Fall Detection using MPU-9250

[peter_war]

I have 3 questions

Hi, i am trying to do a fall detection device using NodeMCU and MPU-9250 module. For a start I am trying to print out the acceleration values from each axis.
This is the code I programmed into the NodeMCU.

void loop() {
                                // put your main code here, to run repeatedly:
  IMU.readSensor();
  //Accelerometer data code
  Serial.print("Accelerometer X axis: "); 
  accex = IMU.getAccelX_mss();
  Serial.print(accex, 3);     // to get the accelerometer value from the data buffer in the X direction, these values are in meter per second square
  Serial.print("               Accelerometer Y axis: ");
  accey = IMU.getAccelY_mss();
  Serial.print(accey, 3);
  accez = IMU.getAccelZ_mss();
  Serial.print("               Accelerometer Z axis: ");
  Serial.println(accez, 3);
}

After I programmed this into the NodeMCU, I was able to get the acceleration values of each axis. as shown below.

1. Why is the z axis acceleration -8, shouldn't it be 0 as well?

Another thing I noticed that, when hold the circuit upside down, the z axis acceleration becomes 11 as shown below.

2)Why did it go high?

3)Similarly, when I tilt it 90 degrees to left and hold it still the x axis acceleration went up to 11 as well. Shouln't it be 0 as well if I hold it still, why is it 11?

Please enlighten me on this. I am new to this MPU-9250 module.

[jremington]

Accelerometers measure the acceleration due to gravity as well as acceleration due to other forces.

They also need to be calibrated, in order to get accurate readings. See this tutorial: Programming and Calibration | ADXL345 Digital Accelerometer | Adafruit Learning System

[anon56112670]

@peter_war

Why is the z axis acceleration -8, shouldn't it be 0 as well?

It looks like gravity is working correctly where you are, even if it is a little low.

[jremington]

@anon56112670

even if it is a little low

It does go all the way to 11, though.