Machine Shop – Page 213 – The Smell of Molten Projects in the Morning

Raspberry Pi 3: Disabling the Build-In WiFi

A streaming media player in the Basement Laboratory Warehouse Wing has a concrete block wall between it and the WiFi router, so that even high(er)-gain USB antennas can’t grab enough signal for reliable streaming. After some fiddling, I snaked a cable from a hub, along the floor joints, to the Pi and declared victory. It turned out the Pi, an old Pi 1 Model B, had some trouble keeping up with the times, and I eventually swapped it for a Pi 3.

Forcing a static address for the wired port followed the now-standard recipe, with eth0 instead of wlan0 in /etc/dhcpcd.conf.

However, plugging a network cable into the Pi 3 then produces two network connections: the wired one I wanted and the aforementioned unreliable WiFi link through the built-in hardware. The only reliable way to turn off the WiFi connection seems to require applying The BFH through a line in /etc/rc.local:

sudo ifconfig wlan0 down

Removing my WiFi credentials from /etc/wpa_supplicant/wpa_supplicant.conf prevents the hardware from connecting before the hammer comes down.

And then it streams perfectly…

2017-02-27

Cheap WS2812 LEDs: Test Fixture Mount

Mounting the ungainly WS2812 LED test fixture seemed like a Good Idea to keep the electricity out of the usual conductive litter:

WS2812 array test fixture - rear — WS2812 array test fixture – rear

The solid model shows more details:

LED Test Fixture - solid model — LED Test Fixture – solid model

The power wires along the array edges slide into the rear (thinner) slot, with enough friction from a few gentle bends to hold the whole mess in place.

The knockoff Arduino Nano rests on the recessed ledge in the pit, with M2 screws and washers at the corners holding it down (the PCB’s built-in holes might work with 1 mm or 0-90 screws, but that’s just crazy talk). I soldered the power wires directly to the coaxial jack pins under the PCB; they snake out to the LEDs through the little trench. There should be another cutout around the USB connector for in-situ programming, although the existing code works fine.

The front (wider) slot holds a piece of translucent white acrylic to diffuse the light:

WS2812 array test fixture - front flash — WS2812 array test fixture – front flash

It’s painfully bright: a few layers of neutral density filter would be appropriate for a desk toy.

The array runs hot enough at MaxPWM = 255 to produce a gentle upward breeze.

It looks even better without the flash:

WS2812 array test fixture - front dark — WS2812 array test fixture – front dark

You’ll find many easier ways to get RGB LED panels, but that’s not the point here; I’m waiting for these things to die an unnatural death.

The OpenSCAD source code as a GitHub Gist:

	// LED Test Fixture
	// Ed Nisley KE4ZNU – February 2017

	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

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

	Insert = [2.8,3.5,4.0]; // M2 threaded insert
	ScrewOD = 2.0;
	WasherOD = 5.0;

	//- Component sizes

	PCBSize = [18.0,43.5,1.6]; // microcontroller PCB

	PCBClear = 2*[ThreadWidth,ThreadWidth,0]; // clearance around board

	PCBShelf = [ThreadWidth,ThreadWidth,0]; // shelf under perimeter

	PCBCavity = PCBSize – PCBShelf + [0,0,2.5]; // support shelf around bottom parts

	LEDPanel = [70,40,4.0]; // lying flat, LEDs upward
	LEDWire = [LEDPanel[0],LEDPanel[1] + 2*5.0,2.0]; // power wires along sides

	Diffuser = [LEDPanel[0],LEDPanel[1] + 2*4.0,3.5];
	echo(str("Diffuser panel: ",Diffuser));

	WallThick = 8.0;
	BaseThick = 3*ThreadThick + Insert[LENGTH] + PCBCavity[2];

	Block = [3*WallThick + PCBSize[0] + LEDPanel[2] + Diffuser[2],
	2*WallThick + IntegerMultiple(max(PCBSize[1],LEDWire[1]),5),
	BaseThick + LEDPanel[0]];

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

	CornerRadius = 5.0;
	NumSides = 4*5;

	//- 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 it

	difference() {

	hull() // main block with rounded corners
	for (i=[-1,1], j=[-1,1])
	translate([i(Block[0]/2 – CornerRadius),j(Block[1]/2 – CornerRadius),,0])
	cylinder(r=CornerRadius,h=Block[2],$fn=NumSides);

	translate([2*WallThick + PCBSize[0] – Block[0],
	0,
	(Block[2]/2 + BaseThick)])
	cube(Block + [0,2*Protrusion,0],center=true); // cut out over PCB

	translate([WallThick + (PCBSize + PCBClear)[0]/2 – Block[0]/2,
	0,
	0]) {
	translate([0,0,(BaseThick + (Protrusion – PCBSize[2])/2)])
	cube(PCBSize + PCBClear + [0,0,Protrusion],center=true); // PCB recess

	translate([0,0,(BaseThick + (Protrusion – PCBCavity[2])/2)])
	cube(PCBCavity + [0,0,Protrusion],center=true); // cavity under PCB

	translate([PCBSize[0]/2 + WallThick/2 – Protrusion/2,PCBSize[1]/2 – 15/2,BaseThick – PCBCavity[2]/2 + Protrusion/2])
	cube([WallThick + PCBShelf[0] + Protrusion,
	15,PCBCavity[2] + Protrusion],center=true); // wiring cutout

	for (i=[-1,1], j=[-1,1]) // screw inserts
	translate([i(PCBSize[0] + ScrewOD)/2,j(PCBSize[1] + ScrewOD)/2,-Protrusion])
	rotate(180/(2*6))
	PolyCyl(Insert[OD],BaseThick + 2*Protrusion,6);
	}

	resize([2*Block[0],0,LEDPanel[0] + Protrusion]) // LED panel outline
	translate([0,0,BaseThick])
	rotate([0,-90,0])
	translate([(LEDPanel[0] + Protrusion)/2,0,0])
	cube(LEDPanel + [Protrusion,0,0],center=true);

	translate([-Block[0]/2 + 2WallThick + PCBSize[0] + LEDWire[2]/2 + 5ThreadWidth,
	0,BaseThick]) // LED wiring recess
	rotate([0,-90,0])
	translate([(LEDWire[0] + Protrusion)/2,0,0])
	cube(LEDWire + [Protrusion,0,0],center=true);


	translate([Block[0]/2 – Diffuser[2]/2 – 5*ThreadWidth,0,BaseThick]) // diffuser
	rotate([0,-90,0])
	translate([(Diffuser[0] + Protrusion)/2,0,0])
	cube(Diffuser + [Protrusion,0,0],center=true);
	}

view raw WS2812 LED Array Test Fixture.scad hosted with ❤ by GitHub

2017-02-24

Cheap WS2812 LEDs: Test Fixture

Given that I no longer trust any of the knockoff Neopixels, I wired the remaining PCB panel into a single hellish test fixture:

WS2812 4x7 LED test fixture - wiring — WS2812 4×7 LED test fixture – wiring

The 22 AWG wires deliver +5 V and Common, with good old-school Wire-Wrap wire passing to the four LEDs betweem them. The data daisy chain snakes through the entire array.

It seems only fitting to use a knockoff Arduino Nano as the controller:

WS2812 4x7 LED test fixture - front — WS2812 4×7 LED test fixture – front

The code descends from an early version of the vacuum tube lights, gutted of all the randomizing and fancy features. It updates the LEDs every 20 ms and, with only 100 points per cycle, the colors tick along fast enough reassure you (well, me) that the thing is doing something: the pattern takes about 20 seconds from one end of the string to the other.

At full throttle the whole array draws 1.68 A = 60 mA × 28 with all LEDs at full white, which happens only during the initial lamp test and browns out the supply (literally: the blue LEDs fade out first and produce an amber glow). The cheap 5 V 500 mA power supply definitely can’t power the entire array at full brightness.

The power supply current waveform looks fairly choppy, with peaks at the 400 Hz PWM frequency:

WS2812 4x7 array - 200 mA VCC — WS2812 4×7 array – 200 mA VCC

With the Tek current probe set at 200 mA/div, the upper trace shows 290 mA RMS. That’s at MaxPWM = 127, which reduces the average current but doesn’t affect the peaks. At full brightness the average current should be around 600 mA, a tad more than the supply can provide, but maybe it’ll survive; the bottom trace shows a nice average, but the minimum hits 4.6 V during peak current.

Assuming that perversity will be conserved as usual, none of the LEDs will fail for as long as I’m willing to let them cook.

The Arduino source code as a GitHub Gist:

	// WS2812 LED array exerciser
	// Ed Nisley – KE4ANU – February 2017

	#include <Adafruit_NeoPixel.h>

	//———-
	// Pin assignments

	const byte PIN_NEO = A3; // DO – data out to first Neopixel

	const byte PIN_HEARTBEAT = 13; // DO – Arduino LED

	//———-
	// Constants

	#define UPDATEINTERVAL 20ul
	const unsigned long UpdateMS = UPDATEINTERVAL – 1ul; // update LEDs only this many ms apart minus loop() overhead

	// number of steps per cycle, before applying prime factors
	#define RESOLUTION 100

	// phase difference between LEDs for slowest color
	#define BASEPHASE (PI/16.0)

	// LEDs in each row
	#define NUMCOLS 4

	// number of rows
	#define NUMROWS 7

	#define NUMPIXELS (NUMCOLS * NUMROWS)

	#define PINDEX(row,col) (row*NUMCOLS + col)

	//———-
	// Globals

	// instantiate the Neopixel buffer array

	Adafruit_NeoPixel strip = Adafruit_NeoPixel(NUMPIXELS, PIN_NEO, NEO_GRB + NEO_KHZ800);

	uint32_t FullWhite = strip.Color(255,255,255);
	uint32_t FullOff = strip.Color(0,0,0);

	struct pixcolor_t {
	byte Prime;
	unsigned int NumSteps;
	unsigned int Step;
	float StepSize;
	float TubePhase;
	byte MaxPWM;
	};

	// colors in each LED
	enum pixcolors {RED, GREEN, BLUE, PIXELSIZE};

	struct pixcolor_t Pixels[PIXELSIZE]; // all the data for each pixel color intensity

	unsigned long MillisNow;
	unsigned long MillisThen;

	//– Figure PWM based on current state

	byte StepColor(byte Color, float Phi) {

	byte Value;

	Value = (Pixels[Color].MaxPWM / 2.0) * (1.0 + sin(Pixels[Color].Step * Pixels[Color].StepSize + Phi));

	// Value = (Value) ? Value : Pixels[Color].MaxPWM; // flash at dimmest points
	// printf("C: %d Phi: %d Value: %d\r\n",Color,(int)(Phi*180.0/PI),Value);

	return Value;
	}


	//– Helper routine for printf()

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

	//——————
	// Set the mood

	void setup() {

	pinMode(PIN_HEARTBEAT,OUTPUT);
	digitalWrite(PIN_HEARTBEAT,LOW); // show we arrived

	Serial.begin(57600);
	fdevopen(&s_putc,0); // set up serial output for printf()

	printf("WS2812 array exerciser\r\nEd Nisley – KE4ZNU – February 2017\r\n");

	/// set up Neopixels

	strip.begin();
	strip.show();

	// lamp test: run a brilliant white dot along the length of the strip

	printf("Lamp test: walking white\r\n");

	strip.setPixelColor(0,FullWhite);
	strip.show();
	delay(250);

	for (int i=1; i<NUMPIXELS; i++) {
	digitalWrite(PIN_HEARTBEAT,HIGH);
	strip.setPixelColor(i-1,FullOff);
	strip.setPixelColor(i,FullWhite);
	strip.show();
	digitalWrite(PIN_HEARTBEAT,LOW);
	delay(250);
	}

	strip.setPixelColor(NUMPIXELS – 1,FullOff);
	strip.show();
	delay(250);

	// fill the array, row by row

	printf(" … fill\r\n");

	for (int i=0; i < NUMROWS; i++) { // for each row
	digitalWrite(PIN_HEARTBEAT,HIGH);
	for (int j=0; j < NUMCOLS; j++) {
	strip.setPixelColor(PINDEX(i,j),FullWhite);
	strip.show();
	delay(100);
	}
	digitalWrite(PIN_HEARTBEAT,LOW);
	}

	// clear to black, column by column

	printf(" … clear\r\n");

	for (int j=NUMCOLS-1; j>=0; j–) { // for each column
	digitalWrite(PIN_HEARTBEAT,HIGH);
	for (int i=NUMROWS-1; i>=0; i–) {
	strip.setPixelColor(PINDEX(i,j),FullOff);
	strip.show();
	delay(100);
	}
	digitalWrite(PIN_HEARTBEAT,LOW);
	}

	delay(1000);

	// set up the color generators

	MillisNow = MillisThen = millis();
	printf("First random number: %ld\r\n",random(10));

	Pixels[RED].Prime = 11;
	Pixels[GREEN].Prime = 7;
	Pixels[BLUE].Prime = 5;
	printf("Primes: (%d,%d,%d)\r\n",Pixels[RED].Prime,Pixels[GREEN].Prime,Pixels[BLUE].Prime);

	unsigned int PixelSteps = (unsigned int) ((BASEPHASE / TWO_PI) *
	RESOLUTION * (unsigned int) max(max(Pixels[RED].Prime,Pixels[GREEN].Prime),Pixels[BLUE].Prime));
	printf("Pixel phase offset: %d deg = %d steps\r\n",(int)(BASEPHASE*(360.0/TWO_PI)),PixelSteps);

	Pixels[RED].MaxPWM = 127;
	Pixels[GREEN].MaxPWM = 127;
	Pixels[BLUE].MaxPWM = 127;

	for (byte c=0; c < PIXELSIZE; c++) {
	Pixels[c].NumSteps = RESOLUTION * (unsigned int) Pixels[c].Prime;
	Pixels[c].Step = (3*Pixels[c].NumSteps)/4;
	Pixels[c].StepSize = TWO_PI / Pixels[c].NumSteps; // in radians per step
	Pixels[c].TubePhase = PixelSteps * Pixels[c].StepSize; // radians per tube

	printf("c: %d Steps: %5d Init: %5d",c,Pixels[c].NumSteps,Pixels[c].Step);
	printf(" PWM: %3d Phi %3d deg\r\n",Pixels[c].MaxPWM,(int)(Pixels[c].TubePhase*(360.0/TWO_PI)));
	}


	}

	//——————
	// Run the mood

	void loop() {

	MillisNow = millis();
	if ((MillisNow – MillisThen) > UpdateMS) {
	digitalWrite(PIN_HEARTBEAT,HIGH);

	unsigned int AllSteps = 0;
	for (byte c=0; c < PIXELSIZE; c++) { // step to next increment in each color
	if (++Pixels[c].Step >= Pixels[c].NumSteps) {
	Pixels[c].Step = 0;
	printf("Color %d steps %5d at %8ld delta %ld ms\r\n",c,Pixels[c].NumSteps,MillisNow,(MillisNow – MillisThen));
	}
	AllSteps += Pixels[c].Step; // will be zero only when all wrap at once
	}

	if (0 == AllSteps) {
	printf("Grand cycle at: %ld\r\n",MillisNow);
	}

	for (int k=0; k < NUMPIXELS; k++) { // for each pixel
	byte Value[PIXELSIZE];
	for (byte c=0; c < PIXELSIZE; c++) { // … for each color
	Value[c] = StepColor(c,-k*Pixels[c].TubePhase); // figure new PWM value
	// Value[c] = (c == RED && Value[c] == 0) ? Pixels[c].MaxPWM : Value[c]; // flash highlight for tracking
	}
	uint32_t UniColor = strip.Color(Value[RED],Value[GREEN],Value[BLUE]);
	strip.setPixelColor(k,UniColor);
	}
	strip.show();

	MillisThen = MillisNow;
	digitalWrite(PIN_HEARTBEAT,LOW);
	}

	}

view raw ArrayTest.ino hosted with ❤ by GitHub

2017-02-23

Vacuum Tube Lights: Plate Wire Plug

After replacing the WS2812 LED in the 21HB5A socket, I drilled out the hole in the disk platter for a 3.5 mm stereo jack, wired a nice knurled metal plug onto the plate lead, and it’s all good:

21HB5A - Audio plug cable — 21HB5A – Audio plug cable

The plug had a rather large cable entry that cried out for a touch of brass:

Audio plug - brass trim turning — Audio plug – brass trim turning

Fancy plugs have a helical spring strain relief insert about the size & shape of that brass snout; might have to buy me some fancy plugs.

This time, I got the alignment right by clamping everything in the lathe while the epoxy cured:

Audio plug - brass trim gluing — Audio plug – brass trim gluing

I flipped the drill end-for-end, which was surely unnecessary.

It’s now sitting on the kitchen table, providing a bit of light during supper while I wait for a WS2812 controller failure. Again.

2017-02-21

Screw Cutting Fixture vs. Lathe Ways

A length of aluminum hex bar became a nice 10-32 screw trimmer:

Screw cutting fixture - 10-32 - first cut — Screw cutting fixture – 10-32 – first cut

The hex neatly fits a 5/8 inch wrench, so I can tighten the jam nuts enough to run the lathe forward, part off the screw, and clean up the end just fine.

Unfortunately, the second test cut didn’t work nearly so well:

Screw cutting fixture - 10-32 - wrecked — Screw cutting fixture – 10-32 – wrecked

With the cross-slide gib adjusted to the snug side of easy, the cut put enough pressure on the parting tool to lift the way on the tailstock side about 4 mil = 0.1 mm. The parting tool submarined under the cut, dislodged the fixture, and didn’t quite stall the motor while the chuck jaws ate into the aluminum.

Well, that was a learning experience.

After tightening the cross-slide gib to the far side of hard-to-turn:

Put a longer screw in the fixture
Grab it in the tailstock drill chuck
Crunch the hex end of the fixture in the spindle chuck
Remove the screw through the spindle (*)
Put a slight taper on the end of the fixture threads with a center drill
Deploy the live center to support the fixture

Like this:

Screw cutting fixture - 10-32 - rechucked — Screw cutting fixture – 10-32 – rechucked

Turns out that angling the bit by 10° dramatically reduces chatter. If I had BR and BL turning tools, I’d be using them with the QCTP set to 0°, but they weren’t included in the set that came with the lathe.

It’s a good thing I’m not fussy about the diameter of that cylindrical section:

Screw cutting fixture - 10-32 - reshaped — Screw cutting fixture – 10-32 – reshaped

I knew the craptastic lathe ways needed, mmmm, improvement and it’s about time to do something.

(*) By concatenating all my ¼ inch socket extension bars into an absurd noodle capped with square-to-hex adapter holding a Philips bit.

2017-02-17

Improved Cable Clips

Those ugly square cable clips cried out for a cylindrical version:

LED Cable Clips - round - solid model — LED Cable Clips – round – solid model

Which prompted a nice button:

LED Cable Clips - button - solid model — LED Cable Clips – button – solid model

Which suggested the square version needed some softening:

LED Cable Clips - square - solid model — LED Cable Clips – square – solid model

Apart from the base plate thickness, all the dimensions scale from the cable OD; I’ll be unsurprised to discover small cables don’t produce enough base area for good long-term foam tape adhesion. Maybe the base must have a minimum size or area?

I won’t replace the ones already on the saw, but these will look better on the next project…

The OpenSCAD source code as a GitHub Gist:

	// Cable Clips
	// Ed Nisley – KE4ZNU – October 2014
	// February 2017 – adapted for USB cables

	Layout = "Show"; // Show Build

	Style = "Button"; // Square Round Button

	//- Extrusion parameters must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2; // extra clearance

	Protrusion = 0.1; // make holes end cleanly

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

	//———————-
	// Dimensions

	CableOD = 3.8; // cable jacket

	Base = [4CableOD,4CableOD,3*ThreadThick]; // overall base and slab thickness

	CornerRadius = CableOD/2; // radius of square corners
	CornerSides = 4*4; // total sides on square corner cylinders

	NumSides = 6*3; // total sides for cylindrical base

	//– Oval clip with central passage

	module CableClip() {

	intersection() {
	if (Style == "Square")
	hull()
	for (i=[-1,1], j=[-1,1])
	translate([i(Base[0]/2 – CornerRadius),j(Base[1]/2 – CornerRadius),0])
	rotate(180/CornerSides) {
	cylinder(r=CornerRadius,h=Base[2] + CableOD/2,$fn=CornerSides,center=false);
	translate([0,0,Base[2] + CableOD/2])
	sphere(d=CableOD,$fn=CornerSides);
	}
	else if (Style == "Round")
	cylinder(d=Base[0],h=Base[2] + 1.00*CableOD,$fn=NumSides);
	else if (Style == "Button")
	resize(Base + [0,0,2*(Base[2] + CableOD)])
	sphere(d=Base[0],$fn=NumSides);

	union() {
	translate([0,0,Base[2]/2]) // base defines slab thickness
	cube(Base,center=true);

	for (j=[-1,1]) // retaining ovals
	translate([0,j(Base[1]/2 – 0.125(Base[1] – CableOD)/2),(Base[2] – Protrusion)])
	resize([Base[0]/0.75,0,0])
	cylinder(d1=0.75*(Base[1]-CableOD),
	d2=(Base[1]-CableOD)/cos(0*180/NumSides),
	h=(CableOD + Protrusion),
	center=false,$fn=NumSides);
	}
	}

	if (Layout == "Show")
	color("Green",0.2)
	translate([0,0,Base[2] + CableOD/2])
	rotate([0,90,0])
	cylinder(d=CableOD,h=2*Base[0],center=true,$fn=48);

	}

	//———————-
	// Build it

	CableClip();

view raw Cable Clips.scad hosted with ❤ by GitHub

2017-02-16

Screw Cutting Fixture: Full-thread Aluminum

By and large, when you follow the recipe, you get the expected result:

Screw cutting fixture - M3x0.5 aluminum - side view — Screw cutting fixture – M3x0.5 aluminum – side view

That’s another length of the same aluminum rod, this time with a full-length M3x0.5 thread down the middle, and a screw with a neatly trimmed end.

Running the lathe spindle in reverse prevents the screw from loosening the jam nuts on the left:

Screw cutting fixture - M3x0.5 aluminum - in lathe chuck — Screw cutting fixture – M3x0.5 aluminum – in lathe chuck

Running the spindle forward does move the screw enough to loosen the nuts. Perhaps I should put wrench flats on the big end of the fixture so I can really torque the nuts.

That front nut was mostly decorative, rather than tight, because I didn’t expect the first attempt to work nearly as well as it did. A bit of filing to taper the end of the thread and it was all good.

That was easy…

2017-02-14