Day: January 27, 2016

Electronics Workbench, Machine Shop, Software

Vacuum Tube LEDS: Neopixel Plate Cap

[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