[Solved] ESP8266 with I2C - recieving just nonsense letters

Projects Networking, Protocols, and Devices
1

Hi everyone,

I'm having troubles connecting an ESP8266 NodeMCU (LoLin V3) to an I2C slave.
The characters recieved are nonsense.

I tried different setups with and without level-shifter, pullup on 5V or 3V3 side, different NodeMCU-Boards (NoName) - all with the same results. An Arduino Nano as master_reader works perfectly, so the slave_sender shouldn't be the problem.

Here's the Code:

#include <Wire.h>

void setup() {
  Wire.begin(2, 0);        // GPIO 2 & 0 correspond to D4 & D3 (On the Nano you just need: Wire.begin();)
  Serial.begin(115200); 
}

void loop() {

  Wire.requestFrom(10, 14);  //request 14 bytes from adress 10 (0x0A)

  Serial.print("I2C: ");

  while (Wire.available()) { // slave may send less than requested
    char c = Wire.read(); // receive a byte as character
    Serial.print(c);         // print the character
  }
  Serial.println();
  delay(1000);
}

The output looks kike this:

I2C: !⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮
I2C: !⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮
I2C: !⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮⸮

....

The wiring looks like this:

NodeMCU ESP 8266     Level-Shifter                  Ardu.Nano
                      3V3      5V
              D4 ---- o         o -- 10k Pullup -- SDA_Slave (A4)
              D3 ---- o         o -- 10k Pullup -- SCL_Slave (A5)
               G ---- o ------- o ---------------- GND

Any suggestions? Google didn't help... :confused:

2

10k resistor, try replacing for 4k7, maybe 3k3

3

Google didn't help

Google always helps, but you need to ask the related question.

Try searching for: i2c pullpu calc

Texas Instruments - I2C Bus Pullup Resistor Calculation

4

My NodeMCU (ESP8266) is receiving well a string from NANO-Slave!
smesp.png

ESP-Codes:

#include <Wire.h>

void setup() 
{
  Wire.begin(2, 0);   // SDA, SCL GPIO 2 & 0 correspond to D4 & D3 (On the Nano you just need: Wire.begin();)
  Serial.begin(115200);
  Serial.print("  ");
}

void loop() 
{
  byte n = Wire.requestFrom(10, 14);  //request 14 bytes from adress 10 (0x0A)
  Serial.print("I2C: ");
  for (int i =0; i<n-1; i++)
  { // slave may send less than requested
    char c = Wire.read(); // receive a byte as character
    Serial.print(c);         // print the character
  }
  Serial.println();
  delay(1000);
}

smesp.png

5

Thank you very much for your answers!!!!
I will try it with another resistor and report, if it worked.

6

Google always helps, but you need to ask the related question.

:slight_smile:

After hours of investigating , taking my setup apart, changing resistors, switching the boards, googling (still working i2c with nano => nano, error with the same nano => esp8266) ....

I finally found this topic: [Solved] ESP8266 to Nano I2C Problems. - Networking, Protocols, and Devices - Arduino Forum

The solution was to add a Line in the setup:

Wire.setClockStretchLimit(4000L);

The slave-nano seems to take to long to compute the reply (put together a char Array with sensor values), so the esp8266 was waiting too long.

The nano as master-reader seems to handle longer delays in its i2c library.

Maybe 4000 µs is overkill (?) but I'll stick to that as a have no oscilloscope to measure the delay time.

Working code:

#include <Wire.h>

void setup() {
  Wire.begin(5, 4);        
  Serial.begin(115200);
  Wire.setClockStretchLimit(4000L);  
}

void loop() {

  Wire.requestFrom(10, 14);  //request 14 bytes from adress 10 (0x0A)

  Serial.print("I2C: ");
   // delay(5);

  while (Wire.available()) { // slave may send less than requested
    char c = Wire.read(); // receive a byte as character
    Serial.print(c);         // print the character
   // delay(5);
  }
  Serial.println();
  delay(1000);
}

:art: I am impressed about the help some unknowing hobby-programmer-dude gets in this forum. Even somebody somewhere loaded my sketch on his own esp, did the wiring, programmed a slave device, made screenshots, shared all this just to help finding the error. Big thank you to everybody helping beginners like me in this forum! I learned so much from reading all your replies on so many questions I came across!