Archive for January 27th, 2016
[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:
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:
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: