Ishraq Ibne Ashraf
and 1 contributors

NAME

Tinkerforge::BrickIMU - Full fledged AHRS with 9 degrees of freedom

CONSTANTS

DEVICE_IDENTIFIER

This constant is used to identify a IMU Brick.

The get_identity() subroutine and the CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.

DEVICE_DISPLAY_NAME

This constant represents the display name of a IMU Brick.

CALLBACK_ACCELERATION

This constant is used with the register_callback() subroutine to specify the CALLBACK_ACCELERATION callback.

CALLBACK_MAGNETIC_FIELD

This constant is used with the register_callback() subroutine to specify the CALLBACK_MAGNETIC_FIELD callback.

CALLBACK_ANGULAR_VELOCITY

This constant is used with the register_callback() subroutine to specify the CALLBACK_ANGULAR_VELOCITY callback.

CALLBACK_ALL_DATA

This constant is used with the register_callback() subroutine to specify the CALLBACK_ALL_DATA callback.

CALLBACK_ORIENTATION

This constant is used with the register_callback() subroutine to specify the CALLBACK_ORIENTATION callback.

CALLBACK_QUATERNION

This constant is used with the register_callback() subroutine to specify the CALLBACK_QUATERNION callback.

FUNCTION_GET_ACCELERATION

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_MAGNETIC_FIELD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_ANGULAR_VELOCITY

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_ALL_DATA

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_ORIENTATION

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_QUATERNION

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_IMU_TEMPERATURE

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_LEDS_ON

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_LEDS_OFF

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_ARE_LEDS_ON

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_ACCELERATION_RANGE

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_ACCELERATION_RANGE

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_MAGNETOMETER_RANGE

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_MAGNETOMETER_RANGE

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_CONVERGENCE_SPEED

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_CONVERGENCE_SPEED

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_CALIBRATION

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_CALIBRATION

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_ACCELERATION_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_ACCELERATION_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_MAGNETIC_FIELD_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_MAGNETIC_FIELD_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_ANGULAR_VELOCITY_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_ANGULAR_VELOCITY_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_ALL_DATA_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_ALL_DATA_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_ORIENTATION_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_ORIENTATION_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_SET_QUATERNION_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_QUATERNION_PERIOD

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_ORIENTATION_CALCULATION_ON

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_ORIENTATION_CALCULATION_OFF

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_IS_ORIENTATION_CALCULATION_ON

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_SEND_TIMEOUT_COUNT

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_ENABLE_STATUS_LED

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_DISABLE_STATUS_LED

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_IS_STATUS_LED_ENABLED

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_PROTOCOL1_BRICKLET_NAME

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_CHIP_TEMPERATURE

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_RESET

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTION_GET_IDENTITY

This constant is used with the get_response_expected(), set_response_expected() and set_response_expected_all() subroutines.

FUNCTIONS

new()

Creates an object with the unique device ID *uid* and adds it to the IP Connection *ipcon*.

get_acceleration()

Returns the calibrated acceleration from the accelerometer for the x, y and z axis in g/1000 (1g = 9.80665m/s²).

If you want to get the acceleration periodically, it is recommended to use the :cb:`Acceleration` callback and set the period with :func:`Set Acceleration Period`.

get_magnetic_field()

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 :cb:`Magnetic Field` callback and set the period with :func:`Set Magnetic Field Period`.

get_angular_velocity()

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 :cb:`Angular Velocity` callback and set the period with :func:`Set Angular Velocity Period`.

get_all_data()

Returns the data from :func:`Get Acceleration`, :func:`Get Magnetic Field` and :func:`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 :cb:`All Data` callback and set the period with :func:`Set All Data Period`.

get_orientation()

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 <https://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 :cb:`Orientation` callback and set the period with :func:`Set Orientation Period`.

get_quaternion()

Returns the current orientation (x, y, z, w) of the IMU as `quaternions <https://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 <https://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 :cb:`Quaternion` callback and set the period with :func:`Set Quaternion Period`.

get_imu_temperature()

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

leds_on()

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

leds_off()

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

are_leds_on()

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

set_acceleration_range()

Not implemented yet.

get_acceleration_range()

Not implemented yet.

set_magnetometer_range()

Not implemented yet.

get_magnetometer_range()

Not implemented yet.

set_convergence_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.

get_convergence_speed()

Returns the convergence speed as set by :func:`Set Convergence Speed`.

set_calibration()

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.

get_calibration()

Returns the calibration for a given type as set by :func:`Set Calibration`.

set_acceleration_period()

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

The default value is 0.

get_acceleration_period()

Returns the period as set by :func:`Set Acceleration Period`.

set_magnetic_field_period()

Sets the period in ms with which the :cb:`Magnetic Field` callback is triggered periodically. A value of 0 turns the callback off.

get_magnetic_field_period()

Returns the period as set by :func:`Set Magnetic Field Period`.

set_angular_velocity_period()

Sets the period in ms with which the :cb:`Angular Velocity` callback is triggered periodically. A value of 0 turns the callback off.

get_angular_velocity_period()

Returns the period as set by :func:`Set Angular Velocity Period`.

set_all_data_period()

Sets the period in ms with which the :cb:`All Data` callback is triggered periodically. A value of 0 turns the callback off.

get_all_data_period()

Returns the period as set by :func:`Set All Data Period`.

set_orientation_period()

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

get_orientation_period()

Returns the period as set by :func:`Set Orientation Period`.

set_quaternion_period()

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

get_quaternion_period()

Returns the period as set by :func:`Set Quaternion Period`.

orientation_calculation_on()

Turns the orientation calculation of the IMU Brick on.

As default the calculation is on.

.. versionadded:: 2.0.2$nbsp;(Firmware)

orientation_calculation_off()

Turns the orientation calculation of the IMU Brick off.

If the calculation is off, :func:`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$nbsp;(Firmware)

is_orientation_calculation_on()

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

.. versionadded:: 2.0.2$nbsp;(Firmware)

get_send_timeout_count()

Returns the timeout count for the different communication methods.

The methods 0-2 are available for all Bricks, 3-7 only for Master Bricks.

This function is mostly used for debugging during development, in normal operation the counters should nearly always stay at 0.

.. versionadded:: 2.3.3$nbsp;(Firmware)

enable_status_led()

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$nbsp;(Firmware)

disable_status_led()

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$nbsp;(Firmware)

is_status_led_enabled()

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

.. versionadded:: 2.3.1$nbsp;(Firmware)

get_protocol1_bricklet_name()

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.

get_chip_temperature()

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.

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!

get_identity()

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|