I2C Communication

Projects Programming
1

I am trying to carry out an I2C communication between arduino and esp. In this case I want to send 6 messages from the slave to the master, but the communication is corrupted from the 5. What is happening? The messages consist of 8 characters where 7 are the message and the 8th use to indicate the end of it.

//Slave part

#include <Wire.h>

String m0_I2C;
String m1_I2C,m2_I2C,m3_I2C,m4_I2C,m5_I2C;


void setup() {
  Wire.begin(8);                // join i2c bus with address #8
  Wire.onRequest(requestEvent); // register request event
  Serial.begin(9600);           // start serial for debug
}

void loop() {

  float m0=22.56;
  float m1=80.0;
  float m2=42.9;
  float m3=200.58;
  float m4=200.0;
  float m5=70.0;


  m0_I2C=floatToString_I2C(m0, 7, 2, true);
  m1_I2C = floatToString_I2C(m1, 7, 2, true);
  m2_I2C=floatToString_I2C(m2, 7, 2, true);
  m3_I2C=floatToString_I2C(m3, 7, 2, true);
  m4_I2C=floatToString_I2C(m4, 7, 2, true);
  m5_I2C=floatToString_I2C(m5, 7, 2, true);
 
  Serial.println (m0.c_str());
  Serial.println (m1.c_str());
  Serial.println (m2_I2C.c_str());
  Serial.println (m3_I2C.c_str());
  Serial.println (m4_I2C.c_str());
  Serial.println (m5_I2C.c_str());
  delay(2000);
}



// function that executes whenever data is requested from master
void requestEvent() {
  Wire.write(m0_I2C.c_str());
  Wire.write(m1_I2C.c_str());
  Wire.write(m2_I2C.c_str()); 
  Wire.write(m3_I2C.c_str());   
  Wire.write(m4_I2C.c_str());   
  Wire.write(m5_I2C.c_str());   
}



String floatToString_I2C( float n, int l, int d, boolean z){
  char c[l+1];
  char s[6];
  String f;

  dtostrf(n,l,d,c);
  f=String(c);

  if(z){
    f.replace(" ","0");
  }
  f.concat("/");    // 8th
 
  return f;
}



//Master part

#include <Wire.h>


void setup() {
  Serial.begin(9600); /* begin serial for debug */
  Wire.begin(5, 4); /* join i2c bus with SDA=D1 and SCL=D2 of NodeMCU */
}

void loop() {

  Wire.beginTransmission(8); /* begin with device address 8 */
  Wire.write("Hello Arduino"); 
  Wire.endTransmission();   

  Wire.requestFrom(8, 50);  // 
  String m0 = "";
  String m1 = "";
  String m2 = "";
  String m3 = "";
  String m4 = "";
  String m5 = "";
  int i=0;
  while (i<50){
    i++;
    char c=Wire.read();
    Serial.println(c);
  }
  m0=comunicacion(8);
  Serial.println(m0);
  m1=comunicacion(8);
  Serial.println(m1);
  m2=comunicacion(8);
  Serial.println(m2);
  m3=comunicacion(8);
  Serial.println(m3);
  m4=comunicacion(8);
  Serial.println(m4);
  m5=comunicacion(8);
  Serial.println(m5);
 
  delay(1000);
}

  String comunicacion(int tamano){
  char punto='/';
  int i=0;
  String variable ="";
  while(i<tamano){
    i++;
    char c=Wire.read();
    Serial.print(c);
    if (c != punto){
      variable.concat(c);
    } 
  }
  return variable;
}
2

char c[l+1]; explain, please.

Why the crazy mix of Strings and strings?

3

// To convert a float to string
// n -> float to convert.
// l -> lenght of the string, default 8.
// d -> decimals, default 2.
// z -> if you want to add ceros at the left, default true.

String floatToString( float n, int l, int d, boolean z){
  char c[l+1];
  String s;

  dtostrf(n,l,d,c);
  s=String(c);

  if(z){
    s.replace(" ","0");
  }
  s.concat("/");

  return s;
}
4

Which Arduino board and which ESP do you use ?
Do you have pullup resistors ? What is their value ?
The Arduino Uno has a 5V I2C bus and only a 32 byte buffer for I2C data.

We don't use readable text with the I2C bus. Can you send binary data ?

5

Koepel:
We don't use readable text with the I2C bus. Can you send binary data ?

But, it is allowed (Wire.print()) and useful in some cases.

6

I've found this post: Increase 32 byte I2C buffer size in Wire library - Networking, Protocols, and Devices - Arduino Forum between two arduino uno, and they can send 192 bytes.

In my case I work with an arduino mega and esp-01

7

Did you increase the buffer size ? So with every update of the Arduino IDE your project will crash if you forget to do that ?

The Arduino Mega 2560 is a 5V board and the ESP-01 with ESP8266 runs at 3.3V.
They say that the ESP8266 is somewhat 5V tolerant, so it might work. I still prefer a level shifter between them.

You can send the same data to the serial monitor to see what you are sending. Is there a seperator between the float numbers ?

If something is not working, than take a step back and do something very simple. Try to send a byte, and test if that is 100% transferred for example one hour long. Then send multiple bytes. Then you can send maybe the float variables as binary data.

GolamMostafa:
But, it is allowed (Wire.print()) and useful in some cases.

Not in the world that I live in :wink: Okay, maybe when the binary data is different on different platforms. But the software float library is fully IEEE compatible.

8

Thanks Koepel!

I've just discovered the limitations of I2C in this post: https://forum.arduino.cc/index.php?topic=54439.0

There are only 5 buffers

Koepel:
Did you increase the buffer size ? So with every update of the Arduino IDE your project will crash if you forget to do that ?