title: Arduino RFID checksum calculation and key visualization
body: <p>I'm using this <a href="http://www.seeedstudio.com/depot/125khz-rfid-module-uart-p-171.html?cPath=144_153" rel="nofollow">RFID</a> module for Arduino Ethernet R3 and I need to retrieve from the Software Serial the card (<a href="http://www.seeedstudio.com/wiki/RFID_tag_combo_%28125khz%29_-_5_pcs" rel="nofollow">TAG</a>) ID that is written outside the tag.
  The module's <a href="http://www.seeedstudio.com//depot/datasheet/RDM630-Spec..pdf" rel="nofollow">datasheet</a> says that 14 bytes are sent to the Arduino. The first is the header, the last the footer, the 2 bytes before the footer are the checksum, and the other 10 bytes are the ASCII data that contains the tag ID.</p>
  
  <p>How can I recreate the ID of the card, and control the checksum? For example with a tag that has this ID:  0013530444, the Arduino response is:</p>
  
  <pre><code>I received: 2
  I received: 51
  I received: 67
  I received: 48
  I received: 48
  I received: 67
  I received: 69
  I received: 55
  I received: 53
  I received: 52
  I received: 67
  I received: 67
  I received: 66
  I received: 3
  </code></pre>
  
  <p>But I've no idea how to print on the screen the ID read by the Arduino. How to calculate the <a href="http://www.seeedstudio.com/wiki/index.php?title=125Khz_RFID_module_-_UART" rel="nofollow">checksum</a>?</p>
  
  <p><a href="http://www.seeedstudio.com/wiki/index.php?title=125Khz_RFID_module_-_UART" rel="nofollow">http://www.seeedstudio.com/wiki/index.php?title=125Khz_RFID_module_-_UART</a></p>
  
  <p>Can anyone help me?</p>