Problem Using pins A4 and A5 for input and output I2C

Question

Hardare used: Arduino nano ( old Bootloader ) Oled Monochrome Display ( 4 pins, 128 x 32 ) MPU 6050

Both display and MPU use A4 and A5 as I2C communication protocol, They interfere, as the MPU is used 2-way and the Display 1-way.

1. How can I change those 2 pins( does not matter witch Display/Sensor )
2. Can this method ( the one you propose ) be used for more cases like this? ( ex 3 sensors )

There is what I tried so far:

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 32 // OLED display height, in pixels

#define OLED_RESET     4 // Reset pin # (or -1 if sharing Arduino reset pin)
#define SCREEN_ADDRESS 0x3C ///< See datasheet for Address; 0x3D for 128x64, 0x3C for 128x32
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

#include "I2Cdev.h"
#include "MPU6050_6Axis_MotionApps20.h"
#if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
    #include "Wire.h"
#endif
MPU6050 mpu;

#define OUTPUT_READABLE_YAWPITCHROLL
#define OUTPUT_READABLE_REALACCEL

// MPU control/status vars
bool dmpReady = false;  // set true if DMP init was successful
uint8_t mpuIntStatus;   // holds actual interrupt status byte from MPU
uint8_t devStatus;      // return status after each device operation (0 = success, !0 = error)
uint16_t packetSize;    // expected DMP packet size (default is 42 bytes)
uint16_t fifoCount;     // count of all bytes currently in FIFO
uint8_t fifoBuffer[64]; // FIFO storage buffer

// orientation/motion vars
Quaternion q;           // [w, x, y, z]         quaternion container
VectorInt16 aa;         // [x, y, z]            accel sensor measurements
VectorInt16 aaReal;     // [x, y, z]            gravity-free accel sensor measurements
VectorInt16 aaWorld;    // [x, y, z]            world-frame accel sensor measurements
VectorFloat gravity;    // [x, y, z]            gravity vector
float euler[3];         // [psi, theta, phi]    Euler angle container
float ypr[3];           // [yaw, pitch, roll]   yaw/pitch/roll container and gravity vector

#define INTERRUPT_PIN 2  // use pin 2 on Arduino Uno & most boards
volatile bool mpuInterrupt = false;
void dmpDataReady() {
  mpuInterrupt = true;
}

void setup() {
  volatile bool mpuInterrupt = false;     // indicates whether MPU interrupt pin has gone high

  if(!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {
    Serial.println(F("SSD1306 allocation failed"));
   for(;;); // Don't proceed, loop forever
  }

  // Clear the buffer
  display.clearDisplay();

  delay(150);

  #if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
        Wire.begin();
        Wire.setClock(400000); // 400kHz I2C clock. Comment this line if having compilation difficulties
    #elif I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE
        Fastwire::setup(400, true);
    #endif

    Serial.println(F("Initializing I2C devices..."));
    mpu.initialize();
    pinMode(INTERRUPT_PIN, INPUT);

    // verify connection
    Serial.println(F("Testing device connections..."));
    Serial.println(mpu.testConnection() ? F("MPU6050 connection successful") : F("MPU6050 connection failed"));

    delay(50);
    
    // load and configure the DMP
    Serial.println(F("Initializing DMP..."));
    devStatus = mpu.dmpInitialize();

  if (devStatus == 0) {
        // Calibration Time: generate offsets and calibrate our MPU6050
        mpu.CalibrateAccel(6);
        mpu.CalibrateGyro(6);
        mpu.PrintActiveOffsets();
        // turn on the DMP, now that it's ready
        Serial.println(F("Enabling DMP..."));
        mpu.setDMPEnabled(true);

        // enable Arduino interrupt detection
        Serial.print(F("Enabling interrupt detection (Arduino external interrupt "));
        Serial.print(digitalPinToInterrupt(INTERRUPT_PIN));
        Serial.println(F(")..."));
        attachInterrupt(digitalPinToInterrupt(INTERRUPT_PIN), dmpDataReady, RISING);
        mpuIntStatus = mpu.getIntStatus();

        // set our DMP Ready flag so the main loop() function knows it's okay to use it
        Serial.println(F("DMP ready! Waiting for first interrupt..."));
        dmpReady = true;

        // get expected DMP packet size for later comparison
        packetSize = mpu.dmpGetFIFOPacketSize();
    } else {
        // ERROR!
        // 1 = initial memory load failed
        // 2 = DMP configuration updates failed
        // (if it's going to break, usually the code will be 1)
        Serial.print(F("DMP Initialization failed (code "));
        Serial.print(devStatus);
        Serial.println(F(")"));
    }

    
  
  Serial.begin(9600);
}

void loop() {
  if (!dmpReady) return;
    // read a packet from FIFO
    if (mpu.dmpGetCurrentFIFOPacket(fifoBuffer)) { // Get the Latest packet 
        
        #ifdef OUTPUT_READABLE_YAWPITCHROLL
            // display Euler angles in degrees
            mpu.dmpGetQuaternion(&q, fifoBuffer);
            mpu.dmpGetGravity(&gravity, &q);
            mpu.dmpGetYawPitchRoll(ypr, &q, &gravity);
            /*
            data.gyro_data[0] = ypr[0] * 180/M_PI;
            data.gyro_data[1] = ypr[1] * 180/M_PI;
            data.gyro_data[2] = ypr[2] * 180/M_PI;
            */
        #endif

        #ifdef OUTPUT_READABLE_REALACCEL
            // display real acceleration, adjusted to remove gravity
            mpu.dmpGetQuaternion(&q, fifoBuffer);
            mpu.dmpGetAccel(&aa, fifoBuffer);
            mpu.dmpGetGravity(&gravity, &q);
            mpu.dmpGetLinearAccel(&aaReal, &aa, &gravity);
            /*
            data.acc_data[0] = aaReal.x;
            data.acc_data[1] = aaReal.y;
            data.acc_data[2] = aaReal.z;
            */
        #endif
    }
    
    display.print(String(ypr[0] * 180/M_PI));
    display.print('/');
    display.print(String(ypr[1] * 180/M_PI));
    display.print('/');
    display.print(String(ypr[2] * 180/M_PI));
    display.print("\n\n");
    display.print(String(aaReal.x));
    display.print('/');
    display.print(String(aaReal.y));
    display.print('/');
    display.print(String(aaReal.z));
    

    //display.print(String(data.id));
    display.display();
    
    
    delay(500);
}

Now I know this looks like a bunch of code thrown together with the hope to work, But it is composed from 2 other of my codes separately for MPU and Display, those work fine.

Answer 1

So after repeated tests I found several problems, software and hardware.

1. The cables I used on the breadboard where facing each other. The metal parts where touching ( from a defect of the cables ). Turned them 90*.

2. The Oled display was NOT Initialized properly. When using display.write() or display.print() you must first put the cursor at (0;0) by display.setCursor(0,0). Furthermore for more compatibility in Setup(){} you have to add display.setTextSize(1) and display.setTextColor(WHITE).

3. Power control. I found the best, either adding a capacitor on the VCC and GND lines when using them to power 2 Sensors at the same time, or ad a 5 mls delay in the first function. delay(5)