This is the description of the Modbus protocol for the IMU Brick. General information and technical specifications for the IMU Brick are summarized in its hardware description.
A general description of the Modbus protocol structure can be found here.
Function ID: | 5 |
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Request: | empty payload |
Response: |
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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 CALLBACK_ORIENTATION and set the period with set_orientation_period.
Function ID: | 6 |
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Request: | empty payload |
Response: |
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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 CALLBACK_QUATERNION and set the period with set_quaternion_period.
Function ID: | 8 |
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Request: | empty payload |
Response: | no response |
Turns the orientation and direction LEDs of the IMU Brick on.
Function ID: | 9 |
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Request: | empty payload |
Response: | no response |
Turns the orientation and direction LEDs of the IMU Brick off.
Function ID: | 10 |
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Request: | empty payload |
Response: |
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Returns true if the orientation and direction LEDs of the IMU Brick are on, false otherwise.
Function ID: | 15 |
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Request: |
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Response: | 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.
Function ID: | 16 |
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Request: | empty payload |
Response: |
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Returns the convergence speed as set by set_convergence_speed.
Function ID: | 1 |
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Request: | empty payload |
Response: |
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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 CALLBACK_ACCELERATION and set the period with set_acceleration_period.
Function ID: | 2 |
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Request: | empty payload |
Response: |
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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 CALLBACK_MAGNETIC_FIELD and set the period with set_magnetic_field_period.
Function ID: | 3 |
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Request: | empty payload |
Response: |
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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 CALLBACK_ANGULAR_VELOCITY and set the period with set_angular_velocity_period.
Function ID: | 4 |
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Request: | empty payload |
Response: |
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Returns the data from get_acceleration, get_magnetic_field and 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 CALLBACK_ALL_DATA and set the period with set_all_data_period.
Function ID: | 7 |
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Request: | empty payload |
Response: |
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Returns the temperature of the IMU Brick. The temperature is given in °C/100.
Function ID: | 11 |
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Request: |
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Response: | no response |
Not implemented yet.
Function ID: | 12 |
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Request: | empty payload |
Response: |
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Not implemented yet.
Function ID: | 13 |
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Request: |
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Response: | no response |
Not implemented yet.
Function ID: | 14 |
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Request: | empty payload |
Response: |
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Not implemented yet.
Function ID: | 17 |
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Request: |
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Response: | no response |
There are several different types that can be calibrated:
Type | Description | Values |
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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.
Function ID: | 18 |
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Request: |
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Response: |
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Returns the calibration for a given type as set by set_calibration.
Function ID: | 37 |
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Request: | empty payload |
Response: | no response |
Turns the orientation calculation of the IMU Brick on.
As default the calculation is on.
New in version 2.0.2 (Firmware).
Function ID: | 38 |
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Request: | empty payload |
Response: | no response |
Turns the orientation calculation of the IMU Brick off.
If the calculation is off, 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).
Function ID: | 39 |
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Request: | empty payload |
Response: |
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Returns true if the orientation calculation of the IMU Brick is on, false otherwise.
New in version 2.0.2 (Firmware).
Function ID: | 238 |
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Request: | empty payload |
Response: | 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.
New in version 2.3.1 (Firmware).
Function ID: | 239 |
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Request: | empty payload |
Response: | 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.
New in version 2.3.1 (Firmware).
Function ID: | 240 |
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Request: | empty payload |
Response: |
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Returns true if the status LED is enabled, false otherwise.
New in version 2.3.1 (Firmware).
Function ID: | 241 |
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Request: |
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Response: |
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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.
Function ID: | 242 |
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Request: | empty payload |
Response: |
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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.
Function ID: | 243 |
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Request: | empty payload |
Response: | 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!
Function ID: | 255 |
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Request: | empty payload |
Response: |
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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.
Function ID: | 19 |
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Request: |
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Response: | no response |
Sets the period in ms with which the CALLBACK_ACCELERATION callback is triggered periodically. A value of 0 turns the callback off.
The default value is 0.
Function ID: | 20 |
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Request: | empty payload |
Response: |
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Returns the period as set by set_acceleration_period.
Function ID: | 21 |
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Request: |
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Response: | no response |
Sets the period in ms with which the CALLBACK_MAGNETIC_FIELD callback is triggered periodically. A value of 0 turns the callback off.
Function ID: | 22 |
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Request: | empty payload |
Response: |
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Returns the period as set by set_magnetic_field_period.
Function ID: | 23 |
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Request: |
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Response: | no response |
Sets the period in ms with which the CALLBACK_ANGULAR_VELOCITY callback is triggered periodically. A value of 0 turns the callback off.
Function ID: | 24 |
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Request: | empty payload |
Response: |
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Returns the period as set by set_angular_velocity_period.
Function ID: | 25 |
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Request: |
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Response: | no response |
Sets the period in ms with which the CALLBACK_ALL_DATA callback is triggered periodically. A value of 0 turns the callback off.
Function ID: | 26 |
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Request: | empty payload |
Response: |
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Returns the period as set by set_all_data_period.
Function ID: | 27 |
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Request: |
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Response: | no response |
Sets the period in ms with which the CALLBACK_ORIENTATION callback is triggered periodically. A value of 0 turns the callback off.
Function ID: | 28 |
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Request: | empty payload |
Response: |
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Returns the period as set by set_orientation_period.
Function ID: | 29 |
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Request: |
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Response: | no response |
Sets the period in ms with which the CALLBACK_QUATERNION callback is triggered periodically. A value of 0 turns the callback off.
Function ID: | 30 |
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Request: | empty payload |
Response: |
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Returns the period as set by set_quaternion_period.
Function ID: | 31 |
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Response: |
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This callback is triggered periodically with the period that is set by set_acceleration_period. The response values are the acceleration for the x, y and z axis.
Function ID: | 32 |
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Response: |
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This callback is triggered periodically with the period that is set by set_magnetic_field_period. The response values are the magnetic field for the x, y and z axis.
Function ID: | 33 |
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Response: |
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This callback is triggered periodically with the period that is set by set_angular_velocity_period. The response values are the angular velocity for the x, y and z axis.
Function ID: | 34 |
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Response: |
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This callback is triggered periodically with the period that is set by 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.
Function ID: | 35 |
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Response: |
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This callback is triggered periodically with the period that is set by set_orientation_period. The response values are the orientation (roll, pitch and yaw) of the IMU Brick in Euler angles. See get_orientation for details.
Function ID: | 36 |
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Response: |
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This callback is triggered periodically with the period that is set by set_quaternion_period. The response values are the orientation (x, y, z, w) of the IMU Brick in quaternions. See get_quaternion for details.