const int redPin = 3;
const int greenPin = 5;
const int bluePin = 6;
const bool invert = true;

int color = 0;
int R, G, B;

void setup() {
  //アナログ端子のため不要
  Serial.begin(9600);
}

void loop() {
  int brightness = 255;

  hueToRGB(color, brightness);

  analogWrite(redPin, R);
  analogWrite(greenPin, G);
  analogWrite(bluePin, B);

  color++;
  Serial.print("["); Serial.print(millis()); Serial.print("] color: "); Serial.println(color);

  if (color > 255) {
    color = 0;
    //消灯して1秒待機
    analogWrite(redPin, 0); analogWrite(greenPin, 0); analogWrite(bluePin, 0); delay(1000);
  }
}

void hueToRGB(int hue, int brightness) {
  unsigned int scaledHue = (hue * 6);

  unsigned int segment = scaledHue / 256;

  unsigned int segmentOffset = scaledHue - (segment * 256);
  unsigned int complement = 0;
  unsigned int prev = (brightness * ( 255 - segmentOffset)) / 256;

  unsigned int next = (brightness * segmentOffset) / 256;
  if (invert) {
    brightness = 255 - brightness;
    complement = 255;
    prev = 255 - prev;
    next = 255 - next;
  }

  switch (segment) {
    case 0: R=brightness; G=next; B=complement; break;          //red
    case 1: R=prev; G=brightness; B=complement; break;          //yerrow
    case 2: R=complement; G=brightness; B=next; break;          //green
    case 3: R=complement; G=prev; B=brightness; break;          //cyan
    case 4: R=next; G=complement; B=brightness; break;          //blue
    case 5: default: R=brightness; G=complement; B=prev; break; //magenta
  }
}