SignalControl.ino
const int NUMBEROFPINS = 4;
const int SIGNALPINS[NUMBEROFPINS] = {13, 12, 10, 9};

const int UP = 1;              // increase brightness
const int DOWN = -1;           // decrease brightness
const int PWMTIME = 20;        // time in msec for one PWM cycle. 20 msec means 50 Hz cycle.
const int PWMINCREASE = 1;     // each PWM cycle is divided into steps of PWMINCREASE msec
int pwmCycle;                  // each PWM cycle starts with 1 and increases each PWMINCREASE msec up to PWMTIME
int brightCycle;               // count PWM cycles
int ledBrightness[NUMBEROFPINS] ; // will store brightness as the PWM width value between 0 and PWMTIME
int ledDimOrBright[NUMBEROFPINS]; // should led get brighter so UP (+1) of must it dimm DOWN (-1)

const int BRIGHTINCREASECYCLES = 2; // after BRIGHTINCREASECYCLES times a complete PWM cycle brightness is increased or decreased

unsigned long previousMillis;  // will store last time PWM cycle was updated

void SignalControl_Init() {
  // initialize digital pin 13 as an output.
  for (int i = 0; i < NUMBEROFPINS; i++) {
    pinMode(SIGNALPINS[i], OUTPUT);
    ledDimOrBright[i] = UP;
  }
  ledBrightness[0] = 1;  // some brightness for this experiment
  ledBrightness[1] = 6;  // some brightness for this experiment
  ledBrightness[2] = 11;  // some brightness for this experiment
  ledBrightness[3] = 17;  // some brightness for this experiment
  pwmCycle = 1;
  brightCycle = 0;
}

void SignalControl_Blink() {
  unsigned long currentMillis = millis();                // current time
  if (currentMillis - previousMillis >= PWMINCREASE) {   // PWMINCREASE msec have passed since last time
    previousMillis = currentMillis;                      // wait for next moment
    pwmCycle = pwmCycle + PWMINCREASE;                   // next PWMINCREASE msec within one PWM cycle
    if (pwmCycle > PWMTIME) {                            // if one PWM cycle is completed, repeat by starting at 1
      pwmCycle = 1;
      brightCycle ++;                                   // increase cycle number
      if (brightCycle > BRIGHTINCREASECYCLES) {         // it is time to increase or decrease brightness
        brightCycle = 0;
        for (int i = 0; i < NUMBEROFPINS; i++) {
          ledBrightness[i] = ledBrightness[i] + ledDimOrBright[i]; // increase or decreas brightness depening on direction
          if (ledBrightness[i] == PWMTIME) {                 // if at maximum, for now invert to dimming
            ledDimOrBright[i] = DOWN;
          };
          if (ledBrightness[i] == 1) {                       // if at minimum, for now invert to more bright. ledBrightness = 0 is used for the state off
            ledDimOrBright[i] = UP;
          };
        };
      };
    };
    for (int i = 0; i < NUMBEROFPINS; i++) {
      digitalWrite(SIGNALPINS[i], (ledBrightness[i] >= pwmCycle) ? (HIGH) : (LOW)); //set output according to the position in the cycle
    };
  };
}