* http://en.wikipedia.org/wiki/QR_code

    Numeric only    Max. 7,089 characters (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
    Alphanumeric    Max. 4,296 characters (0–9, A–Z [upper-case only], space, $, %, *, +, -, ., /, :)
    Binary/byte     Max. 2,953 characters (8-bit bytes) (23624 bits)
    Kanji/Kana  Max. 1,817 characters