int relay = 13;
char input;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(relay, OUTPUT);
  Serial.print("Y: on, N:off");
 

}

void loop() {
  // put your main code here, to run repeatedly:
  input = Serial.read();
  if(input == 'Y'){
    digitalWrite(relay, HIGH);
  }
  if(input == 'N'){
    digitalWrite(relay, LOW);
  }
 
}