Hello,
I apologize in advance for my long post, and ignorance when it comes to interpreting this linear accelerometer data. The only one I have used in the past gave me euler angles, and I had no problem calculating tilt from them.
I am trying to periodically poll the IIS2DLPC for X Y and Z values, and then convert them to a tilt value. The evaluation board is just sitting on my desk not moving, so I thought that the values shouldn't be changing (at least not changing much), but every reading is different.
I did some googling, and I see that linear accelerometers usually output euler angles or quaternions. I assumed the X Y and Z values were euler angles, but regardless of the unit of measurement, I still can't figure out why the values are changing every time I read them when the sensor is not moving at all.
Could someone give me a little guidance on parsing the X Y and Z data output registers?
Here are my register definitions:
//Registers
//#define TILT_RESERVED 0x1FU // - RESERVED
#define TILT_OUT_T_L 0x0DU //R 00001101 00000000 Temp sensor output
#define TILT_OUT_T_H 0x0EU //R 00001110 00000000
#define TILT_WHO_AM_I 0x0FU //R 00001111 01000100 Who am I ID
#define TILT_CTRL1 0x20U //R/W 00100000 00000000
#define TILT_CTRL2 0x21U //R/W 00100001 00000100
#define TILT_CTRL3 0x22U //R/W 00100010 00000000
#define TILT_CTRL4_INT1_PAD_CTRL 0x23U //R/W 00100011 00000000
#define TILT_CTRL5_INT2_PAD_CTRL 0x24U //R/W 00100100 00000000
#define TILT_CTRL6 0x25U //R/W 00100101 00000000
#define TILT_OUT_T 0x26U //R 00100110 00000000 Temp sensor output
#define TILT_STATUS 0x27U //R 00100111 00000000 Status data register
#define TILT_OUT_X_L 0x28U //R 00101000 00000000
#define TILT_OUT_X_H 0x29U //R 00101001 00000000
#define TILT_OUT_Y_L 0x2AU //R 00101010 00000000
#define TILT_OUT_Y_H 0x2BU //R 00101011 00000000
#define TILT_OUT_Z_L 0x2CU //R 00101100 00000000
#define TILT_OUT_Z_H 0x2DU //R 00101101 00000000
#define TILT_FIFO_CTRL 0x2EU //R/W 00101110 00000000 FIFO control register
#define TILT_FIFO_SAMPLES 0x2FU //R 00101111 00000000 Unread samples
#define TILT_TAP_THS_X 0x30U //R/W 00110000 00000000
#define TILT_TAP_THS_Y 0x31U //R/W 00110001 00000000 Tap thresholds
#define TILT_TAP_THS_Z 0x32U //R/W 00110010 00000000
#define TILT_INT_DUR 0x33U //R/W 00110011 00000000 Interrupt duration
#define TILT_WAKE_UP_THS 0x34U //R/W 00110100 00000000
#define TILT_WAKE_UP_DUR 0x35U //R/W 00110101 00000000 Wakeup duration
#define TILT_FREE_FALL 0x36 //R/W 00110110 00000000 Free-fall configuration
#define TILT_STATUS_DUP 0x37 //R 00110111 00000000 Status register
#define TILT_WAKE_UP_SRC 0x38 //R 00111000 00000000 Wakeup source
#define TILT_TAP_SRC 0x39 //R 00111001 00000000 Tap source
#define TILT_SIXD_SRC 0x3A //R 00111010 00000000 6D source
#define TILT_ALL_INT_SRC 0x3B //R 00111011 00000000
#define TILT_X_OFS_USR 0x3C //R/W 00111100 00000000
#define TILT_Y_OFS_USR 0x3D //R/W 00111110 00000000
#define TILT_Z_OFS_USR 0x3E //R/W 00000100 00000000
#define TILT_CTRL7 0x3F //R/W 00000100 00000000Here is where I am storing the values:
typedef struct iis2dlpc
{
uint8_t Temperature_Low_Byte_12bit; //TILT_OUT_T_L
uint8_t Temperature_High_Byte_12bit; //TILT_OUT_T_H
uint8_t Who_Am_I; //TILT_WHO_AM_I
uint8_t Control_Register_1; //TILT_CTRL1
uint8_t Control_Register_2; //TILT_CTRL2
uint8_t Control_Register_3; //TILT_CTRL3
uint8_t Control_Register_4; //TILT_CTRL4_INT1_PAD_CTRL
uint8_t Control_Register_5; //TILT_CTRL5_INT2_PAD_CTRL
uint8_t Control_Register_6; //TILT_CTRL6
uint8_t Temperature_8bit; //TILT_OUT_T
uint8_t Status; //TILT_STATUS
uint8_t X_Axis_Low_Byte; //TILT_OUT_X_L
uint8_t X_Axis_High_Byte; //TILT_OUT_X_H
uint8_t Y_Axis_Low_Byte; //TILT_OUT_Y_L
uint8_t Y_Axis_High_Byte; //TILT_OUT_Y_H
uint8_t Z_Axis_Low_Byte; //TILT_OUT_Z_L
uint8_t Z_Axis_High_Byte; //TILT_OUT_Z_H
uint8_t Fifo_Control; //TILT_FIFO_CTRL
uint8_t Fifo_Samples; //TILT_FIFO_SAMPLES
uint8_t Tap_Threshold_X; //TILT_TAP_THS_X
uint8_t Tap_Threshold_Y; //TILT_TAP_THS_Y
uint8_t Tap_Threshold_Z; //TILT_TAP_THS_Z
uint8_t Interrupt_Duration; //TILT_INT_DUR
uint8_t Wakeup_Threshold; //TILT_WAKE_UP_THS
uint8_t Wakeup_Duration; //TILT_WAKE_UP_DUR
uint8_t Tilt_Free_Fall; //TILT_FREE_FALL
uint8_t Event_Detection_Status; //TILT_STATUS_DUP
uint8_t Wakeup_Source; //TILT_WAKE_UP_SRC
uint8_t Tap_Event_Source; //TILT_TAP_SRC
uint8_t SixD_Src; //TILT_SIXD_SRC
uint8_t All_Interrupt_Src; //TILT_ALL_INT_SRC
uint8_t X_User_Offset; //TILT_X_OFS_USR
uint8_t Y_User_Offset; //TILT_Y_OFS_USR
uint8_t Z_User_Offset; //TILT_Z_OFS_USR
uint8_t Control_Register_7; //TILT_CTRL7
}IIS2DLPC_REGISTERS;When I run a function that reads and prints each register, I get what I expect in the registers that I have written to, and the "WHO_AM_I" register, but the X Y and Z data is different every time I call my function "read and print every register" function.
If you look at the attached image, this is me calling this function twice with a few seconds between each call. Notice the temperature and XYZ data changing. I am printing the HEX and binary representation of each value (sorry for the lack of labels).
