Arduino Ethernet Shield hooked up to LED message display

This hack allows you to display messages to a standard Amplus LED Message Display from Clas Ohlsson. The display is controlled by a remote control and via a RJ14 cable plugged into the screen. Serial data is transmitted from cable to the screen. The LED Message display expects the message you pass to it to be encrypted with a check sum. With the help of Rasmus blog post I could generate this checksum in Arduino. I turned his Perl code into Arduino code that you can see below.

  1. int stringToInt(String thisString) {
  2.   String letters = " !’#$%&’()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[/]^_`abcdefghijklmnopqrstuvwxyz{|}~";
  3.  
  4.   int newstr = 32 + letters.indexOf(thisString);
  5.  
  6.   return newstr;
  7. }
  8.  
  9. String generateMessage(String inputString) {
  10.  
  11.   byte checksum = 0×74;
  12.   int i;
  13.  
  14.   for(i = 0;i < inputString.length();i++) {
  15.       String currentChar    = inputString.substring(i,i+1);
  16.       int asciiChar         = stringToInt(currentChar);
  17.       checksum = checksum ^ asciiChar;
  18.   }
  19.  
  20.    String hexStr =  String(checksum, HEX);
  21.    hexStr.toUpperCase();
  22.    
  23.    String message = "<ID00><L1><PA><FE><MA><WC><FE>" + inputString + hexStr + "<E>";
  24.    return message;
  25.    
  26. }
  27.  
  28. String myString = "My led display message here";
  29.  String mess = generateMessage(myString);
  30.   Serial.print(mess);

Download my Arduino library on Github to try this out.