Author: Ed

Keyboard Tray Raising

Long ago and far away, I moved the keyboards off our desk surfaces to a more convenient location on a tray under the middle drawer. Mary’s desk recently gained a somewhat thinner keyboard with a thumbwheel volume control, so she wanted the tray moved up:

Keyboard Tray Relocation – in place

The supports on either side started out as 2×4 lumber with a slot cut (using the radial arm saw I no longer have) for the aluminum sheet:

Keyboard Tray Relocation – support view

For the record, a pair of screws hold each support to the drawer:

Keyboard Tray Relocation – support screw

Not elegant. Works fine. Good enough!

Tiny Bandsaw™ wasn’t designed for ripsawing lumber, but the same Proxxon 10/14 TPI blade I use for aluminum worked better than I expected to lop a 1-¼ inch strip from the wood slats:

Keyboard Tray Relocation – bandsaw fixture

That’s a reenactment based on a true story. The wood scraps clamped on the bandsaw table leave enough clearance for the 2×4 slide to freely, yet not enough for the blade to wander off track.

You can tell how long ago I built the original trays: nary a trace of 3D printing!

2020-09-21
Nutmeg Season

Well, it’s really zucchini bread season, with grated nutmeg among the spices (*):

Zucchini bread – minus QC sample

Having recently bought a very sharp grater, I hauled out a small vise to save my fingertips:

Nutmeg grating – mini-vise

The dark lunette comes from a previous clamping attempt; it takes a while to find the most secure pin arrangement.

Grate a flat:

Nutmeg grating – first flat

I’ve always enjoyed the surprisingly intricate patterns inside what looks like a bland nut.

Flip it over, flatten the other side, and grab it in an even smaller vise:

Nutmeg grating – flat clamping

In truth, that vise is intended for small cylinders, not flattened nuts, but I figured it’d suffice for light-duty use. Grate parallel to the vise screw, reclamp as needed, and it worked out reasonably well.

Eventually, you have a pile of powder and one cubic nutmeg:

Nutmeg grating – results

I’m sure there’s a way to grate the remaining cube, but I’m unwilling to shred my fingertips.

Tip the powder into a small jar and repeat as needed. Each nutmeg produces about 5 grams and I did three of the things this time.

Yummy!

(*) We omit the cloves and knock the sugar down by half. Your tastes will surely differ.

Update: Mary’s recipe!

2020-09-20
Long-gone Labeling

These appeared while I was extricating the 3-axis positioner from an old project:

Migrated felt-tip pen labels

I’m reasonably sure those labels started with blue ink from my all-time favorite Ultra-Fine-Point Sharpie markers on address labels covered with ordinary matte tape. Fourteen years on, the X, Y, and Drive legends are pretty much indistinguishable.

Nothing lasts …

2020-09-19

Bike Helmet Mirror: Ball Mount

Nine years ago, I didn’t know ~~how~~ enough to design a bike helmet mirror with a ball mount, but even an old dog can learn a new trick:

Helmet Mirror Ball Mount - on helmet — Helmet Mirror Ball Mount – on helmet

However, it’s worth noting my original, butt-ugly Az-El mounts lasted for all of those nine years, admittedly with adjustments along the way, which is far more than the commercial mounts making me unhappy enough to scratch my itch.

The mount adapts the split spherical clamp from the daytime running light:

Helmet Mirror Mount - Ball — Helmet Mirror Mount – Ball

Scaling it down for a 10 mm polypropylene ball around the base of the 30 mm inspection mirror’s shaft simplified everything:

Helmet Mirror Ball Mount - drilled ball test — Helmet Mirror Ball Mount – drilled ball test

I’m reasonably sure I couldn’t have bought 100 polypro balls for eight bucks a decade ago, but we’ll never know. Drilling the hole was a complete botch job, about which more later. The shaft came from a spare mirror mount I made up a while ago; a new shaft appears below.

The solid model, like Gaul, is in three parts divided:

Helmet Mirror Ball Mount - Slic3r — Helmet Mirror Ball Mount – Slic3r

The helmet plate (on the right) has a slight indent more-or-less matching the helmet curvature and gets a layer of good double-stick foam tape. The clamp base (on the left) has a pair of brass inserts epoxied into matching recesses below the M3 clearance holes:

Helmet Mirror Ball Mount - inserts — Helmet Mirror Ball Mount – inserts

A layer of epoxy then sticks the helmet plate in place, with the inserts providing positive alignment:

Helmet Mirror Ball Mount - plates — Helmet Mirror Ball Mount – plates

The clamp screws pull the inserts against the plastic in the clamp base, so they can’t pull out or through, and the plates give the epoxy enough bonding surface that (I’m pretty sure) they won’t ever come apart.

I turned down a 2 mm brass insert to fit inside the butt end of the mirror shaft and topped it off with a random screw harvested from a dead hard drive:

Helmet Mirror Ball Mount - assembled - rear view — Helmet Mirror Ball Mount – assembled – rear view

At the start, it wasn’t obvious the shaft would stay stuck in the ball, so I figured making it impossible to pull out would eliminate the need to find it by the side of the road. As things turned out, the clamp exerts enough force to ensure the shaft ain’t goin’ nowhere, so I’ll plug future shafts with epoxy.

The front side of the clamp looks downright sleek:

Helmet Mirror Ball Mount - assembled - front view — Helmet Mirror Ball Mount – assembled – front view

Well, how about “chunky”?

The weird gray-black highlights are optical effects from clear / natural PETG, rather than embedded grunge; it looks better in person. I should have used retina-burn orange or stylin’ black.

This mount is much smaller than the old one and should, in the event of a crash, not cause much injury. Based on how the running light clamp fractures, I expect the clamp will simply tear out of the base on impact. In the last decade, neither of us has crashed, so I don’t know what the old mount would do.

The clamp is 7 mm thick (front-to-back), set by the M3 washer diameter, with 1.5 mm of ball sticking out on each side. The model has a kerf one thread high (0.25 mm) between the pieces to add clamping force and, with the screws tightened down, moving the ball requires a disturbingly large effort. I added a touch of rosin and that ball straight-up won’t move, which probably means the shaft will bend upon droppage; I have several spare mirrors in stock.

On the other paw, the ball turns smoothly in the clamp and it’s easy to position the shaft as needed: much better than the old Az-El mount!

The inspection mirror hangs from a double ball joint which arrives with a crappy screw + nut. I epoxied the old mirror mount nut in place, but this time around I drilled the plates for a 3 mm stainless SHCS, used a wave washer for a bit of flexible force, and topped it off with a nyloc nut:

Helmet Mirror Ball Mount - mirror joint — Helmet Mirror Ball Mount – mirror joint

I’m unhappy with how it looks and don’t like how the washer hangs in free space between those bumps, so I may eventually turn little brass fittings to even things out. It’s either that or more epoxy.

So far, though, it’s working pretty well and both units meet customer requirements.

The OpenSCAD source code as a GitHub Gist:

	// Bike helmet mirror mount – ball joint
	// Ed Nisley KE4ZNU 2020-09

	/* [Layout options] */

	Layout = "Build"; // [Build, Show, Plate, Base, Clamp]

	//– Extrusion parameters

	// Extrusion parameters

	/* [Hidden] */

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

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

	Protrusion = 0.1; // make holes end cleanly

	inch = 25.4;

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

	//- Basic dimensions

	MountDia = 30.0; // footprint on helmet

	BallDia = 10.0;
	BallRad = BallDia / 2;

	WallThick = IntegerMultiple(2.0,ThreadWidth);
	FloorThick = IntegerMultiple(2.0,ThreadThick);

	CornerRound = 2.0;

	Insert = [3.0,4.0,4.0]; // threaded brass insert
	Screw = [3.0,5.5,25.0]; // clamp screw
	Washer = [3.7,7.0,0.7]; // washer

	ShowGap = 2.0;
	BuildGap = 5.0;

	//– Helmet Interface Plate

	ScrewOC = BallDia + 2*WallThick + Screw[ID];
	echo(str("Screw OC: ",ScrewOC));

	Clamp = [ceil(Washer[OD]), // barely holds washer under screw
	ScrewOC + Washer[OD], // minimal clearance for washer
	BallDia +2*FloorThick // screw fits through insert
	];

	Kerf = ThreadThick;

	echo(str("Clamp: ",Clamp));

	HelmetCX = 60.0; // empirical helmet side curve
	HelmetMX = 3.0;
	HelmetRX = (pow(HelmetMX,2) + pow(HelmetCX,2)/4)/(2*HelmetMX);

	HelmetPlateC = MountDia;
	HelmetPlateTheta = atan(HelmetPlateC/HelmetRX);
	HelmetPlateM = 2HelmetRXpow(sin(HelmetPlateTheta/4),2);

	echo(str("Plate indent: ",HelmetPlateM));

	HelmetPlateThick = max(FloorThick,0.6*Insert[LENGTH]) + HelmetPlateM;

	echo(str("Screw length: ",Clamp.z + Insert[LENGTH]));

	MountSides = 234;

	//———————-
	// 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);
	}


	//———————-
	// Clamp frame around ball

	module ClampFrame() {

	difference() {
	union() {
	hull()
	for (i=[-1,1], j=[-1,1]) {
	translate([i(Clamp.x/2 – CornerRound),j(Clamp.y/2 – CornerRound),Clamp.z/2 – CornerRound])
	sphere(r=CornerRound,$fn=24);
	translate([i(Clamp.x/2 – CornerRound),j(Clamp.y/2 – CornerRound),-Clamp.z/2])
	cylinder(r=CornerRound,$fn=24);
	}
	for (j=[-1,1])
	translate([0,j*ScrewOC/2,0])
	rotate(180/12)
	cylinder(d=Washer[OD],h=Clamp.z/2,$fn=12);

	}

	sphere(d=BallDia + HoleWindage,$fn=48);

	cube([2MountDia,2MountDia,Kerf],center=true);

	for (j=[-1,1])
	translate([0,j*ScrewOC/2,-Screw[LENGTH]])
	rotate(180/6)
	PolyCyl(Screw[ID],2*Screw[LENGTH],6);
	}
	}

	module ClampSelect(Section) {
	XlateZ = (Section == "Top") ? Clamp.z/2 :
	(Section == "Bottom") ? -Clamp.z/2 :
	0;
	intersection(convexity=5) {
	ClampFrame();
	translate([0,0,XlateZ])
	cube([2Clamp.x,2Clamp.y,Clamp.z + 2*Protrusion],center=true);

	}
	}

	//———————-
	// Concave plate fitting helmet shell

	module HelmetPlate() {

	render()
	difference() {
	cylinder(d=MountDia,h=HelmetPlateThick,$fn=MountSides);

	translate([0,0,HelmetPlateThick – HelmetPlateM + HelmetRX])
	sphere(r=HelmetRX,$fn=128);

	for (j=[-1,1])
	translate([0,j*ScrewOC/2,-Protrusion]) {
	PolyCyl(Insert[OD],0.6*Insert[LENGTH] + Protrusion,6);
	PolyCyl(Screw[ID],2*HelmetPlateThick,6);
	}
	}

	}

	//———————-
	// Base of clamp ring

	module MountBase() {

	difference() {
	union() {
	cylinder(d=MountDia,h=FloorThick,$fn=MountSides);
	translate([0,0,FloorThick + Clamp.z/2])
	ClampSelect("Bottom");
	}

	for (j=[-1,1])
	translate([0,j*ScrewOC/2,-Protrusion])
	rotate(180/6)
	PolyCyl(Insert[OD],0.6*Insert[LENGTH] + Protrusion,6);
	}
	}


	//———————-
	// Lash it together


	if (Layout == "Plate") {
	HelmetPlate();
	}

	if (Layout == "Base") {
	MountBase();
	}

	if (Layout == "Clamp") {
	ClampFrame();
	}



	if (Layout == "Show") {
	rotate([180,0,0])
	HelmetPlate();
	translate([0,0,ShowGap]) {
	MountBase();
	color("Ivory",0.3)
	translate([0,0,Clamp.z/2 + FloorThick + ShowGap/2])
	sphere(d=BallDia);
	translate([0,0,Clamp.z/2 + FloorThick + ShowGap])
	ClampSelect("Top");
	}
	}


	if (Layout == "Build") {
	translate([MountDia/2 + BuildGap,0,0])
	HelmetPlate();
	translate([-(MountDia/2 + BuildGap),0,0])
	MountBase();
	translate([0,MountDia/2 + BuildGap,Clamp.z/2])
	rotate([0,180,0])
	rotate(90)
	ClampSelect("Top");
	}

view raw Helmet Mirror Mount – Ball.scad hosted with ❤ by GitHub

The original doodles include a bit of dress-up fairing that didn’t make the cut:

Helmet Mirror Ball Mount - doodles — Helmet Mirror Ball Mount – doodles

2020-09-18

Discrete LM3909: Blue LED Radome

Dropping a simplified ping-pong ball radome for a Piranha RGB LED atop a discrete LM3909 on the AA alkaline cell holder:

Discrete LM3909 Radome - AA alkaline — Discrete LM3909 Radome – AA alkaline

The solid model has screw holes for the lid and the revised LED spider:

Astable Multivibrator - Alkaline AA Base - radome - solid model — Astable Multivibrator – Alkaline AA Base – radome – solid model

The RGB LED needs only two wires, as the LM3909 circuit can blink only one LED. I tried all three colors, but only blue and green justify the LM3909 hairball; red can get along with the astable circuit.

The LED wires connect across a 1 MΩ resistor serving as a mechanical strut between the 9.1 kΩ resistor on the left and the 10 Ω ballast resistor on the right.

Fresh alkaline cells at 3.0 V put 3.3 V across the blue LED with a 37 mA peak current. Older cells at 2.3 V produce 2.9 V at 15 mA. Dead cells at 1.9 V still fire the LED with 2.7 V at 4.2 mA, although the flash is barely visible in ordinary room light.

The lovely blue ball looks better in person!

The OpenSCAD source code as a GitHub Gist:

	// Astable Multivibrator
	// Holder for Alkaline cells
	// Ed Nisley KE4ZNU August 2020
	// 2020-09 add LED radome

	/* [Layout options] */

	Layout = "Build"; // [Build,Show,Lid,Spider]

	/* [Hidden] */

	CellName = "AA"; // [AA] — does not work with anything else
	NumCells = 2; // [2] — likewise

	Struts = -1; // [0:None, -1:Dual, 1:Quad] — Quad is dead

	// Extrusion parameters

	/* [Hidden] */

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

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

	Protrusion = 0.1; // make holes end cleanly

	inch = 25.4;

	//- Basic dimensions

	WallThick = IntegerMultiple(3.0,ThreadWidth);
	CornerRadius = WallThick/2;

	FloorThick = IntegerMultiple(3.0,ThreadThick);

	TopThick = IntegerMultiple(2.0,ThreadThick);

	WireOD = 1.5; // battery & LED wiring
	WireOC = 4;

	Gap = 5.0;

	// Cylindrical cell sizes
	// https://en.wikipedia.org/wiki/List_of_battery_sizes#Cylindrical_batteries

	CELL_NAME = 0;
	CELL_OD = 1;
	CELL_OAL = 2;

	// FIXME search() needs special-casing to properly find AAA and AAAA
	// Which is why CellName is limited to AA

	CellData = [
	["AAAA",8.3,42.5],
	["AAA",10.5,44.5],
	["AA",14.5,50.5],
	["C",26.2,50],
	["D",34.2,61.5],
	["A23",10.3,28.5],
	["CR123A",17.0,34.5],
	["18650",18.8,65.2], // bare 18650 with button end
	["18650Prot",19.0,70.0], // protected 18650 = 19670 plus a bit
	];

	CellIndex = search([CellName],CellData,1,0)[0];
	echo(str("Cell index: ",CellIndex," = ",CellData[CellIndex][CELL_NAME]));

	//- Contact dimensions

	CONTACT_NAME = 0;
	CONTACT_WIDE = 1;
	CONTACT_HIGH = 2;
	CONTACT_THICK = 3; // plate thickness
	CONTACT_TIP = 4; // tip to rear face
	CONTACT_TAB = 5; // solder tab width

	ContactData = [
	["AA+",12.2,12.2,0.3,1.7,3.5], // pos bump
	["AA-",12.2,12.2,0.3,5.0,3.5], // half-compressed neg spring
	["AA+-",28.2,12.2,0.3,5.0,0], // pos-neg bridge

	["Li+",18.5,16.0,0.3,2.8,5.5],
	["Li-",18.5,16.0,0.3,6.0,5.5],
	];

	function ConDat(name,dim) = ContactData[search([name],ContactData,1,0)[0]][dim];

	ContactRecess = 2*ConDat(str(CellName,"+"),CONTACT_THICK);
	ContactOC = CellData[CellIndex][CELL_OD];

	WireBay = 6.0; // room for wiring to contacts

	//- Wire struts

	StrutDia = 1.6; // AWG 14 = 1.6 mm
	StrutSides = 3*4;

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

	StrutBase = [StrutDia,StrutDia + 25ThreadWidth, // ID = wire, OD = buildable
	FloorThick + CellData[CellIndex][CELL_OD]]; // LENGTH = base is flush with cell top

	//- Holder dimensions

	BatterySize = [CellData[CellIndex][CELL_OAL] + // cell
	ConDat(str(CellName,"+"),CONTACT_TIP) + // pos contact
	ConDat(str(CellName,"-"),CONTACT_TIP) – // neg contact
	2*ContactRecess, // sink into wall
	NumCells*CellData[CellIndex][CELL_OD],
	CellData[CellIndex][CELL_OD]
	];

	echo(str("Battery space: ",BatterySize));

	CaseSize = [3*WallThick + // end walls + wiring partition
	BatterySize.x + // cell
	WireBay, // wiring bay
	2*WallThick + BatterySize.y,
	FloorThick + BatterySize.z
	];

	BatteryOffset = (CaseSize.x – (2*WallThick +
	CellData[CellIndex][CELL_OAL] +
	ConDat(str(CellName,"-"),CONTACT_TIP))
	) /2 ;

	ThumbRadius = 0.75 * CaseSize.z;


	StrutOC = [IntegerLessMultiple(CaseSize.x – 2CornerRadius -2StrutBase[OD],5.0),
	IntegerMultiple(CaseSize.y + StrutBase[OD],5.0)];

	StrutAngle = atan(StrutOC.y/StrutOC.x);

	echo(str("Strut OC: ",StrutOC));

	LidSize = [2*WallThick + WireBay + ConDat(str(CellName,"+"),CONTACT_THICK), CaseSize.y, FloorThick/2];

	LidScrew = [2.0,3.8,7.0]; // M2 pan head screw (LENGTH = threaded)
	LidScrewOC = CaseSize.y/2 – CornerRadius – LidScrew[OD]; // allow space around screw head

	//- Piranha LEDs

	PiranhaBody = [8.0,8.0,8.0]; // Z = heatsink fins + body + lens height

	PiranhaPin = 0.0; // trimmed pin length beyond heatsink
	PiranhaPinsOC = [5.0,5.0]; // pin XY distance

	PiranhaRecess = PiranhaBody.z + PiranhaPin/2; // minimum LED recess depth

	BallOD = 40.0; // radome sphere
	BallSides = 4*StrutSides; // nice smoothness

	BallPillar = [norm([PiranhaBody.x,PiranhaBody.y]), // ID
	norm([PiranhaBody.x,PiranhaBody.y]) + 3*WallThick, // OD
	StrutBase[OD] + PiranhaBody.z]; // height to base of chord
	echo(str("Pillar OD: ",BallPillar[OD]));

	BallChordM = BallOD/2 – sqrt(pow(BallOD/2,2) – (pow(BallPillar[OD],2))/4);
	echo(str("Ball chord depth: ",BallChordM));


	//———————-
	// 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);
	}

	// Spider for single LED atop struts, with the ball

	module DualSpider() {

	difference() {
	union() {
	for (j=[-1,1]) {
	translate([0,j*StrutOC.y/2,StrutBase[OD]/2])
	rotate(180/StrutSides)
	sphere(d=StrutBase[OD]/cos(180/StrutSides),$fn=StrutSides);
	translate([0,j*StrutOC.y/2,0])
	rotate(180/StrutSides)
	cylinder(d=StrutBase[OD],h=StrutBase[OD]/2,$fn=StrutSides);
	}

	translate([0,0,StrutBase[OD]/4]) // connecting bars
	cube([StrutBase[OD]*cos(180/StrutSides),StrutOC.y,StrutBase[OD]/2],center=true);

	cylinder(d=BallPillar[OD],h=BallPillar[LENGTH],$fn=BallSides);
	}

	for (j=[-1,1]) // strut wires
	translate([0,j*StrutOC.y/2,-Protrusion])
	PolyCyl(StrutBase[ID],StrutBase[OD]/2,6);

	for (n=[-1,1]) // LED wiring
	rotate(n*90)
	translate([StrutOC.x/3,0,-Protrusion])
	PolyCyl(StrutBase[ID],StrutBase[OD],6);

	translate([0,0,BallOD/2 + BallPillar[LENGTH] – BallChordM]) // ball inset
	sphere(d=BallOD);

	translate([0,0,BallPillar.z – PiranhaRecess + BallPillar.z/2]) // LED inset
	cube(PiranhaBody + [HoleWindage,HoleWindage,BallPillar.z],center=true); // XY clearance

	translate([0,0,StrutBase[OD]/2 + WireOD/2 + 0*Protrusion]) // wire channels
	cube([WireOD,BallPillar[OD] + 2*WallThick,WireOD],center=true);

	}
	}

	//– Overall case with origin at battery center

	module Case() {

	union() {

	difference() {
	union() {
	hull()
	for (i=[-1,1], j=[-1,1])
	translate([i*(CaseSize.x/2 – CornerRadius),
	j*(CaseSize.y/2 – CornerRadius),
	0])
	cylinder(r=CornerRadius/cos(180/8),h=CaseSize.z,$fn=8); // cos() fixes undersize spheres!

	if (Struts)
	for (i = (Struts == 1) ? [-1,1] : -1) { // strut bases
	hull()
	for (j=[-1,1])
	translate([iStrutOC.x/2,jStrutOC.y/2,0])
	rotate(180/StrutSides)
	cylinder(d=StrutBase[OD],h=StrutBase[LENGTH],$fn=StrutSides);

	translate([i*StrutOC.x/2,0,StrutBase[LENGTH]/2])
	cube([2*StrutBase[OD],StrutOC.y,StrutBase[LENGTH]],center=true); // blocks for fairing

	for (j=[-1,1]) // hemisphere caps
	translate([i*StrutOC.x/2,
	j*StrutOC.y/2,
	StrutBase[LENGTH]])
	rotate(180/StrutSides)
	sphere(d=StrutBase[OD]/cos(180/StrutSides),$fn=StrutSides);

	}
	}

	translate([BatteryOffset,0,BatterySize.z/2 + FloorThick]) // cells
	cube(BatterySize + [0,0,Protrusion],center=true);

	translate([BatterySize.x/2 + BatteryOffset + ContactRecess/2 – Protrusion/2, // contacts
	0,
	BatterySize.z/2 + FloorThick])
	cube([ContactRecess + Protrusion,
	ConDat(str(CellName,"+-"),CONTACT_WIDE),
	ConDat(str(CellName,"+-"),CONTACT_HIGH)
	],center=true);

	translate([-(BatterySize.x/2 – BatteryOffset + ContactRecess/2 – Protrusion/2),
	ContactOC/2,
	BatterySize.z/2 + FloorThick])
	cube([ContactRecess + Protrusion,
	ConDat(str(CellName,"+"),CONTACT_WIDE),
	ConDat(str(CellName,"+"),CONTACT_HIGH)
	],center=true);

	translate([-(BatterySize.x/2 – BatteryOffset + ContactRecess/2 – Protrusion/2),
	-ContactOC/2,
	BatterySize.z/2 + FloorThick])
	cube([ContactRecess + Protrusion,
	ConDat(str(CellName,"-"),CONTACT_WIDE),
	ConDat(str(CellName,"-"),CONTACT_HIGH)
	],center=true);

	translate([-CaseSize.x/2 + WireBay/2 + WallThick, // wire bay with screw bosses
	0,
	BatterySize.z/2 + FloorThick + Protrusion/2])
	cube([WireBay,
	2LidScrewOC – LidScrew[ID] – 24*ThreadWidth,
	BatterySize.z + Protrusion
	],center=true);

	for (j=[-1,1]) // screw holes
	translate([-CaseSize.x/2 + WireBay/2 + WallThick,
	j*LidScrewOC,
	CaseSize.z – LidScrew[LENGTH] + Protrusion])
	PolyCyl(LidScrew[ID],LidScrew[LENGTH],6);


	for (j=[-1,1])
	translate([-(BatterySize.x/2 – BatteryOffset + WallThick/2), // contact tabs
	j*ContactOC/2,
	BatterySize.z + FloorThick – Protrusion])
	cube([2*WallThick,
	ConDat(str(CellName,"+"),CONTACT_TAB),
	(BatterySize.z – ConDat(str(CellName,"+"),CONTACT_HIGH))
	],center=true);

	if (false)
	translate([0,0,CaseSize.z]) // finger cutout
	rotate([90,00,0])
	cylinder(r=ThumbRadius,h=2*CaseSize.y,center=true,$fn=22);

	translate([0,0,ThreadThick – Protrusion]) // recess around name
	cube([0.6CaseSize.x,8,2ThreadThick],center=true);

	if (Struts)
	for (i2 = (Struts == 1) ? [-1,1] : -1) { // strut wire holes and fairing
	for (j=[-1,1])
	translate([i2StrutOC.x/2,jStrutOC.y/2,FloorThick])
	rotate(180/StrutSides)
	PolyCyl(StrutBase[ID],2*StrutBase[LENGTH],StrutSides);

	for (i=[-1,1], j=[-1,1]) // fairing cutaways
	translate([iStrutBase[OD] + (i2StrutOC.x/2),
	j*StrutOC.y/2,
	-Protrusion])
	rotate(180/StrutSides)
	PolyCyl(StrutBase[OD],StrutBase[LENGTH] + 2*Protrusion,StrutSides);
	}

	}

	translate([0,0,0])
	linear_extrude(height=2*ThreadThick + Protrusion,convexity=10)
	mirror([0,1,0])
	text(text="KE4ZNU",size=6,spacing=1.20,font="Arial:style:Bold",halign="center",valign="center");

	}
	}


	module Lid() {

	difference() {
	hull()
	for (i=[-1,1], j=[-1,1], k=[-1,1])
	translate([i*(LidSize.x/2 – CornerRadius),
	j*(LidSize.y/2 – CornerRadius),
	k*(LidSize.z – CornerRadius)]) // double thickness for flat bottom
	sphere(r=CornerRadius/cos(180/8),$fn=8);

	translate([0,0,-LidSize.z]) // remove bottom
	cube([(LidSize.x + 2Protrusion),(LidSize.y + 2Protrusion),2*LidSize.z],center=true);

	for (j=[-1,1]) // wire holes
	translate([0,j*WireOC,-Protrusion])
	PolyCyl(WireOD,2*LidSize.z,6);

	for (j=[-1,1])
	translate([0,j*LidScrewOC,-Protrusion])
	PolyCyl(LidScrew[ID],2*LidSize.z,6);

	}
	}


	//——————-
	// Build it!

	if (Layout == "Case")
	Case();

	if (Layout == "Lid")
	Lid();

	if (Layout == "Spider")
	if (Struts == -1)
	DualSpider();
	else
	cube(10,center=true);

	if (Layout == "Build") {
	rotate(90)
	Case();
	translate([0,-(CaseSize.x/2 + LidSize.x/2 + Gap),0])
	rotate(90)
	Lid();
	if (Struts == -1)
	translate([CaseSize.x/2,0,0])
	DualSpider();
	}

	if (Layout == "Show") {
	Case();
	translate([-CaseSize.x/2 + LidSize.x/2,0,(CaseSize.z + Gap)])
	Lid();
	}

view raw Astable Multivibrator – Alkaline Batteries – radome.scad hosted with ❤ by GitHub

2020-09-17

Discrete LM3909: Blue LED Waveforms
The circuitry and instrumentation is essentially the same discrete LM3909 as before:

LM3909 – blue – test setup

With a few minor tweaks:
- Blue LED, forward voltage 2.56 to 2.97 V
- 24 Ω R1
- One Q2 current mirror transistor driving Q3
With a pair of fresh AA alkaline cells producing 3.1 V (not the NiMH Duracells you see in the picture), the blue LED blinks brightly.

The 610 mV peak voltage across R1 shows the LED starts at 25.4 mA:

LM3909 blue – 3.1 V – R1 24 ohm

The capacitor reaches 1 V, then goes about 150 mV into reverse charge during the flash (note the different horizontal scales):

LM3909 blue – 3.1 V – C1 V

The Darlington version of Q1 seems to do a decent job of keeping the cap out of reverse charge. A Shottky diode would add a few hundred mV, but I doubt there’s anything nasty going on inside the cap as it stands.

The blue LED has a forward drop of 2.97 V at 20 mA, so I’m surprised the voltage across it hits 3.1 V at 25 mA:

LM3909 blue – 3.1 V – LED V

Very little of the voltage appears across Q3, the driver transistor:

LM3909 blue – 3.1 V – Q3 coll

With a pair of nearly dead alkaline cells for a 2.0 V supply, the LED current peak drops to 4.6 mA:

LM3909 blue – 2.0 V – R1 24 ohm

The LED lights brightly, then fades away exactly like you’d expect from that waveform.

The cap still charges to about 1 V and stays well above 0 V during the (much longer) flash:

LM3909 blue – 2.0 V – C1 voltage

The voltage across the LED now reaches only 2.7 V, which is substantially higher than the 2.0 V battery supply and exactly why the LM3909 existed:

LM3909 blue – 2.0 V – LED voltage

Q3 continues to saturate, although you can see the effect of the decreased base drive during the flash:

LM3909 blue – 2.0 V – Q3 coll

The blue LED won’t light at 1.3 V, but still gives out a weak flash at 1.7 V, so I’d say the tweaked LM3909 circuitry works reasonably well.
2020-09-16
Monthly Image: Mantis Mating

The Praying Mantis in the Butterfly Bush is definitely female:

Praying Mantis Mating – front

I’d noticed her distended abdomen a day or two earlier, when it was highlighted in the sun and pulsing slowly. The indentations under the male’s legs shows the surface is definitely softer than the hard chitin of most insect armor:

Praying Mantis Mating – rear

The tip of the male’s abdomen twisted around to make contact, but I have no idea what all the little doodads common to both of them back there were doing.

The whole process started in mid-afternoon, they were still locked together six hours later, and the male was gone in the morning. The stories about female mantises eating the males seem greatly exaggerated, but she did manage to catch and eat a moth while otherwise engaged.

We’ll keep watch for ootheca on the tall grasses again, although we’ll never know the rest of their story.

2020-09-15