esp8266-01 and arduino UNO communicating over i2c

Question

i am not able to communicate over i2c with my esp-01 as master and UNO as slave. i get special characters sent back to esp, but my esp is sending correctly... output on my esp-01 output on my esp-01 output on my UNO is output on my UNO

connections are esp-01 gpio-0 to uno A4 and gpio-2 to uno A5 is it because i am not using a level shifter or any mistake in my code..?

here is my esp master code

#include <Wire.h>
#define I2CAddressESPWifi 6
int x=32;
void setup()
{
 Serial.begin(115200);
 Wire.begin(0,2);//Change to Wire.begin() for non ESP.
}
void loop()
{
 Wire.beginTransmission(I2CAddressESPWifi);
 Wire.write(x);
 Wire.endTransmission();
 x++;
 delay(1);//Required. Not sure why!
 Wire.requestFrom(I2CAddressESPWifi,10);
 Serial.print("Request Return:[");
 while (Wire.available())
 {
 delay(100);
 char c = Wire.read();
 Serial.print(c);
 }
 Serial.println("]");
 delay(500);
}

and here is my Uno slave code

#include <Wire.h>
#define I2CAddressESPWifi 6
void setup()
{
 Serial.begin(115200);
 Wire.begin(I2CAddressESPWifi);
 Wire.onReceive(espWifiReceiveEvent);
 Wire.onRequest(espWifiRequestEvent);
}
void loop()
{
 delay(1);
}
void espWifiReceiveEvent(int count)
{
 Serial.print("Received[");
 while (Wire.available())
 {
 char c = Wire.read();
 Serial.print(c);
 }
 Serial.println("]");
}
void espWifiRequestEvent()
{
 String ts = getTime();
 Serial.print("Sending:[");
 Serial.print(ts.c_str());
 Serial.println("]");
 Wire.write(ts.c_str());
}
String getTime(){
 int sec = millis() / 1000;
 int min = sec / 60;
 int hr = min / 60;
 String ts = "U:";
 if (hr<10) ts+="0";
 ts += hr;
 ts +=":";
 if ((min%60)<10) ts+="0";
 ts += min % 60;
 ts +=":";
 if ((sec%60)<10) ts+="0";
 ts += sec % 60;
 return(ts);
}

• Mikael Patel: Pullup resistors?
• Vallabh Rao: no... why should I ? and between what?
• Majenko: Try choosing an address that isn't reserved for special purposes. One that is between 8 and 119 inclusive.
• Vallabh Rao: I tried 15, that didn't make any difference... :(
• Mikael Patel: Pullup resistors on the I2C bus (SDA, SCK) is required if not provided on the board. Check the I2C specification.

Answer 1

Perhaps the Serial.print()s in the slave's request event function are causing too much delay (clock stretching?). You should make the Wire.write() the second statement in that function right after the getTime call. Or you could use Wire.write("Hello") as the only statement in the function, so you can narrow down the problem.