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Topic: Activating low pass filter on MPU6050 (Read 92 times) previous topic - next topic

mcluka

Aug 12, 2017, 11:28 pm Last Edit: Aug 12, 2017, 11:34 pm by mcluka
Dear all,

I would like to activate the low pass filter of 94 Hz bandwidth on my MPU 6050. By reading the documentation (PAGE 13), it says that you activate the appropriate bandwidth by writing the selected number into address 1A (PAGE 6).

Would this inside the void setup be okay to do so?

Code: [Select]
  Wire.beginTransmission(0x68);
  Wire.write(0x1A);  //
  Wire.write(2);     //
  Wire.endTransmission(true);


Kind regards,

L

zhomeslice

Well it is a little more complex than just sending 2 to the address.
You need to get the value of the 0x1A address and insert the 3 bits that you want to change and send the byte back otherwise you lose the other configuration values  included in the 8 bit register.

The segment code below is snipped from the library by  Jeff Rowberg https://github.com/jrowberg/i2cdevlib

I stripped all else out so you have only the code pertaining to the changing of the 1A DLPF values  and removed it from the class so that it can be used directly in your code without creating the class. although you may want to create an MPU6950 class to get simple access to all the attributes of the MPU6050
This is complex but not impossible to understand. 
Code: [Select]
#include "I2Cdev.h"
// class default I2C address is 0x68
// specific I2C addresses may be passed as a parameter here
// AD0 low = 0x68 (default for InvenSense evaluation board)
// AD0 high = 0x69
#define devAddr 0x68

#define MPU6050_RA_CONFIG           0x1A

#define MPU6050_CFG_DLPF_CFG_BIT    2
#define MPU6050_CFG_DLPF_CFG_LENGTH 3

// Options:
#define MPU6050_DLPF_BW_256         0x00
#define MPU6050_DLPF_BW_188         0x01
#define MPU6050_DLPF_BW_98          0x02
#define MPU6050_DLPF_BW_42          0x03
#define MPU6050_DLPF_BW_20          0x04
#define MPU6050_DLPF_BW_10          0x05
#define MPU6050_DLPF_BW_5           0x06

/** Get digital low-pass filter configuration.
 * The DLPF_CFG parameter sets the digital low pass filter configuration. It
 * also determines the internal sampling rate used by the device as shown in
 * the table below.
 *
 * Note: The accelerometer output rate is 1kHz. This means that for a Sample
 * Rate greater than 1kHz, the same accelerometer sample may be output to the
 * FIFO, DMP, and sensor registers more than once.
 *
 * <pre>
 *          |   ACCELEROMETER    |           GYROSCOPE
 * DLPF_CFG | Bandwidth | Delay  | Bandwidth | Delay  | Sample Rate
 * ---------+-----------+--------+-----------+--------+-------------
 * 0        | 260Hz     | 0ms    | 256Hz     | 0.98ms | 8kHz
 * 1        | 184Hz     | 2.0ms  | 188Hz     | 1.9ms  | 1kHz
 * 2        | 94Hz      | 3.0ms  | 98Hz      | 2.8ms  | 1kHz
 * 3        | 44Hz      | 4.9ms  | 42Hz      | 4.8ms  | 1kHz
 * 4        | 21Hz      | 8.5ms  | 20Hz      | 8.3ms  | 1kHz
 * 5        | 10Hz      | 13.8ms | 10Hz      | 13.4ms | 1kHz
 * 6        | 5Hz       | 19.0ms | 5Hz       | 18.6ms | 1kHz
 * 7        |   -- Reserved --   |   -- Reserved --   | Reserved
 * </pre>
 *
 * @return DLFP configuration
 * @see MPU6050_RA_CONFIG
 * @see MPU6050_CFG_DLPF_CFG_BIT
 * @see MPU6050_CFG_DLPF_CFG_LENGTH
 */
uint8_t getDLPFMode() {
    I2Cdev::readBits(devAddr, MPU6050_RA_CONFIG, MPU6050_CFG_DLPF_CFG_BIT, MPU6050_CFG_DLPF_CFG_LENGTH, buffer);
    return buffer[0];
}
/** Set digital low-pass filter configuration.
 * @param mode New DLFP configuration setting
 * @see getDLPFBandwidth()
 * @see MPU6050_DLPF_BW_256
 * @see MPU6050_RA_CONFIG
 * @see MPU6050_CFG_DLPF_CFG_BIT
 * @see MPU6050_CFG_DLPF_CFG_LENGTH
 */
void setDLPFMode(uint8_t mode) {
    I2Cdev::writeBits(devAddr, MPU6050_RA_CONFIG, MPU6050_CFG_DLPF_CFG_BIT, MPU6050_CFG_DLPF_CFG_LENGTH, mode);
}


usage:
Code: [Select]
setDLPFMode(MPU6050_DLPF_BW_98);

The following code is packaged nicely in the I2Cdev.cpp library (Attached) and is designed to handle specific bit manipulation:
Code: [Select]

/* in I2Cdev.cpp: */
int8_t I2Cdev::readBits(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint8_t *data, uint16_t timeout) {
    // 01101001 read byte
    // 76543210 bit numbers
    //    xxx   args: bitStart=4, length=3
    //    010   masked
    //   -> 010 shifted
    uint8_t count, b;
    if ((count = readByte(devAddr, regAddr, &b, timeout)) != 0) {
        uint8_t mask = ((1 << length) - 1) << (bitStart - length + 1);
        b &= mask;
        b >>= (bitStart - length + 1);
        *data = b;
    }
    return count;
}
/** Read single byte from an 8-bit device register.
 * @param devAddr I2C slave device address
 * @param regAddr Register regAddr to read from
 * @param data Container for byte value read from device
 * @param timeout Optional read timeout in milliseconds (0 to disable, leave off to use default class value in I2Cdev::readTimeout)
 * @return Status of read operation (true = success)
 */
int8_t I2Cdev::readByte(uint8_t devAddr, uint8_t regAddr, uint8_t *data, uint16_t timeout) {
    return readBytes(devAddr, regAddr, 1, data, timeout);
}

/** Write multiple bits in an 8-bit device register.
 * @param devAddr I2C slave device address
 * @param regAddr Register regAddr to write to
 * @param bitStart First bit position to write (0-7)
 * @param length Number of bits to write (not more than 8)
 * @param data Right-aligned value to write
 * @return Status of operation (true = success)
 */
bool I2Cdev::writeBits(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint8_t data) {
    //      010 value to write
    // 76543210 bit numbers
    //    xxx   args: bitStart=4, length=3
    // 00011100 mask byte
    // 10101111 original value (sample)
    // 10100011 original & ~mask
    // 10101011 masked | value
    uint8_t b;
    if (readByte(devAddr, regAddr, &b) != 0) {
        uint8_t mask = ((1 << length) - 1) << (bitStart - length + 1);
        data <<= (bitStart - length + 1); // shift data into correct position
        data &= mask; // zero all non-important bits in data
        b &= ~(mask); // zero all important bits in existing byte
        b |= data; // combine data with existing byte
        return writeByte(devAddr, regAddr, b);
    } else {
        return false;
    }
}

/** Write multiple bits in a 16-bit device register.
 * @param devAddr I2C slave device address
 * @param regAddr Register regAddr to write to
 * @param bitStart First bit position to write (0-15)
 * @param length Number of bits to write (not more than 16)
 * @param data Right-aligned value to write
 * @return Status of operation (true = success)
 */
bool I2Cdev::writeBitsW(uint8_t devAddr, uint8_t regAddr, uint8_t bitStart, uint8_t length, uint16_t data) {
    //              010 value to write
    // fedcba9876543210 bit numbers
    //    xxx           args: bitStart=12, length=3
    // 0001110000000000 mask word
    // 1010111110010110 original value (sample)
    // 1010001110010110 original & ~mask
    // 1010101110010110 masked | value
    uint16_t w;
    if (readWord(devAddr, regAddr, &w) != 0) {
        uint16_t mask = ((1 << length) - 1) << (bitStart - length + 1);
        data <<= (bitStart - length + 1); // shift data into correct position
        data &= mask; // zero all non-important bits in data
        w &= ~(mask); // zero all important bits in existing word
        w |= data; // combine data with existing word
        return writeWord(devAddr, regAddr, w);
    } else {
        return false;
    }
}

/** Write single byte to an 8-bit device register.
 * @param devAddr I2C slave device address
 * @param regAddr Register address to write to
 * @param data New byte value to write
 * @return Status of operation (true = success)
 */
bool I2Cdev::writeByte(uint8_t devAddr, uint8_t regAddr, uint8_t data) {
    return writeBytes(devAddr, regAddr, 1, &data);
}

/** Write multiple bytes to an 8-bit device register.
 * @param devAddr I2C slave device address
 * @param regAddr First register address to write to
 * @param length Number of bytes to write
 * @param data Buffer to copy new data from
 * @return Status of operation (true = success)
 */
bool I2Cdev::writeBytes(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint8_t* data) {
    uint8_t status = 0;
    Wire.beginTransmission(devAddr);
    Wire.write((uint8_t) regAddr); // send address
    for (uint8_t i = 0; i < length; i++) {
            Wire.write((uint8_t) data[i]);
    }
    status = Wire.endTransmission();
    return status == 0;
}
HC

mcluka

Hi zhomeslice,

Thank you for your answer. Since I am no expert in Arduino this is quite complex to me. The thing is that I would like to apply the low pass filter for acceleration measurements in all three directions for both sensors (I'm using 2 --> 0x68 and 0x69) for 94Hz bandwidth.

Even though you seem to put quite an effort to answer me, I'm still clueless of what I should include in my code for the filter to be activated. I don't understand anything about specific bit manipulation...

Could you maybe paste just the part of the code that does the activation, since a lot of the code is about defining something that I probably don't even need...

Kind regards and much appreciated,

L

zhomeslice

Hi zhomeslice,

Thank you for your answer. Since I am no expert in Arduino this is quite complex to me. The thing is that I would like to apply the low pass filter for acceleration measurements in all three directions for both sensors (I'm using 2 --> 0x68 and 0x69) for 94Hz bandwidth.

Even though you seem to put quite an effort to answer me, I'm still clueless of what I should include in my code for the filter to be activated. I don't understand anything about specific bit manipulation...

Could you maybe paste just the part of the code that does the activation, since a lot of the code is about defining something that I probably don't even need...

Kind regards and much appreciated,

L
then lets use the library provided by 
Jeff Rowberg 
https://github.com/jrowberg/i2cdevlib


Here is his example code with your requested change added look for the " <<<<<<<<<<< " remark it is quite simple using the libraries he has created.
Code: [Select]
// I2C device class (I2Cdev) demonstration Arduino sketch for MPU6050 class
// 10/7/2011 by Jeff Rowberg <jeff@rowberg.net>
// Updates should (hopefully) always be available at https://github.com/jrowberg/i2cdevlib
//
// Changelog:
//      2013-05-08 - added multiple output formats
//                 - added seamless Fastwire support
//      2011-10-07 - initial release

/* ============================================
I2Cdev device library code is placed under the MIT license
Copyright (c) 2011 Jeff Rowberg

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
===============================================
*/

// I2Cdev and MPU6050 must be installed as libraries, or else the .cpp/.h files
// for both classes must be in the include path of your project
#include "I2Cdev.h"
#include "MPU6050.h"

// Arduino Wire library is required if I2Cdev I2CDEV_ARDUINO_WIRE implementation
// is used in I2Cdev.h
#if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
    #include "Wire.h"
#endif

// class default I2C address is 0x68
// specific I2C addresses may be passed as a parameter here
// AD0 low = 0x68 (default for InvenSense evaluation board)
// AD0 high = 0x69
MPU6050 accelgyro;
//MPU6050 accelgyro(0x69); // <-- use for AD0 high

int16_t ax, ay, az;
int16_t gx, gy, gz;



// uncomment "OUTPUT_READABLE_ACCELGYRO" if you want to see a tab-separated
// list of the accel X/Y/Z and then gyro X/Y/Z values in decimal. Easy to read,
// not so easy to parse, and slow(er) over UART.
#define OUTPUT_READABLE_ACCELGYRO

// uncomment "OUTPUT_BINARY_ACCELGYRO" to send all 6 axes of data as 16-bit
// binary, one right after the other. This is very fast (as fast as possible
// without compression or data loss), and easy to parse, but impossible to read
// for a human.
//#define OUTPUT_BINARY_ACCELGYRO


#define LED_PIN 13
bool blinkState = false;

void setup() {
    // join I2C bus (I2Cdev library doesn't do this automatically)
    #if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
        Wire.begin();
    #elif I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE
        Fastwire::setup(400, true);
    #endif

    // initialize serial communication
    // (38400 chosen because it works as well at 8MHz as it does at 16MHz, but
    // it's really up to you depending on your project)
    Serial.begin(115200);

    // initialize device
    Serial.println("Initializing I2C devices...");
    accelgyro.initialize();
    accelgyro.setDLPFMode(MPU6050_DLPF_BW_98); // <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

    // verify connection
    Serial.println("Testing device connections...");
    Serial.println(accelgyro.testConnection() ? "MPU6050 connection successful" : "MPU6050 connection failed");

    // use the code below to change accel/gyro offset values
    /*
    Serial.println("Updating internal sensor offsets...");
    // -76 -2359 1688 0 0 0
    Serial.print(accelgyro.getXAccelOffset()); Serial.print("\t"); // -76
    Serial.print(accelgyro.getYAccelOffset()); Serial.print("\t"); // -2359
    Serial.print(accelgyro.getZAccelOffset()); Serial.print("\t"); // 1688
    Serial.print(accelgyro.getXGyroOffset()); Serial.print("\t"); // 0
    Serial.print(accelgyro.getYGyroOffset()); Serial.print("\t"); // 0
    Serial.print(accelgyro.getZGyroOffset()); Serial.print("\t"); // 0
    Serial.print("\n");
    accelgyro.setXGyroOffset(220);
    accelgyro.setYGyroOffset(76);
    accelgyro.setZGyroOffset(-85);
    Serial.print(accelgyro.getXAccelOffset()); Serial.print("\t"); // -76
    Serial.print(accelgyro.getYAccelOffset()); Serial.print("\t"); // -2359
    Serial.print(accelgyro.getZAccelOffset()); Serial.print("\t"); // 1688
    Serial.print(accelgyro.getXGyroOffset()); Serial.print("\t"); // 0
    Serial.print(accelgyro.getYGyroOffset()); Serial.print("\t"); // 0
    Serial.print(accelgyro.getZGyroOffset()); Serial.print("\t"); // 0
    Serial.print("\n");
    */

    // configure Arduino LED for
    pinMode(LED_PIN, OUTPUT);
}

void loop() {
    // read raw accel/gyro measurements from device
    accelgyro.getMotion6(&ax, &ay, &az, &gx, &gy, &gz);

    // these methods (and a few others) are also available
    //accelgyro.getAcceleration(&ax, &ay, &az);
    //accelgyro.getRotation(&gx, &gy, &gz);

    #ifdef OUTPUT_READABLE_ACCELGYRO
        // display tab-separated accel/gyro x/y/z values
        Serial.print("a/g:\t");
        Serial.print(ax); Serial.print("\t");
        Serial.print(ay); Serial.print("\t");
        Serial.print(az); Serial.print("\t");
        Serial.print(gx); Serial.print("\t");
        Serial.print(gy); Serial.print("\t");
        Serial.println(gz);
    #endif

    #ifdef OUTPUT_BINARY_ACCELGYRO
        Serial.write((uint8_t)(ax >> 8)); Serial.write((uint8_t)(ax & 0xFF));
        Serial.write((uint8_t)(ay >> 8)); Serial.write((uint8_t)(ay & 0xFF));
        Serial.write((uint8_t)(az >> 8)); Serial.write((uint8_t)(az & 0xFF));
        Serial.write((uint8_t)(gx >> 8)); Serial.write((uint8_t)(gx & 0xFF));
        Serial.write((uint8_t)(gy >> 8)); Serial.write((uint8_t)(gy & 0xFF));
        Serial.write((uint8_t)(gz >> 8)); Serial.write((uint8_t)(gz & 0xFF));
    #endif

    // blink LED to indicate activity
    blinkState = !blinkState;
    digitalWrite(LED_PIN, blinkState);
}


HC

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