 
 // command packet - start, address, data length, command, data[0 to 2], end
 // response packet when idle - 0xAA, 0x00, 0x02, 0x01, 0x83, 0x80, 0xBB
+const int ledPin = 13;
+const int signalPin = 4;
 char get_readID[] = { 0xAA , 0x00, 0x03, 0x25, 0x26, 0x00, 0x00, 0xBB };
 byte response[11];
-const int ledPin = 13;
+bool standby;
+unsigned long elapsed_time = 0;
 
 void setup() {
   Serial.begin(57600);
   RDM880.begin(9600);
   pinMode(ledPin, OUTPUT);
+  pinMode(signalPin, INPUT);
 }
 
 void loop() { 

    i++;

    // LED on if an RFID is detected
    if(response[7] != 0xFF) {
      digitalWrite(ledPin, HIGH);
    }
  }
  Serial.println();
}

  RDM880.write(get_readID, 8);
  delay(100);
  digitalWrite(ledPin, LOW); 
  standby = true;
  response[7] = NULL;

  // read response from RDM880 and print
  int i = 0;
