kriswiner
commented
7 years ago Which MCU are you using?
I don't quite understand you readBytes function. Are you trying to read just two bytes?
Where are you composing the two bytes into an int16_t signed interger? i suspect the latter is your problem.
This is what I use for I2C:
// I2C read/write functions for the BMP280 sensors
void writeByte(uint8_t address, uint8_t subAddress, uint8_t data) { Wire.beginTransmission(address); // Initialize the Tx buffer Wire.write(subAddress); // Put slave register address in Tx buffer Wire.write(data); // Put data in Tx buffer Wire.endTransmission(); // Send the Tx buffer }
uint8_t readByte(uint8_t address, uint8_t subAddress) { uint8_t data; //
datawill store the register data Wire.beginTransmission(address); // Initialize the Tx buffer Wire.write(subAddress); // Put slave register address in Tx buffer Wire.endTransmission(false); // Send the Tx buffer, but send a restart to keep connection alive Wire.requestFrom(address, 1); // Read one byte from slave register address data = Wire.read(); // Fill Rx buffer with result return data; // Return data read from slave register }void readBytes(uint8_t address, uint8_t subAddress, uint8_t count, uint8_t
- dest) { Wire.beginTransmission(address); // Initialize the Tx buffer Wire.write(subAddress); // Put slave register address in Tx buffer Wire.endTransmission(false); // Send the Tx buffer, but send a restart to keep connection alive uint8_t i = 0; Wire.requestFrom(address, count); // Read bytes from slave register address while (Wire.available()) { dest[i++] = Wire.read(); } // Put read results in the Rx buffer
}
On Wed, May 17, 2017 at 2:10 PM, tim77777 notifications@github.com wrote:
Hi, I am wondering about intermittent random values I am getting from the MPU9250 accelerometer. The output always jumps around a little as expected, proportional to the bandwidth that I set. But I also get random high and low values anywhere from -10000's to +10000's. Perhaps there is a clue in the fact that there is often -256 (100000000)and +255 (011111111), also it is much worse on the X axis, though it does happen on all axes. This is my own implementation on a microchip part. I have tried slowing I2C, and inserting delays here and there, but it doesn't make any difference.
There has very very rarely been a random value from the Gyro, but the accelerometer, particularly the X axis (which is read first) spits regularly.
I have tried reading only the single low byte from the X axis and the random values are sometimes well about 255, which would not be possible from an 8 bit value, so I guess the problem is in my I2C routine or maybe even hardware related.
accele_bytes[0] = I2C_read_reg(MPU_ADDRESS, ACCEL_XOUT_L);
char I2C_read_reg(char cntl_add, char value) { char reg_value = 0;
I2CStart(); I2CSend(cntl_add); // prepare to be read //D0 I2CSend(value); // register to be read; I2CRestart(); I2CSend(cntl_add + 1); //read from previously sent register address reg_value = I2CRead(); I2CStop(); return reg_value;}
Any help would be appreciated.
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tim77777
bwilliams-97
Hi, I am wondering about intermittent random values I am getting from the MPU9250 accelerometer. The output always jumps around a little as expected, proportional to the bandwidth that I set. But I also get random high and low values anywhere from -10000's to +10000's. Perhaps there is a clue in the fact that there is often -256 (100000000)and +255 (011111111), also it is much worse on the X axis, though it does happen on all axes. This is my own implementation on a microchip part. I have tried slowing I2C, and inserting delays here and there, but it doesn't make any difference.
There has very very rarely been a random value from the Gyro, but the accelerometer, particularly the X axis (which is read first) spits regularly.
I have tried reading only the single low byte from the X axis and the random values are sometimes well about 255, which would not be possible from an 8 bit value, so I guess the problem is in my I2C routine or maybe even hardware related.
accele_bytes[0] = I2C_read_reg(MPU_ADDRESS, ACCEL_XOUT_L);
char I2C_read_reg(char cntl_add, char value) { char reg_value = 0;
}
Any help would be appreciated.