MQTT - Laser Range Finder Bricklet

This is the description of the MQTT 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 MQTT API bindings is part of their general description.

Examples

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

Simple

Download (example-simple.txt)

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# Change XYZ to the UID of your Laser Range Finder Bricklet

setup:
    # Turn laser on and wait 250ms for very first measurement to be ready
    publish '' to tinkerforge/request/laser_range_finder_bricklet/XYZ/enable_laser 
    
    wait for 0.25s 
    
    # Get current distance
    subscribe to tinkerforge/response/laser_range_finder_bricklet/XYZ/get_distance
    publish '' to tinkerforge/request/laser_range_finder_bricklet/XYZ/get_distance 

cleanup:
    # If you are done, run this to clean up
    publish '' to tinkerforge/request/laser_range_finder_bricklet/XYZ/disable_laser  # Turn laser off

Callback

Download (example-callback.txt)

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# Change XYZ to the UID of your Laser Range Finder Bricklet

setup:
    # Turn laser on and wait 250ms for very first measurement to be ready
    publish '' to tinkerforge/request/laser_range_finder_bricklet/XYZ/enable_laser 
    
    wait for 0.25s 
    
    # Handle incoming distance callbacks
    subscribe to tinkerforge/callback/laser_range_finder_bricklet/XYZ/distance
    publish '{"register": true}' to tinkerforge/register/laser_range_finder_bricklet/XYZ/distance # Register distance callback
    
    # 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!
    publish '{"period": 200}' to tinkerforge/request/laser_range_finder_bricklet/XYZ/set_distance_callback_period

cleanup:
    # If you are done, run this to clean up
    publish '' to tinkerforge/request/laser_range_finder_bricklet/XYZ/disable_laser  # Turn laser off

Threshold

Download (example-threshold.txt)

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# Change XYZ to the UID of your Laser Range Finder Bricklet

setup:
    # Turn laser on and wait 250ms for very first measurement to be ready
    publish '' to tinkerforge/request/laser_range_finder_bricklet/XYZ/enable_laser 
    
    wait for 0.25s 
    
    # Get threshold callbacks with a debounce time of 10 seconds (10000ms)
    publish '{"debounce": 10000}' to tinkerforge/request/laser-range-finder_bricklet/XYZ/set_debounce_period
    
    # Handle incoming distance reached callbacks
    subscribe to tinkerforge/callback/laser_range_finder_bricklet/XYZ/distance_reached
    publish '{"register": true}' to tinkerforge/register/laser_range_finder_bricklet/XYZ/distance_reached # Register distance_reached callback
    
    # Configure threshold for distance "greater than 20 cm"
    publish '{"option": "greater", "min": 20, "max": 0}' to tinkerforge/request/laser_range_finder_bricklet/XYZ/set_distance_callback_threshold

cleanup:
    # If you are done, run this to clean up
    publish '' to tinkerforge/request/laser_range_finder_bricklet/XYZ/disable_laser  # Turn laser off

API

All published payload to an from the MQTT bindings is in the JSON format.

If an error occures, the bindings publish a JSON object containing the error message as attribute "_ERROR". It is published on the corresponding response topic: .../response/... for .../request/... and .../callback/... for .../register/....

Basic Functions

request/laser_range_finder_bricklet/<UID>/get_distance
Response payload:
 
  • distance -- int

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

Sensor hardware version 1 (see request/laser_range_finder_bricklet/<UID>/get_sensor_hardware_version) cannot measure distance and velocity at the same time. Therefore, the distance mode has to be enabled using request/laser_range_finder_bricklet/<UID>/set_mode. Sensor hardware version 3 can measure distance and velocity at the same time. Also the laser has to be enabled, see request/laser_range_finder_bricklet/<UID>/enable_laser.

If you want to get the distance periodically, it is recommended to use the register/laser_range_finder_bricklet/<UID>/distance callback and set the period with request/laser_range_finder_bricklet/<UID>/set_distance_callback_period.

request/laser_range_finder_bricklet/<UID>/get_velocity
Response payload:
 
  • velocity -- int

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 request/laser_range_finder_bricklet/<UID>/get_sensor_hardware_version) cannot measure distance and velocity at the same time. Therefore, the velocity mode has to be enabled using request/laser_range_finder_bricklet/<UID>/set_mode. 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 request/laser_range_finder_bricklet/<UID>/set_configuration) is configured. Also the laser has to be enabled, see request/laser_range_finder_bricklet/<UID>/enable_laser.

If you want to get the velocity periodically, it is recommended to use the register/laser_range_finder_bricklet/<UID>/velocity callback and set the period with request/laser_range_finder_bricklet/<UID>/set_velocity_callback_period.

request/laser_range_finder_bricklet/<UID>/set_mode
Request payload:
 
  • mode -- int (has symbols)

Note

This function is only available if you have a LIDAR-Lite sensor with hardware version 1. Use request/laser_range_finder_bricklet/<UID>/set_configuration for hardware version 3. You can check the sensor hardware version using request/laser_range_finder_bricklet/<UID>/get_sensor_hardware_version.

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 symbols are available for this function:

for mode:

  • "Distance" = 0
  • "VelocityMax13ms" = 1
  • "VelocityMax32ms" = 2
  • "VelocityMax64ms" = 3
  • "VelocityMax127ms" = 4
request/laser_range_finder_bricklet/<UID>/get_mode
Response payload:
 
  • mode -- int (has symbols)

Returns the mode as set by request/laser_range_finder_bricklet/<UID>/set_mode.

The following symbols are available for this function:

for mode:

  • "Distance" = 0
  • "VelocityMax13ms" = 1
  • "VelocityMax32ms" = 2
  • "VelocityMax64ms" = 3
  • "VelocityMax127ms" = 4
request/laser_range_finder_bricklet/<UID>/enable_laser

Activates the laser of the LIDAR.

We recommend that you wait 250ms after enabling the laser before the first call of request/laser_range_finder_bricklet/<UID>/get_distance to ensure stable measurements.

request/laser_range_finder_bricklet/<UID>/disable_laser

Deactivates the laser of the LIDAR.

request/laser_range_finder_bricklet/<UID>/is_laser_enabled
Response payload:
 
  • laser_enabled -- bool

Returns true if the laser is enabled, false otherwise.

request/laser_range_finder_bricklet/<UID>/set_configuration
Request payload:
 
  • acquisition_count -- int
  • enable_quick_termination -- bool
  • threshold_value -- int
  • measurement_frequency -- int

Note

This function is only available if you have a LIDAR-Lite sensor with hardware version 3. Use request/laser_range_finder_bricklet/<UID>/set_mode for hardware version 1. You can check the sensor hardware version using request/laser_range_finder_bricklet/<UID>/get_sensor_hardware_version.

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).

request/laser_range_finder_bricklet/<UID>/get_configuration
Response payload:
 
  • acquisition_count -- int
  • enable_quick_termination -- bool
  • threshold_value -- int
  • measurement_frequency -- int

Returns the configuration as set by request/laser_range_finder_bricklet/<UID>/set_configuration.

New in version 2.0.3 (Plugin).

Advanced Functions

request/laser_range_finder_bricklet/<UID>/set_moving_average
Request payload:
 
  • distance_average_length -- int
  • velocity_average_length -- int

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.

request/laser_range_finder_bricklet/<UID>/get_moving_average
Response payload:
 
  • distance_average_length -- int
  • velocity_average_length -- int

Returns the length moving average as set by request/laser_range_finder_bricklet/<UID>/set_moving_average.

request/laser_range_finder_bricklet/<UID>/get_sensor_hardware_version
Response payload:
 
  • version -- int (has symbols)

Returns the LIDAR-Lite hardware version.

The following symbols are available for this function:

for version:

  • "1" = 1
  • "3" = 3

New in version 2.0.3 (Plugin).

request/laser_range_finder_bricklet/<UID>/get_identity
Response payload:
 
  • uid -- string
  • connected_uid -- string
  • position -- string
  • hardware_version -- [int,int,int]
  • firmware_version -- [int,int,int]
  • device_identifier -- int (has symbols)
  • _display_name -- string

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. If symbolic output is not disabled, the device identifier is mapped to the corresponding name in the format used in topics.

The display name contains the Laser Range Finder's name in a human readable form.

Callback Configuration Functions

request/laser_range_finder_bricklet/<UID>/set_distance_callback_period
Request payload:
 
  • period -- int

Sets the period in ms with which the register/laser_range_finder_bricklet/<UID>/distance callback is triggered periodically. A value of 0 turns the callback off.

The register/laser_range_finder_bricklet/<UID>/distance callback is only triggered if the distance value has changed since the last triggering.

The default value is 0.

request/laser_range_finder_bricklet/<UID>/get_distance_callback_period
Response payload:
 
  • period -- int

Returns the period as set by request/laser_range_finder_bricklet/<UID>/set_distance_callback_period.

request/laser_range_finder_bricklet/<UID>/set_velocity_callback_period
Request payload:
 
  • period -- int

Sets the period in ms with which the register/laser_range_finder_bricklet/<UID>/velocity callback is triggered periodically. A value of 0 turns the callback off.

The register/laser_range_finder_bricklet/<UID>/velocity callback is only triggered if the velocity value has changed since the last triggering.

The default value is 0.

request/laser_range_finder_bricklet/<UID>/get_velocity_callback_period
Response payload:
 
  • period -- int

Returns the period as set by request/laser_range_finder_bricklet/<UID>/set_velocity_callback_period.

request/laser_range_finder_bricklet/<UID>/set_distance_callback_threshold
Request payload:
 
  • option -- string (has symbols)
  • min -- int
  • max -- int

Sets the thresholds for the register/laser_range_finder_bricklet/<UID>/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 symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/laser_range_finder_bricklet/<UID>/get_distance_callback_threshold
Response payload:
 
  • option -- string (has symbols)
  • min -- int
  • max -- int

Returns the threshold as set by request/laser_range_finder_bricklet/<UID>/set_distance_callback_threshold.

The following symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/laser_range_finder_bricklet/<UID>/set_velocity_callback_threshold
Request payload:
 
  • option -- string (has symbols)
  • min -- int
  • max -- int

Sets the thresholds for the register/laser_range_finder_bricklet/<UID>/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 symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/laser_range_finder_bricklet/<UID>/get_velocity_callback_threshold
Response payload:
 
  • option -- string (has symbols)
  • min -- int
  • max -- int

Returns the threshold as set by request/laser_range_finder_bricklet/<UID>/set_velocity_callback_threshold.

The following symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/laser_range_finder_bricklet/<UID>/set_debounce_period
Request payload:
 
  • debounce -- int

Sets the period in ms with which the threshold callbacks

are triggered, if the thresholds

keep being reached.

The default value is 100.

request/laser_range_finder_bricklet/<UID>/get_debounce_period
Response payload:
 
  • debounce -- int

Returns the debounce period as set by request/laser_range_finder_bricklet/<UID>/set_debounce_period.

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the corresponding .../register/... topic and an optional suffix. This suffix can be used to deregister the callback later.

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.

register/laser_range_finder_bricklet/<UID>/distance
Request payload:
 
  • register -- bool
Response payload:
 
  • distance -- int

A callback can be registered for this event by publishing to the .../register/laser_range_finder_bricklet/<UID>/distance[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/laser_range_finder_bricklet/<UID>/distance[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/laser_range_finder_bricklet/<UID>/set_distance_callback_period. The callback payload is the distance value of the sensor.

The register/laser_range_finder_bricklet/<UID>/distance callback is only triggered if the distance value has changed since the last triggering.

register/laser_range_finder_bricklet/<UID>/velocity
Request payload:
 
  • register -- bool
Response payload:
 
  • velocity -- int

A callback can be registered for this event by publishing to the .../register/laser_range_finder_bricklet/<UID>/velocity[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/laser_range_finder_bricklet/<UID>/velocity[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/laser_range_finder_bricklet/<UID>/set_velocity_callback_period. The callback payload is the velocity value of the sensor.

The register/laser_range_finder_bricklet/<UID>/velocity callback is only triggered if the velocity has changed since the last triggering.

register/laser_range_finder_bricklet/<UID>/distance_reached
Request payload:
 
  • register -- bool
Response payload:
 
  • distance -- int

A callback can be registered for this event by publishing to the .../register/laser_range_finder_bricklet/<UID>/distance_reached[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/laser_range_finder_bricklet/<UID>/distance_reached[/<SUFFIX>] topic for each registered suffix.

This callback is triggered when the threshold as set by request/laser_range_finder_bricklet/<UID>/set_distance_callback_threshold is reached. The callback payload is the distance value of the sensor.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by request/laser_range_finder_bricklet/<UID>/set_debounce_period.

register/laser_range_finder_bricklet/<UID>/velocity_reached
Request payload:
 
  • register -- bool
Response payload:
 
  • velocity -- int

A callback can be registered for this event by publishing to the .../register/laser_range_finder_bricklet/<UID>/velocity_reached[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/laser_range_finder_bricklet/<UID>/velocity_reached[/<SUFFIX>] topic for each registered suffix.

This callback is triggered when the threshold as set by request/laser_range_finder_bricklet/<UID>/set_velocity_callback_threshold is reached. The callback payload is the velocity value of the sensor.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by request/laser_range_finder_bricklet/<UID>/set_debounce_period.