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.

Category: Machine Shop

Mechanical widgetry

AD8310 Log Amp Module: Sidesaddle Bracket

This little bracket attaches to a proto board holder, with holes for M3 inserts to mount the AD8310 log amp module:

PCB Side Bracket - 80x120 — PCB Side Bracket – 80×120

Thusly:

AD8310 module bracket on proto board holder - component side — AD8310 module bracket on proto board holder – component side

The OLED display looks a bit faded, which seems to be an interaction between matrix refresh and camera shutter: looks just fine in person!

Not much to see from the other side:

AD8310 module bracket on proto board holder - solder side — AD8310 module bracket on proto board holder – solder side

I should have included an offset to slide it a bit forward; then I could mount it on the other end with clearance for the Nano’s USB port. Maybe next time.

The OpenSCAD source code as a GitHub Gist:

	// Test support frame for proto boards
	// Ed Nisley KE4ZNU – Jan 2017
	// June 2017 – Add side-mount bracket

	Layout = "Bracket";

	ClampFlange = true;

	Channel = false;

	//- Extrusion parameters – must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

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

	Protrusion = 0.1;

	HoleWindage = 0.2;

	//- Screw sizes

	inch = 25.4;

	Tap4_40 = 0.089 * inch;
	Clear4_40 = 0.110 * inch;
	Head4_40 = 0.211 * inch;
	Head4_40Thick = 0.065 * inch;
	Nut4_40Dia = 0.228 * inch;
	Nut4_40Thick = 0.086 * inch;
	Washer4_40OD = 0.270 * inch;
	Washer4_40ID = 0.123 * inch;

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

	Insert = [3.9,4.6,5.8];

	//- PCB sizes

	PCBSize = [80.0,120.0,1.6];
	PCBShelf = 1.5;

	Clearance = 2*[ThreadWidth,ThreadWidth,0];

	WallThick = 4.0;
	FrameHeight = 8.0;

	ScrewOffset = 0.0 + Clear4_40/2;

	ScrewSites = [[-1,1],[-1,1]]; // -1/0/+1 = left/mid/right and bottom/mid/top

	OAHeight = FrameHeight + Clearance[2] + PCBSize[2];
	echo(str("OAH: ",OAHeight));

	FlangeExtension = 3.0;
	FlangeThick = IntegerMultiple(2.0,ThreadThick);
	Flange = PCBSize
	+ 2*[ScrewOffset,ScrewOffset,0]
	+ 2*[Washer4_40OD,Washer4_40OD,0]
	+ [2FlangeExtension,2FlangeExtension,(FlangeThick – PCBSize[2])]
	;

	echo(str("Flange: ",Flange));
	NumSides = 4*5;

	WireChannel = [Flange[0],15.0,3.0 + PCBSize[2]];
	WireChannelOffset = [Flange[0]/2,25.0,(FrameHeight + PCBSize[2] – WireChannel[2]/2)];

	//- Adjust hole diameter to make the size come out right

	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);
	}

	//- Build things

	if (Layout == "Frame")
	difference() {
	union() { // body block
	translate([0,0,OAHeight/2])
	cube(PCBSize + Clearance + [2WallThick,2WallThick,FrameHeight],center=true);

	for (x=[-1,1], y=[-1,1]) { // screw bosses
	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	0])
	cylinder(r=Washer4_40OD,h=OAHeight,$fn=NumSides);
	}

	if (ClampFlange) // flange for work holder
	linear_extrude(height=Flange[2])
	hull()
	for (i=[-1,1], j=[-1,1]) {
	translate([i(Flange[0]/2 – Washer4_40OD/2),j(Flange[1]/2 – Washer4_40OD/2)])
	circle(d=Washer4_40OD,$fn=NumSides);
	}
	}

	for (x=[-1,1], y=[-1,1]) { // screw position indexes

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	-Protrusion])
	rotate(xy180/(2*6))
	PolyCyl(Clear4_40,(OAHeight + 2*Protrusion),6); // screw clearance holes

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	OAHeight – PCBSize[2] – Insert[LENGTH]])
	rotate(xy180/(2*6))
	PolyCyl(Insert[OD],Insert[LENGTH] + Protrusion,6); // inserts

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	OAHeight – PCBSize[2]])
	PolyCyl(1.2*Washer4_40OD,(PCBSize[2] + Protrusion),NumSides); // washers
	}

	translate([0,0,OAHeight/2]) // through hole below PCB
	cube(PCBSize – 2[PCBShelf,PCBShelf,0] + [0,0,2OAHeight],center=true);

	translate([0,0,(OAHeight – (PCBSize[2] + Clearance[2])/2 + Protrusion/2)]) // PCB pocket on top
	cube(PCBSize + Clearance + [0,0,Protrusion],center=true);

	if (Channel)
	translate(WireChannelOffset) // opening for wires from bottom side
	cube(WireChannel + [0,0,Protrusion],center=true);
	}

	// Add-on bracket to hold smaller PCB upright at edge

	PCB2Insert = [3.0,4.9,4.1];
	PCB2OC = 45.0;

	if (Layout == "Bracket")
	difference() {
	hull() // frame body block
	for (x=[-1,1]) // bosses around screws
	translate([x*(PCBSize[0]/2 + ScrewOffset),0,0])
	cylinder(r=Washer4_40OD,h=OAHeight,$fn=NumSides);

	for (x=[-1,1]) // frame screw holes
	translate([x*(PCBSize[0]/2 + ScrewOffset),0,-Protrusion])
	rotate(x180/(26))
	PolyCyl(Clear4_40,(OAHeight + 2*Protrusion),6);

	for (x=[-1,1]) // PCB insert holes
	translate([x*PCB2OC/2,(Washer4_40OD + Protrusion),OAHeight/2])
	rotate([90,0,0])
	cylinder(d=PCB2Insert[OD],h=2*(Washer4_40OD + Protrusion),$fn=6);

	}

view raw Proto Board Holder.scad hosted with ❤ by GitHub

2017-06-07

Monthly Science: Significant Figures vs. Accuracy vs. Precision, Marathon Edition

The rail trail recently sprouted white mile markers:

Rail Trail – Marathon 13 mile marker

This one stood out:

Rail Trail – Marathon 13.10938 mile marker

Not being a marathoner, I had the vague notion a marathon should be an even number of kilometers, because it’s not an even number of miles, but nooooo it’s just an arbitrary distance everybody agreed would be about right for a good long run.

During the rest of the ride, I worked out that 1 micro mile = 5+ milli foot = 60+ milli inch, so the rightmost significant figure in that marker represents increments of, oh, a smidge under ¾ inch. Middle of the hash line marks the spot, perhaps?

I’ve seen similar markers along other courses, with varying numbers of ahem significant figures, and will not say how long it took me to recognize what it represented.

2017-06-01

Bathroom Door Retainer

The weather got warm enough to open the windows before pollen season started, which led to the front bathroom door slamming closed in the middle of the night when a gusty rainstorm blew through town. After far too many years, I decided this was an annoyance up with which I need no longer put.

A few minutes with OpenSCAD and Slic3r produces the shape:

Bathroom Door Retainer - Slic3r — Bathroom Door Retainer – Slic3r

It’s basically an extrusion of a 2D shape with a rectangular recess for the door chewed out.

An hour later, it’s in full effect:

Bathroom Door Retainer - installed — Bathroom Door Retainer – installed

The model now sports a little ball to secure the retainer against the towel bar:

Bathroom Door Retainer - bump — Bathroom Door Retainer – bump

Maybe someday I’ll reprint it.

That was easy …

The cast-iron pig sometimes standing guard as a doorstop in the relatively narrow doorway poses a bit of a foot hazard, so he moves into a closet during the off season. He can now remain there, snug and comfy, until a need for ballast arises.

The OpenSCAD source code as a GitHub Gist:

	// Bathroom Door Retainer
	// Ed Nisley KE4ZNU – May 2017

	Layout = "Show"; // Show Build

	//——-
	//- Extrusion parameters must match reality!

	ThreadThick = 0.20;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

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

	//——-
	// Dimensions

	TowelBarSide = 20.5; // towel bar across flat side
	TowelBarAngle = 45; // rotation of top flat from horizontal

	DoorOffset = 16.0; // from towel bar to door
	DoorThick = 36.5;

	WallThick = 4.0; // minimum wall thickness

	RetainerDepth = 10.0; // thickness of retaining notch

	NumSides = 6*4;
	CornerRad = WallThick;

	BarClipOD = TowelBarSidesqrt(2) + 2WallThick;
	BarClipRad = BarClipOD/2;

	OAH = RetainerDepth + WallThick;

	module LatchPlan() {

	union() {
	linear_extrude(height=OAH,convexity=4)
	difference() {
	union() {
	circle(d=BarClipOD,$fn=NumSides);
	hull()
	for (i=[0,1], j=[0,1])
	translate([i(BarClipRad + DoorOffset + DoorThick + WallThick – CornerRad),j(BarClipRad – CornerRad)])
	circle(r=CornerRad,$fn=4*4);
	}
	rotate(TowelBarAngle) // towel bar shape
	square(size=TowelBarSide,center=true);
	translate([0,-TowelBarSide/sqrt(2)]) // make access slot
	rotate(-TowelBarAngle)
	square(size=[2*TowelBarSide,TowelBarSide],center=false);
	}
	translate([0,-TowelBarSide/sqrt(2),OAH/2])
	rotate([90,0,45])
	sphere(r=TowelBarSide/25,$fn=4*3);
	}
	}

	module Latch() {

	difference() {
	LatchPlan();
	translate([BarClipRad + DoorOffset,-BarClipRad/2,-Protrusion])
	cube([DoorThick,BarClipOD,RetainerDepth + Protrusion],center=false);
	}
	}

	//——-
	// Build it!

	if (Layout == "Show") {
	Latch();
	}

	if (Layout == "Build") {
	translate([0,0,OAH])
	rotate([180,0,0])
	Latch();
	}

view raw Bathroom Door Retainer.scad hosted with ❤ by GitHub

2017-05-29

Kindle Fire Power Button: Some Things Don’t Last

Once again, the single moving part on my first-generation Kindle Fire stopped working. As before, the switch contacts accumulated enough fuzz & contamination to prevent any current flow, but this time the (soft) solder joints attaching the switch body to the PCB failed:

Kindle Fire power switch – failed anchor

My joint cleaning & fluxing wasn’t up to contemporary standards, as shown by the obviously un-fused footprints left in the upper pads:

Kindle Fire power switch – failed anchor joints

The switch frame seems to be unplated steel, which shouldn’t be an excuse.

So I dismantled the switch, cleaned the contacts and tactile bump plate, put it all back together, and did a much better job of surface preparation:

Kindle Fire power switch – rebuilt – right anchor

The other joint:

Kindle Fire power switch – rebuilt – left anchor

And, for completeness, the switch leads:

Kindle Fire power switch – rebuilt – switch pads

I don’t like the way the joint on the right looks, either, but we’ll see how long the whole affair holds together.

This may be the last time I can repair the Kindle, as a bypass cap came loose while I was working on the PCB, the screen has been accumulating dust at an increasing pace, and several latches securing the back of the case have cracked.

Methinks it’s getting on time for a new pocketable memory device; if only Pixel XL phablets had a bigger screen and didn’t cost night onto a kilobuck.

2017-05-14
Zire 71 Protector: Some Things Last

This ABS slab emerged from the Thing-O-Matic in early 2012:

Zire 71 protector in place

The Zire would power on whenever the switches clicked or that little joystick moved, which happened regularly enough to be annoying.

Mary made a small case that matched the other pouches I carry around:

Belt pack – camera case – PDA case

She made the case to fit an HP48 calculator, but it was close enough for the Zire.

Time passed, the Zire died, I started carrying a Kindle Fire in another pocket, but the ABS slab provided a convenient stiffener between some Geek Scratch Paper and the various pencils / pens / markers / screwdrivers / flashlight filling the available space.

Unfortunately, minus the backup of an electronic slab, the protector finally failed along an obvious stress riser:

Zire 71 protector – cracked

I cut a similar rectangle from a sheet of unknown flexy plastic, rounded the corners, clipped the pencils & whatnot to it, and maybe it’ll survive for a while.

2017-05-13

Arduino Joystick

A bag of sub-one-dollar resistive joysticks arrived from halfway around the planet:

Arduino UNO - resistive joystick — Arduino UNO – resistive joystick

A quick-and-dirty test routine showed the sticks start out close to VCC/2:

Welcome to minicom 2.7

OPTIONS: I18n
Compiled on Feb  7 2016, 13:37:27.
Port /dev/ttyACM0, 10:23:45

Press CTRL-A Z for help on special keys

Joystick exercise
Ed Nisley - KE4ZNU - May 2017
00524 - 00513 - 1

That’s from minicom on the serial port, as the Arduino IDE’s built-in serial monitor ignores bare Carriage Return characters.

The joystick hat tilts ±25° from its spring-loaded center position, but the active region seems to cover only 15° of that arc, with a 5° dead zone around the center and 5° of overtravel at the limits. This is not a high-resolution instrument intended for fine motor control operations.

The analog input values range from 0x000 to 0x3FF across the active region. Aim the connector at your tummy to make the axes work the way you’d expect: left / down = minimum, right / up = maximum.

The delay(100) statements may or may not be needed for good analog input values, depending on some imponderables that seem not to apply for this lashup, but they pace the loop() to a reasonable update rate.

Pushing the hat toward the PCB activates the simple switch you can see in the picture. It requires an external pullup resistor (hence the INPUT_PULLUP configuration) and reports low = 0 when pressed.

Those are 0.125 inch (exactly!) holes on a 19.5×26.25 mm grid in a 26.5×34.25 mm PCB. Makes no sense to me, either.

The trivial Arduino source code as a GitHub Gist:

	// Joystick exercise

	#define JOYX A0
	#define JOYY A1
	#define BUTTON 7

	int JoyX,JoyY;
	boolean Button;

	//– Helper routine for printf()

	int s_putc(char c, FILE *t) {
	Serial.write(c);
	}


	void setup() {

	Serial.begin (9600);
	fdevopen(&s_putc,0); // set up serial output for printf()

	Serial.println ("Joystick exercise");
	Serial.println ("Ed Nisley – KE4ZNU – May 2017");

	pinMode(BUTTON,INPUT_PULLUP);
	}

	void loop() {

	JoyX = analogRead(JOYX);
	delay(100);
	JoyY = analogRead(JOYY);
	delay(100);
	Button = digitalRead(BUTTON);

	printf("%05d – %05d – %1d\r",JoyX,JoyY,Button);

	}

view raw JoyStickTest.ino hosted with ❤ by GitHub

2017-05-10

XTC-3D Epoxy Coating: Results

Having figured the mixing ratios, found the mixing trays, and donned my shop apron, I buttered up several iterations of the badge reel case to see how XTC-3D epoxy works on the little things around here.

In all cases, I haven’t done any sanding, buffing, or primping, mostly because I’m not that interested in the final surface finish.

A single coat produces a glossy finish with ripples from the printed threads:

XTC-3D – Hilbert – reflective

Seen straight on, without the glare, a little speck toward the lower right corner shows that cleanliness is next to impossible around here:

XTC-3D – lines – direct

An additional coat atop a Hilbert-curve upper surface comes out somewhat smoother:

XTC-3D – Hilbert – reflective 2

Another view, with less glare, shows the pattern a bit better:

XTC-3D – Hilbert – reflective 1

With no glare, the 3D Honeycomb infill shows through the surface:

XTC-3D – Hilbert – direct

Coating the surface with epoxy definitely makes it more transparent / less translucent by filling in the air gaps.

The sides of that part have only one coat and still show typical 3D printed striations.

Three coats wipe out the striations, along with all other surface detail:

XTC-3D – Bezel – front oblique

The bolt head recesses collected enough epoxy to require reaming / milling, which certainly isn’t what you want in that situation. The bolt holes also shrank, although my usual hand-twisted drill would probably suffice to clear the epoxy.

Another view shows a glint from the smooth surface filling the upper-right recess:

XTC-3D – Bezel – front

Three coats definitely hides the 3D printed threads, although you can see some ridges and edges:

XTC-3D – heavy – oblique

The epoxy isn’t perfectly self-leveling, probably due to my (lack of) technique:

XTC-3D – heavy – reflection

Blowing out the contrast shows the surface finish:

XTC-3D – heavy – direct – boost

Those scratches come from fingernails, after the overnight curing time. The surface is hard, but not impervious to scratching, which is about what you’d expect for a clear epoxy.

Slightly over-thinning the XTC-3D with denatured alcohol in a 0.7 : 0.3 : 0.3 by weight ratio produced a watery liquid that penetrated directly into the surface:

XTC-3D – thinned – oblique

The finish depends critically on what’s below the surface and how much epoxy you apply. I tried to spread it uniformly with a foam brush, but the center came out somewhat rougher than the outer edge:

XTC-3D – thinned – oblique

The striations along the sides filled in a bit, but surely not enough to satisfy anybody who worries about such things.

A specular reflection shows the changing surface smoothness:

XTC-3D – thinned – oblique reflective

Perhaps two coats of thinned epoxy would produce a watertight / airtight part, without changing the overall dimensions by very much. The mechanical properties depend almost entirely on the plastic-to-plastic bond, so I doubt a thin epoxy layer would improve its pressure-handling capabilities.

Few of the parts I make will benefit from an epoxy coating and I definitely don’t want to get into post-processing the parts just to improve their looks!

2017-05-09