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:breadcrumbs: <a href="../../index.html">Home</a> / <a href="../../index.html#software-modbus">Software</a> / Modbus - IMU Brick

.. |device_identifier_constant| unicode:: 0xA0
   :trim:

.. _imu_brick_modbus:

Modbus - IMU Brick
==================

This is the description of the :ref:`Modbus protocol <llproto_modbus>` for the :ref:`IMU Brick <imu_brick>`. General information and technical
specifications for the IMU Brick are summarized in its :ref:`hardware description
<imu_brick_description>`.

.. _imu_brick_modbus_api:

API
---

A general description of the Modbus protocol structure can be found
:ref:`here <llproto_modbus>`.




Basic Functions
^^^^^^^^^^^^^^^



.. modbus:function:: BrickIMU.get_orientation

 :functionid: 5
 :emptyrequest: empty payload

 :response roll: int16
 :response pitch: int16
 :response yaw: int16

 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 <http://en.wikipedia.org/wiki/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 :modbus:func:`CALLBACK_ORIENTATION <BrickIMU.CALLBACK_ORIENTATION>` and set the period with 
 :modbus:func:`set_orientation_period <BrickIMU.set_orientation_period>`.
 
.. modbus:function:: BrickIMU.get_quaternion

 :functionid: 6
 :emptyrequest: empty payload

 :response x: float
 :response y: float
 :response z: float
 :response w: float

 Returns the current orientation (x, y, z, w) of the IMU as 
 `quaternions <http://en.wikipedia.org/wiki/Quaternions_and_spatial_rotation>`__.
 
 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 <http://en.wikipedia.org/wiki/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 :modbus:func:`CALLBACK_QUATERNION <BrickIMU.CALLBACK_QUATERNION>` and set the period with 
 :modbus:func:`set_quaternion_period <BrickIMU.set_quaternion_period>`.
 
.. modbus:function:: BrickIMU.leds_on

 :functionid: 8
 :emptyrequest: empty payload

 :noresponse: no response

 Turns the orientation and direction LEDs of the IMU Brick on.
 
.. modbus:function:: BrickIMU.leds_off

 :functionid: 9
 :emptyrequest: empty payload

 :noresponse: no response

 Turns the orientation and direction LEDs of the IMU Brick off.
 
.. modbus:function:: BrickIMU.are_leds_on

 :functionid: 10
 :emptyrequest: empty payload

 :response leds: bool

 Returns *true* if the orientation and direction LEDs of the IMU Brick
 are on, *false* otherwise.
 
.. modbus:function:: BrickIMU.set_convergence_speed

 :functionid: 15
 :request speed: uint16

 :noresponse: no response

 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.
 
.. modbus:function:: BrickIMU.get_convergence_speed

 :functionid: 16
 :emptyrequest: empty payload

 :response speed: uint16

 Returns the convergence speed as set by :modbus:func:`set_convergence_speed <BrickIMU.set_convergence_speed>`.
 


Advanced Functions
^^^^^^^^^^^^^^^^^^

.. modbus:function:: BrickIMU.get_acceleration

 :functionid: 1
 :emptyrequest: empty payload

 :response x: int16
 :response y: int16
 :response z: int16
 
 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 :modbus:func:`CALLBACK_ACCELERATION <BrickIMU.CALLBACK_ACCELERATION>` and set the period with 
 :modbus:func:`set_acceleration_period <BrickIMU.set_acceleration_period>`.
 
.. modbus:function:: BrickIMU.get_magnetic_field

 :functionid: 2
 :emptyrequest: empty payload

 :response x: int16
 :response y: int16
 :response z: int16

 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 :modbus:func:`CALLBACK_MAGNETIC_FIELD <BrickIMU.CALLBACK_MAGNETIC_FIELD>` and set the period with 
 :modbus:func:`set_magnetic_field_period <BrickIMU.set_magnetic_field_period>`.
 
.. modbus:function:: BrickIMU.get_angular_velocity

 :functionid: 3
 :emptyrequest: empty payload

 :response x: int16
 :response y: int16
 :response z: int16

 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 :modbus:func:`CALLBACK_ANGULAR_VELOCITY <BrickIMU.CALLBACK_ANGULAR_VELOCITY>` and set the period with 
 :modbus:func:`set_angular_velocity_period <BrickIMU.set_angular_velocity_period>`.
 
.. modbus:function:: BrickIMU.get_all_data

 :functionid: 4
 :emptyrequest: empty payload

 :response acc_x: int16
 :response acc_y: int16
 :response acc_z: int16
 :response mag_x: int16
 :response mag_y: int16
 :response mag_z: int16
 :response ang_x: int16
 :response ang_y: int16
 :response ang_z: int16
 :response temperature: int16

 Returns the data from :modbus:func:`get_acceleration <BrickIMU.get_acceleration>`, :modbus:func:`get_magnetic_field <BrickIMU.get_magnetic_field>` 
 and :modbus:func:`get_angular_velocity <BrickIMU.get_angular_velocity>` 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 :modbus:func:`CALLBACK_ALL_DATA <BrickIMU.CALLBACK_ALL_DATA>` and set the period with 
 :modbus:func:`set_all_data_period <BrickIMU.set_all_data_period>`.
 
.. modbus:function:: BrickIMU.get_imu_temperature

 :functionid: 7
 :emptyrequest: empty payload

 :response temperature: int16

 Returns the temperature of the IMU Brick. The temperature is given in 
 °C/100.
 
.. modbus:function:: BrickIMU.set_acceleration_range

 :functionid: 11
 :request range: uint8

 :noresponse: no response

 Not implemented yet.
 
.. modbus:function:: BrickIMU.get_acceleration_range

 :functionid: 12
 :emptyrequest: empty payload

 :response range: uint8

 Not implemented yet.
 
.. modbus:function:: BrickIMU.set_magnetometer_range

 :functionid: 13
 :request range: uint8

 :noresponse: no response

 Not implemented yet.
 
.. modbus:function:: BrickIMU.get_magnetometer_range

 :functionid: 14
 :emptyrequest: empty payload

 :response range: uint8

 Not implemented yet.
 
.. modbus:function:: BrickIMU.set_calibration

 :functionid: 17
 :request typ: uint8
 :request data: int16[10]

 :noresponse: no response

 There are several different types that can be calibrated:
 
 .. csv-table::
  :header: "Type", "Description", "Values"
  :widths: 10, 30, 110
 
  "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.
 
.. modbus:function:: BrickIMU.get_calibration

 :functionid: 18
 :request typ: uint8

 :response data: int16[10]

 Returns the calibration for a given type as set by :modbus:func:`set_calibration <BrickIMU.set_calibration>`.
 
.. modbus:function:: BrickIMU.orientation_calculation_on

 :functionid: 37
 :emptyrequest: empty payload

 :noresponse: no response

 Turns the orientation calculation of the IMU Brick on.
 
 As default the calculation is on.
 
 .. versionadded:: 2.0.2~(Firmware)
 
.. modbus:function:: BrickIMU.orientation_calculation_off

 :functionid: 38
 :emptyrequest: empty payload

 :noresponse: no response

 Turns the orientation calculation of the IMU Brick off.
 
 If the calculation is off, :modbus:func:`get_orientation <BrickIMU.get_orientation>` 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.
 
 .. versionadded:: 2.0.2~(Firmware)
 
.. modbus:function:: BrickIMU.is_orientation_calculation_on

 :functionid: 39
 :emptyrequest: empty payload

 :response orientation_calculation_on: bool

 Returns *true* if the orientation calculation of the IMU Brick
 is on, *false* otherwise.
 
 .. versionadded:: 2.0.2~(Firmware)
 
.. modbus:function:: BrickIMU.enable_status_led

 :functionid: 238
 :emptyrequest: empty payload

 :noresponse: no response

 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.
 
 .. versionadded:: 2.3.1~(Firmware)
 
.. modbus:function:: BrickIMU.disable_status_led

 :functionid: 239
 :emptyrequest: empty payload

 :noresponse: no response

 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.
 
 .. versionadded:: 2.3.1~(Firmware)
 
.. modbus:function:: BrickIMU.is_status_led_enabled

 :functionid: 240
 :emptyrequest: empty payload

 :response enabled: bool

 Returns *true* if the status LED is enabled, *false* otherwise.
 
 .. versionadded:: 2.3.1~(Firmware)
 
.. modbus:function:: BrickIMU.get_protocol1_bricklet_name

 :functionid: 241
 :request port: char

 :response protocol_version: uint8
 :response firmware_version: uint8[3]
 :response name: char[40]

 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.
 
.. modbus:function:: BrickIMU.get_chip_temperature

 :functionid: 242
 :emptyrequest: empty payload

 :response temperature: int16

 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.
 
.. modbus:function:: BrickIMU.reset

 :functionid: 243
 :emptyrequest: empty payload

 :noresponse: no response

 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!
 
.. modbus:function:: BrickIMU.get_identity

 :functionid: 255
 :emptyrequest: empty payload

 :response uid: char[8]
 :response connected_uid: char[8]
 :response position: char
 :response hardware_version: uint8[3]
 :response firmware_version: uint8[3]
 :response device_identifier: uint16

 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 :ref:`here <device_identifier>`.
 |device_identifier_constant|
 


Callback Configuration Functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^



.. modbus:function:: BrickIMU.set_acceleration_period

 :functionid: 19
 :request period: uint32

 :noresponse: no response

 Sets the period in ms with which the :modbus:func:`CALLBACK_ACCELERATION <BrickIMU.CALLBACK_ACCELERATION>` callback is triggered
 periodically. A value of 0 turns the callback off.
 
 The default value is 0.
 
.. modbus:function:: BrickIMU.get_acceleration_period

 :functionid: 20
 :emptyrequest: empty payload

 :response period: uint32

 Returns the period as set by :modbus:func:`set_acceleration_period <BrickIMU.set_acceleration_period>`.
 
.. modbus:function:: BrickIMU.set_magnetic_field_period

 :functionid: 21
 :request period: uint32

 :noresponse: no response

 Sets the period in ms with which the :modbus:func:`CALLBACK_MAGNETIC_FIELD <BrickIMU.CALLBACK_MAGNETIC_FIELD>` callback is triggered
 periodically. A value of 0 turns the callback off.
 
.. modbus:function:: BrickIMU.get_magnetic_field_period

 :functionid: 22
 :emptyrequest: empty payload

 :response period: uint32

 Returns the period as set by :modbus:func:`set_magnetic_field_period <BrickIMU.set_magnetic_field_period>`.
 
.. modbus:function:: BrickIMU.set_angular_velocity_period

 :functionid: 23
 :request period: uint32

 :noresponse: no response

 Sets the period in ms with which the :modbus:func:`CALLBACK_ANGULAR_VELOCITY <BrickIMU.CALLBACK_ANGULAR_VELOCITY>` callback is triggered
 periodically. A value of 0 turns the callback off.
 
.. modbus:function:: BrickIMU.get_angular_velocity_period

 :functionid: 24
 :emptyrequest: empty payload

 :response period: uint32

 Returns the period as set by :modbus:func:`set_angular_velocity_period <BrickIMU.set_angular_velocity_period>`.
 
.. modbus:function:: BrickIMU.set_all_data_period

 :functionid: 25
 :request period: uint32

 :noresponse: no response

 Sets the period in ms with which the :modbus:func:`CALLBACK_ALL_DATA <BrickIMU.CALLBACK_ALL_DATA>` callback is triggered
 periodically. A value of 0 turns the callback off.
 
.. modbus:function:: BrickIMU.get_all_data_period

 :functionid: 26
 :emptyrequest: empty payload

 :response period: uint32

 Returns the period as set by :modbus:func:`set_all_data_period <BrickIMU.set_all_data_period>`.
 
.. modbus:function:: BrickIMU.set_orientation_period

 :functionid: 27
 :request period: uint32

 :noresponse: no response

 Sets the period in ms with which the :modbus:func:`CALLBACK_ORIENTATION <BrickIMU.CALLBACK_ORIENTATION>` callback is triggered
 periodically. A value of 0 turns the callback off.
 
.. modbus:function:: BrickIMU.get_orientation_period

 :functionid: 28
 :emptyrequest: empty payload

 :response period: uint32

 Returns the period as set by :modbus:func:`set_orientation_period <BrickIMU.set_orientation_period>`.
 
.. modbus:function:: BrickIMU.set_quaternion_period

 :functionid: 29
 :request period: uint32

 :noresponse: no response

 Sets the period in ms with which the :modbus:func:`CALLBACK_QUATERNION <BrickIMU.CALLBACK_QUATERNION>` callback is triggered
 periodically. A value of 0 turns the callback off.
 
.. modbus:function:: BrickIMU.get_quaternion_period

 :functionid: 30
 :emptyrequest: empty payload

 :response period: uint32

 Returns the period as set by :modbus:func:`set_quaternion_period <BrickIMU.set_quaternion_period>`.
 


.. _imu_brick_modbus_callbacks:

Callbacks
^^^^^^^^^

.. modbus:function:: BrickIMU.CALLBACK_ACCELERATION

 :functionid: 31

 :response x: int16
 :response y: int16
 :response z: int16


 This callback is triggered periodically with the period that is set by
 :modbus:func:`set_acceleration_period <BrickIMU.set_acceleration_period>`. The response values are the acceleration
 for the x, y and z axis.
 
.. modbus:function:: BrickIMU.CALLBACK_MAGNETIC_FIELD

 :functionid: 32

 :response x: int16
 :response y: int16
 :response z: int16


 This callback is triggered periodically with the period that is set by
 :modbus:func:`set_magnetic_field_period <BrickIMU.set_magnetic_field_period>`. The response values are the magnetic field
 for the x, y and z axis.
 
.. modbus:function:: BrickIMU.CALLBACK_ANGULAR_VELOCITY

 :functionid: 33

 :response x: int16
 :response y: int16
 :response z: int16


 This callback is triggered periodically with the period that is set by
 :modbus:func:`set_angular_velocity_period <BrickIMU.set_angular_velocity_period>`. The response values are the angular velocity
 for the x, y and z axis.
 
.. modbus:function:: BrickIMU.CALLBACK_ALL_DATA

 :functionid: 34

 :response acc_x: int16
 :response acc_y: int16
 :response acc_z: int16
 :response mag_x: int16
 :response mag_y: int16
 :response mag_z: int16
 :response ang_x: int16
 :response ang_y: int16
 :response ang_z: int16
 :response temperature: int16


 This callback is triggered periodically with the period that is set by
 :modbus:func:`set_all_data_period <BrickIMU.set_all_data_period>`. The response values 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.
 
.. modbus:function:: BrickIMU.CALLBACK_ORIENTATION

 :functionid: 35

 :response roll: int16
 :response pitch: int16
 :response yaw: int16


 This callback is triggered periodically with the period that is set by
 :modbus:func:`set_orientation_period <BrickIMU.set_orientation_period>`. The response values are the orientation
 (roll, pitch and yaw) of the IMU Brick in Euler angles. See
 :modbus:func:`get_orientation <BrickIMU.get_orientation>` for details.
 
.. modbus:function:: BrickIMU.CALLBACK_QUATERNION

 :functionid: 36

 :response x: float
 :response y: float
 :response z: float
 :response w: float


 This callback is triggered periodically with the period that is set by
 :modbus:func:`set_quaternion_period <BrickIMU.set_quaternion_period>`. The response values are the orientation
 (x, y, z, w) of the IMU Brick in quaternions. See :modbus:func:`get_quaternion <BrickIMU.get_quaternion>`
 for details.
 


