UPDATE: Fault in processing code - doesn't receive correct data from Arduino

Question

I am receiving data from an LDR which I am inputting into processing. The data seems to be received to Arduino correctly and I have looked at the data being sent via the serial monitor and it all seems correct. However, the data that is being received in processing doesn't reflect the data received by the LDR so I think I have done something wrong here but not sure what as I am fairly new to this all. (Please see image for what is printing in the processing serial monitor).

Any help identifying where I have gone wrong would be so so helpful!

ARDUINO CODE

int rval=0;
int lightval;
//Recorded minimum and maximum values
int minval=0;
int maxval=950;
void setup() 
{
 Serial.begin(9600); 
}
void loop() 
{
 rval = analogRead(1);
 //Serial.println(rval);
 rval=constrain(rval,minval,maxval); 
 lightval=map(rval,minval,maxval,0,255); 
 //Serial.println(lightval);
 Serial.write(lightval);
}

PROCESSING CODE

import processing.serial.*;
Splash paintsplash;
Serial port;
float value=0;
void setup()
{
 size(600,600);
 smooth();
 background(255);
 paintsplash= new Splash();
 port=new Serial(this, Serial.list()[6],9600);
 //printArray(Serial.list());
}
void draw()
{
 paintsplash.display();
 paintsplash.splash();
 delay(200);
 if(0<port.available())
 {
 value=port.read();
 }
 println(value);
 if(value<=75)
 {
 fill(255,137,132);
 }
 else if(value>75 && value<=125)
 {
 fill(32,78,95);
 }
 else
 {
 fill(183,215,216);
 }
}

PROCESSING CLASS - PAINT_SPLASH

class Splash
{ 
 float x;
 float y;
 float size;
 Splash()
 {
 x=0;
 y=0;
 size=int(random(35));
 }
 void display()
 { 
 //fill(255,137,132);
 noStroke(); 
 ellipse(x,y,size,size); 
 } 
 void splash()
 { 
 float xcord=int(random(600));
 float ycord=int(random(600)); 
 pushMatrix();
 translate(xcord,ycord);
 for ( float i =3; i < 29; i ++)
 {
 float splashX = x + random(100); 
 float splashY = y + random(100);
 ellipse(splashX,splashY,size-i,(size-i+random(3)));
 }
 popMatrix();
 } 
}

enter image description here

• Edgar Bonet: Make sure the output you show belongs to the code you show. I doubt you have Serial.println(lightval); in the version whose output we see.
• user62091: Sorry yes I had commented out Serial.println(lightval) when I ran the script and the letters are still there
• Edgar Bonet: Then edit the question to comment out that line. At the risk of repeating myself, please make sure the output you show belongs to the code you show.

Answer 1

You're sending your lightval twice - once as a textual representation of the number, and once as a character representing the lower 8 bits:

Serial.println(lightval);
Serial.write(lightval);

For example:

Q308
R304
Q306

If you take the 308 and AND it with 255 you get 52. 52 as an ASCII character is R.

So you print 308, including a newline, then you print "R". Then you print 304, which would be 48 after ANDing with 255 - which of course is a Q.

• user62091: Thank you so much for this! You were correct, I am now getting the correct values in the Arduino serial monitor! I am now having trouble with the processing side of the code. If you can lend any more of your genius I would be very grateful!