error sending serial data when serialEvent() is used

Core Library Questions

sheva29

error sending serial data when serialEvent() is used

in Core Library Questions • 11 months ago

I am trying to use Arduino and Processing using a potentiometer to control the sizes of the squares that are drawn on top of this image

Getting the color from its same location, so I can blur the picture with the potentiometer by increasing and reducing the size of the squares.

Unfortunately I keep getting this message:

error, disabling serialEvent() for /dev/tty.usbmodem1421

java.lang.reflect.InvocationTargetException

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

at java.lang.reflect.Method.invoke(Method.java:597)

at processing.serial.Serial.serialEvent(Serial.java:279)

at gnu.io.RXTXPort.sendEvent(RXTXPort.java:732)

at gnu.io.RXTXPort.eventLoop(Native Method)

at gnu.io.RXTXPort$MonitorThread.run(RXTXPort.java:1575)

Caused by: java.lang.NullPointerException

at image_pixels_arduino_controller.serialEvent(image_pixels_arduino_controller.java:70)

... 8 more

This is the code. Any suggestion will be much appreciated!

import processing.serial.*;
Serial myPort;
PImage myImage;
void setup() {
size(500, 399);
// List all the available serial ports
println(Serial.list());
// I know that the first port in the serial list on my mac
// is always my Arduino, so I open Serial.list()[0].
// Open whatever port is the one you're using.
myPort = new Serial(this, Serial.list()[4], 9600);
// don't generate a serialEvent() unless you get a newline character:
myPort.bufferUntil('\n');
imageMode(CENTER);
myImage = loadImage("rdjr.jpg");
image(myImage, width/2, height/2);
noStroke();
}
void draw() {
}
void serialEvent( Serial myPort) {
// get the ASCII string:
String inString = myPort.readStringUntil('\n');
if (inString != null) {
// trim off any whitespace:
inString = trim(inString);
// convert to an int and map to the screen:
for ( int i = 0; i < 1000; i++) {
float inByte = float(inString);
float diagonal = dist(0, 0, width, height);
inByte = map(inByte, 0, 1023, 0, diagonal);
int x = int(random(0, width));
int y = int(random(0, height));
color getColor = myImage.get(x, y);
fill(getColor, 50);
rect(x, y, inByte, inByte);
}
}
println(inString);
}

Replies(2)

PhiLho

Re: error sending serial data when serialEvent() is used

11 months ago

In case you don't know what is an NPE; Why do I get a NullPointerException?
It is hard to tell what is the line 70. Trick: export the sketch, look at the generated .java file, you can spot this line.
At a glance, your code seems rather OK, supposing you loaded the image correctly. You should try and avoid to name your function parameter with the same name than a global variable, as general good practice.
Try printing this parameter, in case that's the null variable (unlikely? I have no serial experience). BTW, I moved this topic to this more specialized section...

BTW, why do you repeat 1000 times the same code, without using the i index? If that's to display longer the result, you should read the How do I display a message for a few seconds? article...

sheva29

Re: error sending serial data when serialEvent() is used

11 months ago

So, the code looked fine, but working with the serial library is completely different, so I figured it out with a different example and it worked. Here is the code:

import processing.serial.*;
Serial myPort; // The serial port
int[] serialInArray = new int[3]; // Where we'll put what we receive
int serialCount = 0; // A count of how many bytes we receive
boolean firstContact = false; // Whether we've heard from the microcontroller
PImage myImage; //Variable of the image
int rectSize; // Size of the squares
void setup() {
size(500, 399);
imageMode(CENTER);
myImage = loadImage("rdjr.jpg");
image(myImage, width/2, height/2);
noStroke();
// Print a list of the serial ports, for debugging purposes:
println(Serial.list());
// On Windows machines, this generally opens COM1.
// Open whatever port is the one you're using.
// In my case Serial.list()[4]. is the port where Arduino is connected, make sure to change-
// it to the correct one, from the list that you get depending on your computer
String portName = Serial.list()[4];
myPort = new Serial(this, portName, 9600);
}
void draw() {
for ( int i = 0; i < 1000; i++) {
int x = int(random(0, width));
int y = int(random(0, height));
color getColor = myImage.get(x, y);
fill(getColor, 50);
rect(x, y, rectSize, rectSize);
}
}
void serialEvent(Serial myPort) {
// read a byte from the serial port:
int inByte = myPort.read();
// if this is the first byte received, and it's an A,
// clear the serial buffer and note that you've
// had first contact from the microcontroller.
// Otherwise, add the incoming byte to the array:
if (firstContact == false) {
if (inByte == 'A') {
myPort.clear(); // clear the serial port buffer
firstContact = true; // you've had first contact from the microcontroller
myPort.write('A'); // ask for more
}
}
else {
// Add the latest byte from the serial port to array:
serialInArray[serialCount] = inByte;
serialCount++;
// If we have 3 bytes:
if (serialCount > 2 ) {
rectSize = serialInArray[0];
// print the values (for debugging purposes only):
println(rectSize);
// Send a capital A to request new sensor readings:
myPort.write('A');
// Reset serialCount:
serialCount = 0;
}
}
}

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