Queru on LIS3DH sensor

[Vishal Dongare]

Posted on January 24, 2018 at 09:54

Hi,

I am working on LIS3DH accelerometer sensor, I have interfaced this sensor with STM32F103 series micro controller using SPI interface. When I read X, Y and Z acceleration values, I get some random readings and it too fluctuate lot. The sensor is placed horizontal on PCB, parallel to X , Y axis and perpendicular to Z axis. The reading for all three axes is fluctuate around 0.01 to -0.15. In initialization, all three axes has been enabled.

As I am very new to accelerometer sensor, is my understanding that in the position mentioned above should I get g value for X and Y axis around 0g and for Z axis around 1g correct?

OR it just shows fluctuations in X,Y and Z axis value when there is some movement of sensor and again it get stable value when the sensor is stationary?

[Miroslav BATEK]

Posted on January 24, 2018 at 10:41

Yes, you first assumption is correct. For the the mentioned position X and Y axis should be close to 0g and Z axis around 1g.

Can you please share your sensor configuration and the procedure how do you convert raw value to acceleration in g unit?

[Vishal Dongare]

Posted on January 24, 2018 at 11:00

Thank you so much for your response. Please refer below details.

/* accelerometer register address define */

#define Status_Reg1 ((u8)0x07)

#define Who_Am_I ((u8)0x0F)

#define Ctrl_Reg1 ((u8)0x20)

#define Ctrl_Reg2 ((u8)0x21)

#define Ctrl_Reg3 ((u8)0x22)

#define Ctrl_Reg4 ((u8)0x23)

#define Ctrl_Reg5 ((u8)0x24)

#define Ctrl_Reg6 ((u8)0x25)

#define Status_Reg2 ((u8)0x27)

#define Out_X_L ((u8)0x28)

#define Out_X_H ((u8)0x29)

#define Out_Y_L ((u8)0x2A)

#define Out_Y_H ((u8)0x2B)

#define Out_Z_L ((u8)0x2C)

#define Out_Z_H ((u8)0x2D)

#define INT1_CFG ((u8)0x30)

#define INT1_SRC ((u8)0x31)

#define INT1_THS ((u8)0x32)

#define INT1_DURATION ((u8)0x33)

#define CLICK_CFG ((u8)0x38)

#define CLICK_SRC ((u8)0x39)

#define CLICK_THS ((u8)0x3A)

#define TIME_LIMIT ((u8)0x3B)

#define TIME_LATENCY ((u8)0x3C)

#define TIME_WINDOW ((u8)0x3D)

Below is the sensor configuration at power up. 

/* Ask who am I to comfirm the hardware status */

retCode =ACCELEROMETER_Read(Who_Am_I,&tmp);

if((tmp == 0x33) && (retCode == 0))

{

MEMS_DEVICE.HardWareSta = DEF_MEMS_NONE_ERR;

retCode =0;

#if(DEF_ADDINFO_OUTPUTEN > 0)

printf('[ACC]:OK!\r\n');

#endif

}

else

{

MEMS_DEVICE.HardWareSta = DEF_MEMS_DEVICE_ERR;

retCode =-1;

#if(DEF_ADDINFO_OUTPUTEN > 0)

printf('[ACC]:Error!\r\n');

#endif

}

if(MEMS_DEVICE.HardWareSta != DEF_MEMS_DEVICE_ERR)

{

ACCELEROMETER_Write(Ctrl_Reg1,0x57);//0101:normal/low power mode (100Hz),0:normal mode,111:XYZ enable.

//ACCELEROMETER_Read(Ctrl_Reg1,&tmp);

ACCELEROMETER_Write(Ctrl_Reg2,0x89);//high pass filter enable

//ACCELEROMETER_Read(Ctrl_Reg2,&tmp);

ACCELEROMETER_Write(Ctrl_Reg3,0x00);//disable INT

//ACCELEROMETER_Read(Ctrl_Reg3,&tmp);

ACCELEROMETER_Write(Ctrl_Reg4,0x08);//2: Full scale selection +/- 2G High resolution enable

//ACCELEROMETER_Read(Ctrl_Reg4,&tmp);

ACCELEROMETER_Write(Ctrl_Reg5,0x00);//INT1 IO not latched

//ACCELEROMETER_Read(Ctrl_Reg5,&tmp);

ACCELEROMETER_Write(Ctrl_Reg6,0x02);//INT1 IO active low(??)

//ACCELEROMETER_Read(Ctrl_Reg6,&tmp);

ACCELEROMETER_Write(INT1_DURATION,0x00);//set INT1 mode OR, high event

//ACCELEROMETER_Read(INT1_DURATION,&tmp);

ACCELEROMETER_Write(INT1_CFG,0x2A);//set INT1 mode OR, high and low event 0X3F

//ACCELEROMETER_Read(INT1_CFG,&tmp);

}

Below is are INT1 threshold value as per user configuration stored in non volatile memory.

BSP_ACCELEROMETER_SetInt1Threshold(s_Cfg.accMThreshold, 2000); 

BSP_ACCELEROMETER_SetInt1Duration(s_Cfg.accMDuration, 2000);

g value calculation function.

s8 BSP_ACCELEROMETER_ReadXYZ(MEMS_data_Typedef *MEMS_data,u16 timeout)

{

s8 retCode=0;

u8 X_data_h=0,X_data_l=0,Y_data_h=0,Y_data_l=0,Z_data_h=0,Z_data_l=0,tmp=0;

s16 tmpdata=0;

double x_acc = 0, y_acc = 0,z_acc = 0;

ACCELEROMETER_Read(Out_X_L,&X_data_l);

ACCELEROMETER_Read(Out_X_H,&X_data_h);

// read Y data

ACCELEROMETER_Read(Out_Y_L,&Y_data_l);

ACCELEROMETER_Read(Out_Y_H,&Y_data_h);

// read Z data

ACCELEROMETER_Read(Out_Z_L,&Z_data_l);

ACCELEROMETER_Read(Out_Z_H,&Z_data_h);

/* calculate the data */

tmpdata = X_data_l;

tmpdata |= (X_data_h << 8);

MEMS_data->X_data = tmpdata;

tmpdata = Y_data_l;

tmpdata |= (Y_data_h << 8);

MEMS_data->Y_data = tmpdata;

tmpdata = Z_data_l;

tmpdata |= (Z_data_h << 8);

MEMS_data->Z_data = tmpdata;

x_acc = ((double)MEMS_data->X_data)/16380;

y_acc = ((double)MEMS_data->Y_data)/16380;

z_acc = ((double)MEMS_data->Z_data)/16380;

printf('\r\n[ACC]:X=%lf, Y=%lf, Z=%lf', x_acc,y_acc,z_acc);

return retCode;

}

[Miroslav BATEK]

Posted on January 24, 2018 at 11:07

OK,

you enabled the High pass filter ACCELEROMETER_Write(Ctrl_Reg2,0x89);//high pass filter enable

In this case you will see only changes in the acceleration, in other words, it will remove any DC value like 1g gravity.

[Vishal Dongare]

Posted on January 24, 2018 at 12:29

After disabling high pass filter, I am able to get g value as expected.

Thank you so much for your solution.