Arduino Code

Make sure to to download the NeoPixel Arduino library. Below is front and side code that will change the color of the NeoPixel strip - copy it into your Adafruit Arduino IDE as-is and then mod the LED Pins and number of pixels to make it your own. Remember that to program Trinket you need to download the special Adafruit version of the Arduino IDE from the Introduction to Trinket guide.

The Arduino code presented below works equally well on the Trinket Mini and Trinket Pro. But if you have a Trinket M0 board you will need to use the CircuitPython code on the next page of this guide, no Arduino IDE required!

Side Animation

// Adafruit Trinket+NeoPixel animation for Daft Punk-inspired helmet.
// Contains some ATtiny85-specific stuff; won't run as-is on Uno, etc.

// Operates in HSV (hue, saturation, value) colorspace rather than RGB.
// Animation is an interference pattern between two waves; one controls
// saturation, the other controls value (brightness).  The wavelength,
// direction, speed and type (square vs triangle wave) for each is randomly
// selected every few seconds.  Hue is always linear, but other parameters
// are similarly randomized.

#include <Adafruit_NeoPixel.h>
#include <avr/power.h>

// GLOBAL STUFF --------------------------------------------------------------

#define N_LEDS 29
#define PIN     0

Adafruit_NeoPixel    pixels = Adafruit_NeoPixel(N_LEDS, PIN);
volatile uint16_t    count  = 1; // Countdown to next animation change
extern const uint8_t gamma[];    // Big table at end of this code

volatile struct {
  uint8_t type,      // 0 = square wave, 1 = triangle wave
          value[2];  // 0 = start-of-frame value, 1 = pixel-to-pixel value
  int8_t  inc[2];    // 0 = frame-to-frame increment, 1 = pixel-to-pixel inc
} wave[3];           // 0 = Hue, 1 = Saturation, 2 = Value (brightness)

#define WAVE_H 0     // Array indices for wave[]
#define WAVE_S 1
#define WAVE_V 2
#define FRAME  0     // Array indices for value[] and inc[]
#define PIXEL  1


// INITIALIZATION ------------------------------------------------------------

void setup() {
  pixels.begin();
  randomSeed(analogRead(0)); // Seed random() from a floating pin (D2)

  // Timer/Counter 1 is used to generate a steady ~50 Hz frame rate.
#if F_CPU == 16000000L
  clock_prescale_set(clock_div_1);
  TCCR1  = _BV(PWM1A) | _BV(CS13) | _BV(CS12); // 1:2048 prescale
  OCR1C  = F_CPU / 2048 / 50 - 1;
#else
  TCCR1  = _BV(PWM1A) | _BV(CS13) | _BV(CS11) | _BV(CS10); // 1:1024
  OCR1C  = F_CPU / 1024 / 50 - 1;
#endif
  GTCCR  = 0;          // No PWM out
  TIMSK |= _BV(TOIE1); // Enable overflow interrupt
}

void loop() { } // Not used here -- everything's in interrupt below


// 50 HZ LOOP ----------------------------------------------------------------

ISR(TIMER1_OVF_vect) {
  uint8_t  w, i, n, s, v, r, g, b;
  uint16_t v1, s1;

  if(!(--count)) {              // Time for new animation?
    count = 250 + random(250);  // New effect will run for 5-10 sec.
    for(w=0; w<3; w++) {        // Three waves (H,S,V)...
      wave[w].type = random(2); // Assign random type (square/triangle)
      for(i=0; i<2; i++) {      // For frame and pixel increments...
        while(!(wave[w].inc[i] = random(15) - 7)); // Set non-zero random
        // wave value is never initialized; it's allowed to carry over
      }
      wave[w].value[PIXEL] = wave[w].value[FRAME];
    }
    wave[WAVE_S].inc[PIXEL] *= 16; // Make saturation & value
    wave[WAVE_V].inc[PIXEL] *= 16; // blinkier along strip
  } else { // Continue current animation; update waves
    for(w=0; w<3; w++) {
      wave[w].value[FRAME] += wave[w].inc[FRAME];   // OK if this wraps!
      wave[w].value[PIXEL]  = wave[w].value[FRAME];
    }
  }

  // Render current animation frame.  COGNITIVE HAZARD: fixed point math.

  for(i=0; i<N_LEDS; i++) { // For each LED along strip...

    // Coarse (8-bit) HSV-to-RGB conversion, hue first:
    n   = (wave[WAVE_H].value[PIXEL] % 43) * 6; // Angle within sextant; 0-255
    switch(wave[WAVE_H].value[PIXEL] / 43) {    // Sextant number; 0-5
      case 0 : r = 255    ; g =   n    ; b =   0    ; break; // R to Y
      case 1 : r = 254 - n; g = 255    ; b =   0    ; break; // Y to G
      case 2 : r =   0    ; g = 255    ; b =   n    ; break; // G to C
      case 3 : r =   0    ; g = 254 - n; b = 255    ; break; // C to B
      case 4 : r =   n    ; g =   0    ; b = 255    ; break; // B to M
      default: r = 255    ; g =   0    ; b = 254 - n; break; // M to R
    }

    // Saturation = 1-256 to allow >>8 instead of /255
    s = wave[WAVE_S].value[PIXEL];
    if(wave[WAVE_S].type) {     // Triangle wave?
      if(s & 0x80) {            // Downslope
        s    = (s & 0x7F) << 1;
        s1   = 256 - s;
      } else {                  // Upslope
        s  <<= 1;
        s1   = 1   + s;
        s    = 255 - s;
      }
    } else {                    // Square wave
      if(s & 0x80) {            // 100% saturation
        s1 = 256;
        s  =   0;
      } else {                  // 0% saturation (white)
        s1 =   1;
        s  = 255;
      }
    }

    // Value (brightness) = 1-256 for similar reasons
    v  = wave[WAVE_V].value[PIXEL];
    v1 = (wave[WAVE_V].type) ?                      // Triangle wave?
         ((v & 0x80) ? 64 - ((v & 0x7F) << 1) :    // Downslope
                         1 + ( v         << 1)  ) : // Upslope
         ((v & 0x80) ? 256 : 1);                    // Square wave; on/off

    pixels.setPixelColor(i,
      pgm_read_byte(&gamma[((((r * s1) >> 8) + s) * v1) >> 8]),
      pgm_read_byte(&gamma[((((g * s1) >> 8) + s) * v1) >> 8]),
      pgm_read_byte(&gamma[((((b * s1) >> 8) + s) * v1) >> 8]));

    // Update wave values along length of strip (values may wrap, is OK!)
    for(w=0; w<3; w++) wave[w].value[PIXEL] += wave[w].inc[PIXEL];
  }

  pixels.show();
}

// Gamma correction improves appearance of midrange colors.
// This table is positioned down here because it's a big annoying
// distraction.  The 'extern' near the top lets us reference it earlier.
const uint8_t gamma[] PROGMEM = {
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  1,  1,  1,
    1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,
    2,  3,  3,  3,  3,  3,  3,  3,  4,  4,  4,  4,  4,  5,  5,  5,
    5,  6,  6,  6,  6,  7,  7,  7,  7,  8,  8,  8,  9,  9,  9, 10,
   10, 10, 11, 11, 11, 12, 12, 13, 13, 13, 14, 14, 15, 15, 16, 16,
   17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 24, 24, 25,
   25, 26, 27, 27, 28, 29, 29, 30, 31, 32, 32, 33, 34, 35, 35, 36,
   37, 38, 39, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 50,
   51, 52, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68,
   69, 70, 72, 73, 74, 75, 77, 78, 79, 81, 82, 83, 85, 86, 87, 89,
   90, 92, 93, 95, 96, 98, 99,101,102,104,105,107,109,110,112,114,
  115,117,119,120,122,124,126,127,129,131,133,135,137,138,140,142,
  144,146,148,150,152,154,156,158,160,162,164,167,169,171,173,175,
  177,180,182,184,186,189,191,193,196,198,200,203,205,208,210,213,
  215,218,220,223,225,228,231,233,236,239,241,244,247,249,252,255 };

Front Animation

// Fiery demon horns (rawr!) for Adafruit Trinket/Gemma.
// Adafruit invests time and resources providing this open source code, 
// please support Adafruit and open-source hardware by purchasing 
// products from Adafruit!
#include <Adafruit_NeoPixel.h>
#include <avr/power.h>

#define N_HORNS 1
#define N_LEDS 30 // Per horn
#define PIN     0
Adafruit_NeoPixel pixels = Adafruit_NeoPixel(N_HORNS * N_LEDS, PIN);

//      /\  ->   Fire-like effect is the sum of multiple triangle
// ____/  \____  waves in motion, with a 'warm' color map applied.
#define N_WAVES 6     // Number of simultaneous waves (per horn)
// Coordinate space for waves is 16x the pixel spacing,
// allowing fixed-point math to be used instead of floats.
struct {
  int16_t  lower;     // Lower bound of wave
  int16_t  upper;     // Upper bound of wave
  int16_t  mid;       // Midpoint (peak) ((lower+upper)/2)
  uint8_t  vlower;    // Velocity of lower bound
  uint8_t  vupper;    // Velocity of upper bound
  uint16_t intensity; // Brightness at peak
} wave[N_HORNS][N_WAVES];
long fade; // Decreases brightness as wave moves

// Gamma correction improves appearance of midrange colors
uint8_t gamma[] PROGMEM = {
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  1,  1,  1,
    1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,
    2,  3,  3,  3,  3,  3,  3,  3,  4,  4,  4,  4,  4,  5,  5,  5,
    5,  6,  6,  6,  6,  7,  7,  7,  7,  8,  8,  8,  9,  9,  9, 10,
   10, 10, 11, 11, 11, 12, 12, 13, 13, 13, 14, 14, 15, 15, 16, 16,
   17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 24, 24, 25,
   25, 26, 27, 27, 28, 29, 29, 30, 31, 32, 32, 33, 34, 35, 35, 36,
   37, 38, 39, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 50,
   51, 52, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68,
   69, 70, 72, 73, 74, 75, 77, 78, 79, 81, 82, 83, 85, 86, 87, 89,
   90, 92, 93, 95, 96, 98, 99,101,102,104,105,107,109,110,112,114,
  115,117,119,120,122,124,126,127,129,131,133,135,137,138,140,142,
  144,146,148,150,152,154,156,158,160,162,164,167,169,171,173,175,
  177,180,182,184,186,189,191,193,196,198,200,203,205,208,210,213,
  215,218,220,223,225,228,231,233,236,239,241,244,247,249,252,255 };

static void random_wave(uint8_t h,uint8_t w) {          // Randomize one wave struct
  wave[h][w].upper     = -1;                            // Always start just below head of strip
  wave[h][w].lower     = -16 * (3 + random(4));         // Lower end starts ~3-7 pixels back
  wave[h][w].mid       = (wave[h][w].lower + wave[h][w].upper) / 2;
  wave[h][w].vlower    = 3 + random(4);                 // Lower end moves at ~1/8 to 1/4 pixel/frame
  wave[h][w].vupper    = wave[h][w].vlower + random(4); // Upper end moves a bit faster, spreading wave
  wave[h][w].intensity = 300 + random(600);
}

void setup() {
  uint8_t h, w;

  randomSeed(analogRead(1));
  pixels.begin();
  for(h=0; h<N_HORNS; h++) {
    for(w=0; w<N_WAVES; w++) random_wave(h, w);
  }
  fade = 234 + N_LEDS / 2;
  if(fade > 255) fade = 255;

  // A ~100 Hz timer interrupt on Timer/Counter1 makes everything run
  // at regular intervals, regardless of current amount of motion.
#if F_CPU == 16000000L
  clock_prescale_set(clock_div_1);
  TCCR1  = _BV(PWM1A) | _BV(CS13) | _BV(CS11) | _BV(CS10); // 1:1024 prescale
  OCR1C  = F_CPU / 1024 / 100 - 1;
#else
  TCCR1  = _BV(PWM1A) | _BV(CS13) | _BV(CS11); // 1:512 prescale
  OCR1C  = F_CPU / 512 / 100 - 1;
#endif
  GTCCR  = 0;          // No PWM out
  TIMSK |= _BV(TOIE1); // Enable overflow interrupt
}

void loop() { } // Not used -- everything's in interrupt below

ISR(TIMER1_OVF_vect) {
  uint8_t  h, w, i, r, g, b;
  int16_t  x;
  uint16_t sum;

  for(h=0; h<N_HORNS; h++) {              // For each horn...
    for(x=7, i=0; i<N_LEDS; i++, x+=16) { // For each LED along horn...
      for(sum=w=0; w<N_WAVES; w++) {      // For each wave of horn...
        if((x < wave[h][w].lower) || (x > wave[h][w].upper)) continue; // Out of range
        if(x <= wave[h][w].mid) { // Lower half of wave (ramping up to peak brightness)
          sum += wave[h][w].intensity * (x - wave[h][w].lower) / (wave[h][w].mid - wave[h][w].lower);
        } else {               // Upper half of wave (ramping down from peak)
          sum += wave[h][w].intensity * (wave[h][w].upper - x) / (wave[h][w].upper - wave[h][w].mid);
        }
      }
      // Now the magnitude (sum) is remapped to color for the LEDs.
      // A blackbody palette is used - fades white-yellow-red-black.
      if(sum < 255) {        // 0-254 = black to red-1
        r = pgm_read_byte(&gamma[sum]);
        g = b = 0;
      } else if(sum < 510) { // 255-509 = red to yellow-1
        r = 255;
        g = pgm_read_byte(&gamma[sum - 255]);
        b = 0;
      } else if(sum < 765) { // 510-764 = yellow to white-1
        r = g = 255;
        b = pgm_read_byte(&gamma[sum - 510]);
      } else {               // 765+ = white
        r = g = b = 255;
      }
      pixels.setPixelColor(h * N_LEDS + i, r, g, b);
    }

    for(w=0; w<N_WAVES; w++) { // Update wave positions for each horn
      wave[h][w].lower += wave[h][w].vlower;  // Advance lower position
      if(wave[h][w].lower >= (N_LEDS * 16)) { // Off end of strip?
        random_wave(h, w);                    // Yes, 'reboot' wave
      } else {                                // No, adjust other values...
        wave[h][w].upper    +=  wave[h][w].vupper;
        wave[h][w].mid       = (wave[h][w].lower + wave[h][w].upper) / 2;
        wave[h][w].intensity = (wave[h][w].intensity * fade) / 256; // Dimmer
      }
    }
  }
  pixels.show();
}
This guide was first published on Sep 04, 2014. It was last updated on Oct 21, 2018. This page (Arduino Code) was last updated on Oct 07, 2018.