Nodejs send data to Arduino using serial

Question

I have some nodejs code that sends data through serial port. My problem is I'm coding the arduino part blinded. Since I can't see the data that my arduino reads from serial.

Node.js

serialport.write('3');

Arduino.ino

char rcved = Serial.read();

I need to see what I get in rcved. But when I tried:

Serial.println(rcved);

and then opening the Serial Monitor I get the error that the Serial port is busy. I understand that it is being used by Node.js to send the data.. But how can I see what my arduino code is reading then!?

The error:

processing.app.SerialException: Error opening serial port 'COM4'.
at processing.app.Serial.<init>(Unknown Source)
at processing.app.Serial.<init>(Unknown Source)
at processing.app.SerialMonitor$3.<init>(SerialMonitor.java:94)
at processing.app.SerialMonitor.open(SerialMonitor.java:94)
at processing.app.Editor.handleSerial(Editor.java:2536)
at processing.app.EditorToolbar.mousePressed(EditorToolbar.java:357)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Caused by: jssc.SerialPortException: Port name - COM4; Method name -     openPort(); Exception type - Port busy.
at jssc.SerialPort.openPort(SerialPort.java:164)
... 37 more
Error opening serial port 'COM4'.

Please help! I need this to debug

Thank you

bummi · Accepted Answer · 2015-07-14 16:43:41Z

Sending serial messages to the Arduino is not as easy as simply passing in a String. Unfortunately you have to send the String character by character which the Arduino will receive and concatenate back to a String. After you sent the last character you need to send one final new line character (/n) which is a signal for the Arduino to stop concatenating and evaluate the message.

This is what you need to do in your Node.js server:

// Socket.IO message from the browser
socket.on('serialEvent', function (data) {

    // The message received as a String
    console.log(data);

    // Sending String character by character
    for(var i=0; i<data.length; i++){
        myPort.write(new Buffer(data[i], 'ascii'), function(err, results) {
            // console.log('Error: ' + err);
            // console.log('Results ' + results);
        });
    }

    // Sending the terminate character
    myPort.write(new Buffer('\n', 'ascii'), function(err, results) {
        // console.log('err ' + err);
        // console.log('results ' + results);
    });
});

And this is the Arduino code that receives this:

String inData = "";

void loop(){
    while (Serial.available() > 0) {
        char received = Serial.read();
        inData.concat(received);

        // Process message when new line character is received
        if (received == '\n') {
            // Message is ready in inDate
        }
    }
}

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