As i mentioned before I read 100 samples in self-test mode and they all have the same value. Yours are changing so I think I should try another gyro :smileysilly:
At this moment i can't give you data from logic analyzer but I will get it in a few days.
I need only Z axis data but since it is recommended to read all 3 axis I do it.
Here is the code:
#define FXAS21002C_H_OUT_X_MSB 0x01
#define FXAS21002C_H_WHO_AM_I 0x0C
#define FXAS21002C_H_CTRL_REG0 0x0D
#define FXAS21002C_H_CTRL_REG1 0x13
enum gyroODR {
GODR_800HZ,
GODR_400HZ,
GODR_200HZ,
GODR_100HZ,
GODR_50HZ,
GODR_12_5HZ,
GODR_6_25HZ,
GODR_1_56HZ
};
enum gyroFSR {
GFS_2000DPS,
GFS_1000DPS,
GFS_500DPS,
GFS_250DPS
};
enum gyroMODE {
MODE_STANDBY,
MODE_READY,
MODE_ACTIVE
};
typedef struct
{
int16_t x;
int16_t y;
int16_t z;
} raw_data;
uint8_t SpiRxBuffer[6];
raw_data raw;
float prev_z;
int16_t cal_z;
void GyroInit(){
/*
Gyro is now in Standby mode every register
changes should be made in this mode
*/
// check connection by reading whoami register, it should always be 0xD7
if(SpiRead(FXAS21002C_H_WHO_AM_I, 1) != 0xD7){
return;
}
HAL_Delay(1);
SpiWrite(FXAS21002C_H_CTRL_REG0, (GFS_250DPS)); // set FSR
SpiWrite(FXAS21002C_H_CTRL_REG1, (GODR_100HZ | MODE_ACTIVE)); // set ODR and switch to active mode
HAL_Delay(100);
}
void GyroReadData(){
prev_z = raw.z;
SpiRead(FXAS21002C_H_OUT_X_MSB, 6);
raw.x = (int16_t)(SpiRxBuffer[0] << 8 | SpiRxBuffer[1]);
raw.y = (int16_t)(SpiRxBuffer[2] << 8 | SpiRxBuffer[3]);
raw.z = (int16_t)(SpiRxBuffer[4] << 8 | SpiRxBuffer[5]);
}
void GyroCalibrate(){
for(int i = 0; i < 100; i++){
GyroReadData();
cal_z += raw.z;
HAL_Delay(10);
}
cal_z = cal_z/100;
}
float GyroGetAngle(float dt, float a, float b){
float a1 = 0; // current angle
a1 = ((((a-cal_z)+(b-cal_z))/2.0)*dt*0.0078125) + a1; // cal_z is calibration offset
return a1;
};
int main(void){
float sum = 0;
GyroInit();
GyroCalibrate()
//self-test mode
//SpiWrite(FXAS21002C_H_CTRL_REG1, (GODR_100HZ | (1<<5) |MODE_ACTIVE));
while(1){
GyroReadData();
sum += GyroGetAngle(0.01, raw.z, prev_z); //args: Ts, current, prev
printf("%f\r\n", sum);
HAL_Delay(10);
}
}
It's a very good gryo but there is a one little catch. You can't read from both gyro and acc using SPI 
I was wondering why everyone use I2C rather than SPI :smileygrin:
Hello Karol,
For the integration:
I'm not sure about your formula.
I would use this one:
α0 = 0 // Initialization. Can be assigned from a magnetometer data to get the absolute position
Rectangular integration
α1 = (ωz1-ωzOff)*K*Ts + α0
Trapezoidal integration
α1 = ((ωz1-ωzOff) + (ωz0-ωzOff) /2) *K*Ts + α0
ωz1 : current Gyro Velocity (count)
ωz0 : previous Gyro Velocity (count)
ωzOff :Gyro Velocity Offset (count)
K : sensitivity (°/s/count)
α1 : current angle (°)
α0 : previous anglular position (°)
Ts : sampling time (s)
To improve the accuracy I suggest you to increase the sensor data rate. You can also compute the sampling time using a timer: it can be more accurate than using a static value (0.01).
For the SelfTest
Please take a look at the table below. The value you have looks to be okay.
Anthony
Hello Anthony,
Thanks for info about Self-Test. I wasn't sure if it should be constant value.
About integration:
I'm using similar method, P is the area of individual trapeze, a is just sum of these areas and in my case ωz is yours ωz - ωzOff
The problem is "a" does not reflect reality. As i mentioned before it gives me 20 deg when i clearly rotate of approximately 90deg.
I'm a beginner in gyro world :smileysilly:
Also another question. I know the gyro has 800Hz ODR, but can I read from it at 1kHz rate and get useful data?
Hello Karol,
I'm using similar method, P is the area of individual trapeze a is just sum of these areas and in my case ωz is yours ωz - ωzOff
Yes, you perform the "offset calibration" as you mentioned in your 1st message "At the begining I do a simple calibration ( read 100 values, sum them up, divide by 100). I substract this value from the reading and then multiply by sensitivity sepcified in datasheet" .
So yes, your integration should be good.
The problem is "a" does not reflect reality. As i mentioned before it gives me 20 deg when i clearly rotate of approximately 90deg.
I understood your issue. Can you share your source code with me? It's really hard to know what is not okay. Maybe the sensor is not well configured. You can all try to extend the gyroscope range up to 2000dps.
I did a test with our RD-KL25-AGMP01 Datalogger board, recording data at 100Hz. I got pretty good results with the trapezoidal integration. I attached an excel spreadsheet if you want to look at the accuracy and formulas.
Thanks for info about Self-Test. I wasn't sure if it should be constant value.
Yes Karol, it should change each time. Take a look at the plots below:
With Self-Test Without Self-Test
Here an example code:
bool bFXAS21002_GetRawGyroData(tRawGyroData* __pt_data)
{
static uint8_t __au8_Buffer[6];
int16_t __i16_SingleData;
//_bFXAS21002_Write(FXAS21002_CTRL_REG1,0x27); //selftest
if(_bFXAS21002_ReadBlock(FXAS21002_OUT_X_MSB,__au8_Buffer,6))
{
__i16_SingleData = (int16_t)( (__au8_Buffer[0]<<8) + __au8_Buffer[1]);
__pt_data->i16X = __i16_SingleData;
__i16_SingleData = (int16_t)( (__au8_Buffer[2]<<8) + __au8_Buffer[3]);
__pt_data->i16Y = __i16_SingleData;
__i16_SingleData = (int16_t)( (__au8_Buffer[4]<<8) + __au8_Buffer[5]);
__pt_data->i16Z = __i16_SingleData;
return TRUE;
}
return FALSE;
}
Also another question. I know the gyro has 800Hz ODR, but can I read from it at 1kHz rate and get useful data?
Yes you can do it, but you will have some identical data. I suggest you to synchronize the data collection with the sensor data rate by enabling the data ready interruption (SRC_DRDY) to avoid that.
Anthony
