Arduino loop over a function is always displaying 0 as final values

Question

I trying to loop over a function in arduino to get values for 2000 times, and then divide it by 2000 to get an average offset:

int16_t x_offset = 0;
int16_t y_offset = 0;
int16_t z_offset = 0;

And inside setup():

for(int i=0; i<2000;i++)
 {
 GetXYZ(x_offset, y_offset, z_offset);
 x_offset += x_offset;
 y_offset += y_offset;
 z_offset += z_offset; 
 Serial.println(x_offset);
 delay(3);
 }
 x_offset /= 2000;
 y_offset /= 2000;
 z_offset /= 2000;
 Serial.println(x_offset);Serial.println("...");Serial.println(y_offset);Serial.println("...");
Serial.println(z_offset);Serial.println("...");

Here is the GetXYZ() function:

void GetXYZ( int16_t &x, int16_t &y, int16_t &z) {
 // Get the gyro values
 Wire.beginTransmission(MPU);
 Wire.write(0x43); // first register of gyro values
 Wire.endTransmission(false);
 Wire.requestFrom(MPU,6);
 x = Wire.read() << 8 | Wire.read();
 y = Wire.read() << 8 | Wire.read();
 z = Wire.read() << 8 | Wire.read();
}

The values printed in the serial of x_offset, y_offset and z_offset are always 0.

Answer 1

There's a couple of things wrong here:

1. You are just getting the last read value doubled:

   x_offset += x_offset;

However x_offset is always replaced with the lates reading. You're not summing anything.

2. To get anything other than 0 out of dividing an integer by 2000 the value stored in the integer would have to be> 2000. But since you can only store a maximum of 32767 in your int16_t variables, even if you didn't have the problem in point 1, the variables would overflow and the results would be meaningless.

You need to:

• Use a second variable per axis to store your total
• Ensure that it is big enough to store the maximum reading ×ばつ 2000. I'd suggest a long or int32_t.

For instance:

int16_t x_offset = 0;
int16_t y_offset = 0;
int16_t z_offset = 0;
int32_t x_total = 0;
int32_t y_total = 0;
int32_t z_total = 0;

And inside setup():

for(int i=0; i<2000;i++)
 {
 GetXYZ(x_offset, y_offset, z_offset);
 x_total += x_offset;
 y_total += y_offset;
 z_total += z_offset; 
 Serial.println(x_offset);
 delay(3);
 }
 x_total /= 2000;
 y_total /= 2000;
 z_total /= 2000;
 Serial.println(x_total);Serial.println("...");Serial.println(y_total);Serial.println("...");
Serial.println(z_total);Serial.println("...");

• alim1990: Oh, I didn't noticed that. Thanks it works now.