MPU6050 raw values check

Using Arduino Sensors
1

Hi

I've been trying to read raw values from MPU6050 and my problem is, instead of getting negative values when i go the opposite direction (accelerometer) or rotate the opposite direction (gyroscope), i get the end scale reading.
My gyro FS is set to 1 i.e. +/- 500 deg/s and accelerometer AFS is set to 1 i.e. +/- 8g.
When I try to read Z axis gyro readings, instead of getting negative values, i get something in the range of 65500. And in the case of the accerometer z-axis, when i hold the MPU6050 upside down, I exected to get a raw value in the ballpark of -4096 but again, it reads something in the range of 65500.
Can someone help me with this? What am I missing?

2

Code.

3

Fair enough. Here you go

#include <SPI.h>
#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);
long gyro_x, gyro_y, gyro_z;
long acc_x, acc_y, acc_z, acc_total_vector;
int temperature;
long gyro_x_cal, gyro_y_cal, gyro_z_cal;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  if(!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {
    //Serial.println(F("SSD1306 allocation failed"));
    for(;;); // Don't proceed, loop forever
  }
  display.display();
  delay(100);
  display.clearDisplay();
  display.setTextSize(2);
  display.setTextColor(SSD1306_WHITE); 
  display.setCursor(0,1);
  display.println("Gyro setup...");
  display.display();
  delay(500);
  //Activate the MPU-6050
  Wire.beginTransmission(0x68);                                        //Start communicating with the MPU-6050
  Wire.write(0x6B);                                                    //Send turn-on command
  Wire.write(0x00);                                                    //Send reset command
  Wire.endTransmission();                                              //End the transmission 
  delay(200);
  //Configure the accelerometer (+/-8g)
  Wire.beginTransmission(0x68);                                        //Start communicating with the MPU-6050
  Wire.write(0x1C);                                                    //Send accelerometer self-test command
  Wire.write(0x10);                                                    
  Wire.endTransmission();
  //Configure the gyroscope (+/-500 deg/s)
  Wire.beginTransmission(0x68);
  Wire.write(0x1B);
  Wire.write(0x10);
  Wire.endTransmission();  
  display.println("Setup done");
  display.display();//End the transmission
  delay(200);
  
}

void loop() {
  readmpu();
  display.setCursor(25,10);
  display.print(acc_z);
  display.display();
  delay(50);
  display.clearDisplay();
  
}
void readmpu()
{
  Wire.beginTransmission(0x68);                                        //Start communicating with the MPU-6050
  Wire.write(0x3B);                                                    //Send the requested starting register
  Wire.endTransmission();                                              //End the transmission
  Wire.requestFrom(0x68,14);                                           //Request 14 bytes from the MPU-6050
  while(Wire.available() < 14);                                        //Wait until all the bytes are received
  acc_x = Wire.read()<<8|Wire.read();                                  //Add the low and high byte to the acc_x variable
  acc_y = Wire.read()<<8|Wire.read();                                  //Add the low and high byte to the acc_y variable
  acc_z = Wire.read()<<8|Wire.read();                                  //Add the low and high byte to the acc_z variable
  temperature = Wire.read()<<8|Wire.read();                            //Add the low and high byte to the temperature variable
  gyro_x = Wire.read()<<8|Wire.read();                                 //Add the low and high byte to the gyro_x variable
  gyro_y = Wire.read()<<8|Wire.read();                                 //Add the low and high byte to the gyro_y variable
  gyro_z = Wire.read()<<8|Wire.read();  
}
4

Shouldn't these be "int"?

5

it doesnt make any difference, the error still is the same

6

These should be 16 bit signed integers, e.g.

int16_t gyro_x, gyro_y, gyro_z;
int16_t acc_x, acc_y, acc_z, acc_total_vector;

Also, in C/C++ this is not guaranteed to work in the correct order (it does in gcc, but not with some other compilers).

  acc_x = Wire.read()<<8|Wire.read();                                  //Add the low and high byte to the acc_x variable

Instead use something like the following:

// MPU-6050 Short Example Sketch
// By Arduino User JohnChi
// August 17, 2014
// Public Domain
#include<Wire.h>
const int MPU_addr = 0x68; // I2C address of the MPU-6050
int16_t AcX, AcY, AcZ, Tmp, GyX, GyY, GyZ;

void setup() {
  Wire.begin();
  Wire.beginTransmission(MPU_addr);
  Wire.write(0x6B);  // PWR_MGMT_1 register
  Wire.write(0);     // set to zero (wakes up the MPU-6050)
  Wire.endTransmission(true);
  Serial.begin(9600);
}

void loop() {
  Wire.beginTransmission(MPU_addr);
  Wire.write(0x3B);  // starting with register 0x3B (ACCEL_XOUT_H)
  Wire.endTransmission(false);
  Wire.requestFrom(MPU_addr, 14); // request a total of 14 registers
  int16_t t = Wire.read();
  AcX = (t << 8) | Wire.read(); // 0x3B (ACCEL_XOUT_H) & 0x3C (ACCEL_XOUT_L)
  t = Wire.read();
  AcY = (t << 8) | Wire.read(); // 0x3D (ACCEL_YOUT_H) & 0x3E (ACCEL_YOUT_L)
  t = Wire.read();
  AcZ = (t << 8) | Wire.read(); // 0x3F (ACCEL_ZOUT_H) & 0x40 (ACCEL_ZOUT_L)
  t = Wire.read();
  Tmp = (t << 8) | Wire.read(); // 0x41 (TEMP_OUT_H) & 0x42 (TEMP_OUT_L)
  t = Wire.read();
  GyX = (t << 8) | Wire.read(); // 0x43 (GYRO_XOUT_H) & 0x44 (GYRO_XOUT_L)
  t = Wire.read();
  GyY = (t << 8) | Wire.read(); // 0x45 (GYRO_YOUT_H) & 0x46 (GYRO_YOUT_L)
  t = Wire.read();
  GyZ = (t << 8) | Wire.read(); // 0x47 (GYRO_ZOUT_H) & 0x48 (GYRO_ZOUT_L)
  t = Wire.read();
  Serial.print("AcX = "); Serial.print(AcX);
  Serial.print(" | AcY = "); Serial.print(AcY);
  Serial.print(" | AcZ = "); Serial.print(AcZ);
  Serial.print(" | Tmp = "); Serial.print(Tmp / 340.00 + 36.53); //equation for temperature in degrees C from datasheet
  Serial.print(" | GyX = "); Serial.print(GyX);
  Serial.print(" | GyY = "); Serial.print(GyY);
  Serial.print(" | GyZ = "); Serial.println(GyZ);
  delay(333);
}
7

Hey thanks a lot for your timely response! Your first suggestion to use signed 16bit integers worked perfectly!!

Also if you dont mind, could you elaborate on the second change you suggested??

8

acc_x = Wire.read()<<8|Wire.read();

In the C/C++ language, there is no requirement for left to right ordering of the function calls above, so you may end up with the two bytes swapped. Depends on the compiler.

1 Like
9

aka "int" (on AVRs)

10

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