Perl - 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 Perl 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 Perl API bindings is part of their general description.

Examples

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

Simple

Download (example_simple.pl)

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#!/usr/bin/perl  

use Tinkerforge::IPConnection;
use Tinkerforge::BrickletLaserRangeFinder;

use constant HOST => 'localhost';
use constant PORT => 4223;
use constant UID => 'XYZ'; # Change to your UID

my $ipcon = Tinkerforge::IPConnection->new(); # Create IP connection
my $lrf = Tinkerforge::BrickletLaserRangeFinder->new(&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->enable_laser();
select(undef, undef, undef, 0.25);

# Get current distance (unit is cm)
my $distance = $lrf->get_distance();
print "Distance: $distance cm\n";

print "Press any key to exit...\n";
<STDIN>;
$ipcon->disconnect();

Callback

Download (example_callback.pl)

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#!/usr/bin/perl  

use Tinkerforge::IPConnection;
use Tinkerforge::BrickletLaserRangeFinder;

use constant HOST => 'localhost';
use constant PORT => 4223;
use constant UID => 'XYZ'; # Change to your UID

my $ipcon = Tinkerforge::IPConnection->new(); # Create IP connection
my $lrf = Tinkerforge::BrickletLaserRangeFinder->new(&UID, $ipcon); # Create device object

# Callback function for distance callback (parameter has unit cm)
sub cb_distance
{
    my ($distance) = @_;

    print "Distance: ".$distance." cm\n";
}

$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->enable_laser();
select(undef, undef, undef, 0.25);

# 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->set_distance_callback_period(1000);

# Register distance callback to function cb_distance
$lrf->register_callback($lrf->CALLBACK_DISTANCE, 'cb_distance');

print "Press any key to exit...\n";
<STDIN>;
$ipcon->disconnect();

Threshold

Download (example_threshold.pl)

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#!/usr/bin/perl  

use Tinkerforge::IPConnection;
use Tinkerforge::BrickletLaserRangeFinder;

use constant HOST => 'localhost';
use constant PORT => 4223;
use constant UID => 'XYZ'; # Change to your UID

my $ipcon = Tinkerforge::IPConnection->new(); # Create IP connection
my $lrf = Tinkerforge::BrickletLaserRangeFinder->new(&UID, $ipcon); # Create device object

# Callback for distance greater than 20 cm
sub cb_reached
{
    my ($distance) = @_;

    print "Distance ".$distance." cm\n";
}

$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->enable_laser();
select(undef, undef, undef, 0.25);

# Get threshold callbacks with a debounce time of 10 seconds (10000ms)
$lrf->set_debounce_period(10000);

# Register threshold reached callback to function cb_reached
$lrf->register_callback($lrf->CALLBACK_DISTANCE_REACHED, 'cb_reached');

# Configure threshold for "greater than 20 cm"
$lrf->set_distance_callback_threshold('>', 20, 0);

print "Press any key to exit...\n";
<STDIN>;
$ipcon->disconnect();

API

Generally, every subroutine of the Perl bindings can report an error as Tinkerforge::Error object via croak(). The object has a get_code() and a get_message() subroutine. There are different error code:

  • Error->ALREADY_CONNECTED = 11
  • Error->NOT_CONNECTED = 12
  • Error->CONNECT_FAILED = 13
  • Error->INVALID_FUNCTION_ID = 21
  • Error->TIMEOUT = 31
  • Error->INVALID_PARAMETER = 41
  • Error->FUNCTION_NOT_SUPPORTED = 42
  • Error->UNKNOWN_ERROR = 43

All methods listed below are thread-safe.

Basic Functions

BrickletLaserRangeFinder->new($uid, $ipcon)
Parameters:
  • $uid -- string
  • $ipcon -- IPConnection
Return type:

BrickletLaserRangeFinder

Creates an object with the unique device ID $uid:

$laser_range_finder = BrickletLaserRangeFinder->new("YOUR_DEVICE_UID", $ipcon);

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

BrickletLaserRangeFinder->get_distance()
Return type:int

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 set_mode(). Also the laser has to be enabled, see enable_laser().

If you want to get the distance periodically, it is recommended to use the callback CALLBACK_DISTANCE and set the period with set_distance_callback_period().

BrickletLaserRangeFinder->get_velocity()
Return type:int

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 set_mode(). Also the laser has to be enabled, see enable_laser().

If you want to get the velocity periodically, it is recommended to use the callback CALLBACK_VELOCITY and set the period with set_velocity_callback_period().

BrickletLaserRangeFinder->set_mode($mode)
Parameters:$mode -- int
Return type:undef

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
BrickletLaserRangeFinder->get_mode()
Return type:int

Returns the mode as set by set_mode().

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
BrickletLaserRangeFinder->enable_laser()
Return type:undef

Activates the laser of the LIDAR.

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

BrickletLaserRangeFinder->disable_laser()
Return type:undef

Deactivates the laser of the LIDAR.

BrickletLaserRangeFinder->is_laser_enabled()
Return type:bool

Returns true if the laser is enabled, false otherwise.

Advanced Functions

BrickletLaserRangeFinder->set_moving_average($distance_average_length, $velocity_average_length)
Parameters:
  • $distance_average_length -- int
  • $velocity_average_length -- int
Return type:

undef

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.

BrickletLaserRangeFinder->get_moving_average()
Return type:[int, int]

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

The returned array contains the elements distance_average_length and velocity_average_length.

BrickletLaserRangeFinder->get_api_version()
Return type:[int, int, int]

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.

BrickletLaserRangeFinder->get_response_expected($function_id)
Parameters:$function_id -- int
Return type:bool

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 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 set_response_expected() for the list of function ID constants available for this function.

BrickletLaserRangeFinder->set_response_expected($function_id, $response_expected)
Parameters:
  • $function_id -- int
  • $response_expected -- bool
Return type:

undef

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:

  • 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->set_response_expected_all($response_expected)
Parameters:$response_expected -- bool
Return type:undef

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

BrickletLaserRangeFinder->get_identity()
Return type:[string, string, char, [int, int, int], [int, int, int], int]

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 array contains the elements uid, connected_uid, position, hardware_version, firmware_version and device_identifier.

Callback Configuration Functions

BrickletLaserRangeFinder->register_callback($id, $callback)
Parameters:
  • $id -- int
  • $callback -- string
Return type:

undef

Registers a callback with ID $id to the function named $callback. The available IDs with corresponding function signatures are listed below.

BrickletLaserRangeFinder->set_distance_callback_period($period)
Parameters:$period -- int
Return type:undef

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

CALLBACK_DISTANCE is only triggered if the distance value has changed since the last triggering.

The default value is 0.

BrickletLaserRangeFinder->get_distance_callback_period()
Return type:int

Returns the period as set by set_distance_callback_period().

BrickletLaserRangeFinder->set_velocity_callback_period($period)
Parameters:$period -- int
Return type:undef

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

CALLBACK_VELOCITY is only triggered if the velocity value has changed since the last triggering.

The default value is 0.

BrickletLaserRangeFinder->get_velocity_callback_period()
Return type:int

Returns the period as set by set_velocity_callback_period().

BrickletLaserRangeFinder->set_distance_callback_threshold($option, $min, $max)
Parameters:
  • $option -- char
  • $min -- int
  • $max -- int
Return type:

undef

Sets the thresholds for the CALLBACK_DISTANCE_REACHED callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the distance value is outside the min and max values
'i' Callback is triggered when the distance value is inside the min and max values
'<' Callback is triggered when the distance value is smaller than the min value (max is ignored)
'>' Callback 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 = '>'
BrickletLaserRangeFinder->get_distance_callback_threshold()
Return type:[char, int, int]

Returns the threshold as set by set_distance_callback_threshold().

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 array contains the elements option, min and max.

BrickletLaserRangeFinder->set_velocity_callback_threshold($option, $min, $max)
Parameters:
  • $option -- char
  • $min -- int
  • $max -- int
Return type:

undef

Sets the thresholds for the CALLBACK_VELOCITY_REACHED callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the velocity is outside the min and max values
'i' Callback is triggered when the velocity is inside the min and max values
'<' Callback is triggered when the velocity is smaller than the min value (max is ignored)
'>' Callback 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 = '>'
BrickletLaserRangeFinder->get_velocity_callback_threshold()
Return type:[char, int, int]

Returns the threshold as set by set_velocity_callback_threshold().

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 array contains the elements option, min and max.

BrickletLaserRangeFinder->set_debounce_period($debounce)
Parameters:$debounce -- int
Return type:undef

Sets the period in ms with which the threshold callbacks

are triggered, if the thresholds

keep being reached.

The default value is 100.

BrickletLaserRangeFinder->get_debounce_period()
Return type:int

Returns the debounce period as set by set_debounce_period().

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the register_callback() function of the device object. The first parameter is the callback ID and the second parameter the callback function name:

sub my_callback
{
    print "@_[0]";
}

$laser_range_finder->register_callback(BrickletLaserRangeFinder->CALLBACK_EXAMPLE, 'my_callback')

The callback function will be called from an internal thread of the IP Connection. In contrast to many other programming languages, variables are not automatically shared between threads in Perl. If you want to share a global variable between a callback function and the rest for your program it has to be marked as :shared. See the documentation of the threads::shared Perl module for more details.

The available constants with inherent number and 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.

BrickletLaserRangeFinder->CALLBACK_DISTANCE
Parameters:$distance -- int

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

CALLBACK_DISTANCE is only triggered if the distance value has changed since the last triggering.

BrickletLaserRangeFinder->CALLBACK_VELOCITY
Parameters:$velocity -- int

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

CALLBACK_VELOCITY is only triggered if the velocity has changed since the last triggering.

BrickletLaserRangeFinder->CALLBACK_DISTANCE_REACHED
Parameters:$distance -- int

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

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

BrickletLaserRangeFinder->CALLBACK_VELOCITY_REACHED
Parameters:$velocity -- int

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

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

Constants

BrickletLaserRangeFinder->DEVICE_IDENTIFIER

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

The get_identity() function and the CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.

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