I2C coding issue

Development Boards Arduino
1

I am working on a 3D printer having a Generation 6 electronics board (atmega644). I have connected it with Arduino Uno and established communication via I2C. I need to send a signal from the printer to a pin on Arduino say pin 2. Whenever a g code is executed, the printer will send a signal to Arduino. So when G1 is executed, I want LED connected to pin 2 of Arduino to light up and when G28 is executed, I want it to be off. Currently, I have this in printer

#include <Wire.h>

//i2c address of the gen 6
int REP_RAP_ADDR = 4;
//my address
int CP_ADDR = 5;
void setup()
{  
  Wire.begin(4);
}
void loop
{
  Wire.beginTransmission (5);
  Wire.send ("G1"); 
  Wire.send ("G28");
}

And this in Arduino.

#include <Wire.h>

//i2c address of the gen 6
int REP_RAP_ADDR = 4;
//my address
int CP_ADDR = 5;
int ledPin = 2;

void receiveEvent(int howMany)
{
  while(0 < Wire.available()) // loop through all
    Wire.receive(); // receive byte as a character  
}

void setup()
{
  Wire.begin(CP_ADDR);
  Wire.onReceive(receiveEvent); // register event so that anything received on i2c is sent to the serial 
  pinMode(ledPin, OUTPUT);  
}

void loop()
{
 char str1[] = "G1";
 char str2[] = "G28"; 
  
  if (strcmp(str1, ____) == 0){
  
    
      //turn dispenser on
      digitalWrite(2, HIGH); }
    
    if (strcmp(str2,_____ ) == 0) {
    
      //turn dispenser off
      digitalWrite(2, LOW);}
   
}

_____ is the string of incoming data which I am unable to store.

But it is not working. Any suggestions.

2

It doesn’t look like your code should do anything.

You have essentially,

if (true)

{

pin 2 high

}

if(true)

{

pin 2 low

}

Therefor, pin2 will always be low.

I don’t see anywhere that you actually put the received i2c data into a string.

3

What you are saying, is absolutely correct.

I should be comparing the received data with str1 or str2 but I am unable to figure out how to store the incoming data and then comparing step will come afterwards.

First a little help on storing the incoming data into an array.

4

to get your wire buffer into an array you can try this

char incoming[4]; // Set this to the maximum expected string length +1 for a null char 
int length;
void Loop(){
if(Wire.available > 0){
    delay(100); // The arduino is faster than serial, wait to make sure all the data is there, otherwise you'll end up with only half your data in the array
    length = Wire.available()
    for (int i = 0; i < length; i++) {
        if(i > 4){                       //prevent data corruption in case you accidentally receive more than the array can hold
            incoming[4] = "\0";  //put a null char at the end of the array
            break;
        } 
        incoming[i] = Wire.receive();
        }
    }
    // Compare function goes here
}
5

Shouldn’t it go into the void receiveEvent, like this

void receiveEvent(int howMany)
{
  char incoming[4]; // Set this to the maximum expected string length +1 for a null char 
  int length;
  while(0 < Wire.available()) // loop through all
   {
     delay(100); 
    length = Wire.available();
    for (int i = 0; i < length; i++) {
        if(i > 4){                       //prevent data corruption in case you accidentally receive more than the array can hold
            incoming[4] = '\0';  //put a null char at the end of the array
            break;
        } 
        incoming[i] = Wire.receive();
        }
    }
    char str1[] = "G1";
 char str2[] = "G28"; 
  
  if (strcmp(str1, incoming) == 0){
  
    
      //turn dispenser on
      digitalWrite(2, HIGH); }
    
    if (strcmp(str2, incoming) == 0) {
    
      //turn dispenser off
      digitalWrite(2, LOW);}
}

This

incoming[4] = “\0”;

should be like this

incoming[4] = ‘\0’;

And the void loop will be empty, like this,

void loop()
{  
}

Correct me if I am wrong.

6

This doesn’t seem very robust to me. What you should be doing is sending a null ‘\0’ at the end of your string to the Arduino (signifying a stop byte or something) and doing something like this on the receiving end

char buff[MAX_BUFF_SIZE];

void receive_data(void)
{
  static int i = 0;
  while(data_available())
  {
     buff[i] = received_byte();
     
     if (buff[i]=='\0')
     {
        do_compare_strings_thingy(buff);
        i = 0;
      } else {
         i++;
         if (i > MAX_BUFF_SIZE) {i = 0;}
      }
   }
}
7

I have this code in Reprap.

#include <Wire.h>

#define reprap 6
#define slave 5

void setup ()
 {
 Wire.begin (reprap);
 }
 
void loop()
{
  Wire.beginTransmission (slave);
  Wire.send ("G1"); 
  Wire.endTransmission();

  delay (1000);
  
  Wire.beginTransmission (slave);
  Wire.send ("G28");
  Wire.endTransmission();

  delay (1000);

}

And this in Arduino.

#include <Wire.h>

#define slave 5
#define LED 13

void receiveEvent (int howMany)
 {
  char buf [10];
  byte i = 0;

  while (Wire.available () > 0)
    {
    char c = Wire.receive ();
    if (i < sizeof (buf) - 1)  // check for overflow
      buf [i++] = c;
    }  // end of while

   buf [i] = 0;  // terminating null
   
  if (memcmp (buf, "G1", 2) == 0)
    digitalWrite (LED, HIGH);
  else if (memcmp (buf, "G28", 3) == 0)
    digitalWrite (LED, LOW);
}  // end of receiveEvent


void setup () 
{
  Wire.begin (slave);
  Wire.onReceive (receiveEvent);
  pinMode (LED, OUTPUT);
}  // end of setup

void loop() 
{
// nothing in main loop
}

The Reprap works through a software Repsnapper that sends G-Codes in this format:

G28 X0 Y0

G1 X10 Y10

According to the coding, Arduino should recognize when a command with G1 or G28 is executed but currently the LED is not turning ON and OFF according to the commands given. It just keeps on blinking every second. What could be the problem here :?