speakers:

RPi 2 Streaming Player - USB sound gadget — RPi 2 Streaming Player – USB sound gadget

It’s a shame that USB audio gadget is so big, because it crowds out standard USB plugs to the side.

The most satisfactory LED configuration for a translucent case with an external WiFi adapter seems to be:

dtparam=pwr_led_trigger=cpu0
dtparam=act_led_trigger=mmc0

The rest of the code remains unchanged as shown in that GitHub Gist.

Bomb the bass!

2017-01-03

Loop Antenna Splice Reinforcement

Those solder joints and finicky little wires seem much too fragile on their own:

LF Loop Antenna - complete joint — LF Loop Antenna – complete joint

This should help:

Loop Antenna Splice - assembled — Loop Antenna Splice – assembled

Foam blocks hold the ribbon cable in place and provide a bit of strain relief around the hard plastic edge:

Loop Antenna Splice - hardware — Loop Antenna Splice – hardware

The brass inserts in the bottom block (on the left) got epoxied in place, because they must provide quite a bit of force to clamp the foam. Their larger knurled end sits flush with the outside surface and the smaller end has one thread thickness of clearance below the inner surface.

A last look at the wiring:

Loop Antenna Splice - wiring — Loop Antenna Splice – wiring

I think the preamp must sit at some distance from the antenna to prevent feedback, but that remains to be seen.

The M2’s nozzle accumulated a huge blob of PETG that turned into a giant smear:

Loop Antenna Splice - PETG booger — Loop Antenna Splice – PETG booger

Fortunately, it’s on the inside where nobody will ever see it. If you know where to look, it’s barely visible from the outside.

The solid model shows off the structure a bit better:

Loop Antenna Splice - show view — Loop Antenna Splice – show view

The inside view:

Loop Antenna Splice - bottom — Loop Antenna Splice – bottom

The OpenSCAD source code as a GitHub Gist:

	// Ribbon cable loop antenna splice
	// Ed Nisley KE4ZNU December 2016

	Layout = "Text";

	//- Extrusion parameters must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

	inch = 25.4;

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

	//———-
	// Dimensions

	Cable = [200,48.0,1.5]; // X = longer than anything else

	Splice = [15.0,53.0,5.0]; // epoxy blob around joints

	Foam = [15.0,Splice[1],2.0];
	CornerRadius = 5.0;

	ID = 0;
	OD = 1;
	LENGTH = 2;

	Insert = [3.9,4.6 – 0.1,5.8]; // 4-40 knurled brass insert

	Screw = [2.7,5.5,2.0]; // OD = head LENGTH = head thickness
	Washer = [3.0,8.0,0.8];

	BlockOA = [60.0, // convenient length
	Splice[1] + 4*Washer[OD], // clearance around washer on top
	2(Insert[LENGTH] + 2ThreadThick)]; // insert sets both thicknesses

	NumScrews = 2; // screws along each side of cable
	ScrewOC = [BlockOA[0] / NumScrews,
	BlockOA[1] – 2*Washer[OD],
	2*BlockOA[2] // ensure complete holes
	];

	TextThick = 3*ThreadThick; // depth of text into surface
	TextFit = HoleWindage/2; // clearance around text polygons

	//———————-
	// Useful routines

	module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes
	Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
	FixDia = Dia / cos(180/Sides);
	cylinder(d=(FixDia + HoleWindage),h=Height,$fn=Sides);
	}

	//—–
	// Blocky model of cable + splice + wire tap for subtraction

	module Antenna() {
	union() {
	cube(Cable,center=true);
	cube(Splice,center=true);
	for (i=[-1,1])
	translate([0,-Splice[1]/2,0])
	cube([Splice[0]/2,Splice[1],2*Foam[2]],center=true);
	}
	}

	// Outside shape of splice Block, less screw clearance

	module SpliceBlock() {
	difference() {
	hull()
	for (i=[-1,1], j=[-1,1])
	translate([i(BlockOA[0]/2 – CornerRadius),j(BlockOA[1]/2 – CornerRadius),-BlockOA[2]/2])
	cylinder(r=CornerRadius,h=BlockOA[2],$fn=4*8);
	for (i = [0:NumScrews – 1], j=[-1,1])
	translate([-BlockOA[0]/2 + ScrewOC[0]/2 + iScrewOC[0],jScrewOC[1]/2,-(BlockOA[2]/2 + Protrusion)])
	PolyCyl(Screw[ID],BlockOA[2] + 2*Protrusion,6);
	}
	}

	// Splice block less cable

	module ShapedBlock() {
	difference() {
	SpliceBlock();
	Antenna();
	}
	}

	// Bottom

	module BottomPlate() {
	difference() {
	ShapedBlock();
	translate([0,0,BlockOA[2]/2])
	cube(BlockOA + 2*[Protrusion,Protrusion,0],center=true);
	Antenna(Splice);
	for (i = [0:NumScrews – 1], j=[-1,1])
	translate([-BlockOA[0]/2 + ScrewOC[0]/2 + iScrewOC[0],jScrewOC[1]/2,-(BlockOA[2]/2 + Protrusion)])
	PolyCyl(Insert[OD],2*Insert[LENGTH],6);
	for (i=[-1,1])
	translate([i*((BlockOA[0] – Foam[0] + Protrusion)/2),0,(BlockOA[2]/2 – Cable[2]/2 – Foam[2])])
	cube([Foam[0] + Protrusion,Foam[1],BlockOA[2]],center=true);
	}
	}

	// Top

	module TopPlate() {
	difference() {
	ShapedBlock();
	translate([0,0,-BlockOA[2]/2])
	cube(BlockOA + 2*[Protrusion,Protrusion,0],center=true);
	Antenna(Splice);
	for (i=[-1,1])
	translate([i*((BlockOA[0] – Foam[0] + Protrusion)/2),0,-(BlockOA[2]/2 – Cable[2]/2 – Foam[2])])
	cube([Foam[0] + Protrusion,Foam[1],BlockOA[2]],center=true);
	rotate(90) {
	translate([0,6,BlockOA[2]/2 – TextThick])
	TextHack("KE4ZNU",8,0.0,1.15,TextThick + Protrusion);
	translate([0,-6,BlockOA[2]/2 – TextThick])
	TextHack("2016·12",6,0.0,1.20,TextThick + Protrusion);
	}
	}
	}

	module TextHack(Text="sample",Size=10,Offset=0.0,Space=1.0,Thick=ThreadThick) {
	linear_extrude(height=Thick,convexity=10)
	offset(r=Offset)
	text(Text,font=":bold",size=Size,spacing=Space,halign="center",valign="center");
	}


	//———-
	// Build them

	if (Layout == "Antenna")
	Antenna();

	if (Layout == "SpliceBlock")
	SpliceBlock();

	if (Layout == "ShapedBlock")
	ShapedBlock();

	if (Layout == "Bottom")
	BottomPlate();

	if (Layout == "Top")
	TopPlate();

	if (Layout == "Text") {
	translate([0,6,0])
	TextHack("KE4ZNU",8,-TextFit,1.15,TextThick);
	translate([0,-6,0])
	TextHack("2016·12",6,-TextFit,1.20,TextThick);
	}

	if (Layout == "Show") {
	translate([0,0,5])
	TopPlate();
	translate([0,0,-5])
	BottomPlate();
	color("Orange",0.2)
	Antenna();
	}

	if (Layout == "Build") {
	translate([0,-0.6*BlockOA[1],BlockOA[2]/2])
	rotate([180,0,0])
	TopPlate();
	translate([0,0.6*BlockOA[1],BlockOA[2]/2])
	BottomPlate();
	}

view raw Loop Antenna Splice.scad hosted with ❤ by GitHub

2016-12-27