function gera_senha($chars=6)
{
    $s="a b c d e f g h i j k l m n o p q r s t u v w x y z";
    $s.=" 1 2 3 4 5 6 7 8 9 0";
    srand((float)microtime()*1000000);
    $apwd=explode(" ",$s);
    shuffle($apwd);
    $chr=$apwd[array_rand($apwd)];
    for ($i=0;$i<$chars;$i++) {
        $pwd.=$chr;
        while (strstr($pwd,$chr)!==false) {
            shuffle($apwd);
            $chr=$apwd[array_rand($apwd)];
        }
    }
    return $pwd;
}