This is the description of the C/C++ 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 C/C++ API bindings is part of their general description.
The example code below is Public Domain (CC0 1.0).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | #include <stdio.h>
#include "ip_connection.h"
#include "brick_imu.h"
#define HOST "localhost"
#define PORT 4223
#define UID "ayQskyoNrCW" // Change to your UID
int main() {
// Create IP connection
IPConnection ipcon;
ipcon_create(&ipcon);
// Create device object
IMU imu;
imu_create(&imu, UID, &ipcon);
// Connect to brickd
if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
fprintf(stderr, "Could not connect\n");
exit(1);
}
// Don't use device before ipcon is connected
// Get current quaternion
float x, y, z, w;
if(imu_get_quaternion(&imu, &x, &y, &z, &w) < 0) {
fprintf(stderr, "Could not get quaternion, probably timeout\n");
exit(1);
}
printf("x: %f\ny: %f\nz: %f\nw: %f\n", x, y, z, w);
printf("Press key to exit\n");
getchar();
ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
}
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 | #include <stdio.h>
#include "ip_connection.h"
#include "brick_imu.h"
#define HOST "localhost"
#define PORT 4223
#define UID "ayQskyoNrCW" // Change to your UID
// Quaternion callback
void cb_quaternion(float x, float y, float z, float w, void *user_data) {
(void)user_data; // avoid unused parameter warning
printf("x: %f\ny: %f\nz: %f\nw: %f\n\n", x, y, z, w);
}
int main() {
// Create IP connection
IPConnection ipcon;
ipcon_create(&ipcon);
// Create device object
IMU imu;
imu_create(&imu, UID, &ipcon);
// Connect to brickd
if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
fprintf(stderr, "Could not connect\n");
exit(1);
}
// Don't use device before ipcon is connected
// Set period for quaternion callback to 1s
imu_set_quaternion_period(&imu, 1000);
// Register "quaternion callback" to cb_quaternion
imu_register_callback(&imu,
IMU_CALLBACK_QUATERNION,
(void *)cb_quaternion,
NULL);
printf("Press key to exit\n");
getchar();
ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
}
|
Every function of the C/C++ bindings returns an integer which describes an error code. Data returned from the device, when a getter is called, is handled via call by reference. These parameters are labeled with the ret_ prefix.
Possible error codes are:
as defined in ip_connection.h.
All functions listed below are thread-safe.
Creates the device object imu with the unique device ID uid and adds it to the IPConnection ipcon:
IMU imu;
imu_create(&imu, "YOUR_DEVICE_UID", &ipcon);
This device object can be used after the IP connection has been connected (see examples above).
Removes the device object imu from its IPConnection and destroys it. The device object cannot be used anymore afterwards.
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 IMU_CALLBACK_ORIENTATION and set the period with imu_set_orientation_period().
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 IMU_CALLBACK_QUATERNION and set the period with imu_set_quaternion_period().
Turns the orientation and direction LEDs of the IMU Brick on.
Turns the orientation and direction LEDs of the IMU Brick off.
Returns true if the orientation and direction LEDs of the IMU Brick are on, false otherwise.
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.
Returns the convergence speed as set by imu_set_convergence_speed().
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 IMU_CALLBACK_ACCELERATION and set the period with imu_set_acceleration_period().
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 IMU_CALLBACK_MAGNETIC_FIELD and set the period with imu_set_magnetic_field_period().
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 IMU_CALLBACK_ANGULAR_VELOCITY and set the period with imu_set_angular_velocity_period().
Returns the data from imu_get_acceleration(), imu_get_magnetic_field() and imu_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 IMU_CALLBACK_ALL_DATA and set the period with imu_set_all_data_period().
Returns the temperature of the IMU Brick. The temperature is given in °C/100.
Not implemented yet.
Not implemented yet.
Not implemented yet.
Not implemented yet.
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 defines are available for this function:
Returns the calibration for a given type as set by imu_set_calibration().
The following defines are available for this function:
Turns the orientation calculation of the IMU Brick on.
As default the calculation is on.
New in version 2.0.2 (Firmware).
Turns the orientation calculation of the IMU Brick off.
If the calculation is off, imu_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).
Returns true if the orientation calculation of the IMU Brick is on, false otherwise.
New in version 2.0.2 (Firmware).
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.
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 imu_set_response_expected(). 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 imu_set_response_expected() for the list of function ID defines available for this function.
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 defines are available for this function:
Changes the response expected flag for all setter and callback configuration functions of this device at once.
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).
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).
Returns true if the status LED is enabled, false otherwise.
New in version 2.3.1 (Firmware).
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.
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.
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!
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.
Registers a callback with ID id to the function callback. The user_data will be given as a parameter of the callback.
The available IDs with corresponding function signatures are listed below.
Sets the period in ms with which the IMU_CALLBACK_ACCELERATION callback is triggered periodically. A value of 0 turns the callback off.
The default value is 0.
Returns the period as set by imu_set_acceleration_period().
Sets the period in ms with which the IMU_CALLBACK_MAGNETIC_FIELD callback is triggered periodically. A value of 0 turns the callback off.
Returns the period as set by imu_set_magnetic_field_period().
Sets the period in ms with which the IMU_CALLBACK_ANGULAR_VELOCITY callback is triggered periodically. A value of 0 turns the callback off.
Returns the period as set by imu_set_angular_velocity_period().
Sets the period in ms with which the IMU_CALLBACK_ALL_DATA callback is triggered periodically. A value of 0 turns the callback off.
Returns the period as set by imu_set_all_data_period().
Sets the period in ms with which the IMU_CALLBACK_ORIENTATION callback is triggered periodically. A value of 0 turns the callback off.
Returns the period as set by imu_set_orientation_period().
Sets the period in ms with which the IMU_CALLBACK_QUATERNION callback is triggered periodically. A value of 0 turns the callback off.
Returns the period as set by imu_set_quaternion_period().
Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the imu_register_callback() function. The parameters consist of the device object, the callback ID, the callback function and optional user data:
void my_callback(int p, void *user_data) { printf("parameter: %d\n", p); } imu_register_callback(&imu, IMU_CALLBACK_EXAMPLE, (void *)my_callback, NULL);
The available constants with corresponding callback function signatures 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.
void callback(int16_t x, int16_t y, int16_t z, void *user_data)
This callback is triggered periodically with the period that is set by imu_set_acceleration_period(). The parameters are the acceleration for the x, y and z axis.
void callback(int16_t x, int16_t y, int16_t z, void *user_data)
This callback is triggered periodically with the period that is set by imu_set_magnetic_field_period(). The parameters are the magnetic field for the x, y and z axis.
void callback(int16_t x, int16_t y, int16_t z, void *user_data)
This callback is triggered periodically with the period that is set by imu_set_angular_velocity_period(). The parameters are the angular velocity for the x, y and z axis.
void callback(int16_t acc_x, int16_t acc_y, int16_t acc_z, int16_t mag_x, int16_t mag_y, int16_t mag_z, int16_t ang_x, int16_t ang_y, int16_t ang_z, int16_t temperature, void *user_data)
This callback is triggered periodically with the period that is set by imu_set_all_data_period(). 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.
void callback(int16_t roll, int16_t pitch, int16_t yaw, void *user_data)
This callback is triggered periodically with the period that is set by imu_set_orientation_period(). The parameters are the orientation (roll, pitch and yaw) of the IMU Brick in Euler angles. See imu_get_orientation() for details.
void callback(float x, float y, float z, float w, void *user_data)
This callback is triggered periodically with the period that is set by imu_set_quaternion_period(). The parameters are the orientation (x, y, z, w) of the IMU Brick in quaternions. See imu_get_quaternion() for details.
This constant is used to identify a IMU Brick.
The imu_get_identity() function and the IPCON_CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.