Error writing to serial: port not opened after already reading from serial

Processing Electronics (Arduino, etc.)
1

I’m trying to create a code that works with arduino by sending commands back and forth between the two. Processing is receiving commands from arduino easily enough but Processing is giving error “RuntimeException: Error writing to serial port COM4: Port not opened” when trying to write to serial.

import processing.video.*;
import processing.serial.*;

Serial port;
Capture camera;

String filePath = "C:/Users/Junor/OneDrive/Desktop/Pictures/";
String pictureCue = "Picture";
String readyCue = "Readying";
String serialRead = null;
int lf = 10;
int counter = 1;
Boolean pictureFlag = false;


void setup() {
  // Initialize port
  port = new Serial(this, Serial.list()[1], 9600);
  port.clear();
  serialRead = port.readStringUntil(lf);
  serialRead = null;
  
  // Call serialReady until return true
  while(serialReady(port) == false) {}
  // Let function serialEvent run
  pictureFlag = true;
  port.bufferUntil('\n');
  
  // Initialize live camera feed
  size(640,480);
  camera = new Capture(this, Capture.list()[0]);
  camera.start();
}

void captureEvent(Capture camera) {
  camera.read();
  
}

void draw() {
  image (camera, 0, 0);
}

void serialEvent(Serial port) {
  if (pictureFlag == false) {
    noLoop();
    exit();
  }
  else {
    loop();
    
    port.bufferUntil(lf);
    if (port.available() > 0) {
      serialRead = port.readString();
    
      if (serialRead != null) {
        if (serialRead.equals(pictureCue) == true) {
          println(serialRead);
          println("Picture " + counter);
          saveFrame(filePath + counter + ".png");
          counter++;
          port.write("Saved\n");
        }
      }
    }
  }
}

Boolean serialReady(Serial port) {
  Boolean readyFlag = false;
  port.bufferUntil(lf);
  if (port.available() > 0) {
    serialRead = port.readString();
    print(serialRead);
    if (serialRead != null) {
      if (serialRead.equals(readyCue) == true) {
        readyFlag = true;
      }
      else {readyFlag = false;}
    }
  }

  if (readyFlag == true)
    print ("readyFlag " + readyFlag);
// *
// *
  port.write("Ready\n");    // Calling the error here
// *
// *
  return readyFlag;
}

Clearly, “Port not opened” doesn’t mean what I think it means, since in order to get to the spot that is flagged as the error it has to receive a specified string to move on. Is there something I declared incorrectly or out of order or something? I know I’ve had a problem like that in the past.

2

Hello,

I was getting same error.

I added some brackets in the if() statement so you only did a port.write() when readyFlag was true :

if (readyFlag == true)
    { // glv added
    print ("readyFlag " + readyFlag);
// *
    port.write("Ready\n");    // Calling the error here
    } // glv added
// *

After all that was said and done I did a rewrite and only used the serialEvent() for handshaking and not the serialReady(Serial port) and got this working.

I also used trim() to clean up incoming serial strings:
if (serialRead.trim().equals("pictureCue") == true)
:)

I wrote some Arduino code to do the serial handshaking .

:)

3

Fantastic, exactly what I needed! I took your suggestions and added trim functions, as well as condensed it all into serialEvent. Turned out much cleaner this way in the end as well, and gets rid of my loop problem.
Thanks you so much, this had been bugging me for a day or two now. That one step has practically finished the project

1 Like
4

Great!

I also use a lot of println() statements to see progress of code and that really helps debugging code.

I have a few other topics on serial communication with hints and tips that may be of interest.

Have fun!