Possible to connect 3 MPU9250 to Node MCU without multiplixer?

Question

Is the idea of connecting AD0 pins of MPU9250 is still valid like the 2nd answer of this question? - How to change i2c address for mpu9250?

I have connected 2 sensor as test. SCL & SDA of both parallel with D1 & D2 of node mcu. Then connected AD0 of both sensors to different I/O pin of node mcu but it didnt work. What could be the solution?

Code to control 1 sensor:- It worked when I set AD0 to high and changed address to 0x69

#include "MPU9250.h"

// an MPU9250 object with the MPU-9250 sensor on I2C bus 0 with address 0x68
MPU9250 IMU(Wire,0x68);
int status;


void setup() {
  // serial to display data
  Serial.begin(115200);
  while(!Serial) {}

  // start communication with IMU 
  status = IMU.begin();
  if (status < 0) {
    Serial.println("IMU initialization unsuccessful");
    Serial.println("Check IMU wiring or try cycling power");
    Serial.print("Status: ");
    Serial.println(status);
    while(1) {}
  }
}

void loop() {
  // read the sensor
  IMU.readSensor();
  // display the data
  Serial.print(IMU.getAccelX_mss(),6);
  Serial.print("\t");
  Serial.print(IMU.getAccelY_mss(),6);
  Serial.print("\t");
  Serial.print(IMU.getAccelZ_mss(),6);
  Serial.print("\t");
  Serial.print(IMU.getGyroX_rads(),6);
  Serial.print("\t");
  Serial.print(IMU.getGyroY_rads(),6);
  Serial.print("\t");
  Serial.print(IMU.getGyroZ_rads(),6);
  Serial.print("\t");
  Serial.print(IMU.getMagX_uT(),6);
  Serial.print("\t");
  Serial.print(IMU.getMagY_uT(),6);
  Serial.print("\t");
  Serial.print(IMU.getMagZ_uT(),6);
  Serial.print("\t");
  Serial.println(IMU.getTemperature_C(),6);
  delay(100);
}

Code to control 2 sensors:-

#include "MPU9250.h"

// an MPU9250 object with the MPU-9250 sensor on I2C bus 0 with address 0x68
MPU9250 IMU1(Wire,0x68);
MPU9250 IMU2(Wire,0x68);

int status;


void setup() {
  // serial to display data
  Serial.begin(115200);
  pinMode(D7, OUTPUT);
  pinMode(D8, OUTPUT);


}

void IMU_1() {
  digitalWrite(D7, LOW);
  digitalWrite(D8, HIGH);
  IMU1.begin();
  IMU1.readSensor();
  Serial.print("IMU 1 is active: "); Serial.print(IMU1.getAccelX_mss(),6);
  digitalWrite(D8, LOW);
}

void IMU_2() {
  digitalWrite(D7, HIGH);
  digitalWrite(D8, LOW);
  IMU2.begin();
  IMU2.readSensor();
  Serial.println("IMU 2 is active: "); Serial.print(IMU2.getAccelX_mss(),6);
  digitalWrite(D7, LOW);
}

void loop() {

IMU_1();
IMU_2();


  delay(500);


}

Result:- It Shows reading on one sensor but the 2nd sensor shows '0' every time.

What's the best way to use 3 I2C sensors when there is only 1 I2C bus?

Answer 1

It sounds like the MPU9250 has a pin, AD0, that lets you switch the device between 2 fixed I2C addresses.

That gives you an easy solution if you need to use 2 of them.

For more, the post you linked suggests keeping them all at the same AD0 state except the one you want to talk to. You’d switch that one’s AD0 pin to the other state, which would cause it’s I2C address, and then talk to it at that address, which would be unique on the I2C bus.

That approach should work, but it’s a bit of a hack.

You say "I have connected 2 sensor as test. SCL & SDA of both parallel with D1 & D2 of node mcu. Then connected AD0 of both sensors to different I/O pin of node mcu but it didn't work." What didn't work? What happens? What output do you get What pins on your mcu are connected to AD0 on your 3 different MPU9250 modules? Where is the code that manipulates the digital pins to select one and only one of your MPU9250 modules for reading?

You need to throughly explain your setup, including the different pin assignments and how they are supposed to work. Don't leave us to read your code and try and figure out your intentions.

Looking at your code it looks like you're using D7 and D8 on your mcu to try to control which MPU9250 is active. However i don't see any code the sets D7 and D8 as outputs.

Why don’t you want to use an I2C address mapping chip? They are readily available, and the ones I’ve seen would let you address up to 8 I2C devices that are hard-wired with the same address.