HSV colour cycling LED on Arduino

Pretty much everyone tries the RGB colour cycler when they get their first Arduino. This variant cycles through the HSV colour wheel, though at fixed saturations and values.

Code:

// HSV fade/bounce for Arduino - scruss.com - 2010/09/12
// Note that there's some legacy code left in here which seems to do nothing
// but should do no harm ...

// don't futz with these, illicit sums later
#define RED       9 // pin for red LED
#define GREEN    10 // pin for green - never explicitly referenced
#define BLUE     11 // pin for blue - never explicitly referenced
#define SIZE    255
#define DELAY    10
#define HUE_MAX  6.0
#define HUE_DELTA 0.01

long deltas[3] = {
  5, 6, 7 };
long rgb[3];
long rgbval;
// for reasons unknown, if value !=0, the LED doesn't light. Hmm ...
// and saturation seems to be inverted
float hue=0.0, saturation=1.0, value=1.0;

/*
chosen LED SparkFun sku: COM-09264
 has Max Luminosity (RGB): (2800, 6500, 1200)mcd
 so we normalize them all to 1200 mcd -
 R  1200/2800  =  0.428571428571429   =   109/256
 G  1200/6500  =  0.184615384615385   =    47/256
 B  1200/1200  =  1.0                 =   256/256
 */
long bright[3] = {
  109, 47, 256};

long k, temp_value;

void setup () {
  randomSeed(analogRead(4));
  for (k=0; k<3; k++) {
    pinMode(RED + k, OUTPUT);
    rgb[k]=0;
    analogWrite(RED + k, rgb[k] * bright[k]/256);
    if (random(100) > 50) {
      deltas[k] = -1 * deltas[k]; // randomize direction
    }
  }
}

void loop() {
  hue += HUE_DELTA;
  if (hue > HUE_MAX) {
    hue=0.0;
  }
  rgbval=HSV_to_RGB(hue, saturation, value);
  rgb[0] = (rgbval & 0x00FF0000) >> 16; // there must be better ways
  rgb[1] = (rgbval & 0x0000FF00) >> 8;
  rgb[2] = rgbval & 0x000000FF;
  for (k=0; k<3; k++) { // for all three colours
    analogWrite(RED + k, rgb[k] * bright[k]/256);
  }
  delay(DELAY);
}

long HSV_to_RGB( float h, float s, float v ) {
  /* modified from Alvy Ray Smith's site: http://www.alvyray.com/Papers/hsv2rgb.htm */
  // H is given on [0, 6]. S and V are given on [0, 1].
  // RGB is returned as a 24-bit long #rrggbb
  int i;
  float m, n, f;

  // not very elegant way of dealing with out of range: return black
  if ((s<0.0) || (s>1.0) || (v<0.0) || (v>1.0)) {
    return 0L;
  }

  if ((h < 0.0) || (h > 6.0)) {
    return long( v * 255 ) + long( v * 255 ) * 256 + long( v * 255 ) * 65536;
  }
  i = floor(h);
  f = h - i;
  if ( !(i&1) ) {
    f = 1 - f; // if i is even
  }
  m = v * (1 - s);
  n = v * (1 - s * f);
  switch (i) {
  case 6:
  case 0:
    return long(v * 255 ) * 65536 + long( n * 255 ) * 256 + long( m * 255);
  case 1:
    return long(n * 255 ) * 65536 + long( v * 255 ) * 256 + long( m * 255);
  case 2:
    return long(m * 255 ) * 65536 + long( v * 255 ) * 256 + long( n * 255);
  case 3:
    return long(m * 255 ) * 65536 + long( n * 255 ) * 256 + long( v * 255);
  case 4:
    return long(n * 255 ) * 65536 + long( m * 255 ) * 256 + long( v * 255);
  case 5:
    return long(v * 255 ) * 65536 + long( m * 255 ) * 256 + long( n * 255);
  }
}

The circuit is very simple:

  • Digital pin 9 → 165Ω resistor → LED Red pin
  • Digital pin 10 → 100Ω resistor → LED Green pin
  • Digital pin 11 → 100Ω resistor → LED Blue pin
  • GND → LED common cathode.

The different resistor values are to provide a limited current to the Triple Output LED RGB – Diffused, as each channel has different requirements. The 165Ω resistor is actually two 330Ω in parallel; I didn’t have the right value, and this was the closest I could make with what I had.

3 thoughts on “HSV colour cycling LED on Arduino”

  1. Hi,
    Is that a bug in the code at line 70- where you return 0 if V is not = 1?

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