MATLAB/Octave - IMU Brick – Tinkerforge

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# MATLAB/Octave - IMU Brick

This is the description of the MATLAB/Octave API bindings for the IMU Brick. General information and technical specifications for the IMU Brick are summarized in its hardware description.

An installation guide for the MATLAB/Octave API bindings is part of their general description.

## Examples

The example code below is Public Domain (CC0 1.0).

### Callback (MATLAB)

Download (matlab_example_callback.m)

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    function matlab_example_callback()
        import com.tinkerforge.IPConnection;
        import com.tinkerforge.BrickIMU;

        HOST = 'localhost';
        PORT = 4223;
        UID = '6QFQff'; % Change to your UID

        ipcon = IPConnection(); % Create IP connection
        imu = BrickIMU(UID, ipcon); % Create device object

        ipcon.connect(HOST, PORT); % Connect to brickd
        % Don't use device before ipcon is connected

        % Set Period for quaternion callback to 1s (1000ms)
        % Note: The callback is only called every second if the
        %       quaternion has changed since the last call!
        imu.setQuaternionPeriod(1000);

        % Register quaternion callback to function cb_quaternion
        set(imu, 'QuaternionCallback', @(h, e) cb_quaternion(e));

        input('Press any key to exit...\n', 's');
        ipcon.disconnect();
    end

    % Callback function for quaternion callback
    function cb_quaternion(e)
        fprintf('x: %f\ny: %f\nz: %f\nw: %f\n\n', e.x, e.y, e.z, e.w);
    end

### Callback (Octave)

Download (octave_example_callback.m)

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    function octave_example_callback()
        more off;

        HOST = "localhost";
        PORT = 4223;
        UID = "6QFQff"; % Change to your UID

        ipcon = java_new("com.tinkerforge.IPConnection"); % Create IP connection
        imu = java_new("com.tinkerforge.BrickIMU", UID, ipcon); % Create device object

        ipcon.connect(HOST, PORT); % Connect to brickd
        % Don't use device before ipcon is connected

        % Set Period for quaternion callback to 1s (1000ms)
        % Note: The callback is only called every second if the
        %       quaternion has changed since the last call!
        imu.setQuaternionPeriod(1000);

        % Register quaternion callback to function cb_quaternion
        imu.addQuaternionCallback(@cb_quaternion);

        input("Press any key to exit...\n", "s");
        ipcon.disconnect();
    end

    % Callback function for quaternion callback
    function cb_quaternion(e)
        fprintf("x: %s\n", e.x.toString());
        fprintf("y: %s\n", e.y.toString());
        fprintf("z: %s\n", e.z.toString());
        fprintf("w: %s\n", e.w.toString());
        fprintf("\n");
    end

## API

Generally, every method of the MATLAB bindings that returns a value can throw a `TimeoutException`. This exception gets thrown if the device did not respond. If a cable based connection is used, it is unlikely that this exception gets thrown (assuming nobody unplugs the device). However, if a wireless connection is used, timeouts will occur if the distance to the device gets too big.

Beside the `TimeoutException` there is also a `NotConnectedException` that is thrown if a method needs to communicate with the device while the IP Connection is not connected.

Since the MATLAB bindings are based on Java and Java does not support multiple return values and return by reference is not possible for primitive types, we use small classes that only consist of member variables. The member variables of the returned objects are described in the corresponding method descriptions.

The package for all Brick/Bricklet bindings and the IP Connection is `com.tinkerforge.*`

All methods listed below are thread-safe.

### Basic Functions

public class `BrickIMU`(String uid, IPConnection ipcon)

  Creates an object with the unique device ID `uid`.

  In MATLAB:

      import com.tinkerforge.BrickIMU;

      imu = BrickIMU('YOUR_DEVICE_UID', ipcon);

  In Octave:

      imu = java_new("com.tinkerforge.BrickIMU", "YOUR_DEVICE_UID", ipcon);

  This object can then be used after the IP Connection is connected (see examples above).

public BrickIMU.Orientation `getOrientation`()

  Returns the current orientation (roll, pitch, yaw) of the IMU Brick as Euler angles in one-hundredth degree. Note that Euler angles always experience a gimbal lock.

  We recommend that you use quaternions instead.

  The order to sequence in which the orientation values should be applied is roll, yaw, pitch.

  If you want to get the orientation periodically, it is recommended to use the callback `OrientationCallback` and set the period with `setOrientationPeriod()`.

  The returned object has the public member variables `short roll`, `short pitch` and `short yaw`.

public BrickIMU.Quaternion `getQuaternion`()

  Returns the current orientation (x, y, z, w) of the IMU as quaternions.

  You can go from quaternions to Euler angles with the following formula:

      xAngle = atan2(2*y*w - 2*x*z, 1 - 2*y*y - 2*z*z)
      yAngle = atan2(2*x*w - 2*y*z, 1 - 2*x*x - 2*z*z)
      zAngle =  asin(2*x*y + 2*z*w)

  This process is not reversible, because of the gimbal lock.

  It is also possible to calculate independent angles. You can calculate yaw, pitch and roll in a right-handed vehicle coordinate system according to DIN70000 with:

      yaw   =  atan2(2*x*y + 2*w*z, w*w + x*x - y*y - z*z)
      pitch = -asin(2*w*y - 2*x*z)
      roll  = -atan2(2*y*z + 2*w*x, -w*w + x*x + y*y - z*z))

  Converting the quaternions to an OpenGL transformation matrix is possible with the following formula:

      matrix = [[1 - 2*(y*y + z*z),     2*(x*y - w*z),     2*(x*z + w*y), 0],
                [    2*(x*y + w*z), 1 - 2*(x*x + z*z),     2*(y*z - w*x), 0],
                [    2*(x*z - w*y),     2*(y*z + w*x), 1 - 2*(x*x + y*y), 0],
                [                0,                 0,                 0, 1]]

  If you want to get the quaternions periodically, it is recommended to use the callback `QuaternionCallback` and set the period with `setQuaternionPeriod()`.

  The returned object has the public member variables `float x`, `float y`, `float z` and `float w`.

public void `ledsOn`()

  Turns the orientation and direction LEDs of the IMU Brick on.

public void `ledsOff`()

  Turns the orientation and direction LEDs of the IMU Brick off.

public boolean `areLedsOn`()

  Returns true if the orientation and direction LEDs of the IMU Brick are on, false otherwise.

public void `setConvergenceSpeed`(int speed)

  Sets the convergence speed of the IMU Brick in °/s. The convergence speed determines how the different sensor measurements are fused.

  If the orientation of the IMU Brick is off by 10° and the convergence speed is set to 20°/s, it will take 0.5s until the orientation is corrected. However, if the correct orientation is reached and the convergence speed is too high, the orientation will fluctuate with the fluctuations of the accelerometer and the magnetometer.

  If you set the convergence speed to 0, practically only the gyroscope is used to calculate the orientation. This gives very smooth movements, but errors of the gyroscope will not be corrected. If you set the convergence speed to something above 500, practically only the magnetometer and the accelerometer are used to calculate the orientation. In this case the movements are abrupt and the values will fluctuate, but there won't be any errors that accumulate over time.

  In an application with high angular velocities, we recommend a high convergence speed, so the errors of the gyroscope can be corrected fast. In applications with only slow movements we recommend a low convergence speed. You can change the convergence speed on the fly. So it is possible (and recommended) to increase the convergence speed before an abrupt movement and decrease it afterwards again.

  You might want to play around with the convergence speed in the Brick Viewer to get a feeling for a good value for your application.

  The default value is 30.

public int `getConvergenceSpeed`()

  Returns the convergence speed as set by `setConvergenceSpeed()`.

### Advanced Functions

public BrickIMU.Acceleration `getAcceleration`()

  Returns the calibrated acceleration from the accelerometer for the x, y and z axis in mG (G/1000, 1G = 9.80605m/s²).

  If you want to get the acceleration periodically, it is recommended to use the callback `AccelerationCallback` and set the period with `setAccelerationPeriod()`.

  The returned object has the public member variables `short x`, `short y` and `short z`.

public BrickIMU.MagneticField `getMagneticField`()

  Returns the calibrated magnetic field from the magnetometer for the x, y and z axis in mG (Milligauss or Nanotesla).

  If you want to get the magnetic field periodically, it is recommended to use the callback `MagneticFieldCallback` and set the period with `setMagneticFieldPeriod()`.

  The returned object has the public member variables `short x`, `short y` and `short z`.

public BrickIMU.AngularVelocity `getAngularVelocity`()

  Returns the calibrated angular velocity from the gyroscope for the x, y and z axis in °/14.375s (you have to divide by 14.375 to get the value in °/s).

  If you want to get the angular velocity periodically, it is recommended to use the callback `AngularVelocityCallback` and set the period with `setAngularVelocityPeriod()`.

  The returned object has the public member variables `short x`, `short y` and `short z`.

public BrickIMU.AllData `getAllData`()

  Returns the data from `getAcceleration()`, `getMagneticField()` and `getAngularVelocity()` as well as the temperature of the IMU Brick.

  The temperature is given in °C/100.

  If you want to get the data periodically, it is recommended to use the callback `AllDataCallback` and set the period with `setAllDataPeriod()`.

  The returned object has the public member variables `short accX`, `short accY`, `short accZ`, `short magX`, `short magY`, `short magZ`, `short angX`, `short angY`, `short angZ` and `short temperature`.

public short `getIMUTemperature`()

  Returns the temperature of the IMU Brick. The temperature is given in °C/100.

public void `setAccelerationRange`(short range)

  Not implemented yet.

public short `getAccelerationRange`()

  Not implemented yet.

public void `setMagnetometerRange`(short range)

  Not implemented yet.

public short `getMagnetometerRange`()

  Not implemented yet.

public void `setCalibration`(short typ, short[] data)

  There are several different types that can be calibrated:

  Type | Description | Values
  --- | --- | ---
  0 | Accelerometer Gain | `[mul x, mul y, mul z, div x, div y, div z, 0, 0, 0, 0]`
  1 | Accelerometer Bias | `[bias x, bias y, bias z, 0, 0, 0, 0, 0, 0, 0]`
  2 | Magnetometer Gain | `[mul x, mul y, mul z, div x, div y, div z, 0, 0, 0, 0]`
  3 | Magnetometer Bias | `[bias x, bias y, bias z, 0, 0, 0, 0, 0, 0, 0]`
  4 | Gyroscope Gain | `[mul x, mul y, mul z, div x, div y, div z, 0, 0, 0, 0]`
  5 | Gyroscope Bias | `[bias xl, bias yl, bias zl, temp l, bias xh, bias yh, bias zh, temp h, 0, 0]`

  The calibration via gain and bias is done with the following formula:

      new_value = (bias + orig_value) * gain_mul / gain_div

  If you really want to write your own calibration software, please keep in mind that you first have to undo the old calibration (set bias to 0 and gain to 1/1) and that you have to average over several thousand values to obtain a usable result in the end.

  The gyroscope bias is highly dependent on the temperature, so you have to calibrate the bias two times with different temperatures. The values `xl`, `yl`, `zl` and `temp l` are the bias for `x`, `y`, `z` and the corresponding temperature for a low temperature. The values `xh`, `yh`, `zh` and `temp h` are the same for a high temperatures. The temperature difference should be at least 5°C. If you have a temperature where the IMU Brick is mostly used, you should use this temperature for one of the sampling points.

  Note

  We highly recommend that you use the Brick Viewer to calibrate your IMU Brick.

  The following constants are available for this function:

  - BrickIMU.CALIBRATION_TYPE_ACCELEROMETER_GAIN = 0
  - BrickIMU.CALIBRATION_TYPE_ACCELEROMETER_BIAS = 1
  - BrickIMU.CALIBRATION_TYPE_MAGNETOMETER_GAIN = 2
  - BrickIMU.CALIBRATION_TYPE_MAGNETOMETER_BIAS = 3
  - BrickIMU.CALIBRATION_TYPE_GYROSCOPE_GAIN = 4
  - BrickIMU.CALIBRATION_TYPE_GYROSCOPE_BIAS = 5

public short[] `getCalibration`(short typ)

  Returns the calibration for a given type as set by `setCalibration()`.

  The following constants are available for this function:

  - BrickIMU.CALIBRATION_TYPE_ACCELEROMETER_GAIN = 0
  - BrickIMU.CALIBRATION_TYPE_ACCELEROMETER_BIAS = 1
  - BrickIMU.CALIBRATION_TYPE_MAGNETOMETER_GAIN = 2
  - BrickIMU.CALIBRATION_TYPE_MAGNETOMETER_BIAS = 3
  - BrickIMU.CALIBRATION_TYPE_GYROSCOPE_GAIN = 4
  - BrickIMU.CALIBRATION_TYPE_GYROSCOPE_BIAS = 5

public void `orientationCalculationOn`()

  Turns the orientation calculation of the IMU Brick on.

  As default the calculation is on.

  New in version 2.0.2 (Firmware).

public void `orientationCalculationOff`()

  Turns the orientation calculation of the IMU Brick off.

  If the calculation is off, `getOrientation()` will return the last calculated value until the calculation is turned on again.

  The trigonometric functions that are needed to calculate the orientation are very expensive. We recommend to turn the orientation calculation off if the orientation is not needed, to free calculation time for the sensor fusion algorithm.

  As default the calculation is on.

  New in version 2.0.2 (Firmware).

public boolean `isOrientationCalculationOn`()

  Returns true if the orientation calculation of the IMU Brick is on, false otherwise.

  New in version 2.0.2 (Firmware).

public short[] `getAPIVersion`()

  Returns the version of the API definition (major, minor, revision) implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.

public boolean `getResponseExpected`(short functionId)

  Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.

  For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For callback configuration functions it is enabled by default too, but can be disabled by `setResponseExpected()`. For setter functions it is disabled by default and can be enabled.

  Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

  See `setResponseExpected()` for the list of function ID constants available for this function.

public void `setResponseExpected`(short functionId, boolean responseExpected)

  Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and callback configuration functions (default value: true). For getter functions it is always enabled and callbacks it is always disabled.

  Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

  The following function ID constants are available for this function:

  - BrickIMU.FUNCTION_LEDS_ON = 8
  - BrickIMU.FUNCTION_LEDS_OFF = 9
  - BrickIMU.FUNCTION_SET_ACCELERATION_RANGE = 11
  - BrickIMU.FUNCTION_SET_MAGNETOMETER_RANGE = 13
  - BrickIMU.FUNCTION_SET_CONVERGENCE_SPEED = 15
  - BrickIMU.FUNCTION_SET_CALIBRATION = 17
  - BrickIMU.FUNCTION_SET_ACCELERATION_PERIOD = 19
  - BrickIMU.FUNCTION_SET_MAGNETIC_FIELD_PERIOD = 21
  - BrickIMU.FUNCTION_SET_ANGULAR_VELOCITY_PERIOD = 23
  - BrickIMU.FUNCTION_SET_ALL_DATA_PERIOD = 25
  - BrickIMU.FUNCTION_SET_ORIENTATION_PERIOD = 27
  - BrickIMU.FUNCTION_SET_QUATERNION_PERIOD = 29
  - BrickIMU.FUNCTION_ORIENTATION_CALCULATION_ON = 37
  - BrickIMU.FUNCTION_ORIENTATION_CALCULATION_OFF = 38
  - BrickIMU.FUNCTION_ENABLE_STATUS_LED = 238
  - BrickIMU.FUNCTION_DISABLE_STATUS_LED = 239
  - BrickIMU.FUNCTION_RESET = 243

public void `setResponseExpectedAll`(boolean responseExpected)

  Changes the response expected flag for all setter and callback configuration functions of this device at once.

public void `enableStatusLED`()

  Enables the status LED.

  The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

  The default state is enabled.

  New in version 2.3.1 (Firmware).

public void `disableStatusLED`()

  Disables the status LED.

  The status LED is the blue LED next to the USB connector. If enabled is is on and it flickers if data is transfered. If disabled it is always off.

  The default state is enabled.

  New in version 2.3.1 (Firmware).

public boolean `isStatusLEDEnabled`()

  Returns true if the status LED is enabled, false otherwise.

  New in version 2.3.1 (Firmware).

public BrickIMU.Protocol1BrickletName `getProtocol1BrickletName`(char port)

  Returns the firmware and protocol version and the name of the Bricklet for a given port.

  This functions sole purpose is to allow automatic flashing of v1.x.y Bricklet plugins.

  The returned object has the public member variables `short protocolVersion`, `short[] firmwareVersion` and `String name`.

public short `getChipTemperature`()

  Returns the temperature in °C/10 as measured inside the microcontroller. The value returned is not the ambient temperature!

  The temperature is only proportional to the real temperature and it has an accuracy of +-15%. Practically it is only useful as an indicator for temperature changes.

public void `reset`()

  Calling this function will reset the Brick. Calling this function on a Brick inside of a stack will reset the whole stack.

  After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

public BrickIMU.Identity `getIdentity`()

  Returns the UID, the UID where the Brick is connected to, the position, the hardware and firmware version as well as the device identifier.

  The position can be '0'-'8' (stack position).

  The device identifier numbers can be found here. There is also a constant for the device identifier of this Brick.

  The returned object has the public member variables `String uid`, `String connectedUid`, `char position`, `short[] hardwareVersion`, `short[] firmwareVersion` and `int deviceIdentifier`.

### Callback Configuration Functions

public void `setAccelerationPeriod`(long period)

  Sets the period in ms with which the `AccelerationCallback` callback is triggered periodically. A value of 0 turns the callback off.

  The default value is 0.

public long `getAccelerationPeriod`()

  Returns the period as set by `setAccelerationPeriod()`.

public void `setMagneticFieldPeriod`(long period)

  Sets the period in ms with which the `MagneticFieldCallback` callback is triggered periodically. A value of 0 turns the callback off.

public long `getMagneticFieldPeriod`()

  Returns the period as set by `setMagneticFieldPeriod()`.

public void `setAngularVelocityPeriod`(long period)

  Sets the period in ms with which the `AngularVelocityCallback` callback is triggered periodically. A value of 0 turns the callback off.

public long `getAngularVelocityPeriod`()

  Returns the period as set by `setAngularVelocityPeriod()`.

public void `setAllDataPeriod`(long period)

  Sets the period in ms with which the `AllDataCallback` callback is triggered periodically. A value of 0 turns the callback off.

public long `getAllDataPeriod`()

  Returns the period as set by `setAllDataPeriod()`.

public void `setOrientationPeriod`(long period)

  Sets the period in ms with which the `OrientationCallback` callback is triggered periodically. A value of 0 turns the callback off.

public long `getOrientationPeriod`()

  Returns the period as set by `setOrientationPeriod()`.

public void `setQuaternionPeriod`(long period)

  Sets the period in ms with which the `QuaternionCallback` callback is triggered periodically. A value of 0 turns the callback off.

public long `getQuaternionPeriod`()

  Returns the period as set by `setQuaternionPeriod()`.

### Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with "set" function of MATLAB. The parameters consist of the IP Connection object, the callback name and the callback function. For example, it looks like this in MATLAB:

    function cb_example(e)
        fprintf('Parameter: %s\n', e.param);
    end

    set(device, 'ExampleCallback', @(h, e) cb_example(e));

Due to a difference in the Octave Java support the "set" function cannot be used in Octave. The registration is done with "add*Callback" functions of the device object. It looks like this in Octave:

    function cb_example(e)
        fprintf("Parameter: %s\n", e.param);
    end

    device.addExampleCallback(@cb_example);

It is possible to add several callbacks and to remove them with the corresponding "remove*Callback" function.

The parameters of the callback are passed to the callback function as fields of the structure `e`, which is derived from the `java.util.EventObject` class. The available callback names with corresponding structure fields are described below.

Note

Using callbacks for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

public callback `BrickIMU.AccelerationCallback`

  Parameters:

  - x -- short
  - y -- short
  - z -- short

  This callback is triggered periodically with the period that is set by `setAccelerationPeriod()`. The parameters are the acceleration for the x, y and z axis.

  In MATLAB the `set()` function can be used to register a callback function to this callback.

  In Octave a callback function can be added to this callback using the `addAccelerationCallback()` function. An added callback function can be removed with the `removeAccelerationCallback()` function.

public callback `BrickIMU.MagneticFieldCallback`

  Parameters:

  - x -- short
  - y -- short
  - z -- short

  This callback is triggered periodically with the period that is set by `setMagneticFieldPeriod()`. The parameters are the magnetic field for the x, y and z axis.

  In MATLAB the `set()` function can be used to register a callback function to this callback.

  In Octave a callback function can be added to this callback using the `addMagneticFieldCallback()` function. An added callback function can be removed with the `removeMagneticFieldCallback()` function.

public callback `BrickIMU.AngularVelocityCallback`

  Parameters:

  - x -- short
  - y -- short
  - z -- short

  This callback is triggered periodically with the period that is set by `setAngularVelocityPeriod()`. The parameters are the angular velocity for the x, y and z axis.

  In MATLAB the `set()` function can be used to register a callback function to this callback.

  In Octave a callback function can be added to this callback using the `addAngularVelocityCallback()` function. An added callback function can be removed with the `removeAngularVelocityCallback()` function.

public callback `BrickIMU.AllDataCallback`

  Parameters:

  - accX -- short
  - accY -- short
  - accZ -- short
  - magX -- short
  - magY -- short
  - magZ -- short
  - angX -- short
  - angY -- short
  - angZ -- short
  - temperature -- short

  This callback is triggered periodically with the period that is set by `setAllDataPeriod()`. The parameters are the acceleration, the magnetic field and the angular velocity for the x, y and z axis as well as the temperature of the IMU Brick.

  In MATLAB the `set()` function can be used to register a callback function to this callback.

  In Octave a callback function can be added to this callback using the `addAllDataCallback()` function. An added callback function can be removed with the `removeAllDataCallback()` function.

public callback `BrickIMU.OrientationCallback`

  Parameters:

  - roll -- short
  - pitch -- short
  - yaw -- short

  This callback is triggered periodically with the period that is set by `setOrientationPeriod()`. The parameters are the orientation (roll, pitch and yaw) of the IMU Brick in Euler angles. See `getOrientation()` for details.

  In MATLAB the `set()` function can be used to register a callback function to this callback.

  In Octave a callback function can be added to this callback using the `addOrientationCallback()` function. An added callback function can be removed with the `removeOrientationCallback()` function.

public callback `BrickIMU.QuaternionCallback`

  Parameters:

  - x -- float
  - y -- float
  - z -- float
  - w -- float

  This callback is triggered periodically with the period that is set by `setQuaternionPeriod()`. The parameters are the orientation (x, y, z, w) of the IMU Brick in quaternions. See `getQuaternion()` for details.

  In MATLAB the `set()` function can be used to register a callback function to this callback.

  In Octave a callback function can be added to this callback using the `addQuaternionCallback()` function. An added callback function can be removed with the `removeQuaternionCallback()` function.

### Constants

public static final int `BrickIMU.DEVICE_IDENTIFIER`

  This constant is used to identify a IMU Brick.

  The `getIdentity()` function and the `EnumerateCallback` callback of the IP Connection have a `deviceIdentifier` parameter to specify the Brick's or Bricklet's type.

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