function generate_code($length = 8) {

              // start with a blank password
              $password = "";

              // define possible characters
              $possible = "aAb0BcBdD2eEf3gGhHjJ4kKLmMnN5opPqQrRsS6tTu8UvVwW7xXyY9zZ";

              // set up a counter
              $i = 0;

              // add random characters to $password until $length is reached
              while ($i < $length) {

                // pick a random character from the possible ones
                $char = substr($possible, mt_rand(0, strlen($possible)-1), 1);

                // we don't want this character if it's already in the password
                if (!strstr($password, $char)) {
                  $password .= $char;
                  $i++;
                }

              }

              // done!
              return $password;

        }