Improvements – Page 158 – The Smell of Molten Projects in the Morning

Raspberry Pi Model B+ Reset Connector

Turns out Raspberry Pi boards have provision for a Reset switch, but you gotta dig for it. On the Model B+, it’s labeled RUN:

Raspberry Pi BPlus - RUN header — Raspberry Pi BPlus – RUN header

Soldering in that 2-pin header and plugging a pushbutton switch on a short cable will suffice until I get around to thinking of / scrounging a suitable case.

Poking the button forces a power-on reset, which you shouldn’t do with the RPi running, lest you trash the filesystem. After shutting down with sudo halt, however, the switch does exactly what’s needed: restarts the CPU from scratch.

The RPi draws little enough power that there’s no point in actually pulling the plug; stressing that Micro-B connector is definitely a Bad Idea.

2016-02-07

Linux Mint Login: HTML vs. GDM

Linux Mint uses an HTM-based login screen that displays an assortment of lush images. That would be fine, except that on the Lenovo Q150, the rendering engine (or whatever you call it) drives one core at full throttle whenever the login screen is up. That turns out to be all the time when I’m signed in through ssh and, for that box, the HTML engine is just a sucking chest wound.

To fix that:

System → Login → Theme tab

Mint Linux - Login Theme Selection — Mint Linux – Login Theme Selection

Then pick any theme using GDM rather than HTML; they’re marked to the right of the theme name.

Being that type of guy, I picked SimpleGreeter, which presents a dead-centered field in a blank screen:

Mint Linux - SimpleGreeter Login — Mint Linux – SimpleGreeter Login

Set it to auto-select the previous user (in the Options tab) and you’re good to go.

Burns zero CPU and works for me, anyhow.

2016-02-04

Knurled Metric Inserts

These seem like they ought to come in handy for fastening things to 3D printed objects:

Kurled Inserts - M2 M3 M5 — Kurled Inserts – M2 M3 M5

The assorted screws come from the Small Can o’ Small Screwlike Things, all harvested from various dead bits of consumer electronics:

These would benefit from a heated staking tool that slides them into the hole parallel to the axis and flush with the surface. Such things are commercially available, of course, but for my simple needs something involving a cartridge heater, a wall wart, and a drill press may suffice.

It would be better if the inserts had actual knurls, rather than splines. So it goes.

For the record (thread x length x Knurl OD x Body OD):

M2 x 4 x 3.5 x 2.8
M2 x 6 x 3.5 x 2.7
M3 x 4 x 4.5 x 3.8
M3 x 8 x 5.0 x 3.9
M5 x 10 x 7.5 x 6.9

The actual measurements seem to vary within ±0.02 of nominal and I doubt the manufacturing consistency justifies any assumption tighter than ±0.1 mm.

The M3 inserts really do have two different ODs.

The M5 insert was listed as “7 mm OD” and measures 7.5 mm, which suggests a typo in the description.

The polygonal hole adjustment I use produces dead-on diameters for small vertical holes:

HoleWindage = 0.2;

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);
}

So an ordinary cylinder() with the nominal knurl OD or a PolyCyl() with the nominal body OD should suffice. Horizontal holes can probably use a plain old cylinder() with the nominal body OD, because they need reaming anyway.

Perhaps a dab of epoxy would bond better with the plastic around a nominal-size hole than forcing the insert into an undersized hole or heat-bonding the insert. Some experimentation is in order.

Ten bucks for the entire collection (five bags of 50 inserts each = 250 little brass doodads = 4¢ each), shipped free halfway around the planet, seemed reasonable, given that inch size knurled brass inserts run anywhere from 50¢ to upwards of $2 a pop and a Genuine Helicoil 4-40 insert sets you back just shy of a buck.

An Amazon vendor offers 4-40 inserts for $0.24 each in single quantities, but with $9.25 shipping. [le sigh]

Inch-size inserts with knurled rings intended for ultrasonic bonding seem to be 5¢ to 15¢ on eBay. I think the straight-side versions will work better than the tapered ones for heat or epoxy bonding.

It knurls my knuckles that we here in the US haven’t gone solidly metric. Yes, I have a goodly assortment of metric hardware in addition to the harvested fasteners shown above, but it definitely wasn’t cheap & readily available.

2016-02-03

Vacuum Tube LEDs: Halogen Lamp Base

This lamp needs a base for its (minimal) electronics:

Vacuum Tube LEDs - plate lead - overview — Vacuum Tube LEDs – plate lead – overview

The solid model won’t win many stylin’ points:

Vacuum Tube Lights - lamp base solid model — Vacuum Tube Lights – lamp base solid model

It’s big and bulky, with a thick wall and base, because that ceramic lamp socket wants to screw down onto something solid. The screw holes got tapped 6-32, the standard electrical box screw size.

The odd little hole on the far side accommodates a USB-to-serial adapter that both powers the lamp and lets you reprogram the Arduino Pro Mini without tearing the thing apart:

Vacuum Tube Lights - USB adapter cutout — Vacuum Tube Lights – USB adapter cutout

The sloped roof makes the hole printable in the obvious orientation:

Lamp Base - USB port — Lamp Base – USB port

There’s an ugly story behind the horizontal line just above the USB adapter that I’ll explain in a bit.

The adapter hole begins 1.2 mm above the interior floor to let the adapter sit on a strip of double-sticky foam tape. I removed the standard header socket and wired the adapter directly to the Arduino Pro Mini with 24 AWG U-wires:

Lamp Base - interior — Lamp Base – interior

I didn’t want to use pin connectors on the lamp cable leads, but without those you (well, I) can’t take the base off without un-/re-soldering the wires in an awkward location; the fact that I hope to never take it apart is irrelevant. Next time, I’ll use a longer wire from the plate cap and better connectors, but this was a trial fit that became Good Enough for the purpose.

And then It Just Worked… although black, rather than cyan, plastic would look spiffier.

Bluish phases look icy cold:

Vacuum Tube LEDs - halogen lamp - purple phase — Vacuum Tube LEDs – halogen lamp – purple phase

Reddish phases look Just Right for a hot lamp:

Vacuum Tube LEDs - halogen lamp - red phase — Vacuum Tube LEDs – halogen lamp – red phase

A ring of white double sided foam tape now holds the plate cap in place; that should be black, too.

The OpenSCAD source code adds the base to the plate cap as a GitHub gist:

	// Vacuum Tube LED Lights
	// Ed Nisley KE4ZNU January 2016

	Layout = "LampBase"; // Show Build Cap LampBase USBPort

	Section = true; // cross-section the object

	//- 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);


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

	Pixel = [7.0,10.0,3.0]; // ID = contact patch, OD = PCB dia, LENGTH = overall thickness


	//———————-
	// 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(r=(FixDia + HoleWindage)/2,
	h=Height,
	$fn=Sides);
	}

	//———————-
	// Tube cap

	CapTube = [4.0,3/16 * inch,10.0]; // brass tube for flying lead to cap LED

	CapSize = [Pixel[ID],(Pixel[OD] + 3.0),(CapTube[OD] + 2*Pixel[LENGTH])];

	CapSides = 6*4;

	module Cap() {

	difference() {
	union() {
	cylinder(d=CapSize[OD],h=(CapSize[LENGTH]),$fn=CapSides); // main cap body
	translate([0,0,CapSize[LENGTH]]) // rounded top
	scale([1.0,1.0,0.65])
	sphere(d=CapSize[OD]/cos(180/CapSides),$fn=CapSides); // cos() fixes slight undersize vs cylinder
	cylinder(d1=(CapSize[OD] + 23ThreadWidth),d2=CapSize[OD],h=1.5*Pixel[LENGTH],$fn=CapSides); // skirt
	}

	translate([0,0,-Protrusion]) // bore for wiring to LED
	PolyCyl(CapSize[ID],(CapSize[LENGTH] + 3*ThreadThick + Protrusion),CapSides);

	translate([0,0,-Protrusion]) // PCB recess with clearance for tube dome
	PolyCyl(Pixel[OD],(1.5*Pixel[LENGTH] + Protrusion),CapSides);

	translate([0,0,(1.5*Pixel[LENGTH] – Protrusion)]) // small step + cone to retain PCB
	cylinder(d1=(Pixel[OD]/cos(180/CapSides)),d2=Pixel[ID],h=(Pixel[LENGTH] + Protrusion),$fn=CapSides);

	translate([0,0,(CapSize[LENGTH] – CapTube[OD]/(2*cos(180/8)))]) // hole for brass tube holding wire loom
	rotate([90,0,0]) rotate(180/8)
	PolyCyl(CapTube[OD],CapSize[OD],8);
	}

	}

	//———————-
	// Aperture for USB-to-serial adapter snout
	// These are all magic numbers, of course

	module USBPort() {

	translate([0,28.0])
	rotate([90,0,0])
	linear_extrude(height=28.0)
	polygon(points=[
	[0,0],
	[8.0,0],
	[8.0,4.0],
	// [4.0,4.0],
	[4.0,6.5],
	[-4.0,6.5],
	// [-4.0,4.0],
	[-8.0,4.0],
	[-8.0,0],
	]);
	}


	//———————-
	// Box for Leviton ceramic lamp base

	module LampBase() {

	Bottom = 5.0;
	Base = [3.75inch,4.5inch,25.0 + Bottom];
	Sides = 12*4;

	Stud = [0.107 * inch,15.0,Base[LENGTH]]; // 6-32 mounting screws, OD = ceramic boss size
	StudOC = 3.5 * inch;

	union() {
	difference() {
	rotate(180/Sides)
	cylinder(d=Base[OD],h=Base[LENGTH],$fn=Sides);
	rotate(180/Sides)
	translate([0,0,Bottom])
	cylinder(d=Base[ID],h=Base[LENGTH],$fn=Sides);
	translate([0,-Base[OD]/2,Bottom + 1.2]) // mount on double-sided foam tape
	rotate(0)
	USBPort();
	}
	for (i = [-1,1])
	translate([i*StudOC/2,0,0])
	rotate(180/8)
	difference() {
	cylinder(d=Stud[OD],h=Stud[LENGTH],$fn=8);
	translate([0,0,Bottom])
	PolyCyl(Stud[ID],(Stud[LENGTH] – (Bottom – Protrusion)),6);
	}
	}
	}


	//———————-
	// Build it

	if (Layout == "Cap") {
	if (Section)
	difference() {
	Cap();
	translate([-CapSize[OD],0,CapSize[LENGTH]])
	cube([2CapSize[OD],2CapSize[OD],3*CapSize[LENGTH]],center=true);
	}
	else
	Cap();
	}

	if (Layout == "LampBase")
	LampBase();

	if (Layout == "USBPort")
	USBPort();

	if (Layout == "Build") {
	Cap();
	Spigot();
	}

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2016-01-29

Darning Foot Modification

Mary wanted an opening in the front of the Darning Foot I didn’t modify the last time around, so I grabbed it in a machinist’s vise, grabbed that in the bench vise, and freehanded a Dremel slitting saw:

Darning Foot - saw-cut foot — Darning Foot – saw-cut foot

A bit of file work and it looks pretty good, although neither of us like the blurred-from-the-factory red lines:

Darning Foot - opened foot — Darning Foot – opened foot

This one retains the pin that lifts it as the needle rises, so it’s a hopping foot.

2016-01-28

Vacuum Tube LEDS: Ersatz Plate Cap

Lighting up that old voltage regulator tube conclusively demonstrated there’s no point in conjuring high voltages in this day & age. Nay, verily, merely lighting the filament of some tubes would require more power than seems reasonable.

A 1B3GT high-voltage regulator tube in the Box o’ Hollow State Electronics suggested a different approach:

With only a slight loss of historical accuracy, one could light the tube from the top with a Neopixel LED tucked into a similar cap, with power-and-data arriving through a suitably antiqued flying lead. That won’t work on tubes like that 1B3GT with an actual plate terminal at the top, nor with small Noval / miniature 7-pin tubes topped with an evacuation tip, but it’s fine for tubes like this 6SN7GTB:

Obviously, you want a relatively small cap atop the tube, lest the LED visually overwhelm the tube. Some preliminary tests (a.k.a. screwing around) showed that the mica spacer holding the dual triode elements together lights up wonderfully well and diffuses the glow throughout the tube.

Adafruit has relatively large round (and smaller roundish) Neopixel breakout boards, but I bought a bunch of knockoff Neopixels mounted on a 10 mm circular PCB from the usual eBay supplier:

Vacuum Tube LEDs - plate lead - connections — Vacuum Tube LEDs – plate lead – connections

Some PET braid tucked into a snippet of brass tubing dresses up a length of what might once have been audio cable. The braid wants to fray on the ends; confining it with heatstink or brass tubing is mandatory.

That’s a 1 µF ceramic SMD cap soldered between the +5 V and Gnd traces, atop a snippet of Kapton tape, in the hopes that it will help the 100 nF cap (on the other side of the board) tamp down the voltage dunks from PWM current pulses through that long thin wire. The leads come off toward the center to bend neatly upward into the cap.

Duplicating that old plate cap on the 1B3GT would be a fool’s errand, so I went full frontal Vader:

Vacuum Tube Lights - cap solid model - Overview — Vacuum Tube Lights – cap solid model – Overview

The interior recesses the LED far enough to allow for the tube’s top curvature, with a conical adapter to the smaller wiring channel that allows for more plastic supporting the brass tube:

Vacuum Tube Lights - cap solid model - section — Vacuum Tube Lights – cap solid model – section

A glob of epoxy inside the cap anchors the PCB and fuses all the loose ends / floppy wires / braid strands into a solid block that will never come apart again.

It should be printed (or primered and painted) with opaque black or maybe Bakelite Brown, but right now I have cyan PETG and want to see how it plays, soooo:

The cap floats in mid-air over a defunct Philips 60 W halogen bulb that I’ve been saving for just such an occasion. Obviously, you must epoxy / glue the cap in place for a permanent display.

The OpenSCAD source code as a Github gist:

	// Vacuum Tube LED Lights
	// Ed Nisley KE4ZNU January 2016

	Layout = "Cap"; // Show Build Cap Box Octal Noval Mini7

	Section = true; // cross-section the object

	//- 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
	// https://en.wikipedia.org/wiki/Tube_socket#Summary_of_Base_Details

	T_NAME = 0;
	T_NUMPINS = 1; // Socket specifications
	T_PINCIRC = 2;
	T_PINDIA = 3;
	T_SOCKDIA = 4;

	TubeBase = [
	["Mini7", 8, 9.53, 1.016, 19.0],
	["Octal", 8, 17.45, 2.36, 33.0],
	["Noval",10, 11.89, 1.1016,20.5],
	];

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

	Pixel = [7.0,10.0,3.0]; // ID = contact patch, OD = PCB dia, LENGTH = overall thickness

	//———————-
	// 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(r=(FixDia + HoleWindage)/2,
	h=Height,
	$fn=Sides);
	}

	//———————-
	// Tube cap

	CapTube = [4.0,3/16 * inch,10.0]; // brass tube for flying lead to cap LED

	CapSize = [Pixel[ID],(Pixel[OD] + 3.0),(CapTube[OD] + 2*Pixel[LENGTH])];

	CapSides = 6*4;

	module Cap() {

	difference() {
	union() {
	cylinder(d=CapSize[OD],h=(CapSize[LENGTH]),$fn=CapSides); // main cap body
	translate([0,0,CapSize[LENGTH]]) // rounded top
	scale([1.0,1.0,0.65])
	sphere(d=CapSize[OD]/cos(180/CapSides),$fn=CapSides); // cos() fixes slight undersize vs cylinder
	cylinder(d1=(CapSize[OD] + 23ThreadWidth),d2=CapSize[OD],h=1.5*Pixel[LENGTH],$fn=CapSides); // skirt
	}

	translate([0,0,-Protrusion]) // bore for wiring to LED
	PolyCyl(CapSize[ID],(CapSize[LENGTH] + 3*ThreadThick + Protrusion),CapSides);

	translate([0,0,-Protrusion]) // PCB recess with clearance for tube dome
	PolyCyl(Pixel[OD],(1.5*Pixel[LENGTH] + Protrusion),CapSides);

	translate([0,0,(1.5*Pixel[LENGTH] – Protrusion)]) // step + cone to retain PCB
	cylinder(d1=(Pixel[OD]/cos(180/CapSides)),d2=Pixel[ID],h=(Pixel[LENGTH] + Protrusion),$fn=CapSides);

	translate([0,0,(CapSize[LENGTH] – CapTube[OD]/(2*cos(180/8)))]) // hole for brass tube holding wire loom
	rotate([90,0,0]) rotate(180/8)
	PolyCyl(CapTube[OD],CapSize[OD],8);
	}

	}



	//———————-
	// Build it

	if (Layout == "Cap") {
	if (Section)
	difference() {
	Cap();
	translate([-CapSize[OD],0,CapSize[LENGTH]])
	cube([2CapSize[OD],2CapSize[OD],3*CapSize[LENGTH]],center=true);
	}
	else
	Cap();
	}

	if (Layout == "Build") {
	Cap();
	Spigot();
	}

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2016-01-26

Ham It Up Noise Source Enable Switch

Some rummaging produced a tiny DPDT switch that actually fit the holes intended for a pin header on the recently arrived Ham It Up board, at least after I amputated 2/3 of the poor thing’s legs:

Ham-It-Up - noise source switch - B — Ham-It-Up – noise source switch – B

The new SMA noise output jack sits in the front left, with the white “noise on” LED just left of the switch:

Ham-It-Up - noise source switch - A — Ham-It-Up – noise source switch – A

There’s no way to measure these things accurately, at least as far as I can tell, but the holes came out pretty close to where they should be. The new SMA connector lined up horizontally with the existing IF output jack and vertically with the measured / rounded-to-the-nearest-millimeter on-center distance:

Ham It Up - noise SMA drilling — Ham It Up – noise SMA drilling

The Enable switch doesn’t quite line up with the LED, so the holes will always look like I screwed up:

Ham-It-Up - noise source switch - case holes — Ham-It-Up – noise source switch – case holes

That’s OK, nobody will ever notice.

Now, to stack up enough adapters to get from the SMA on the Ham It Up board to the N connector on the spectrum analyzer …

2016-01-20