Archive for January 27th, 2016

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: