// timing in microseconds
uint32_t timerInterval = 2000;
uint32_t previousMicros = 0;

struct Pulse {
  uint32_t startTime;
  uint16_t pulseWidth;
  bool isOn;
};

Pulse Pulses[3] = {
  {0, 1000, false},
  {0, 1500, false},
  {0, 2000, false}
};

int leds[3] = {3, 5, 6};

void setup() {
  Serial.begin(115200);
  Serial.println(F("Software PWM"));
  for (uint8_t cnt = 0; cnt < 3; cnt++) {
    pinMode(leds[cnt], OUTPUT);
  }
}

void loop() {
  unsigned long currentMicros = micros();

  if (currentMicros - previousMicros >= timerInterval) {
    previousMicros = currentMicros;
    for (int i = 0; i < 3; i++)
      if (Pulses[i].pulseWidth > 0) {
        digitalWrite(leds[i], HIGH);
      }
  } else {
    for (int i = 0; i < 3; i++) {
      if (currentMicros - previousMicros >= Pulses[i].pulseWidth && Pulses[i].pulseWidth < 2000 ) {

        digitalWrite(leds[i], LOW);
      }
    }
  }
}