void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  for (int i=2;i<7;i++) pinMode(i, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  Serial.println("Switching on");
  for (int i=2;i<7;i++) {
    digitalWrite(i, HIGH);
    delay(100);
  }
  while (digitalRead(19)==LOW) {delay(10);}

  Serial.println("Switching off");
  for (int i=2;i<7;i++) {
    digitalWrite(i, LOW);
    delay(100);
  }
  delay(100);
  Serial.println("Play with potentiometer");
  while (true) {
    int val = analogRead(A0);
    val = map(val,0,1024,0,255);
    for (int i=2;i<7;i++) analogWrite(i, val);
    delay(100);
  }
}