Using @bill-shirley answer with a little addition
function str_to_hex($string) {
$hexstr = unpack('H*', $string);
return array_shift($hexstr);
}
function hex_to_str($string) {
return hex2bin("$string");
}
Usage:
$str = "Go placidly amidst the noise";
$hexstr = str_to_hex($str);// 476f20706c616369646c7920616d6964737420746865206e6f697365
$strstr = hex_to_str($str);// Go placidly amidst the noise