Java - Laser Range Finder Bricklet

This is the description of the Java API bindings for the Laser Range Finder Bricklet. General information and technical specifications for the Laser Range Finder Bricklet are summarized in its hardware description.

An installation guide for the Java API bindings is part of their general description.

Examples

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

Simple

Download (ExampleSimple.java)

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import com.tinkerforge.IPConnection;
import com.tinkerforge.BrickletLaserRangeFinder;

public class ExampleSimple {
    private static final String HOST = "localhost";
    private static final int PORT = 4223;

    // Change XYZ to the UID of your Laser Range Finder Bricklet
    private static final String UID = "XYZ";

    // Note: To make the example code cleaner we do not handle exceptions. Exceptions
    //       you might normally want to catch are described in the documentation
    public static void main(String args[]) throws Exception {
        IPConnection ipcon = new IPConnection(); // Create IP connection
        BrickletLaserRangeFinder lrf =
          new BrickletLaserRangeFinder(UID, ipcon); // Create device object

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

        // Turn laser on and wait 250ms for very first measurement to be ready
        lrf.enableLaser();
        Thread.sleep(250);

        // Get current distance
        int distance = lrf.getDistance(); // Can throw com.tinkerforge.TimeoutException
        System.out.println("Distance: " + distance + " cm");

        System.out.println("Press key to exit"); System.in.read();
        lrf.disableLaser(); // Turn laser off
        ipcon.disconnect();
    }
}

Callback

Download (ExampleCallback.java)

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import com.tinkerforge.IPConnection;
import com.tinkerforge.BrickletLaserRangeFinder;

public class ExampleCallback {
    private static final String HOST = "localhost";
    private static final int PORT = 4223;

    // Change XYZ to the UID of your Laser Range Finder Bricklet
    private static final String UID = "XYZ";

    // Note: To make the example code cleaner we do not handle exceptions. Exceptions
    //       you might normally want to catch are described in the documentation
    public static void main(String args[]) throws Exception {
        IPConnection ipcon = new IPConnection(); // Create IP connection
        BrickletLaserRangeFinder lrf =
          new BrickletLaserRangeFinder(UID, ipcon); // Create device object

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

        // Turn laser on and wait 250ms for very first measurement to be ready
        lrf.enableLaser();
        Thread.sleep(250);

        // Add distance listener
        lrf.addDistanceListener(new BrickletLaserRangeFinder.DistanceListener() {
            public void distance(int distance) {
                System.out.println("Distance: " + distance + " cm");
            }
        });

        // Set period for distance callback to 0.2s (200ms)
        // Note: The distance callback is only called every 0.2 seconds
        //       if the distance has changed since the last call!
        lrf.setDistanceCallbackPeriod(200);

        System.out.println("Press key to exit"); System.in.read();
        lrf.disableLaser(); // Turn laser off
        ipcon.disconnect();
    }
}

Threshold

Download (ExampleThreshold.java)

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import com.tinkerforge.IPConnection;
import com.tinkerforge.BrickletLaserRangeFinder;

public class ExampleThreshold {
    private static final String HOST = "localhost";
    private static final int PORT = 4223;

    // Change XYZ to the UID of your Laser Range Finder Bricklet
    private static final String UID = "XYZ";

    // Note: To make the example code cleaner we do not handle exceptions. Exceptions
    //       you might normally want to catch are described in the documentation
    public static void main(String args[]) throws Exception {
        IPConnection ipcon = new IPConnection(); // Create IP connection
        BrickletLaserRangeFinder lrf =
          new BrickletLaserRangeFinder(UID, ipcon); // Create device object

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

        // Turn laser on and wait 250ms for very first measurement to be ready
        lrf.enableLaser();
        Thread.sleep(250);

        // Get threshold callbacks with a debounce time of 10 seconds (10000ms)
        lrf.setDebouncePeriod(10000);

        // Add distance reached listener
        lrf.addDistanceReachedListener(new BrickletLaserRangeFinder.DistanceReachedListener() {
            public void distanceReached(int distance) {
                System.out.println("Distance: " + distance + " cm");
            }
        });

        // Configure threshold for distance "greater than 20 cm"
        lrf.setDistanceCallbackThreshold('>', 20, 0);

        System.out.println("Press key to exit"); System.in.read();
        lrf.disableLaser(); // Turn laser off
        ipcon.disconnect();
    }
}

API

Generally, every method of the Java bindings that returns a value can throw a TimeoutException. This exception gets thrown if the device did not respond. If a cable based connection is used, it is unlikely that this exception gets thrown (assuming nobody unplugs the device). However, if a wireless connection is used, timeouts will occur if the distance to the device gets too big.

Beside the TimeoutException there is also a NotConnectedException that is thrown if a method needs to communicate with the device while the IP Connection is not connected.

Since Java does not support multiple return values and return by reference is not possible for primitive types, we use small classes that only consist of member variables. The member variables of the returned objects are described in the corresponding method descriptions.

The package for all Brick/Bricklet bindings and the IP Connection is com.tinkerforge.*

All methods listed below are thread-safe.

Basic Functions

public class BrickletLaserRangeFinder(String uid, IPConnection ipcon)

Creates an object with the unique device ID uid:

BrickletLaserRangeFinder laserRangeFinder = new BrickletLaserRangeFinder("YOUR_DEVICE_UID", ipcon);

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

public int getDistance()

Returns the measured distance. The value has a range of 0 to 4000 and is given in cm.

Sensor hardware version 1 (see getSensorHardwareVersion()) cannot measure distance and velocity at the same time. Therefore, the distance mode has to be enabled using setMode(). Sensor hardware version 3 can measure distance and velocity at the same time. Also the laser has to be enabled, see enableLaser().

If you want to get the distance periodically, it is recommended to use the DistanceListener listener and set the period with setDistanceCallbackPeriod().

public short getVelocity()

Returns the measured velocity. The value has a range of -12800 to 12700 and is given in 1/100 m/s.

Sensor hardware version 1 (see getSensorHardwareVersion()) cannot measure distance and velocity at the same time. Therefore, the velocity mode has to be enabled using setMode(). Sensor hardware version 3 can measure distance and velocity at the same time, but the velocity measurement only produces stables results if a fixed measurement rate (see setConfiguration()) is configured. Also the laser has to be enabled, see enableLaser().

If you want to get the velocity periodically, it is recommended to use the VelocityListener listener and set the period with setVelocityCallbackPeriod().

public void setMode(short mode)

Note

This function is only available if you have a LIDAR-Lite sensor with hardware version 1. Use setConfiguration() for hardware version 3. You can check the sensor hardware version using getSensorHardwareVersion().

The LIDAR-Lite sensor (hardware version 1) has five different modes. One mode is for distance measurements and four modes are for velocity measurements with different ranges.

The following modes are available:

  • 0: Distance is measured with resolution 1.0 cm and range 0-400 cm
  • 1: Velocity is measured with resolution 0.1 m/s and range is 0-12.7 m/s
  • 2: Velocity is measured with resolution 0.25 m/s and range is 0-31.75 m/s
  • 3: Velocity is measured with resolution 0.5 m/s and range is 0-63.5 m/s
  • 4: Velocity is measured with resolution 1.0 m/s and range is 0-127 m/s

The default mode is 0 (distance is measured).

The following constants are available for this function:

  • BrickletLaserRangeFinder.MODE_DISTANCE = 0
  • BrickletLaserRangeFinder.MODE_VELOCITY_MAX_13MS = 1
  • BrickletLaserRangeFinder.MODE_VELOCITY_MAX_32MS = 2
  • BrickletLaserRangeFinder.MODE_VELOCITY_MAX_64MS = 3
  • BrickletLaserRangeFinder.MODE_VELOCITY_MAX_127MS = 4
public short getMode()

Returns the mode as set by setMode().

The following constants are available for this function:

  • BrickletLaserRangeFinder.MODE_DISTANCE = 0
  • BrickletLaserRangeFinder.MODE_VELOCITY_MAX_13MS = 1
  • BrickletLaserRangeFinder.MODE_VELOCITY_MAX_32MS = 2
  • BrickletLaserRangeFinder.MODE_VELOCITY_MAX_64MS = 3
  • BrickletLaserRangeFinder.MODE_VELOCITY_MAX_127MS = 4
public void enableLaser()

Activates the laser of the LIDAR.

We recommend that you wait 250ms after enabling the laser before the first call of getDistance() to ensure stable measurements.

public void disableLaser()

Deactivates the laser of the LIDAR.

public boolean isLaserEnabled()

Returns true if the laser is enabled, false otherwise.

public void setConfiguration(short acquisitionCount, boolean enableQuickTermination, short thresholdValue, int measurementFrequency)

Note

This function is only available if you have a LIDAR-Lite sensor with hardware version 3. Use setMode() for hardware version 1. You can check the sensor hardware version using getSensorHardwareVersion().

The Aquisition Count defines the number of times the Laser Range Finder Bricklet will integrate acquisitions to find a correlation record peak. With a higher count, the Bricklet can measure longer distances. With a lower count, the rate increases. The allowed values are 1-255.

If you set Enable Quick Termination to true, the distance measurement will be terminated early if a high peak was already detected. This means that a higher measurement rate can be achieved and long distances can be measured at the same time. However, the chance of false-positive distance measurements increases.

Normally the distance is calculated with a detection algorithm that uses peak value, signal strength and noise. You can however also define a fixed Threshold Value. Set this to a low value if you want to measure the distance to something that has very little reflection (e.g. glass) and set it to a high value if you want to measure the distance to something with a very high reflection (e.g. mirror). Set this to 0 to use the default algorithm. The other allowed values are 1-255.

Set the Measurement Frequency in Hz to force a fixed measurement rate. If set to 0, the Laser Range Finder Bricklet will use the optimal frequency according to the other configurations and the actual measured distance. Since the rate is not fixed in this case, the velocity measurement is not stable. For a stable velocity measurement you should set a fixed measurement frequency. The lower the frequency, the higher is the resolution of the calculated velocity. The allowed values are 10Hz-500Hz (and 0 to turn the fixed frequency off).

The default values for Acquisition Count, Enable Quick Termination, Threshold Value and Measurement Frequency are 128, false, 0 and 0.

New in version 2.0.3 (Plugin).

public BrickletLaserRangeFinder.Configuration getConfiguration()

Returns the configuration as set by setConfiguration().

New in version 2.0.3 (Plugin).

The returned object has the public member variables short acquisitionCount, boolean enableQuickTermination, short thresholdValue and int measurementFrequency.

Advanced Functions

public void setMovingAverage(short distanceAverageLength, short velocityAverageLength)

Sets the length of a moving averaging for the distance and velocity.

Setting the length to 0 will turn the averaging completely off. With less averaging, there is more noise on the data.

The range for the averaging is 0-30.

The default value is 10.

public BrickletLaserRangeFinder.MovingAverage getMovingAverage()

Returns the length moving average as set by setMovingAverage().

The returned object has the public member variables short distanceAverageLength and short velocityAverageLength.

public short getSensorHardwareVersion()

Returns the LIDAR-Lite hardware version.

The following constants are available for this function:

  • BrickletLaserRangeFinder.VERSION_1 = 1
  • BrickletLaserRangeFinder.VERSION_3 = 3

New in version 2.0.3 (Plugin).

public short[] getAPIVersion()

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.

public boolean getResponseExpected(short functionId)

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 listener 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.

public void setResponseExpected(short functionId, boolean responseExpected)

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 listener configuration functions (default value: true). For getter functions it is always 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.

The following function ID constants are available for this function:

  • BrickletLaserRangeFinder.FUNCTION_SET_DISTANCE_CALLBACK_PERIOD = 3
  • BrickletLaserRangeFinder.FUNCTION_SET_VELOCITY_CALLBACK_PERIOD = 5
  • BrickletLaserRangeFinder.FUNCTION_SET_DISTANCE_CALLBACK_THRESHOLD = 7
  • BrickletLaserRangeFinder.FUNCTION_SET_VELOCITY_CALLBACK_THRESHOLD = 9
  • BrickletLaserRangeFinder.FUNCTION_SET_DEBOUNCE_PERIOD = 11
  • BrickletLaserRangeFinder.FUNCTION_SET_MOVING_AVERAGE = 13
  • BrickletLaserRangeFinder.FUNCTION_SET_MODE = 15
  • BrickletLaserRangeFinder.FUNCTION_ENABLE_LASER = 17
  • BrickletLaserRangeFinder.FUNCTION_DISABLE_LASER = 18
  • BrickletLaserRangeFinder.FUNCTION_SET_CONFIGURATION = 25
public void setResponseExpectedAll(boolean responseExpected)

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

public BrickletLaserRangeFinder.Identity getIdentity()

Returns the UID, the UID where the Bricklet is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be 'a', 'b', 'c' or 'd'.

The device identifier numbers can be found here. There is also a constant for the device identifier of this Bricklet.

The returned object has the public member variables String uid, String connectedUid, char position, short[] hardwareVersion, short[] firmwareVersion and int deviceIdentifier.

Listener Configuration Functions

public void setDistanceCallbackPeriod(long period)

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

The DistanceListener listener is only triggered if the distance value has changed since the last triggering.

The default value is 0.

public long getDistanceCallbackPeriod()

Returns the period as set by setDistanceCallbackPeriod().

public void setVelocityCallbackPeriod(long period)

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

The VelocityListener listener is only triggered if the velocity value has changed since the last triggering.

The default value is 0.

public long getVelocityCallbackPeriod()

Returns the period as set by setVelocityCallbackPeriod().

public void setDistanceCallbackThreshold(char option, int min, int max)

Sets the thresholds for the DistanceReachedListener listener.

The following options are possible:

Option Description
'x' Listener is turned off
'o' Listener is triggered when the distance value is outside the min and max values
'i' Listener is triggered when the distance value is inside the min and max values
'<' Listener is triggered when the distance value is smaller than the min value (max is ignored)
'>' Listener is triggered when the distance value is greater than the min value (max is ignored)

The default value is ('x', 0, 0).

The following constants are available for this function:

  • BrickletLaserRangeFinder.THRESHOLD_OPTION_OFF = 'x'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_SMALLER = '<'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_GREATER = '>'
public BrickletLaserRangeFinder.DistanceCallbackThreshold getDistanceCallbackThreshold()

Returns the threshold as set by setDistanceCallbackThreshold().

The following constants are available for this function:

  • BrickletLaserRangeFinder.THRESHOLD_OPTION_OFF = 'x'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_SMALLER = '<'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_GREATER = '>'

The returned object has the public member variables char option, int min and int max.

public void setVelocityCallbackThreshold(char option, short min, short max)

Sets the thresholds for the VelocityReachedListener listener.

The following options are possible:

Option Description
'x' Listener is turned off
'o' Listener is triggered when the velocity is outside the min and max values
'i' Listener is triggered when the velocity is inside the min and max values
'<' Listener is triggered when the velocity is smaller than the min value (max is ignored)
'>' Listener is triggered when the velocity is greater than the min value (max is ignored)

The default value is ('x', 0, 0).

The following constants are available for this function:

  • BrickletLaserRangeFinder.THRESHOLD_OPTION_OFF = 'x'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_SMALLER = '<'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_GREATER = '>'
public BrickletLaserRangeFinder.VelocityCallbackThreshold getVelocityCallbackThreshold()

Returns the threshold as set by setVelocityCallbackThreshold().

The following constants are available for this function:

  • BrickletLaserRangeFinder.THRESHOLD_OPTION_OFF = 'x'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_SMALLER = '<'
  • BrickletLaserRangeFinder.THRESHOLD_OPTION_GREATER = '>'

The returned object has the public member variables char option, short min and short max.

public void setDebouncePeriod(long debounce)

Sets the period in ms with which the threshold listeners

are triggered, if the thresholds

keep being reached.

The default value is 100.

public long getDebouncePeriod()

Returns the debounce period as set by setDebouncePeriod().

Listeners

Listeners can be registered to receive time critical or recurring data from the device. The registration is done with "add*Listener" functions of the device object.

The parameter is a listener class object, for example:

device.addExampleListener(new BrickletLaserRangeFinder.ExampleListener() {
    public void property(int value) {
        System.out.println("Value: " + value);
    }
});

The available listener classes with inherent methods to be overwritten are described below. It is possible to add several listeners and to remove them with the corresponding "remove*Listener" function.

Note

Using listeners 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.

public class BrickletLaserRangeFinder.DistanceListener()

This listener can be added with the addDistanceListener() function. An added listener can be removed with the removeDistanceListener() function.

public void distance(int distance)

This listener is triggered periodically with the period that is set by setDistanceCallbackPeriod(). The parameter is the distance value of the sensor.

The DistanceListener listener is only triggered if the distance value has changed since the last triggering.

public class BrickletLaserRangeFinder.VelocityListener()

This listener can be added with the addVelocityListener() function. An added listener can be removed with the removeVelocityListener() function.

public void velocity(short velocity)

This listener is triggered periodically with the period that is set by setVelocityCallbackPeriod(). The parameter is the velocity value of the sensor.

The VelocityListener listener is only triggered if the velocity has changed since the last triggering.

public class BrickletLaserRangeFinder.DistanceReachedListener()

This listener can be added with the addDistanceReachedListener() function. An added listener can be removed with the removeDistanceReachedListener() function.

public void distanceReached(int distance)

This listener is triggered when the threshold as set by setDistanceCallbackThreshold() is reached. The parameter is the distance value of the sensor.

If the threshold keeps being reached, the listener is triggered periodically with the period as set by setDebouncePeriod().

public class BrickletLaserRangeFinder.VelocityReachedListener()

This listener can be added with the addVelocityReachedListener() function. An added listener can be removed with the removeVelocityReachedListener() function.

public void velocityReached(short velocity)

This listener is triggered when the threshold as set by setVelocityCallbackThreshold() is reached. The parameter is the velocity value of the sensor.

If the threshold keeps being reached, the listener is triggered periodically with the period as set by setDebouncePeriod().

Constants

public static final int BrickletLaserRangeFinder.DEVICE_IDENTIFIER

This constant is used to identify a Laser Range Finder Bricklet.

The getIdentity() function and the EnumerateListener listener of the IP Connection have a deviceIdentifier parameter to specify the Brick's or Bricklet's type.

public static final String BrickletLaserRangeFinder.DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Laser Range Finder Bricklet.