magento 1.9 – Generate tiny coupon code

I used

Use automatic generation

Magento promo code but all codes generated uppercase as F1Z8Z2FPQQYL

How can I generate the tiny coupon ?!

I found the code but I do not understand it. How to generate coupon code in lower case!

    public function generateCode ()
{
$ format = $ this-> getFormat ();
if (! format of $) {
$ format = Mage_SalesRule_Helper_Coupon :: COUPON_FORMAT_ALPHANUMERIC;
}
$ length = max (1, (int) $ this-> getLength ());
$ split = max (0, (int) $ this-> getDash ());
$ suffix = $ this-> getSuffix ();
$ prefix = $ this-> getPrefix ();

$ splitChar = $ this-> getDelimiter ();
$ charset = Mage :: helper (& # 39; salesrule / coupon & # 39;) -> getCharset ($ format);

$ code = & # 39;
$ charsetSize = count ($ charset);
for ($ i = 0; $ i<$length; $i++) {
            $char = $charset[mt_rand(0, $charsetSize - 1)];
            if ($split > 0 && ($ i% $ split) == 0 && $ i! = 0) {
$ char = $ splitChar. $ char;
}
$ code. = $ char;
}

$ code = $ prefix. $ code. suffix $;
return $ code;
}