const int ledPin=21;
const int frequency=500;
const int ledChannel=0;
const int resolution=8;
void setup() {
  // put your setup code here, to run once:
  //configure led pwm functionalities
  ledcSetup(ledChannel,frequency,resolution);
  //attach the channel to the gpio to be controlled
  ledcAttachPin(ledPin,ledChannel);
}

void loop() {
  // put your main code here, to run repeatedly:
  //to increase led brightness
  for(int dutyCycle=0;dutyCycle<=255;dutyCycle++)
  {
    //changing the led brightness with pwm 
    ledcWrite(ledChannel,dutyCycle);
    delay(15);
  }
  }