In addition to the code below, you’ll need the output from the Python program on the prior page (or we also include it later on this page).
#include <Adafruit_NeoPixel.h>
#include "data.h" // Output of Python script
#define NUM_LEDS 40
#define PIN 6
Adafruit_NeoPixel strip = Adafruit_NeoPixel(NUM_LEDS, PIN, NEO_GRB);
#define numPixels (sizeof(colors) / sizeof(colors[0]))
uint32_t pixelNum;
uint16_t pr = 0, pg = 0, pb = 0; // Prev R, G, B
void setup() {
strip.begin();
randomSeed(analogRead(A0));
pixelNum = random(numPixels); // Begin at random point
}
void loop() {
uint32_t totalTime, fadeTime, holdTime, startTime, elapsed;
uint16_t nr, ng, nb, r, g, b, i;
uint8_t hi, lo, r8, g8, b8, frac;
// Read next 16-bit (5/6/5) color
hi = pgm_read_byte(&colors[pixelNum * 2 ]);
lo = pgm_read_byte(&colors[pixelNum * 2 + 1]);
if(++pixelNum >= numPixels) pixelNum = 0;
// Expand to 24-bit (8/8/8)
r8 = (hi & 0xF8) | (hi >> 5);
g8 = (hi << 5) | ((lo & 0xE0) >> 3) | ((hi & 0x06) >> 1);
b8 = (lo << 3) | ((lo & 0x1F) >> 2);
// Apply gamma correction, further expand to 16/16/16
nr = (uint8_t)pgm_read_byte(&gamma8[r8]) * 257; // New R/G/B
ng = (uint8_t)pgm_read_byte(&gamma8[g8]) * 257;
nb = (uint8_t)pgm_read_byte(&gamma8[b8]) * 257;
totalTime = random(250, 2500); // Semi-random pixel-to-pixel time
fadeTime = random(0, totalTime); // Pixel-to-pixel transition time
if(random(10) < 3) fadeTime = 0; // Force scene cut 30% of time
holdTime = totalTime - fadeTime; // Non-transition time
startTime = millis();
for(;;) {
elapsed = millis() - startTime;
if(elapsed >= fadeTime) elapsed = fadeTime;
if(fadeTime) {
r = map(elapsed, 0, fadeTime, pr, nr); // 16-bit interp
g = map(elapsed, 0, fadeTime, pg, ng);
b = map(elapsed, 0, fadeTime, pb, nb);
} else { // Avoid divide-by-zero in map()
r = nr;
g = ng;
b = nb;
}
for(i=0; i<NUM_LEDS; i++) {
r8 = r >> 8; // Quantize to 8-bit
g8 = g >> 8;
b8 = b >> 8;
frac = (i << 8) / NUM_LEDS; // LED index scaled to 0-255
if((r8 < 255) && ((r & 0xFF) >= frac)) r8++; // Boost some fraction
if((g8 < 255) && ((g & 0xFF) >= frac)) g8++; // of LEDs to handle
if((b8 < 255) && ((b & 0xFF) >= frac)) b8++; // interp > 8bit
strip.setPixelColor(i, r8, g8, b8);
}
strip.show();
if(elapsed >= fadeTime) break;
}
delay(holdTime);
pr = nr; // Prev RGB = new RGB
pg = ng;
pb = nb;
}
Points of interest in the Arduino sketch:
- The colors are from actual films, but the timing is semi-random…the goal isn’t to match specific scene tempos, just needed believable color sequences. Some transitions are abrupt cuts, others fade (implying a camera pan or something moving in or out of frame).
- Color interpolation takes place in 16-bit space…LEDs are only 8-bit, but some fraction of the LEDs is used to get in-between shades.
- The NeoPixel library periodically disables interrupts and is known to mess with timekeeping functions like millis(). That’s okay for this application…we’re not precisely beat-matching any source material, just measuring relative time.
- Need something less bright? Change NUM_LEDS to a smaller value and some NeoPixels will remain off.
Upload sketch to a Metro board (or Arduino Uno or compatible) with NeoPixel shield installed. Power from a quality USB supply. This can then be plugged into a basic lamp timer. The sketch starts at a random point in the color data, so it’s not repeating the same sequence every time it powers up.
Aim it at the ceiling to wash a room in color, similar to the glow from a TV, or directly toward curtains if you need more brightness.
If Python is unavailable on your system, or if it’s just easier this way, here are the entire gamma and color tables. Create a new tab in the Arduino sketch, name it “data.h”, then cut and paste this whole thing:
Page last edited March 08, 2024
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