Delphi/Lazarus - IMU Brick

This is the description of the Delphi/Lazarus 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 Delphi/Lazarus API bindings is part of their general description.

Examples

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

Callback

Download (ExampleCallback.pas)

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program ExampleCallback;

{$ifdef MSWINDOWS}{$apptype CONSOLE}{$endif}
{$ifdef FPC}{$mode OBJFPC}{$H+}{$endif}

uses
  SysUtils, IPConnection, BrickIMU;

type
  TExample = class
  private
    ipcon: TIPConnection;
    imu: TBrickIMU;
  public
    procedure QuaternionCB(sender: TBrickIMU; 
                           const x: single; const y: single;
                           const z: single; const w: single);
    procedure Execute;
  end;

const
  HOST = 'localhost';
  PORT = 4223;
  UID = 'a4JriVLwq7E'; { Change to your UID }

var
  e: TExample;

{ Quaternion callback }
procedure TExample.QuaternionCB(sender: TBrickIMU; 
                                const x: single; const y: single;
                                const z: single; const w: single);
begin
  WriteLn(Format('x: %.6f', [x]));
  WriteLn(Format('y: %.6f', [y]));
  WriteLn(Format('z: %.6f', [z]));
  WriteLn(Format('w: %.6f', [w]));
  WriteLn('');
end;

procedure TExample.Execute;
begin
  { Create IP connection }
  ipcon := TIPConnection.Create;

  { Create device object }
  imu := TBrickIMU.Create(UID, ipcon);

  { Connect to brickd }
  ipcon.Connect(HOST, PORT);
  { Don't use device before ipcon is connected }

  { Set period for quaternion callback to 1s }
  imu.SetQuaternionPeriod(1000);

  { Register "quaternion callback" to procedure QuaternionCB }
  imu.OnQuaternion := {$ifdef FPC}@{$endif}QuaternionCB;

  WriteLn('Press key to exit');
  ReadLn;
  ipcon.Destroy; { Calls ipcon.Disconnect internally }
end;

begin
  e := TExample.Create;
  e.Execute;
  e.Destroy;
end.

API

Since Delphi does not support multiple return values directly, we use the out keyword to return multiple values from a function.

All functions and procedures listed below are thread-safe.

Basic Functions

constructor TBrickIMU.Create(const uid: string; ipcon: TIPConnection)

Creates an object with the unique device ID uid:

imu := TBrickIMU.Create('YOUR_DEVICE_UID', ipcon);

This object can then be used after the IP Connection is connected (see examples above).

procedure TBrickIMU.GetOrientation(out roll: smallint; out pitch: smallint; out yaw: smallint)

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 OnOrientation and set the period with SetOrientationPeriod.

procedure TBrickIMU.GetQuaternion(out x: single; out y: single; out z: single; out w: single)

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 OnQuaternion and set the period with SetQuaternionPeriod.

procedure TBrickIMU.LedsOn

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

procedure TBrickIMU.LedsOff

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

function TBrickIMU.AreLedsOn: boolean

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

procedure TBrickIMU.SetConvergenceSpeed(const speed: word)

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 TBrickIMU.GetConvergenceSpeed: word

Returns the convergence speed as set by SetConvergenceSpeed.

Advanced Functions

procedure TBrickIMU.GetAcceleration(out x: smallint; out y: smallint; out z: smallint)

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 OnAcceleration and set the period with SetAccelerationPeriod.

procedure TBrickIMU.GetMagneticField(out x: smallint; out y: smallint; out z: smallint)

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 OnMagneticField and set the period with SetMagneticFieldPeriod.

procedure TBrickIMU.GetAngularVelocity(out x: smallint; out y: smallint; out z: smallint)

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 OnAngularVelocity and set the period with SetAngularVelocityPeriod.

procedure TBrickIMU.GetAllData(out accX: smallint; out accY: smallint; out accZ: smallint; out magX: smallint; out magY: smallint; out magZ: smallint; out angX: smallint; out angY: smallint; out angZ: smallint; out temperature: smallint)

Returns the data from GetAcceleration, GetMagneticField and GetAngularVelocity 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 OnAllData and set the period with SetAllDataPeriod.

function TBrickIMU.GetIMUTemperature: smallint

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

procedure TBrickIMU.SetAccelerationRange(const range: byte)

Not implemented yet.

function TBrickIMU.GetAccelerationRange: byte

Not implemented yet.

procedure TBrickIMU.SetMagnetometerRange(const range: byte)

Not implemented yet.

function TBrickIMU.GetMagnetometerRange: byte

Not implemented yet.

procedure TBrickIMU.SetCalibration(const typ: byte; const data: array [0..9] of smallint)

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 constants are available for this function:

  • BRICK_IMU_CALIBRATION_TYPE_ACCELEROMETER_GAIN = 0
  • BRICK_IMU_CALIBRATION_TYPE_ACCELEROMETER_BIAS = 1
  • BRICK_IMU_CALIBRATION_TYPE_MAGNETOMETER_GAIN = 2
  • BRICK_IMU_CALIBRATION_TYPE_MAGNETOMETER_BIAS = 3
  • BRICK_IMU_CALIBRATION_TYPE_GYROSCOPE_GAIN = 4
  • BRICK_IMU_CALIBRATION_TYPE_GYROSCOPE_BIAS = 5
function TBrickIMU.GetCalibration(const typ: byte): array [0..9] of smallint

Returns the calibration for a given type as set by SetCalibration.

The following constants are available for this function:

  • BRICK_IMU_CALIBRATION_TYPE_ACCELEROMETER_GAIN = 0
  • BRICK_IMU_CALIBRATION_TYPE_ACCELEROMETER_BIAS = 1
  • BRICK_IMU_CALIBRATION_TYPE_MAGNETOMETER_GAIN = 2
  • BRICK_IMU_CALIBRATION_TYPE_MAGNETOMETER_BIAS = 3
  • BRICK_IMU_CALIBRATION_TYPE_GYROSCOPE_GAIN = 4
  • BRICK_IMU_CALIBRATION_TYPE_GYROSCOPE_BIAS = 5
procedure TBrickIMU.OrientationCalculationOn

Turns the orientation calculation of the IMU Brick on.

As default the calculation is on.

New in version 2.0.2 (Firmware).

procedure TBrickIMU.OrientationCalculationOff

Turns the orientation calculation of the IMU Brick off.

If the calculation is off, GetOrientation 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 TBrickIMU.IsOrientationCalculationOn: boolean

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

New in version 2.0.2 (Firmware).

function TBrickIMU.GetAPIVersion: array [0..2] of byte

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.

function TBrickIMU.GetResponseExpected(const functionId: byte): boolean

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 SetResponseExpected. 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 SetResponseExpected for the list of function ID constants available for this function.

procedure TBrickIMU.SetResponseExpected(const functionId: byte; const responseExpected: boolean)

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 constants are available for this function:

  • BRICK_IMU_FUNCTION_LEDS_ON = 8
  • BRICK_IMU_FUNCTION_LEDS_OFF = 9
  • BRICK_IMU_FUNCTION_SET_ACCELERATION_RANGE = 11
  • BRICK_IMU_FUNCTION_SET_MAGNETOMETER_RANGE = 13
  • BRICK_IMU_FUNCTION_SET_CONVERGENCE_SPEED = 15
  • BRICK_IMU_FUNCTION_SET_CALIBRATION = 17
  • BRICK_IMU_FUNCTION_SET_ACCELERATION_PERIOD = 19
  • BRICK_IMU_FUNCTION_SET_MAGNETIC_FIELD_PERIOD = 21
  • BRICK_IMU_FUNCTION_SET_ANGULAR_VELOCITY_PERIOD = 23
  • BRICK_IMU_FUNCTION_SET_ALL_DATA_PERIOD = 25
  • BRICK_IMU_FUNCTION_SET_ORIENTATION_PERIOD = 27
  • BRICK_IMU_FUNCTION_SET_QUATERNION_PERIOD = 29
  • BRICK_IMU_FUNCTION_ORIENTATION_CALCULATION_ON = 37
  • BRICK_IMU_FUNCTION_ORIENTATION_CALCULATION_OFF = 38
  • BRICK_IMU_FUNCTION_ENABLE_STATUS_LED = 238
  • BRICK_IMU_FUNCTION_DISABLE_STATUS_LED = 239
  • BRICK_IMU_FUNCTION_RESET = 243
procedure TBrickIMU.SetResponseExpectedAll(const responseExpected: boolean)

Changes the response expected flag for all setter and callback configuration functions of this device at once.

procedure TBrickIMU.EnableStatusLED

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).

procedure TBrickIMU.DisableStatusLED

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 TBrickIMU.IsStatusLEDEnabled: boolean

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

New in version 2.3.1 (Firmware).

procedure TBrickIMU.GetProtocol1BrickletName(const port: char; out protocolVersion: byte; out firmwareVersion: array [0..2] of byte; out 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.

function TBrickIMU.GetChipTemperature: smallint

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.

procedure TBrickIMU.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!

procedure TBrickIMU.GetIdentity(out uid: string; out connectedUid: string; out position: char; out hardwareVersion: array [0..2] of byte; out firmwareVersion: array [0..2] of byte; out deviceIdentifier: word)

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.

Callback Configuration Functions

procedure TBrickIMU.SetAccelerationPeriod(const period: longword)

Sets the period in ms with which the OnAcceleration callback is triggered periodically. A value of 0 turns the callback off.

The default value is 0.

function TBrickIMU.GetAccelerationPeriod: longword

Returns the period as set by SetAccelerationPeriod.

procedure TBrickIMU.SetMagneticFieldPeriod(const period: longword)

Sets the period in ms with which the OnMagneticField callback is triggered periodically. A value of 0 turns the callback off.

function TBrickIMU.GetMagneticFieldPeriod: longword

Returns the period as set by SetMagneticFieldPeriod.

procedure TBrickIMU.SetAngularVelocityPeriod(const period: longword)

Sets the period in ms with which the OnAngularVelocity callback is triggered periodically. A value of 0 turns the callback off.

function TBrickIMU.GetAngularVelocityPeriod: longword

Returns the period as set by SetAngularVelocityPeriod.

procedure TBrickIMU.SetAllDataPeriod(const period: longword)

Sets the period in ms with which the OnAllData callback is triggered periodically. A value of 0 turns the callback off.

function TBrickIMU.GetAllDataPeriod: longword

Returns the period as set by SetAllDataPeriod.

procedure TBrickIMU.SetOrientationPeriod(const period: longword)

Sets the period in ms with which the OnOrientation callback is triggered periodically. A value of 0 turns the callback off.

function TBrickIMU.GetOrientationPeriod: longword

Returns the period as set by SetOrientationPeriod.

procedure TBrickIMU.SetQuaternionPeriod(const period: longword)

Sets the period in ms with which the OnQuaternion callback is triggered periodically. A value of 0 turns the callback off.

function TBrickIMU.GetQuaternionPeriod: longword

Returns the period as set by SetQuaternionPeriod.

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done by assigning a procedure to an callback property of the device object:

procedure TExample.MyCallback(sender: TBrickIMU; const param: word);
begin
  WriteLn(param);
end;

imu.OnExample := {$ifdef FPC}@{$endif}example.MyCallback;

The available callback property and their type of parameters 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.

property TBrickIMU.OnAcceleration
procedure(sender: TBrickIMU; const x: smallint; const y: smallint; const z: smallint) of object;

This callback is triggered periodically with the period that is set by SetAccelerationPeriod. The parameters are the acceleration for the x, y and z axis.

property TBrickIMU.OnMagneticField
procedure(sender: TBrickIMU; const x: smallint; const y: smallint; const z: smallint) of object;

This callback is triggered periodically with the period that is set by SetMagneticFieldPeriod. The parameters are the magnetic field for the x, y and z axis.

property TBrickIMU.OnAngularVelocity
procedure(sender: TBrickIMU; const x: smallint; const y: smallint; const z: smallint) of object;

This callback is triggered periodically with the period that is set by SetAngularVelocityPeriod. The parameters are the angular velocity for the x, y and z axis.

property TBrickIMU.OnAllData
procedure(sender: TBrickIMU; const accX: smallint; const accY: smallint; const accZ: smallint; const magX: smallint; const magY: smallint; const magZ: smallint; const angX: smallint; const angY: smallint; const angZ: smallint; const temperature: smallint) of object;

This callback is triggered periodically with the period that is set by SetAllDataPeriod. 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.

property TBrickIMU.OnOrientation
procedure(sender: TBrickIMU; const roll: smallint; const pitch: smallint; const yaw: smallint) of object;

This callback is triggered periodically with the period that is set by SetOrientationPeriod. The parameters are the orientation (roll, pitch and yaw) of the IMU Brick in Euler angles. See GetOrientation for details.

property TBrickIMU.OnQuaternion
procedure(sender: TBrickIMU; const x: single; const y: single; const z: single; const w: single) of object;

This callback is triggered periodically with the period that is set by SetQuaternionPeriod. The parameters are the orientation (x, y, z, w) of the IMU Brick in quaternions. See GetQuaternion for details.

Constants

const BRICK_IMU_DEVICE_IDENTIFIER

This constant is used to identify a IMU Brick.

The GetIdentity function and the OnEnumerate callback of the IP Connection have a deviceIdentifier parameter to specify the Brick's or Bricklet's type.

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