I have interfaced ADXL375 & I have some below. I have attached the code.

1. The offset I am getting is huge.
It is 1g approx on both x & y axis & 1.5g on z-axis.
I don't know what could be problem. I read offset registers , they are all zero in ADXL375.
I had read thread on Analog forum, someone gad same problem with offset +4G on z axis.
He had removed the IC & resoldered new one & problem gone.
But I wan't to know what could be exact reason?

2. For ODR <= 800Hz, we multiply register value with 49 to get g value i.e:
g = (register_value * 49)

But when OCR = 1600 or 3200Hz, what is the factor.
I had red in datasheet that in this case LSB is always zero. So what will be coversion factor or it will remain same = 49.


3. I had calibrated the adxl375 by placing it in z = +1g & other axis = 0.
But I have seen example in which calibrate in all six axis is done:
https://learn.adafruit.com/adxl345-digital-accelerometer/programming

But how to calculate final offset from these six offset values?
Or should I take there average.

4. Edit: I have been able to read DEV id properly & SPi speed is 3.75Mhz.

#define ADXL_REG_DEV_ID          (0x00)
#define ADXL_VAL_DEV_ID          (0xe5)
#define ADXL_REG_PW_CTRL         (0x2d)
#define ADXL_REG_INT_EN          (0x2e)
#define ADXL_REG_INT_MAP          (0x2f)
#define ADXL_REG_DATA_FM         (0x31)
#define ADXL_REG_DATA_RATE       (0x2c)
#define ADXL_REG_DATAX0          (0x32)


void main(void)
{
    configure_adxl375();

    while(1)
    {
        //take 100 samples & average
        adxl_read_offset_values(&x_val , &y_val ,&z_val);
        x_val *= 49;
        y_val *= 49;
        z_val *= 49;
    
        //offset for x:1274 , y: 1225 , z:1597
    }

}



void adxl_read_g_values(int16_t *x_val , int16_t *y_val , int16_t *z_val)
{
    uint8_t values[6];
    uint32_t error 

    adxl_read_reister(ADXL_REG_DATAX0 , 6U , &values[0]);

    *x_val = (s16_t)( ((u16_t)values[1] << 8U) | ((u16_t)values[0]) ) ;
    *y_val = (s16_t)( ((u16_t)values[3] << 8U) | ((u16_t)values[2]) ) ;
    *z_val = (s16_t)( ((u16_t)values[5] << 8U) | ((u16_t)values[4]) ) ;     
}



void configure_adxl375(void)
{
    uint8_t data;

    SPI_MODE(3);

    data = adxl_read(ADXL_REG_DEV_ID);
    if(0xe5 != data)
    {
        error_trap();
    }

/* power ctrl */
    adxl_write(ADXL_REG_PW_CTRL , 0x00);
    adxl_write_register(ADXL_REG_DATA_FM , 0x0bU);
    adxl_write_register(ADXL_REG_DATA_RATE , 0x0dU);
    adxl_write_register(ADXL_REG_PW_CTRL , 0x08U);

}



void adxl_write_register(uint8_t address , uint8_t value)
{
    ADXL_CS_ENABLE();

    adxl_spi_byte(address);
    adxl_spi_byte(value);
    ADXL_CS_DISABLE();

}




void adxl_read_reister(uint8_t address , uint32_t no_bytes , uint8_t *values)
{
    uint32_t cnt;
    uint8_t reg_add = 0x80U | address;      /* msb is high fro reading */
    
    if(no_bytes > 1U)   /* for multi read bit 6 is also set */
    {
        reg_add = reg_add | 0x40U;
    } 

    ADXL_CS_ENABLE();

/* send address */
    adxl_spi_byte(reg_add);


/* sent bytes */     
    for(cnt = 0U ; (cnt< no_bytes) ; cnt++ )
    {
        values[cnt] = adxl_spi_byte(0xffU);
    }

    ADXL_CS_DISABLE();

}

 

1. Way I have done calibration now:
I have take gain & offset errros into account.
Took two readings in +x axis & -ve axis.
Value at +x axis (1000mg) comes out to 1500mg.
Value at -x axis(-1000mg) comes out to 789mg.

From here I have calculated gain & offset error for x axis, by two point calibration.
Similarly for other two axis.

Is it correct method?

2. Why so much error? Only thermal stress can produce so much error?

3.
For ODR <= 800Hz, we multiply register value with 49 to get g value i.e:
g = (register_value * 49)
But when OCR = 1600 or 3200Hz, what is the factor.

 

1. If, ODR = 3200 then number of sampes I can take per sec is 1600 without aliasing right?

2. What is the final g value from three axis. Is it:
g = ( (x*x + y*y + z*z) ^ 0.5 ) / 3

3.If I configure ODR = 3200 & not able to take sample at Data ready interrupt. Then does that mean new data will overwrite older data & 3 axis data read can be corrupted or whenever I read 3 axis data it is always reliable & current data?

I read 3 axis data at once.