Weird random data being sent from Arduino to Processing

Question

I'm trying to read data from a photocell resistor and my Arduino Diecimila and then graph it in real-time with Processing.

It should be painfully simple; but it’s growing into a little bit of a nightmare for me.

The code I'm running on my Arduino:

int photoPin;

void setup(){

  photoPin = 0;
  Serial.begin(9600);
}

void loop(){

  int val = int(map(analogRead(photoPin), 0, 1023, 0, 254));
  Serial.println(val); // Sending data over Serial
}

The code I'm running in Processing:

import processing.serial.*;

Serial photocell;

int[] yvals;

void setup(){

  size(300, 150);
  photocell = new Serial(this, Serial.list()[0], 9600);
  photocell.bufferUntil(10);
  yvals = new int[width];
}

void draw(){

  background(0);
  for( int i = 1; i < width; i++ ){
    yvals[i - 1] = yvals[i];
  }

  if(photocell.available() > 0){
    yvals[width - 1] = photocell.read();
  }

  for(int i = 1; i < width; i++){
    stroke(#ff0000);
    line(i, yvals[i], i, height);
  }
  println(photocell.read()); // For debugging
}

I've tested both bits of code separately, and I know that they work. It's only when I try to have the input from the Arduino going to Processing that the problems start.

When I view the data in Arduino's "Serial Monitor", I get a nice constant flow of data that seems to look valid.

But when I read that same data through Processing, I get a repeating pattern of random values.

Josh Sandlin · Accepted Answer · 2008-11-02 02:03:28Z

4

After a closer look at the resources at hand, I realized that the problem had already been solved for me by the folks over at http://arduino.cc

http://arduino.cc/en/Tutorial/Graph

Oh how much time I could have saved if I had seen that earlier.

answered Nov 2, 2008 at 2:03

Josh Sandlin

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1 Comment

Peter Mortensen Over a year ago

What specifically was it?

Peter Mortensen · Accepted Answer · 2022-12-07 01:19:18Z

2

You could transmit that data with the Plotly Arduino API, which along with the documentation and setup is available here. Basic idea: you can continuously stream data from your Arduino, or transmit a single chunk.

Then, if you want to embed it into a site, you'll want to grab the URL and use this snippet:

<iframe id="igraph" 
        src="https://plot.ly/~abhishek.mitra.963/1/400/250/" 
        width="400" 
        height="250" 
        seamless="seamless" 
        scrolling="no"></iframe>

You can change the width/height dimensions in that snippet. Note: you need to swap in your own URL there to get it stream through.

Here's an example of how it looks to stream Arduino data

Enter image description here

Full disclosure: I work for Plotly.

edited Dec 7, 2022 at 1:19

Peter Mortensen

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answered Nov 6, 2013 at 2:56

Mateo Sanchez

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