Java - Laser Range Finder Bricklet

Note

This Bricklet is currently in the prototype stage and the software/hardware as well as the documentation is in an incomplete state.

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.BrickletLaserRangeFinder;
import com.tinkerforge.IPConnection;

public class ExampleSimple {
    private static final String HOST = "localhost";
    private static final int PORT = 4223;
    private static final String UID = "XYZ"; // Change to your UID

    // 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 (unit is cm)
        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();
        ipcon.disconnect();
    }
}

Callback

Download (ExampleCallback.java)

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

public class ExampleCallback {
    private static final String HOST = "localhost";
    private static final int PORT = 4223;
    private static final String UID = "XYZ"; // Change to your UID

    // 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);

        // Set Period for distance callback to 1s (1000ms)
        // Note: The distance callback is only called every second if the 
        //       distance has changed since the last call!
        lrf.setDistanceCallbackPeriod(1000);

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

        System.out.println("Press key to exit"); System.in.read();
        ipcon.disconnect();
    }
}

Threshold

Download (ExampleThreshold.java)

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

public class ExampleThreshold {
    private static final String HOST = "localhost";
    private static final int PORT = 4223;
    private static final String UID = "XYZ"; // Change to your UID

    // 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);

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

        // Add and implement distance reached listener 
        // (called if distance is greater than 20 cm)
        lrf.addDistanceReachedListener(new BrickletLaserRangeFinder.DistanceReachedListener() {
            public void distanceReached(int distance) {
                System.out.println("Distance: " + distance + " cm.");
            }
        });

        System.out.println("Press key to exit"); System.in.read();
        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.

The Laser Range Finder Bricklet knows different modes. Distances are only measured in the distance measurement mode, see setMode(). Also the laser has to be enabled, see enableLaser().

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

public short getVelocity()

Returns the measured velocity. The value has a range of 0 to 12700 and is given in 1/100 m/s.

The Laser Range Finder Bricklet knows different modes. Velocity is only measured in the velocity measurement modes, see setMode(). Also the laser has to be enabled, see enableLaser().

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

public void setMode(short mode)

The LIDAR 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.

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[] 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 and listeners 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:

  • 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
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.

DistanceListener 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.

VelocityListener 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.

DistanceListener 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.

VelocityListener 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.

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