Tag: Improvements

Making the world a better place, one piece at a time

Astable Multivibrator: DSO150 vs. Fast Blinky

A bipolar transistor version of the astable multivibrator with a yellow Pirhana LED required absurdly large capacitors for a reasonable blink rate and, seeing as how I need a demo circuit for Show-n-Tells, it seemed a good candidate for a faster blink. I replaced a 100 µF cap with the 22 µF electrolytic cap from the other side, installed a 2 µF cap (which, judging from the lack of polarity indicators, may be a film cap) from the Squidwrench ~~junk heap~~ parts bin in its place, and hitched up the DSO150 because I brought it along:

DSO150 with fast LED blinky

Worked the first time and caught it in mid-blink! [grin]

The DSO150’s triggering remains a mystery, as it seems difficult to get a stable trace from a perfectly reasonable waveform. The scope didn’t trigger well on the astable’s original seconds-long pulses, perhaps due to a DC blocking cap in the triggering circuitry (whatever it may look like), but this waveform should be dead simple.

Having gained a visceral understanding of why MOSFET astables produce better battery life, this bipolar transistor design is just a milestone along the way.

2019-02-27
Juki TL-2010Q LED

For the record, Juki thinks this SMD LED provides enough light around the needle of Mary’s TL-2010Q sewing machine:

Juki TL-2010Q – OEM LED light

A detailed look at the active ingredient:

Juki TL-2010Q – OEM SMD LED

The 30 Ω resistor drops exactly 2.0 V, so the white LED runs at 67 mA.

We think it’s a glowworm, compared to the COB LED bar across the back of the arm:

Juki TL-2010Q COB LED – installed – rear view

I can do better than that, although not with juice from their 5 V power supply.

2019-02-24
Sewing Machine Light Bar Current

After more use and brightness tweaking, the COB light bars on the Juki TL-2010Q and Kenmore 158 now have 2.2 Ω ballast resistors setting the LED current to 370 mA and 300 mA, respectively:

Juki TL-2010Q COB LED – 2.2 ohm header

Changing from 2.0 Ω to 2.2 Ω produces a noticeable decrease in light, so 10% steps around 2 Ω seem to be about the right increment. The COB LED strips claim 6 W at 12 V = 500 mA nominal, so they’re running well under the spec.

Given that cheap 1% metal film resistor assortments use E6 or E12 value steps, at best, we may need two resistors in parallel for the next adjustments.

2019-02-21

SJCAM M20 Camera: Tour Easy Seat Mount

The general idea is to replace this:

M20 in waterproof case - Tour Easy seat — M20 in waterproof case – Tour Easy seat

With this:

SJCAM M20 Mount - Tour Easy side view — SJCAM M20 Mount – Tour Easy side view

Thereby solving two problems:

Pitifully small battery capacity
Wobbly camera support

The battery is an Anker PowerCore 13000 Power Bank plugged into the M20’s USB port. Given that SJCAM’s 1 A·h batteries barely lasted for a typical hour of riding, the 13 A·h PowerCore will definitely outlast my legs. The four blue dots just ahead of the strap around the battery show it’s fully charged and the blue light glowing through the case around the M20 indicates it’s turned on.

The solid model has four parts:

SJCAM M20 Mount - Fit layout — SJCAM M20 Mount – Fit layout

Which, as always, incorporates improvements based on the actual hardware on the bike.

A strap-and-buckle belt harvested from a defunct water pack holds the battery into the cradle and the cradle onto the rack, with a fuzzy velcro strip stuck to the bottom to prevent sliding:

SJCAM M20 Mount - Tour Easy rear view — SJCAM M20 Mount – Tour Easy rear view

The shell around the camera is basically a box minus the camera:

SJCAM M20 Mount - Show - shell — SJCAM M20 Mount – Show – shell

The shell builds as three separate slabs, with the center section having cutouts ahead of the camera’s projections to let it slide into place:

SJCAM M20 Mount - Show - shell sections — SJCAM M20 Mount – Show – shell sections

The new shell version is 30.5 mm thick, so a 40 mm screw will stick out maybe 5 mm beyond the nylon locknut. I trust the screws will get lost in the visual noise of the bike.

A peg sticking out behind the USB jack anchors the cable in place:

SJCAM M20 Mount - Show - shell sections - USB side — SJCAM M20 Mount – Show – shell sections – USB side

The front slab and center top have curves matching the M20 case:

SJCAM M20 Mount - Show - shell sections - button side — SJCAM M20 Mount – Show – shell sections – button side

The camera model has a tidy presentation option:

SJCAM M20 Mount - Show - M20 body — SJCAM M20 Mount – Show – M20 body

And an ugly option to knock the protruberances out of the shell:

SJCAM M20 Mount - Show - M20 body - knockouts — SJCAM M20 Mount – Show – M20 body – knockouts

The square-ish post on the base fits into an angled socket in the clamp around the seat rail:

SJCAM M20 Mount - Show - clamp — SJCAM M20 Mount – Show – clamp

The numbers correspond to the “Look Angle” of the socket pointing the camera toward overtaking traffic. The -20° in the first clamp shows a bit too much rack:

SJCAM M20 Mount - first ride - traffic - 2019-02-06 — SJCAM M20 Mount – first ride – traffic – 2019-02-06

It may not matter, though, as sometimes you want to remember what’s on the right:

SJCAM M20 Mount - first ride - 2019-02-06 — SJCAM M20 Mount – first ride – 2019-02-06

FWIW, the track veering off onto the grass came from a fat-tire bike a few days earlier. Most of the rail trail had cleared by the time we tried it, with some ice and snow in rock cuts and shaded areas.

Contrary to the first picture, I later remounted the camera under the seat rail with its top side downward. The M20 has a “rotate video” mode for exactly that situation, which I forgot to turn off in the fancy new mount, so I rotated the pix afterward.

A 3 mm screw extends upward through the hole in the socket to meet a threaded brass insert epoxied into the shell base, as shown in the uglified M20 model. Despite appearances, the hole is perpendicular to both the socket and the shell, so you can tweak the Look Angle without reprinting the shell.

All in all, the mount works well. We await better riding weather …

The OpenSCAD source code as a GitHub Gist:

	// SJCAM M20 Camera Mount for Tour Easy seat back rail
	// Ed Nisley – KE4ZNU
	// 2019-02

	/* [Layout Options] */

	Layout = "Fit"; // [Show,Fit,Build]

	Part = "Shell"; // [Cradle,Shell,Clamp,ShellSections,M20,Interposer,Battery,Buttons]

	LookAngle = [0,5,-25]; // camera angle, looking backwards


	/* [Extrusion Parameters] */

	ThreadWidth = 0.40;
	ThreadThick = 0.25;

	HoleWindage = 0.2;

	Protrusion = 0.1;

	//—–
	// Dimensions

	/* [Hidden] */

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

	ClampScrew = [5.0,10.0,50.0]; // ID=thread OD=washer LENGTH=total
	ClampInsert = [5.0,7.5,10.5]; // brass insert

	MountScrew = [3.0,7.0,23]; // ID=thread OD=washer LENGTH=tune to fit clamp arch
	MountInsert = [3.0,4.95,8.0]; // ID=screw OD, OD=knurl dia

	EmbossDepth = 2*ThreadThick + Protrusion; // recess depth + Protrusion beyond surface

	DebossHeight = EmbossDepth; // text height + Protrusion into part

	Projection = 10; // stick-out to punch through shell sides & suchlike

	SupportColor = "Yellow";
	FadeColor = "Green";
	FadeAlpha = 0.25;

	//—–
	// Useful routines

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

	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);
	}

	//—–
	// M20 Camera
	// Looks backwards from seat = usual right-hand coordinates work fine
	// X parallel to bike frame, Y parallel to seat strut, Z true vertical

	M20 = [24.5,40.5,54.0];

	M20tm = 4.0; // chord height at top of case
	M20tr = (pow(M20tm,2) + pow(M20.y,2)/4) / (2*M20tm); // … radius
	echo(str("Top radius: ",M20tr));

	M20TopSides = 334;
	echo(str(" … sides: ",M20TopSides));

	M20fm = 1.0; // chord height at front of case
	M20fr = (pow(M20fm,2) + pow(M20.y,2)/4) / (2*M20fm); // … radius
	echo(str("Front radius: ",M20fr));

	M20FrontSides = ceil(M20fr / M20tr * M20TopSides); // make arc sides match up
	echo(str(" … sides: ",M20FrontSides));

	Lens = [19.0,22.5,5.5]; // ID=optical element, OD=tube
	LensBezel = [23.0,24.5,2.5]; // ID=lens tube, OD=bezel
	LensOffset = [-M20fm,0,41.5]; // bottom of case to lens centerline

	LensCap = [Lens[OD],24.5,4.5]; // silicone lens cap

	Spkr = [0.75,M20.y,14.3]; // speaker recess below LCD

	Switch = [8.0,1.0,38.0]; // selection switches
	SwitchOffset = [9.0,0,0]; // from rear to center of switches

	Jack = [10.0,0.1,36.0]; // jack and MicroSD card access, slightly enlarged
	JackOffset = [10.0,0,30.0]; // rear, bottom to center of jack block

	USB = [JackOffset.x – Jack.x/2,20.0,10.0]; // strut under USB plug
	USBOffset = [0,0,33.5]; // bottom to center of jack

	SDCard = [2.0,0.1,12.0]; // SD Card slot
	SDOffset = [9.0,0,20.0]; // bottom, rear to center of slot

	Button = [8.5,10.5,M20tm]; // ID = button, OD = bezel
	ButtonOC = 18.0; // on-center Y separation, assume X centered

	Screen = [0.1,31,24]; // LCD on rear face
	ScreenOffset = [0,0,33];

	BarLEDs = [0.1 + M20fm,12.0,5.0]; // Bar LEDs on front face
	BarLEDsOffset = [-M20fm,0,12.5];

	PwrLED = [3.5,3.5,0.1 + M20tm]; // power LED on top
	PwrLEDOffset = [2.5,0,0];

	RearLEDs = [1.0,2.0,0.1]; // charge and power LED openings above LCD
	RearLEDsOffset = [0,13.0/2,M20tm + 3.0]; // .. from top center of case

	module Buttons(KO) {
	for (j = [-1,1])
	translate([0,j*ButtonOC/2,0]) {
	cylinder(d=Button[OD],h=Button[LENGTH],$fn=12);
	if (KO)
	translate([0,0,M20tm])
	cylinder(d1=Button[OD],d2=1.5*Button[OD],h=Button.z,$fn=12);
	}
	}

	module M20Shape(Knockout = false) {

	difference() {
	intersection() {
	translate([0,0,M20.z/2 – M20tr]) // top curve
	rotate([0,90,0]) rotate(180/M20TopSides)
	cylinder(r=M20tr,h=2*(M20.x + Protrusion),$fn=M20TopSides,center=true);
	translate([M20.x/2 – M20fr,0,0])
	rotate(180/M20FrontSides)
	cylinder(r=M20fr,h=2*M20.z,$fn=M20FrontSides,center=true);
	cube(M20,center=true);
	}
	translate([Spkr.x/2 – M20.x/2 – Protrusion,0,Spkr.z/2 – Protrusion/2 – M20.z/2])
	cube(Spkr + [Protrusion,2*Protrusion,Protrusion],center=true);
	}

	translate([M20.x/2,0,-M20.z/2] + LensOffset)
	rotate([0,90,0])
	cylinder(d=Lens[OD] + HoleWindage,h=(Knockout ? Projection : Lens[LENGTH]),$fn=443,center=false);

	translate([M20.x/2 + M20fm/2,0,-M20.z/2] + LensOffset) // lens bezel
	rotate([0,90,0])
	cylinder(d1=LensBezel[OD],d2=Lens[OD],h=LensBezel[LENGTH],$fn=443,center=false);

	translate([-M20.x/2 + SwitchOffset.x, // side switches
	-(Switch.y + M20.y – Protrusion)/2,
	0])
	cube(Switch + [0,Protrusion,0] + (Knockout ? [0,Projection,0] : [0,0,0]),center=true);

	if (Knockout)
	translate([(M20.x/2 – M20fm)/2,-M20.y/2,0]) // side switch slide-in clearance
	cube([M20.x/2 – M20fm,2*Switch.y,Switch.z],center=true);

	translate([-M20.x/2 + JackOffset.x,
	(Jack.y + M20.y – Protrusion)/2,
	JackOffset.z – M20.z/2])
	cube(Jack + [0,Protrusion,0] + (Knockout ? [0,Projection,0] : [0,0,0]),center=true);

	translate([0,0,M20.z/2 – M20tm]) // top control buttons
	Buttons(Knockout);

	if (Knockout)
	translate([(M20.x – M20fm)/4,0,M20.z/2 – M20tm + Button[LENGTH]/2]) // slide-in button clearance
	cube([(M20.x – M20fm)/2,ButtonOC + Button[OD],Button[LENGTH]],center=true);

	translate([-(M20.x + Screen.x – Protrusion)/2,0,-M20.z/2] + ScreenOffset)
	cube(Screen + [Protrusion,0,0] + (Knockout ? [Projection,0,0] : [0,0,0]),center=true);

	for (j = [-1,1])
	translate([-M20.x/2 + Protrusion,j*RearLEDsOffset.y,M20.z/2 – RearLEDsOffset.z])
	rotate([0,-90,0]) rotate(180/6)
	PolyCyl(RearLEDs[OD],Knockout ? Projection : RearLEDs[LENGTH],6);

	translate([M20.x/2 + BarLEDs.x/2,0,-M20.z/2] + BarLEDsOffset)
	cube(BarLEDs + (Knockout ? [Projection,0,0] : [0,0,0]),center=true);

	translate([0,0,M20.z/2 – M20tm] + PwrLEDOffset)
	rotate(180/8)
	PolyCyl(PwrLED[OD],(Knockout ? Projection : PwrLED[LENGTH]),8);

	if (Knockout) {
	translate([0,0,-M20.z/2])
	rotate([180,0,0]) { // mounting screw
	PolyCyl(MountScrew[ID],MountScrew[LENGTH],6);
	translate([0,0,MountScrew[LENGTH] – Protrusion])
	PolyCyl(MountScrew[OD],MountScrew[ID] + 4*ThreadThick,6); // SHCS head is about 1 ID long
	}

	translate([0,0,-(M20.z/2 + MountInsert[LENGTH] + 4*ThreadWidth – Protrusion)])
	PolyCyl(MountInsert[OD],MountInsert[LENGTH] + 4*ThreadWidth,6); // insert inside Interposer
	}

	}

	//—–
	// Shell
	// Wraps around camera

	NomWall = 3.0;

	ShellWall = [IntegerMultiple(NomWall,ThreadThick),
	IntegerMultiple(NomWall,ThreadWidth),
	IntegerMultiple(NomWall,ThreadWidth)];
	ShellRadius = ShellWall.x;
	ShellSides = 8;

	ShellOA = M20 + 2*ShellWall;
	echo(str("Shell OA: ",ShellOA));

	Interposer = [M20.x – M20fm,M20.x – M20fm,10.0]; // if you can't be smart, be square

	module Shell() {

	Screw = [3.0,6.75,30]; // ID=thread OD=washer LENGTH
	ScrewClear = 1.0; // additional washer clearance
	ScrewSides = 8;

	ScrewOC = M20 + [0,Screw[ID]/cos(180/ScrewSides),Screw[ID]/cos(180/ScrewSides)]; // use PolyCyl hole dia, ignore .x value

	difference() {
	union() {
	hull()
	for (i=[-1,1], j=[-1,1], k=[-1,1])
	translate([i(ShellOA.x – 2ShellRadius)/2,
	j(ShellOA.y – 2ShellRadius)/2,
	k(ShellOA.z – 2ShellRadius)/2])
	sphere(r=ShellRadius/cos(180/ShellSides),$fn=ShellSides); // fix low-poly approx radius

	for (j=[-1,1], k=[-1,1]) // screw bosses, full length
	translate([0,jScrewOC.y/2,kScrewOC.z/2])
	rotate([0,90,0]) rotate(180/ScrewSides)
	cylinder(d=Screw[OD] + ScrewClear,h=ShellOA.x,center=true,$fn=ScrewSides);

	translate([-(ShellOA.x – USB.x – ShellWall.x)/2, // USB plug support strut
	(M20.y + USB.y)/2 – ShellRadius,
	-M20.z/2] + USBOffset)
	hull()
	for (i=[-1,1], j=[-1,1], k=[-1,1])
	translate([i(USB.x + ShellWall.x – 2ShellRadius)/2,
	j(USB.y – 2ShellRadius)/2,
	k(USB.z – 2ShellRadius)/2])
	rotate(0*180/ShellSides) rotate([90,0,90])
	sphere(r=ShellRadius/cos(180/ShellSides),$fn=ShellSides);

	translate([-M20fm/2,0,-ShellOA.z/2 – Interposer.z + Protrusion/2])
	InterposerShape(Embiggen = false);
	}

	render(convexity=4) // remove camera shape from interior
	M20Shape(Knockout = true);

	for (j=[-1,1], k=[-1,1]) // screw bores
	translate([-ShellOA.x,jScrewOC.y/2,kScrewOC.z/2])
	rotate([0,90,0]) rotate(180/ScrewSides)
	PolyCyl(Screw[ID],2*ShellOA.x,ScrewSides);

	translate([ShellOA.x/2 – ThreadThick + Protrusion/2,0,-5]) // recess for legend
	cube([EmbossDepth,ShellOA.y – 12,7],center=true);

	translate([0,(M20.y + 1.5*SDCard.z)/2 + ThreadWidth,-M20.z/2 + SDOffset.z])
	resize([M20.x,0,0])
	sphere(d=1.5*SDCard.z,$fn=24);

	}

	translate([ShellOA.x/2 – DebossHeight,0,-5])
	rotate([90,0,90])
	linear_extrude(height=DebossHeight,convexity=20)
	text(text="KE4ZNU",size=5,spacing=1.20,font="Arial:style:Bold",halign="center",valign="center");


	// Totally ad-hoc support structures

	if (false)
	color(SupportColor) {
	for (j=[-1,1], k=[0,1])
	translate([-ShellOA.x/2 + Screw[LENGTH],jShellOA.y/2,kShellOA.z])
	rotate([0,90,0])
	SupportScrew(Dia=Screw[OD] + ScrewClear,Length=ShellOA.x – Screw[LENGTH],Num=ScrewSides);
	}
	}

	// Generate support structure for screw boss

	module SupportScrew(Dia,Length,Num = 6) {
	for (a=[0 : 360/Num : 360/2])
	rotate(a)
	translate([0,0,(Length + ThreadThick)/2])
	cube([Dia – 2ThreadWidth,2ThreadWidth,Length – ThreadThick],center=true);
	}

	// Generate interposer block
	// Origin at center bottom surface for E-Z rotation

	module InterposerShape(Embiggen = false) {

	translate([0,0,Interposer.z/2])
	if (Embiggen) {
	minkowski() {
	cube(Interposer,center=true);
	cube(HoleWindage,center=true);
	}
	}
	else
	cube(Interposer + [-Protrusion,0,Protrusion],center=true); // avoid slivers, merge with shell
	}

	// Cut shell sections for printing
	// "Front" = lens end, toward +X direction
	// origin centered on M20.xyz and ShellOA.xyz

	module ShellSection(Section="Front") {

	if (Section == "Front") // include front curve
	intersection() {
	Shell();
	translate([ShellOA.x – (M20fm + ShellWall.x),0,0])
	cube([ShellOA.x,2ShellOA.y,2ShellOA.z],center=true);
	}
	else if (Section == "Center") // exclude front curve for E-Z printing
	intersection() {
	Shell();
	translate([-M20fm/2,0,0])
	cube([M20.x – M20fm,2ShellOA.y,2ShellOA.z],center=true);
	}
	else if (Section == "Back") // flush with LCD on rear face
	intersection() {
	Shell();
	translate([-ShellOA.x + (ShellWall.x),0,0])
	cube([ShellOA.x,2ShellOA.y,2ShellOA.z],center=true);
	}

	}

	//—–
	// Clamp
	// Grips seat frame rail
	// Uses shell rounding values for tidiness
	// Adjust MountScrew[LENGTH] to put head more-or-less flush with clamp arch

	RailOD = 20.0; // slightly elliptical in bent section
	RailSides = 234;

	ClampOA = [60.0,40.0,ClampScrew[LENGTH]]; // set clamp size to avoid weird screw spacing
	echo(str("Clamp OA: ",ClampOA));

	ClampOffset = 0.0; // raise clamp to allow more room for mount

	ClampTop = ClampOA.z/2 + ClampOffset;
	InsertCap = 6*ThreadThick; // fill layers atop inserts

	Kerf = 2.0;

	module Clamp(Support = false) {

	RibThick = 2*ThreadWidth;
	NumRibs = IntegerMultiple(ceil(ClampOA.y / 4.0),2); // space ribs roughly 4 mm apart
	RibSpace = ClampOA.y / NumRibs;
	echo(str("Ribs: ",NumRibs," spaced: ",RibSpace));

	ClampScrewOC = IntegerMultiple(ClampOA.x – ClampScrew[OD] – 10*ThreadWidth,1.0);
	echo(str("ClampScrew OC: ",ClampScrewOC));

	difference() {
	hull()
	for (i=[-1,1], j=[-1,1], k=[-1,1])
	translate([i(ClampOA.x – 2ShellRadius)/2,
	j(ClampOA.y – 2ShellRadius)/2,
	k(ClampOA.z – 2ShellRadius)/2 + ClampOffset])
	sphere(r=ShellRadius/cos(180/ShellSides),$fn=ShellSides);

	cube([2ClampOA.x,2ClampOA.y,Kerf],center=true); // split across middle

	rotate([90,0,0]) // seat rail
	cylinder(d=RailOD,h=2*ClampOA.y,$fn=RailSides,center=true);

	for (i=[-1,1]) // clamp inserts
	translate([i*ClampScrewOC/2,0,0])
	rotate(180/6)
	PolyCyl(ClampInsert[OD],ClampTop – InsertCap,6);

	for (i=[-1,1]) // clamp screw clearance
	translate([i*ClampScrewOC/2,0,-(ClampOA.z/2 – ClampOffset) – InsertCap])
	rotate(180/6)
	PolyCyl(ClampScrew[ID],ClampOA.z,6);

	translate([0,0,ClampTop + 0.7*Interposer.z]) // mounting bolt hole
	rotate(LookAngle)
	translate([0,0,ShellOA.z/2]) {
	M20Shape(Knockout = true);
	translate([0,0,-ShellOA.z/2 – Interposer.z])
	InterposerShape(Embiggen = true);
	}

	translate([ClampOA.x/2 – (EmbossDepth – Protrusion)/2, // recess for LookAngle.z
	0,
	ClampOA.z/4 + ClampOffset])
	cube([EmbossDepth,17,8],center=true);

	translate([0.3*ClampOA.x, // recess for LookAngle.z
	-(ClampOA.y/2 – (EmbossDepth – Protrusion)/2),
	ClampOA.z/4 + ClampOffset])
	cube([10,EmbossDepth,8],center=true);

	translate([0,0,-ClampOA.z/2 + (EmbossDepth – Protrusion)/2]) // recess bottom legend
	cube([35,10,EmbossDepth],center=true);
	}

	translate([ClampOA.x/2 – DebossHeight,0,ClampOA.z/4 + ClampOffset]) // LookAngle.z legend
	rotate([90,0,90])
	linear_extrude(height=DebossHeight,convexity=20)
	text(text=str(LookAngle.z),size=6,spacing=1.20,
	font="Arial:style:Bold",halign="center",valign="center");

	translate([0.3*ClampOA.x,-ClampOA.y/2 + DebossHeight + Protrusion/2,ClampOA.z/4 + ClampOffset]) // LookAngle.y legend
	rotate([90,0,00])
	linear_extrude(height=DebossHeight,convexity=20)
	text(text=str(LookAngle.y),size=6,spacing=1.20,
	font="Arial:style:Bold",halign="center",valign="center");

	translate([0,0,-ClampOA.z/2])
	linear_extrude(height=DebossHeight,convexity=20)
	mirror([0,1,0])
	text(text="KE4ZNU",size=5,spacing=1.20,
	font="Arial:style:Bold",halign="center",valign="center");


	if (Support) {
	difference() {
	color(SupportColor)
	union() {
	for (j=[-NumRibs/2:NumRibs/2])
	translate([0,j*RibSpace,0])
	rotate([90,0,0])
	cylinder(d=RailOD – 2ThreadThick,h=RibThick,$fn=23*4,center=true);
	cube([RailOD – 4ThreadWidth,NumRibsRibSpace,Kerf + 2*ThreadThick],center=true);
	}
	cube([2ClampOA.x,2ClampOA.y,Kerf],center=true); // split across middle
	}
	}

	}


	//—–
	// Battery
	// Based on Anker PowerCore, simplified shapes
	// Includes port & button punchouts

	Battery = [97.5,80.0,22.5]; // X=length, Y includes rounded edges, Z = Y dia

	module BatteryShape() {

	USB = [Projection,38,10]; // clearance around USB output ports
	USBOffset = [0,25.5,0]; // from -Y edge to center of USB block

	ChargeBtn = [11.0 + 5.0,10,5.0 + 5.0]; // charge level check button, enlarged
	Btnc = ChargeBtn.z; // figure button recess into battery curve
	Btnr = Battery.z/2;
	Btnm = Btnr – sqrt(pow(Btnr,2) – pow(Btnc,2)/4);
	ChargeBtnOffset = [17.0,0,0]; // from +X edge to center, centered on Z

	BatterySides = 234;

	hull()
	for (j=[-1,1])
	translate([0,j*(Battery.y – Battery.z)/2,0])
	rotate([0,90,0])
	cylinder(d=Battery.z,h=Battery.x,$fn=BatterySides,center=true);
	translate([(Battery.x + USB.x)/2 – Protrusion,-Battery.y/2 + USBOffset.y,0])
	cube(USB,center=true);
	translate([Battery.x/2 – ChargeBtnOffset.x,Battery.y/2 + ChargeBtn.y/2 – 2*Btnm,0])
	cube(ChargeBtn,center=true);
	}

	//—–
	// Battery cradle

	RackWidth = 89.0; // flat width between rack rails

	CradleWall = [4.0,4.0,3.0]; // wall thickness
	CradleRadius = 2.0; // corner rounding

	CradlePad = 0.5; // cushion around battery
	BatteryBase = CradleWall.z + CradlePad; // actual bottom surface of battery

	CradleOA = [Battery.x + 2*CradleWall.x,
	min((Battery.y + 2*CradleWall.y),RackWidth),
	BatteryBase + Battery.z/3];
	echo(str("Cradle OA: ",CradleOA));

	module Cradle() {

	difference() {
	hull()
	for (i=[-1,1], j=[-1,1]) { // box with tidy rounded corners
	translate([i*(CradleOA.x/2 – CradleRadius),
	j*(CradleOA.y/2 – CradleRadius),
	1*(CradleOA.z – CradleRadius)])
	sphere(r=CradleRadius,$fn=6);
	translate([i*(CradleOA.x/2 – CradleRadius),
	j*(CradleOA.y/2 – CradleRadius),
	0*(CradleOA.z/2 – CradleRadius)])
	cylinder(r=CradleRadius,h=CradleOA.z/2,$fn=6);
	}

	translate([0,0,Battery.z/2 + BatteryBase]) // minus the battery
	minkowski(convexity=3) { // … slightly embiggened
	BatteryShape();
	cube(2*CradlePad,center=true);
	}

	if (false) // reveal insets for debug
	translate([0,0,-Protrusion])
	cube(CradleOA + [0,0,CradleOA.z],center=false);

	translate([0,0,CradleWall.z – ThreadThick + Protrusion/2]) // recess top legend
	cube([55,20,EmbossDepth],center=true);
	translate([0,0,(EmbossDepth – Protrusion)/2]) // recess bottom legend
	cube([70,15,EmbossDepth],center=true);
	}

	translate([0,4.0,CradleWall.z – DebossHeight – Protrusion])
	linear_extrude(height=DebossHeight,convexity=20)
	text(text="PowerCore",size=6,spacing=1.20,
	font="Arial:style:Bold",halign="center",valign="center");

	translate([0,-4.0,CradleWall.z – DebossHeight – Protrusion])
	linear_extrude(height=DebossHeight,convexity=20)
	text(text="13000",size=6,spacing=1.20,
	font="Arial:style:Bold",halign="center",valign="center");

	linear_extrude(height=DebossHeight,convexity=20)
	mirror([0,1,0])
	text(text="KE4ZNU",size=10,spacing=1.20,
	font="Arial:style:Bold",halign="center",valign="center");


	}


	//—–
	// Build things

	// Layouts for design & tweaking

	if (Layout == "Show")

	if (Part == "Battery")
	BatteryShape();

	else if (Part == "Buttons")
	Buttons();

	else if (Part == "Interposer")
	InterposerShape(Embiggen = false);

	else if (Part == "Shell")
	Shell();

	else if (Part == "M20")
	M20Shape(Knockout = false);

	else if (Part == "ShellSections") {
	translate([ShellOA.x,0,0])
	ShellSection(Section="Front");
	translate([0,0,0])
	ShellSection(Section="Center");
	translate([-ShellOA.x,0,0])
	ShellSection(Section="Back");
	}

	else if (Part == "Clamp") {
	Clamp(Support = false);
	color(FadeColor,FadeAlpha)
	rotate([90,0,0])
	cylinder(d=RailOD,h=2*ClampOA.y,$fn=RailSides,center=true);
	}

	else if (Part == "Cradle") {
	Cradle();
	translate([0,0,Battery.z/2 + CradleWall.z])
	color(FadeColor,FadeAlpha)
	BatteryShape();
	}

	// Build layouts for top-level parts

	if (Layout == "Build")

	if (Part == "Cradle")
	Cradle();

	else if (Part == "Clamp") {
	translate([0,0.7*ClampOA.y,0])
	difference() {
	translate([0,0,-Kerf/2])
	Clamp(Support = true);
	translate([0,0,-ClampOA.z])
	cube(2*ClampOA,center=true);
	}
	translate([0,-0.7*ClampOA.y,-0])
	difference() {
	translate([0,0,-Kerf/2])
	rotate([0,180,0])
	Clamp(Support = true);
	translate([0,0,-ClampOA.z])
	cube(2*ClampOA,center=true);
	}
	}

	else if (Part == "Shell") {
	translate([0,-1.2*ShellOA.y,ShellOA.x/2])
	rotate([0,90,180])
	ShellSection(Section="Front");
	translate([0,0,M20.x/2])
	rotate([0,-90,0])
	ShellSection(Section="Center");
	translate([0,1.4*ShellOA.y,ShellOA.x/2])
	rotate([0,-90,180])
	ShellSection(Section="Back");
	}

	// Ad-hoc arrangement to see how it all goes together

	if (Layout == "Fit") {
	rotate(180) {
	Cradle();
	translate([0,0,Battery.z/2 + CradleWall.z])
	color(FadeColor,FadeAlpha)
	BatteryShape();
	}
	translate([0,-100,0]) {
	Clamp();
	color(FadeColor,FadeAlpha)
	rotate([90,0,0])
	cylinder(d=RailOD,h=2*ClampOA.y,$fn=RailSides,center=true);
	}

	translate([0,-100,(ClampOA.z + ShellOA.z)/2 + Interposer.z])
	translate([0,0,-ShellOA.z/2 + Interposer.z])
	rotate(LookAngle)
	translate([0,0,ShellOA.z/2]) {
	Shell();
	color(FadeColor,FadeAlpha)
	M20Shape(Knockout = false);
	}
	}

view raw SJCAM M20 Mount.scad hosted with ❤ by GitHub

2019-02-20

“5 W” G4 COB LED Specsmanship

A bag of G4 COB LEDs arrived from halfway around the planet:

G4 COB LEDs – 15 and 18 LED modules

Those are “5 W” and “4 W” cool white modules, respectively, with another set of 4 W warm white looking pretty much the same. There’s no provision for heatsinking, which makes the wattage seem suspect; halogen G4 bulbs run around 20 W, for whatever that’s worth.

The silicone overlay becomes nearly transparent when seen through an ordinary desktop document scanner:

Circular 12V COB 18 LED panel

Highlighting the PCB copper pours shows 18 LEDs arranged in three series groups of six LEDs in parallel:

Circular 12V COB 18 LED panel – copper layout

The “smart IC” touted in the writeup turns out to be a bridge rectifier for AC or DC power:

G4 COB LED – 18 LED – components

The SMD resistors on all 15 modules measure 27.6 Ω, more or less, and seem randomly oriented face-up or face-down. I assume that one is face-down; maybe it’s just unlabeled on both sides.

Back of the envelope: there’s no way it will dissipate 5 W. The bridge drops 1.4 V = 2×0.7, the LEDs drop maybe 9 V, leaving the resistor with 1.6 V to pass all of 60 mA, so call it 700 mW.

Some measurements:

G4 COB LED measurements

With 12 VDC applied to the pins, the bridge drops 1.6 V, the LEDs 8.2 V, and the resistor 2.2 V, with 80 mA through the whole affair dissipating just under 1 W.

Huh.

Cranking the supply until the current hits 200 mA puts 15.7 V across the pins for a total dissipation of 3.1 W, burning 1.7 W in the LEDs and 1.1 W in the resistor.

Cranking the supply to 21.3 V drives 410 mA, dissipates just under 9 W total, produces a curl of rosin smoke from the PCB, and maybe delaminates the silicone around some of the LEDs.

OK, now I have a crash test dummy.

Given complete control over the application, I’ll strip everything off the PCB and bond it to a heatsink of some sort. With 6 LEDs in parallel, 120 mA (6 × 20 mA) total current might be reasonable and 200 mA (6 × 30 mA) probably won’t kill the things outright. Plus, I have spares.

An external 18 Ω resistor should suffice. Perhaps a pair of 6 Ω SMD resistors on the PCB, with fine-tuning through an external resistor. Call it 250 mW apiece: don’t use little bitty SMD resistors.

2019-02-19
YAGV Hackage
I’ve been using YAGV (Yet Another G-Code Viewer) as a quick command-line Guilloché visualizer, even though it’s really intended for 3D printing previews:

YAGV previewer.png

Oddly (for a command-line program), it (seems to) lack any obvious keyboard shortcut to bail out; none of my usual finger macros work.

A quick hack to the main /usr/share/yagv/yagv file makes Ctrl-Q bail out, thusly:
```
diff yagv /usr/share/yagv/yagv 
18a19
> import sys
364a366,367
> 		if symbol==pyglet.window.key.Q and modifiers & pyglet.window.key.MOD_CTRL:
> 			sys.exit()
```
I tacked the code onto an existing issue, but yagv may be a defunct project. Tweaking the source works for me.

The Ubuntu 18.04 LTS repo has what claims to be version 0.4, but the yagv GitHub repository (also claiming to be 0.4) includes code ignoring G-Code comments. Best to build the files from source (which, being Python, they already are), then add my Ctrl-Q hack, because my GCMC Guilloché generator adds plenty of comments.
2019-02-16
Engraving Guilloché Patterns

Flushed with success from engraving a hard drive platter for the 21HB5A tube, I bandsawed an acrylic square from a scrap sheet and unleashed the diamond drag bit on it:

Guilloche 540237875 – engraved at -0.50mm

That’s side-lit against a dark blue background. The long scratch and assorted dirt come from its protracted stay in the scrap pile.

If you look closely, you’ll see a few slightly wider loops, which came from a false start at Z=-0.1 mm.

Engraving at -0.5 mm looked pretty good:

Guilloche 540237875 – engraved at -0.50mm – detail

Despite an angular resolution of 2°, the curves came out entirely smooth enough. The gritty scratchiness resulted in a pile of chaff covering the engraved area; perhaps some oil or lube or whatever would help.

Rescaling the pattern to fit a CD platter worked fine, too:

Guilloche 540237875 – CD engraving

Polycarbonate seems to deform slightly, rather than scratch, leaving the final product with no chaff at all:

In this case, the doubled lines come from the reflection off the aluminized lower surface holding all the data.

That CD should be unreadable by now …

[Update: Welcome, Adafruit! More on Guilloché pattern generation and engraving them with the MPCNC. ]

2019-02-14