int Led = 6 ; // Arduino built in LED
int SENSOR = A7 ; // define the Hall magnetic sensor
int val; // define numeric variables 


void setup ()
{

  pinMode (Led, OUTPUT) ;    // define LED as output
  pinMode (SENSOR, INPUT) ;  // define the Hall magnetic sensor line as input
  digitalWrite (Led, LOW);   //initialise
}
 
void loop ()
{
  val = analogRead (SENSOR) ; // read sensor line
  
  if (val < 30) // when the Hall sensor detects a magnetic field, Arduino LED lights up
  {
    digitalWrite (Led, HIGH);
  }
  else
  {
    digitalWrite (Led, LOW);
  }
  delay(100);
}