// the number of the LED pin
const int ledPin1 = 27;  // GPIO27
const int ledPin2 = 26;  // GPIO27

// setting PWM properties
const int freq = 1000;
const int ledChannel1 = 0;
const int ledChannel2 = 1;
const int resolution = 8;
 
void setup(){
  // configure LED PWM functionalitites
  ledcSetup(ledChannel1, freq, resolution);
  ledcSetup(ledChannel2, freq, resolution);
  // attach the channel to the GPIO to be controlled
  ledcAttachPin(ledPin1, ledChannel1);
  ledcAttachPin(ledPin2, ledChannel2);
}
 
void loop(){
  // increase the LED brightness
  for(int dutyCycle1 = 0; dutyCycle1 <= 50; dutyCycle1++){   
    // changing the LED brightness with PWM
    ledcWrite(ledChannel1, dutyCycle1);
    ledcWrite(ledChannel2, dutyCycle1);
    delay(15);
  }

  // decrease the LED brightness
  for(int dutyCycle = 50; dutyCycle >= 0; dutyCycle--){
    // changing the LED brightness with PWM
    ledcWrite(ledChannel1, dutyCycle);  
    ledcWrite(ledChannel2, dutyCycle);  
    delay(15);
  }
}