---

int pd=2;                      //Photodiode to digital pin 2
int led=7;                   //LED to digital pin 7  
int senRead=0;                 //Readings from sensor to analog pin 0  
int limit = 900;            // play with system to find this limit
void setup()    
 {  
  pinMode(pd,OUTPUT);  
  pinMode(led,OUTPUT);  
  digitalWrite(pd,HIGH);       //supply 5 volts to photodiode  
  digitalWrite(led,LOW);      // LED initially off  
  Serial.begin(9600);         
 }  
void loop()  
 {  
  int val=analogRead(senRead);  //photodiode reading
  Serial.println(val);      
  if(val <= limit)              //If obstacle is nearer than the Threshold range  
  {  
   digitalWrite(led,HIGH);     // LED will be ON
   delay(20);  
  }  
  else if(val > limit)          //If obstacle is not in Threshold range  
  {  
   digitalWrite(led,LOW);      //LED is OFF
   delay(20);  
  }