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Messenger library for Arduino
by Thomas Ouellet Fredericks


  • I prefer you try to contact me through this thread on the Arduino forum
  • But if I do not answer, you can email me with questions here: mrtoftrash [at] gmail [dot] com


Latest version of Messenger including Max5 and Processing examples


  • 1.5 : Added readDouble() as suggested by Lorenzo C.
  • 1.4 : Added copyString() and checkString()
  • 1.3 : Added readLong() as suggested by G. Paolo Sani
  • 1.2 : Modified header file so it compiles in Arduino 12 and up
  • 1.1 : Added an attach method for a callback function
  • 1.0 : Initial release


Messenger is a "toolkit" that facilitates the parsing of ASCII messages. Messenger buffers characters until it receives a carriage return (CR). It then considers the message complete and available. The message is split into many elements as defined by a separator. The default separator is the space character, but can be any character other than NULL, LF or CR.


  • Do not use the Arduino IDE's "serial monitor" to test Messenger because it does not send a carriage return and therefore never "completes" sent messages!
  • Messenger only provides methods for incoming messages. The internal Serial.print() functions work just fine for outgoing messages.
  • All of your host software code that you designed for SimpleMessageSystem should still be compatible with Messenger. You will simply have to modify your Arduino code.


Messenger(byte separator)

       -- or --


You can create an instance of Messenger by specifying a message separator. If you do not specify a separator, the space character will be selected.

General Methods

void attach(callbackFuntion)

Attaches a callback function that is executed once a message is completed. This is the preferred way of working with Messenger (see example at the bottom of this page).

byte process(int serialData)

Returns true if a message has been completed and is available. Once a message is completed, it will be split into elements that you should be read immediately with read or string methods because every call to process() erases the completed message if there are any leftover elements.

byte available()

returns true if there are any elements available in the completed message. You must make a call to process() before using available().

Read Methods

You must make a call to process() to complete a message before trying to read it's elements. Every time you use a read method, the read element (even if it is not of the proper type) is removed from the completed message and Messenger will point to the next one. Use available() to check if their are any elements left to read.

int readInt()

Returns the element as an integer. Returns 0 if the element was not a number.

long readLong()

Returns the element as an long. Returns 0 if the element was not a number.

char readChar()

Returns the element as a character. If the character is part of a word, the whole word is removed from the completed message.

String Methods

void copyString(char* target, byte maxSize)

Copies the element as a string into the the array pointed by the target char array. maxSize must match the size of the target char array. The element is removed from the completed message.

byte checkString(char* toCheck)

Compares the element to the string toCheck.

  • If there is a match, the method returns true (1) and removes the element from the completed message.
  • If there is no match, the method returns false (0) and does not remove the element from the completed message.


Included in the download, you will find examples for Processing and Max5. Here is an example of how you would use Messenger in your Arduino code:

// This example sets all the values of the digital pins with a list through a callback function 

#include <Messenger.h>
// Instantiate Messenger object with the default separator (the space character)
Messenger message = Messenger(); 

// Create the callback function
void messageReady() {
    int pin = 0;
       // Loop through all the available elements of the message
       while ( message.available() ) {
	// Set the pin as determined by the message
         digitalWrite( pin, message.readInt() );

void setup() {
  // Initiate Serial Communication
  // Attach the callback function to the Messenger

void loop() {
  // The following line is the most effective way of using Serial and Messenger's callback
  while ( Serial.available() )  message.process( () );