The New Hotness

[Edit: Welcome Hackaday! You might prefer real vacuum tubes; searching for “vacuum tube leds” will turn up more posts about this long-running project. And, yes, I lit up a tube, just for old time’s sake, and have some plans for that huge triode.]

A single (knockoff) Neopixel hovers over a defunct halogen bulb:

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

The Arduino code comes from stripping down the Hard Drive Platter Mood Light to suit just one Neopixel, with the maximum PWM values favoring the red-blue-purple end of the color wheel:

	Pixels[RED].Prime = 3;
	Pixels[GREEN].Prime = 5;
	Pixels[BLUE].Prime = 7;
	printf("Primes: (%d,%d,%d)\r\n",Pixels[RED].Prime,Pixels[GREEN].Prime,Pixels[BLUE].Prime);

	Pixels[RED].MaxPWM = 255;
	Pixels[GREEN].MaxPWM = 64;
	Pixels[BLUE].MaxPWM = 255;

Unlike the Mood Light’s dozen Neopixels jammed into the platter’s hub ring, running one Neopixel at full throttle atop the tube doesn’t overheat the poor controller. In a 22 °C room, PWM 255 white raises the cap’s interior temperature to 35 °C, which looks like a horrific 40 °C/W thermal coefficient if you figure the dissipation at 300 mW = 5 V x 60 mA.

Feeding those parameters into the raised sine wave equation causes the cap to tick along at 27 °C for an average dissipation of 120 mW, which sounds about right:

113 mW = 5 V x (20 + 20 + 5 mA) / 2

The effect is striking in a dark room, but it’s hard to photograph; the halogen capsule inside the bulb resembles a Steampunk glass jellyfish:

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

That ceramic light socket should stand on a round base with room for the Arduino controller. I think powering it from a wall wart through a USB cable makes sense, with a USB-to-serial converter epoxied inside the box for reprogramming.

It looks pretty good, methinks, should you like that sort of thing.

The Arduino source code as a GitHub gist:

	// Neopixel mood lighting for vacuum tubes
	// Ed Nisley – KE4ANU – January 2016

	#include <Adafruit_NeoPixel.h>

	//———-
	// Pin assignments

	const byte PIN_NEO = 6; // DO – data out to first Neopixel

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

	//———-
	// Constants

	#define UPDATEINTERVAL 25ul
	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

	// want to randomize the startup a little?
	#define RANDOMIZE true

	//———-
	// Globals

	// instantiate the Neopixel buffer array

	Adafruit_NeoPixel strip = Adafruit_NeoPixel(1, 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;
	byte MaxPWM;
	};

	unsigned int PlatterSteps;

	// 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

	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("Vacuum Tube Mood Light with Neopixels\r\nEd Nisley – KE4ZNU – January 2016\r\n");

	/// set up Neopixels

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

	// lamp test: a brilliant white dot

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

	for (byte i=0; i<3 ; i++) {
	for (int j=0; j < strip.numPixels(); j++) { // fill LEDs with white
	strip.setPixelColor(j,FullWhite);
	}
	strip.show();
	delay(500);

	for (int j=0; j < strip.numPixels(); j++) { // fill LEDs with black
	strip.setPixelColor(j,FullOff);
	}
	strip.show();
	delay(500);
	}

	// set up the color generators

	MillisNow = MillisThen = millis();
	if (RANDOMIZE)
	randomSeed(MillisNow + analogRead(7));
	else
	printf("Start not randomized\r\n");
	printf("First random number: %ld\r\n",random(10));

	Pixels[RED].Prime = 3;
	Pixels[GREEN].Prime = 5;
	Pixels[BLUE].Prime = 7;
	printf("Primes: (%d,%d,%d)\r\n",Pixels[RED].Prime,Pixels[GREEN].Prime,Pixels[BLUE].Prime);

	Pixels[RED].MaxPWM = 255;
	Pixels[GREEN].MaxPWM = 64;
	Pixels[BLUE].MaxPWM = 255;

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

	printf("c: %d Steps: %d Init: %d",c,Pixels[c].NumSteps,Pixels[c].Step);
	printf(" PWM: %d\r\n",Pixels[c].MaxPWM);
	}


	}

	//——————
	// Run the mood

	void loop() {

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

	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("Cycle %d steps %d at %8ld delta %ld ms\r\n",c,Pixels[c].NumSteps,MillisNow,(MillisNow – MillisThen));
	}
	}

	byte Value[PIXELSIZE];
	for (byte c=0; c < PIXELSIZE; c++) { // … for each color
	Value[c] = StepColor(c,0.0); // 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]);
	for (int j=0; j < strip.numPixels(); j++) { // fill LEDs with color
	strip.setPixelColor(j,UniColor);
	}
	strip.show();

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

	}

view raw TubeMood.ino hosted with ❤ by GitHub

The New Hotness

Vacuum Tube LEDS: Neopixel Plate Cap