I2C still not working

[kriswiner]

I can read the I2C addresses of the I2C sensors with pins 21/22 but I cannot read the WHO_AM_I byte.
This works on the Teensy and STM32L4:

 uint8_t readByte(uint8_t address, uint8_t subAddress)
{
  uint8_t data; // `data` will store the register data   
  Wire.beginTransmission(address);         // Initialize the Tx buffer
  Wire.write(subAddress);                  // Put slave register address in Tx buffer
  Wire.endTransmission(false);             // Send the Tx buffer, but send a restart to keep connection alive
  Wire.requestFrom(address, 1);            // Read one byte from slave register address 
  data = Wire.read();                      // Fill Rx buffer with result
  return data;                             // Return data read from slave register
}

[me-no-dev]

what is that slave device that you are trying to access?

[kriswiner]

MPU9250 and MS5637.

[kriswiner]

OK, I confirmed I can read the I2C pressure/temperature sensor MS5637, which essentially uses one byte at a time for reads and writes. Here is the sketch that works just fine:

#include "Wire.h"   

// See MS5637-02BA03 Low Voltage Barometric Pressure Sensor Data Sheet
#define MS5637_RESET      0x1E
#define MS5637_CONVERT_D1 0x40
#define MS5637_CONVERT_D2 0x50
#define MS5637_ADC_READ   0x00

#define MS5637_ADDRESS 0x76   // Address of altimeter

#define SerialDebug true  // set to true to get Serial output for debugging

#define ADC_256  0x00 // define pressure and temperature conversion rates
#define ADC_512  0x02
#define ADC_1024 0x04
#define ADC_2048 0x06
#define ADC_4096 0x08
#define ADC_8192 0x0A
#define ADC_D1   0x40
#define ADC_D2   0x50

// Specify sensor full scale
uint8_t OSR = ADC_8192;     // set pressure amd temperature oversample rate
  
// Pin definitions
int intPin = 14;  

int myLed = 5;

uint16_t Pcal[8];         // calibration constants from MS5637 PROM registers
unsigned char nCRC;       // calculated check sum to ensure PROM integrity
uint32_t D1 = 0, D2 = 0;  // raw MS5637 pressure and temperature data
double dT, OFFSET, SENS, TT2, OFFSET2, SENS2;  // First order and second order corrections for raw S5637 temperature and pressure data
    
int16_t tempCount;            // temperature raw count output
float   temperature;          // Stores the MPU9250 gyro internal chip temperature in degrees Celsius
double Temperature, Pressure; // stores MS5637 pressures sensor pressure and temperature

// global constants for 9 DoF fusion and AHRS (Attitude and Heading Reference System)
float pi = 3.141592653589793238462643383279502884f;

void setup()
{
  Serial.begin(115200);
  delay(4000);
  
  Wire.begin(21,22); // 21/22 are default on ESP32
  Wire.setClock(400000); // choose 400 kHz I2C rate
//  Wire.setClockStretchLimit(1000000);
  delay(1000);
  
  // Set up the interrupt pin, its set as active high, push-pull
  pinMode(intPin, INPUT);
  pinMode(myLed, OUTPUT);
  digitalWrite(myLed, LOW);
  
  I2Cscan();// look for I2C devices on the bus
    
  // Reset the MS5637 pressure sensor
  MS5637Reset();
  delay(100);
  Serial.println("MS5637 pressure sensor reset...");
  // Read PROM data from MS5637 pressure sensor
  MS5637PromRead(Pcal);
  Serial.println("PROM dta read:");
  Serial.print("C0 = "); Serial.println(Pcal[0]);
  unsigned char refCRC = Pcal[0] >> 12;
  Serial.print("C1 = "); Serial.println(Pcal[1]);
  Serial.print("C2 = "); Serial.println(Pcal[2]);
  Serial.print("C3 = "); Serial.println(Pcal[3]);
  Serial.print("C4 = "); Serial.println(Pcal[4]);
  Serial.print("C5 = "); Serial.println(Pcal[5]);
  Serial.print("C6 = "); Serial.println(Pcal[6]);
  
  nCRC = MS5637checkCRC(Pcal);  //calculate checksum to ensure integrity of MS5637 calibration data
  Serial.print("Checksum = "); Serial.print(nCRC); Serial.print(" , should be "); Serial.println(refCRC);  
}

void loop()
{  

    D1 = MS5637Read(ADC_D1, OSR);  // get raw pressure value
    D2 = MS5637Read(ADC_D2, OSR);  // get raw temperature value
    dT = D2 - Pcal[5]*pow(2,8);    // calculate temperature difference from reference
    OFFSET = Pcal[2]*pow(2, 17) + dT*Pcal[4]/pow(2,6);
    SENS = Pcal[1]*pow(2,16) + dT*Pcal[3]/pow(2,7);
 
    Temperature = (2000 + (dT*Pcal[6])/pow(2, 23))/100;           // First-order Temperature in degrees Centigrade
//
// Second order corrections
    if(Temperature > 20) 
    {
      TT2 = 5*dT*dT/pow(2, 38); // correction for high temperatures
      OFFSET2 = 0;
      SENS2 = 0;
    }
    if(Temperature < 20)                   // correction for low temperature
    {
      TT2      = 3*dT*dT/pow(2, 33); 
      OFFSET2 = 61*(100*Temperature - 2000)*(100*Temperature - 2000)/16;
      SENS2   = 29*(100*Temperature - 2000)*(100*Temperature - 2000)/16;
    } 
    if(Temperature < -15)                      // correction for very low temperature
    {
      OFFSET2 = OFFSET2 + 17*(100*Temperature + 1500)*(100*Temperature + 1500);
      SENS2 = SENS2 + 9*(100*Temperature + 1500)*(100*Temperature + 1500);
    }
 // End of second order corrections
 //
     Temperature = Temperature - T2/100;
     OFFSET = OFFSET - OFFSET2;
     SENS = SENS - SENS2;
 
     Pressure = (((D1*SENS)/pow(2, 21) - OFFSET)/pow(2, 15))/100;  // Pressure in mbar or kPa

    float altitude = 145366.45*(1. - pow((Pressure/1013.25), 0.190284));
   
    if(SerialDebug) {
    Serial.print("Digital temperature value = "); Serial.print( (float)Temperature, 2); Serial.println(" C"); // temperature in degrees Celsius
    Serial.print("Digital temperature value = "); Serial.print(9.*(float) Temperature/5. + 32., 2); Serial.println(" F"); // temperature in degrees Fahrenheit
    Serial.print("Digital pressure value = "); Serial.print((float) Pressure, 2);  Serial.println(" mbar");// pressure in millibar
    Serial.print("Altitude = "); Serial.print(altitude, 2); Serial.println(" feet");
    }   
 
   digitalWrite(myLed, !digitalRead(myLed));
   delay(500);
}

//===================================================================================================================
//====== Set of useful function to access acceleration. gyroscope, magnetometer, and temperature data
//===================================================================================================================

// I2C communication with the MS5637 is a little different from that with the MPU9250 and most other sensors
// For the MS5637, we write commands, and the MS5637 sends data in response, rather than directly reading
// MS5637 registers

        void MS5637Reset()
        {
        Wire.beginTransmission(MS5637_ADDRESS);  // Initialize the Tx buffer
        Wire.write(MS5637_RESET);                // Put reset command in Tx buffer
        Wire.endTransmission();                  // Send the Tx buffer
        }
        
        void MS5637PromRead(uint16_t * destination)
        {
        uint8_t data[2] = {0,0};
        for (uint8_t ii = 0; ii < 7; ii++) {
          Wire.beginTransmission(MS5637_ADDRESS);  // Initialize the Tx buffer
          Wire.write(0xA0 | ii << 1);              // Put PROM address in Tx buffer
          Wire.endTransmission(false);             // Send the Tx buffer, but send a restart to keep connection alive
          uint8_t i = 0;
          Wire.requestFrom(MS5637_ADDRESS, 2);     // Read two bytes from slave PROM address 
          while (Wire.available()) {
          data[i++] = Wire.read(); }               // Put read results in the Rx buffer
          destination[ii] = (uint16_t) (((uint16_t) data[0] << 8) | data[1]); // construct PROM data for return to main program
        }
        }

        uint32_t MS5637Read(uint8_t CMD, uint8_t OSR)  // temperature data read
        {
        uint8_t data[3] = {0,0,0};
        Wire.beginTransmission(MS5637_ADDRESS);  // Initialize the Tx buffer
        Wire.write(CMD | OSR);                   // Put pressure conversion command in Tx buffer
        Wire.endTransmission(false);             // Send the Tx buffer, but send a restart to keep connection alive
        
        switch (OSR)
        {
          case ADC_256: delay(1); break;         // delay for conversion to complete
          case ADC_512: delay(3); break;
          case ADC_1024: delay(4); break;
          case ADC_2048: delay(6); break;
          case ADC_4096: delay(10); break;
          case ADC_8192: delay(20); break;
        }
       
        Wire.beginTransmission(MS5637_ADDRESS);  // Initialize the Tx buffer
        Wire.write(0x00);                        // Put ADC read command in Tx buffer
        Wire.endTransmission(false);             // Send the Tx buffer, but send a restart to keep connection alive
        uint8_t i = 0;
        Wire.requestFrom(MS5637_ADDRESS, 3);     // Read three bytes from slave PROM address 
        while (Wire.available()) {
        data[i++] = Wire.read(); }               // Put read results in the Rx buffer
        return (uint32_t) (((uint32_t) data[0] << 16) | (uint32_t) data[1] << 8 | data[2]); // construct PROM data for return to main program
        }

unsigned char MS5637checkCRC(uint16_t * n_prom)  // calculate checksum from PROM register contents
{
  int cnt;
  unsigned int n_rem = 0;
  unsigned char n_bit;
  
  n_prom[0] = ((n_prom[0]) & 0x0FFF);  // replace CRC byte by 0 for checksum calculation
  n_prom[7] = 0;
  for(cnt = 0; cnt < 16; cnt++)
  {
    if(cnt%2==1) n_rem ^= (unsigned short) ((n_prom[cnt>>1]) & 0x00FF);
    else         n_rem ^= (unsigned short)  (n_prom[cnt>>1]>>8);
    for(n_bit = 8; n_bit > 0; n_bit--)
    {
        if(n_rem & 0x8000)    n_rem = (n_rem<<1) ^ 0x3000;
        else                  n_rem = (n_rem<<1);
    }
  }
  n_rem = ((n_rem>>12) & 0x000F);
  return (n_rem ^ 0x00);
}


// simple function to scan for I2C devices on the bus
void I2Cscan() 
{
    // scan for i2c devices
  byte error, address;
  int nDevices;

  Serial.println("Scanning...");

  nDevices = 0;
  for(address = 1; address < 127; address++ ) 
  {
    // The i2c_scanner uses the return value of
    // the Write.endTransmisstion to see if
    // a device did acknowledge to the address.
    Wire.beginTransmission(address);
    error = Wire.endTransmission();

    if (error == 0)
    {
      Serial.print("I2C device found at address 0x");
      if (address<16) 
        Serial.print("0");
      Serial.print(address,HEX);
      Serial.println("  !");

      nDevices++;
    }
    else if (error==4) 
    {
      Serial.print("Unknown error at address 0x");
      if (address<16) 
        Serial.print("0");
      Serial.println(address,HEX);
    }    
  }
  if (nDevices == 0)
    Serial.println("No I2C devices found\n");
  else
    Serial.println("done\n");
}

But if I try to read the MPU9250 which requires write of a device address, then a register address (more than one byte), then I can not read any data from it. Here is the multi-byte I2C function:

  uint8_t readByte(uint8_t address, uint8_t subAddress)
{
  uint8_t data; // `data` will store the register data   
  Wire.beginTransmission(address);         // Initialize the Tx buffer
  Wire.write(subAddress);                  // Put slave register address in Tx buffer
  Wire.endTransmission(false);             // Send the Tx buffer, but send a restart to keep connection alive
  Wire.requestFrom(address, 1);            // Read one byte from slave register address 
  data = Wire.read();                      // Fill Rx buffer with result
  return data;                             // Return data read from slave register
}

Some how the second byte is causing the I2C bus to get hing up. Not sure why but this is the reason most I2C devices cannot be read by the ESP32 except for the very simple (command and response types) ones. Although now that I look at both readByte functions, they look pretty similar so now I don't know why one works and one does not.

[Nourfdss]

@kriswiner hey man can you please explain how did you connect the MS5637 to the esp32 im trying to conect the mpu6050 motion sensor but i failed

[kriswiner]

I connected pin 21 to SDA, pin 22 to SCL and then 3V3 and GND. But this won't help you since i can't get anything but the I2C address out of the companion MPU9250. There is something different about the Invensense I2C bus/controller that is causing the I2C bus to latch up. Might be a clock stretching issue. I have seen this before on the ESP8266/85. I am using 4K7 pullips on the I2C lines, which usually works for a variety of controllers including the ESP8266/85. But somehow the ESP32 is having trouble with it.

[Nourfdss]

So now what is the solution if i wanna get the motion sensor connected to esp32 i tried alot to find in the internet i did not fine anything

[kriswiner]

Don't know, I'd like to get the other I2C sensors working as well. I am going to test more but I have not been able to get the MPU9250 to work yet.

Lokks like we will both have to just wait until this is fixed. Or go backt o using the ESP8266/85!

[Nourfdss]

Okay man if i got anything i will post it here and let u know ,good luck

[me-no-dev]

guys calm down :) i'm working on it and so far I can read MPU fine. Update will be up soon.

[kriswiner]

No disresepect intended, you guys are doing great work!

Just trying to do my part ;>

I am looking forward to your fix.

[me-no-dev]

issue with MPU was directly connected to the fact that before you read from it, you do not send stop (Wire.endTransfer(false)). Now that I have that fixed, I can not write more than 9 bytes to I2C... cat and mouse with this bus

[me-no-dev]

please try the latest commit

[kriswiner]

I just tried the new core and I am still having the same problem. I can see the I2C devices on the bus but cannot read from the MPU9250 WHO_AM_I register. This is the output I get:

Scanning...
I2C device found at address 0x68  !
I2C device found at address 0x76  !
done

MPU9250 9-axis motion sensor...
MPU9250 I AM FF I should be 71
Could not connect to MPU9250: 0xFF

I verified I can still get data from the MS5637 alone. That is, if I only ask for MS5637 data, read and write from/to MS5637 only then everything works, but when I try to talk with the MPU9250 the bus gets stuck and I can't talk to either.

[kriswiner]

I also verified that I can get data from the VEML6040 I2C RGBW sensor. So some work and some don't. Odd...

[kriswiner]

But cannot read the BMX055:

Scanning...
I2C device found at address 0x10  !
I2C device found at address 0x18  !
I2C device found at address 0x1E  !
I2C device found at address 0x59  !
I2C device found at address 0x68  !
I2C device found at address 0x69  !
I2C device found at address 0x6A  !
done

BMX055 accelerometer...
BMX055 ACC I AM 0xFF I should be 0xFA
BMX055 gyroscope...
BMX055 GYRO I AM 0xFF I should be 0xF
BMX055 magnetometer...
BMX055 MAG I AM 0xFF I should be 0x32
Could not connect to BMX055: 0xFF