AVR Freaks

I have built an AS7 project.   There are several issues.

I am going to the pub.

I will address the "issues" and connect it to real hardware tomorrow.

David.

There is no mythical "gravity cancellation" in MPU6050 datsheet....

The Z axis is slightly more noisier (but each and every axis can measure gravity, else one could not tilt sensor)

If there was a mythical "cancellation of gravity", one could not rotate the sensor (ex : one rotates it round Y axis: X should measure gravity (with a sign depending on luck and skill).

That -90 ° rotation around X or Y axis, swapping Y -resp X- and Z -  would be a way of knowing whether this failure is Z axis specific, or affects every axis (if every axis is affected, seems a software issue).

"

dbrion0606 wrote:

There is no mythical "gravity cancellation" in MPU6050 datsheet....

aweill wrote:

"I was thinking of processing in the OP's code - not by the MPU6050 itself."

Well, I bet you read OP code, did not you...

and you noticed that, nowhere, "gravity cancellation" occured (main read rawdata, scales them by dividing (float)  by 2**13, prints them as they are; and that 's all)

So, this "gravity cancellation" remains  a myth. (it may occur later in SW, if one has a reliable information of rotation, but OP very wisely deals ... with rawdata ... the very name of his project)

main countains (among other things)

  Read_Accel_Values();

                        // Divide raw values by sensitivity scale factor
                        Xa = Acc_x/16384.0;
                        Ya = Acc_y/16384.0;
                        Za = Acc_z/16384.0;
                        
                        //Print Data
                        print( " Ax = %s g\t",Xa, 3, 2);
                        print(" Ay = %s g\t",Ya, 3, 2);
                        print(" Az = %s g\n\n",Za, 3, 2);

(Xa ... Za are floats:  print -I would have called it myPrint... but it doesnot solve anything -  is defined (from usart.c)  as

void print(char msg[30],double data,char intpart,char floatpart){
        dtostrf( data, intpart, floatpart, float_ );
        sprintf(buffer,msg,float_);
        USART_SendString(buffer); // buffer exists, is [20] in usart.h
}
 

I would rewrite :

void Read_Accel_Values()
{
        MPU_Start_Loc_Accel();          // Define the start address from where to read data (ACCEL_XOUT_H)
        Acc_x = (((int)I2C_Read_Ack()<<8) | (int)I2C_Read_Ack());
        Acc_y = (((int)I2C_Read_Ack()<<8) | (int)I2C_Read_Ack());
        Acc_z = (((int)I2C_Read_Ack()<<8) | (int)I2C_Read_Nack());
        I2C_Stop();
}

as

void Read_Accel_Values()
{
    int x1, x2, y1, y2, z1, z2;
    
        MPU_Start_Loc_Accel();          // Define the start address from where
        to read data (ACCEL_XOUT_H)
         x1 = (int)I2C_Read_Ack();
         x2 = (int)I2C_Read_Ack();
         Acc_x = (x1 << 8) | x2; // 
        // Acc_x = (((int)I2C_Read_Ack()<<8) | (int)I2C_Read_Ack());
        if (debug){ 
                sprintf(buffer, "%d %d %d \n",x1, x2, Acc_x ); /*
        this is overkill but I do not miss anyhing; there is room enaugh in buffer -glob.var. like debug*/
               USART_SendString(buffer);
}
        Same conversions for y....
        Acc_y = (((int)I2C_Read_Ack()<<8) | (int)I2C_Read_Ack());
        Acc_z = (((int)I2C_Read_Ack()<<8) | (int)I2C_Read_Nack());
        I2C_Stop();
}

Acc_x = (((int)I2C_Read_Ack()<<8) | (int)I2C_Read_Ack());

The compiler doesn't guarantee that the two I2C_Read_Ack()s will be called in any particular order. Either the first or the second might be called first. You need to call them explicitly in order like this:

Acc_x = (int)I2C_Read_Ack()<<8;

Acc_x |= I2C_Read_Ack();

or this, depending on the byte order:

Acc_x = I2C_Read_Ack();

Acc_x |= (int)I2C_Read_Ack()<<8;

Ah, I see there's an issue with signed values. Take the last sample:

z1=58 z2=-120 Acc_z=-120

It looks like I2C_Read_Ack() returns data as a signed 8-bit value and not an unsigned 8-bit value. Change this:

         x1 = (int)I2C_Read_Ack();
         x2 = (int)I2C_Read_Ack();

to this:

         x1 = (uint8_t)I2C_Read_Ack();
         x2 = (uint8_t)I2C_Read_Ack();