Writes binary data to the serial port. This data is sent as a byte or series of bytes; to send the characters representing the digits of a number use the print() function instead.
Serial: serial port object. See the list of available serial ports for each board on the Serial main page.
val: a value to send as a single byte
str: a string to send as a series of bytes
buf: an array to send as a series of bytes
len: the number of bytes to be sent from the array
write() will return the number of bytes written, though reading that number is optional