sending strings from processing

Forum 2005-2010 (read only) Software Interfacing
1

Hi. I'm having a lot of trouble sending a string from Processing to an Arduino. I am simply trying to send a string from processing ("light") and have the arduino light up an LED. The arduino code works fine if I type in "light" as a command in the arduino environment. My actual script is longer than the one I have posted and I need to be able to send and manipulate strings for my application. I've looked at the few posts about troubleshooting this issue but I have been unable to make my code work properly
thanks

this is my processing code

import processing.serial.*;
import cc.arduino.*;
Serial port;    //Create object from Serial class

void setup() {
  size(200, 200);
  noStroke();
  frameRate(10);
  //Open the port that the board is connected to and use the same speed (9600bps)
  port = new Serial(this, Serial.list()[0], 9600);
}

void draw() {
 port.write("light");
 delay (1000);
}

and this is my arduino code

#include <WString.h>                // include the String library
#define maxLength 5
String inString = String(maxLength);       // allocate a new String


int ledPinTop[] = {
  3, 5}; //3-red,5-blue,6-green
int ledPinBot[] = {
  9, 10}; //9-red,10-blue,11-green
const byte RED[] = {
  0, 255}; 
const byte BLUE[] = {
  255, 0}; 
const byte OFF[] = {
  255, 255}; 
  
    
void setup() {
  // open the serial port:
  Serial.begin(9600);
   
   for(int i = 0; i < 2; i++){
    pinMode(ledPinTop[i], OUTPUT);   
    pinMode(ledPinBot[i], OUTPUT);  
  }
  setColor(ledPinTop, OFF);       //Turn off led 1
  setColor(ledPinBot, OFF);       //Turn off led 2
  DDRC = 0xff;
}

void loop () {
  // See if there's incoming serial data:
  if(Serial.available() > 0) {
    // read the incoming data as a char:
    char inChar = Serial.read();
    if (inString.length() < maxLength) {
      inString.append(inChar);
    }    
  }
  if (inString.equals("light")){
     setColor(ledPinBot, BLUE); 
  }
}


void setColor(int* led, const byte* color){
  byte tempByte[] = {
    color[0], color[1]                                        };
  for(int i = 0; i < 2; i++){
    analogWrite(led[i], 255 - tempByte[i]);
  }
}
2

Hi,

if you receive a wrong character, you will never get a right result, because the string is not cleared after a string is received.
I think it is best to enclose your strings with special characters for start and end, for example:

$light#

then you can receive characters and throw them away as long as you don't receive the cgaracter $.
If you receive the character $, clear the string and append all next coming characters until you receive the character #. Then analyze the string ans start from the beginning to receive the next command.

good luck
Michael

3

Thanks for the help. Adding special characters to the script has helped me troubleshoot the issue.

I also realized that I was running into to problems because I was sending too many messages through the serial cable too quickly to the series of arduinos that I have connected by rs485. I now have my code set up so that a message is only sent if it registers change (before I had it set up so that it sent a message every loop whether or not there the new message was different than the previous message).