Then you make a completely new Processing sketch (or command line java app) with the same TCPClient object you've been using to make your rendering clients:

// A client object
TCPClient client;

In setup(), initialize the Client object. Here, a settings XML file is required. This file tells the client what its local dimensions are, as well as its location within the master dimensions. # indicates a comment and end all lines with a semi-colon (and no spaces!) Here is an example:

<settings>
	<id>555</id>
	<name>an asynch client</name>  <!-- optional -->
        <!-- Server address. Localhost for testing. -->
	<server>
		<ip>localhost</ip>
		<port>9002</port> 
	</server>
        <!-- IMPORTANT!!! Set to true to make this an async client. -->
	<asynchronous>true</asynchronous>
        <!-- IMPORTANT!!! Set to true if you would like to also receive data from server. -->
	<asynchreceive>false</asynchreceive>
	<verbose>false</verbose>
</settings>

Once you've created the XML file, you can make the client object in setup() and start it!

  // make a new Client using an XML file
  client = new TCPClient(this, "asynch.xml");
  client.start();
  

Then, whenever you want, send a message. It could be information from a sensor, a microphone or just some protocol you make up! The message will find its way to all of your clients. The code looks like this:

public void mousePressed() {
  client.broadcast("Your message here!");
}

Or you can broadcast from draw().

client.broadcast("Your message here!");		

If you would like to receive data from the server, make sure you set asynchreceive to tru in your XML file and add a dataEvent() to your sketch.

//--------------------------------------
    // asynchreceive must be set to true in
    // asynch.xml to receive data here
    public void dataEvent(TCPClient c) {
    	println("Raw message: " + c.getRawMessage());
    	if (c.messageAvailable()) {
    		String[] msgs = c.getDataMessage();
    		for (int i = 0; i < msgs.length; i++) {
    			println("Parsed message: " + msgs[i]);
    		}
    	}
    	
    }

Note: The converse is true as well. If asynchreceive is set to true in the xml file, you must have a dataEvent() in your sketch.