MQTT - IMU Brick

This is the description of the MQTT 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 MQTT API bindings is part of their general description.

Examples

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

Simple

Download (example-simple.txt)

1
2
3
4
5
6
# Change XXYYZZ to the UID of your IMU Brick

setup:
    # Get current quaternion
    subscribe to tinkerforge/response/imu_brick/XXYYZZ/get_quaternion
    publish '' to tinkerforge/request/imu_brick/XXYYZZ/get_quaternion

Callback

Download (example-callback.txt)

1
2
3
4
5
6
7
8
9
# Change XXYYZZ to the UID of your IMU Brick

setup:
    # Handle incoming quaternion callbacks
    subscribe to tinkerforge/callback/imu_brick/XXYYZZ/quaternion
    publish '{"register": true}' to tinkerforge/register/imu_brick/XXYYZZ/quaternion # Register quaternion callback
    
    # Set period for quaternion callback to 1s (1000ms)
    publish '{"period": 1000}' to tinkerforge/request/imu_brick/XXYYZZ/set_quaternion_period

API

All published payloads to and from the MQTT bindings are in JSON format.

If an error occures, the bindings publish a JSON object containing the error message as attribute "_ERROR". It is published on the corresponding response topic: .../response/... for .../request/... and .../callback/... for .../register/....

Basic Functions

request/imu_brick/<UID>/get_orientation
Response payload:
  • roll -- int
  • pitch -- int
  • yaw -- int

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 register/imu_brick/<UID>/orientation callback and set the period with request/imu_brick/<UID>/set_orientation_period.

request/imu_brick/<UID>/get_quaternion
Response payload:
  • x -- float
  • y -- float
  • z -- float
  • w -- float

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 register/imu_brick/<UID>/quaternion callback and set the period with request/imu_brick/<UID>/set_quaternion_period.

request/imu_brick/<UID>/leds_on

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

request/imu_brick/<UID>/leds_off

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

request/imu_brick/<UID>/are_leds_on
Response payload:
  • leds -- bool

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

request/imu_brick/<UID>/set_convergence_speed
Request payload:
  • speed -- int

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.

request/imu_brick/<UID>/get_convergence_speed
Response payload:
  • speed -- int

Returns the convergence speed as set by request/imu_brick/<UID>/set_convergence_speed.

Advanced Functions

request/imu_brick/<UID>/get_acceleration
Response payload:
  • x -- int
  • y -- int
  • z -- int

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 register/imu_brick/<UID>/acceleration callback and set the period with request/imu_brick/<UID>/set_acceleration_period.

request/imu_brick/<UID>/get_magnetic_field
Response payload:
  • x -- int
  • y -- int
  • z -- int

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 register/imu_brick/<UID>/magnetic_field callback and set the period with request/imu_brick/<UID>/set_magnetic_field_period.

request/imu_brick/<UID>/get_angular_velocity
Response payload:
  • x -- int
  • y -- int
  • z -- int

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 register/imu_brick/<UID>/angular_velocity callback and set the period with request/imu_brick/<UID>/set_angular_velocity_period.

request/imu_brick/<UID>/get_all_data
Response payload:
  • acc_x -- int
  • acc_y -- int
  • acc_z -- int
  • mag_x -- int
  • mag_y -- int
  • mag_z -- int
  • ang_x -- int
  • ang_y -- int
  • ang_z -- int
  • temperature -- int

Returns the data from request/imu_brick/<UID>/get_acceleration, request/imu_brick/<UID>/get_magnetic_field and request/imu_brick/<UID>/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 register/imu_brick/<UID>/all_data callback and set the period with request/imu_brick/<UID>/set_all_data_period.

request/imu_brick/<UID>/get_imu_temperature
Response payload:
  • temperature -- int

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

request/imu_brick/<UID>/set_acceleration_range
Request payload:
  • range -- int

Not implemented yet.

request/imu_brick/<UID>/get_acceleration_range
Response payload:
  • range -- int

Not implemented yet.

request/imu_brick/<UID>/set_magnetometer_range
Request payload:
  • range -- int

Not implemented yet.

request/imu_brick/<UID>/get_magnetometer_range
Response payload:
  • range -- int

Not implemented yet.

request/imu_brick/<UID>/set_calibration
Request payload:
  • typ -- int (has symbols)
  • data -- [int,... (x10)]

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 symbols are available for this function:

for typ:

  • "AccelerometerGain" = 0
  • "AccelerometerBias" = 1
  • "MagnetometerGain" = 2
  • "MagnetometerBias" = 3
  • "GyroscopeGain" = 4
  • "GyroscopeBias" = 5
request/imu_brick/<UID>/get_calibration
Request payload:
  • typ -- int (has symbols)
Response payload:
  • data -- [int,... (x10)]

Returns the calibration for a given type as set by request/imu_brick/<UID>/set_calibration.

The following symbols are available for this function:

for typ:

  • "AccelerometerGain" = 0
  • "AccelerometerBias" = 1
  • "MagnetometerGain" = 2
  • "MagnetometerBias" = 3
  • "GyroscopeGain" = 4
  • "GyroscopeBias" = 5
request/imu_brick/<UID>/orientation_calculation_on

Turns the orientation calculation of the IMU Brick on.

As default the calculation is on.

New in version 2.0.2 (Firmware).

request/imu_brick/<UID>/orientation_calculation_off

Turns the orientation calculation of the IMU Brick off.

If the calculation is off, request/imu_brick/<UID>/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.

New in version 2.0.2 (Firmware).

request/imu_brick/<UID>/is_orientation_calculation_on
Response payload:
  • orientation_calculation_on -- bool

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

New in version 2.0.2 (Firmware).

request/imu_brick/<UID>/set_spitfp_baudrate_config
Request payload:
  • enable_dynamic_baudrate -- bool
  • minimum_dynamic_baudrate -- int

The SPITF protocol can be used with a dynamic baudrate. If the dynamic baudrate is enabled, the Brick will try to adapt the baudrate for the communication between Bricks and Bricklets according to the amount of data that is transferred.

The baudrate will be increased exponentially if lots of data is send/received and decreased linearly if little data is send/received.

This lowers the baudrate in applications where little data is transferred (e.g. a weather station) and increases the robustness. If there is lots of data to transfer (e.g. Thermal Imaging Bricklet) it automatically increases the baudrate as needed.

In cases where some data has to transferred as fast as possible every few seconds (e.g. RS485 Bricklet with a high baudrate but small payload) you may want to turn the dynamic baudrate off to get the highest possible performance.

The maximum value of the baudrate can be set per port with the function request/imu_brick/<UID>/set_spitfp_baudrate. If the dynamic baudrate is disabled, the baudrate as set by request/imu_brick/<UID>/set_spitfp_baudrate will be used statically.

The minimum dynamic baudrate has a value range of 400000 to 2000000 baud.

By default dynamic baudrate is enabled and the minimum dynamic baudrate is 400000.

New in version 2.3.5 (Firmware).

request/imu_brick/<UID>/get_spitfp_baudrate_config
Response payload:
  • enable_dynamic_baudrate -- bool
  • minimum_dynamic_baudrate -- int

Returns the baudrate config, see request/imu_brick/<UID>/set_spitfp_baudrate_config.

New in version 2.3.5 (Firmware).

request/imu_brick/<UID>/get_send_timeout_count
Request payload:
  • communication_method -- int (has symbols)
Response payload:
  • timeout_count -- int

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.

The following symbols are available for this function:

for communication_method:

  • "None" = 0
  • "USB" = 1
  • "SPIStack" = 2
  • "Chibi" = 3
  • "RS485" = 4
  • "WIFI" = 5
  • "Ethernet" = 6
  • "WIFIV2" = 7

New in version 2.3.3 (Firmware).

request/imu_brick/<UID>/set_spitfp_baudrate
Request payload:
  • bricklet_port -- char
  • baudrate -- int

Sets the baudrate for a specific Bricklet port ('a' - 'd'). The baudrate can be in the range 400000 to 2000000.

If you want to increase the throughput of Bricklets you can increase the baudrate. If you get a high error count because of high interference (see request/imu_brick/<UID>/get_spitfp_error_count) you can decrease the baudrate.

If the dynamic baudrate feature is enabled, the baudrate set by this function corresponds to the maximum baudrate (see request/imu_brick/<UID>/set_spitfp_baudrate_config).

Regulatory testing is done with the default baudrate. If CE compatibility or similar is necessary in you applications we recommend to not change the baudrate.

The default baudrate for all ports is 1400000.

New in version 2.3.3 (Firmware).

request/imu_brick/<UID>/get_spitfp_baudrate
Request payload:
  • bricklet_port -- char
Response payload:
  • baudrate -- int

Returns the baudrate for a given Bricklet port, see request/imu_brick/<UID>/set_spitfp_baudrate.

New in version 2.3.3 (Firmware).

request/imu_brick/<UID>/get_spitfp_error_count
Request payload:
  • bricklet_port -- char
Response payload:
  • error_count_ack_checksum -- int
  • error_count_message_checksum -- int
  • error_count_frame -- int
  • error_count_overflow -- int

Returns the error count for the communication between Brick and Bricklet.

The errors are divided into

  • ACK checksum errors,
  • message checksum errors,
  • framing errors and
  • overflow errors.

The errors counts are for errors that occur on the Brick side. All Bricklets have a similar function that returns the errors on the Bricklet side.

New in version 2.3.3 (Firmware).

request/imu_brick/<UID>/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.

New in version 2.3.1 (Firmware).

request/imu_brick/<UID>/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.

New in version 2.3.1 (Firmware).

request/imu_brick/<UID>/is_status_led_enabled
Response payload:
  • enabled -- bool

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

New in version 2.3.1 (Firmware).

request/imu_brick/<UID>/get_protocol1_bricklet_name
Request payload:
  • port -- char
Response payload:
  • protocol_version -- int
  • firmware_version -- [int,int,int]
  • name -- string

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.

request/imu_brick/<UID>/get_chip_temperature
Response payload:
  • temperature -- int

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.

request/imu_brick/<UID>/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!

request/imu_brick/<UID>/get_identity
Response payload:
  • uid -- string
  • connected_uid -- string
  • position -- char
  • hardware_version -- [int,int,int]
  • firmware_version -- [int,int,int]
  • device_identifier -- int (has symbols)
  • _display_name -- string

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. If symbolic output is not disabled, the device identifier is mapped to the corresponding name in the format used in topics.

The display name contains the IMU's name in a human readable form.

Callback Configuration Functions

request/imu_brick/<UID>/set_acceleration_period
Request payload:
  • period -- int

Sets the period in ms with which the register/imu_brick/<UID>/acceleration callback is triggered periodically. A value of 0 turns the callback off.

The default value is 0.

request/imu_brick/<UID>/get_acceleration_period
Response payload:
  • period -- int

Returns the period as set by request/imu_brick/<UID>/set_acceleration_period.

request/imu_brick/<UID>/set_magnetic_field_period
Request payload:
  • period -- int

Sets the period in ms with which the register/imu_brick/<UID>/magnetic_field callback is triggered periodically. A value of 0 turns the callback off.

request/imu_brick/<UID>/get_magnetic_field_period
Response payload:
  • period -- int

Returns the period as set by request/imu_brick/<UID>/set_magnetic_field_period.

request/imu_brick/<UID>/set_angular_velocity_period
Request payload:
  • period -- int

Sets the period in ms with which the register/imu_brick/<UID>/angular_velocity callback is triggered periodically. A value of 0 turns the callback off.

request/imu_brick/<UID>/get_angular_velocity_period
Response payload:
  • period -- int

Returns the period as set by request/imu_brick/<UID>/set_angular_velocity_period.

request/imu_brick/<UID>/set_all_data_period
Request payload:
  • period -- int

Sets the period in ms with which the register/imu_brick/<UID>/all_data callback is triggered periodically. A value of 0 turns the callback off.

request/imu_brick/<UID>/get_all_data_period
Response payload:
  • period -- int

Returns the period as set by request/imu_brick/<UID>/set_all_data_period.

request/imu_brick/<UID>/set_orientation_period
Request payload:
  • period -- int

Sets the period in ms with which the register/imu_brick/<UID>/orientation callback is triggered periodically. A value of 0 turns the callback off.

request/imu_brick/<UID>/get_orientation_period
Response payload:
  • period -- int

Returns the period as set by request/imu_brick/<UID>/set_orientation_period.

request/imu_brick/<UID>/set_quaternion_period
Request payload:
  • period -- int

Sets the period in ms with which the register/imu_brick/<UID>/quaternion callback is triggered periodically. A value of 0 turns the callback off.

request/imu_brick/<UID>/get_quaternion_period
Response payload:
  • period -- int

Returns the period as set by request/imu_brick/<UID>/set_quaternion_period.

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the corresponding .../register/... topic and an optional suffix. This suffix can be used to deregister the callback later.

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.

register/imu_brick/<UID>/acceleration
Request payload:
  • register -- bool
Response payload:
  • x -- int
  • y -- int
  • z -- int

A callback can be registered for this event by publishing to the .../register/imu_brick/<UID>/acceleration[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/imu_brick/<UID>/acceleration[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/imu_brick/<UID>/set_acceleration_period. The callback payload members are the acceleration for the x, y and z axis.

register/imu_brick/<UID>/magnetic_field
Request payload:
  • register -- bool
Response payload:
  • x -- int
  • y -- int
  • z -- int

A callback can be registered for this event by publishing to the .../register/imu_brick/<UID>/magnetic_field[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/imu_brick/<UID>/magnetic_field[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/imu_brick/<UID>/set_magnetic_field_period. The callback payload members are the magnetic field for the x, y and z axis.

register/imu_brick/<UID>/angular_velocity
Request payload:
  • register -- bool
Response payload:
  • x -- int
  • y -- int
  • z -- int

A callback can be registered for this event by publishing to the .../register/imu_brick/<UID>/angular_velocity[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/imu_brick/<UID>/angular_velocity[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/imu_brick/<UID>/set_angular_velocity_period. The callback payload members are the angular velocity for the x, y and z axis.

register/imu_brick/<UID>/all_data
Request payload:
  • register -- bool
Response payload:
  • acc_x -- int
  • acc_y -- int
  • acc_z -- int
  • mag_x -- int
  • mag_y -- int
  • mag_z -- int
  • ang_x -- int
  • ang_y -- int
  • ang_z -- int
  • temperature -- int

A callback can be registered for this event by publishing to the .../register/imu_brick/<UID>/all_data[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/imu_brick/<UID>/all_data[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/imu_brick/<UID>/set_all_data_period. The callback payload members 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.

register/imu_brick/<UID>/orientation
Request payload:
  • register -- bool
Response payload:
  • roll -- int
  • pitch -- int
  • yaw -- int

A callback can be registered for this event by publishing to the .../register/imu_brick/<UID>/orientation[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/imu_brick/<UID>/orientation[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/imu_brick/<UID>/set_orientation_period. The callback payload members are the orientation (roll, pitch and yaw) of the IMU Brick in Euler angles. See request/imu_brick/<UID>/get_orientation for details.

register/imu_brick/<UID>/quaternion
Request payload:
  • register -- bool
Response payload:
  • x -- float
  • y -- float
  • z -- float
  • w -- float

A callback can be registered for this event by publishing to the .../register/imu_brick/<UID>/quaternion[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/imu_brick/<UID>/quaternion[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/imu_brick/<UID>/set_quaternion_period. The callback payload members are the orientation (x, y, z, w) of the IMU Brick in quaternions. See request/imu_brick/<UID>/get_quaternion for details.