code to reverse a bin2hex() function

function hex2bin($data) {
    $len = strlen($data);
    for($i=0;$i<$len;$i+=2) {
    	$newdata .= pack("C",hexdec(substr($data,$i,2)));
    }
   return $newdata;
}

just pass it the hex string and it will return the decoded data:

$coded="68656c6c6f";
$decoded=hex2bin($coded);