Program 

int sensorvalue=0;
void setup()
{ pinMode(A0,INPUT);
  pinMode(13, OUTPUT);
  Serial.begin(9600); }
void loop()
{ sensorvalue=analogRead(A0);
  Serial.println(sensorvalue);
  if(sensorvalue>=30)
  {     digitalWrite(13,HIGH);     } 
  else
  {     digitalWrite(13,LOW);      }  
}