MQTT - Laser Range Finder Bricklet 2.0

This is the description of the MQTT API bindings for the Laser Range Finder Bricklet 2.0. General information and technical specifications for the Laser Range Finder Bricklet 2.0 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).

API

All published payloads to and from the MQTT bindings are in 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_v2_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.

The laser has to be enabled, see request/laser_range_finder_v2_bricklet/<UID>/set_enable.

If you want to get the value periodically, it is recommended to use the register/laser_range_finder_v2_bricklet/<UID>/distance callback. You can set the callback configuration with request/laser_range_finder_v2_bricklet/<UID>/set_distance_callback_configuration.

request/laser_range_finder_v2_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.

The velocity measurement only produces stables results if a fixed measurement rate (see request/laser_range_finder_v2_bricklet/<UID>/set_configuration) is configured. Also the laser has to be enabled, see request/laser_range_finder_v2_bricklet/<UID>/set_enable.

If you want to get the value periodically, it is recommended to use the register/laser_range_finder_v2_bricklet/<UID>/velocity callback. You can set the callback configuration with request/laser_range_finder_v2_bricklet/<UID>/set_velocity_callback_configuration.

request/laser_range_finder_v2_bricklet/<UID>/set_enable
Request payload:
 
  • enable -- bool

Enables the laser of the LIDAR if set to true.

We recommend that you wait 250ms after enabling the laser before the first call of request/laser_range_finder_v2_bricklet/<UID>/get_distance to ensure stable measurements.

request/laser_range_finder_v2_bricklet/<UID>/get_enable
Response payload:
 
  • enable -- bool

Returns the value as set by request/laser_range_finder_v2_bricklet/<UID>/set_enable.

request/laser_range_finder_v2_bricklet/<UID>/set_configuration
Request payload:
 
  • acquisition_count -- int
  • enable_quick_termination -- bool
  • threshold_value -- int
  • measurement_frequency -- int

The Acquisition 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.

request/laser_range_finder_v2_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_v2_bricklet/<UID>/set_configuration.

request/laser_range_finder_v2_bricklet/<UID>/set_distance_led_config
Request payload:
 
  • config -- int (has symbols)

Configures the distance LED to be either turned off, turned on, blink in heartbeat mode or show the distance (brighter = object is nearer).

The default value is 3 (show distance).

The following symbols are available for this function:

for config:

  • "Off" = 0
  • "On" = 1
  • "ShowHeartbeat" = 2
  • "ShowDistance" = 3
request/laser_range_finder_v2_bricklet/<UID>/get_distance_led_config
Response payload:
 
  • config -- int (has symbols)

Returns the LED configuration as set by request/laser_range_finder_v2_bricklet/<UID>/set_distance_led_config

The following symbols are available for this function:

for config:

  • "Off" = 0
  • "On" = 1
  • "ShowHeartbeat" = 2
  • "ShowDistance" = 3

Advanced Functions

request/laser_range_finder_v2_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 0-255.

The default value is 10.

request/laser_range_finder_v2_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_v2_bricklet/<UID>/set_moving_average.

request/laser_range_finder_v2_bricklet/<UID>/set_offset_calibration
Request payload:
 
  • offset -- int

The offset is given in cm and added to the measured distance. It is saved in non-volatile memory, you only have to set it once.

The Bricklet comes with a per-sensor factory-calibrated offset value, you should not have to call this function.

If you want to re-calibrate the offset you first have to set it to 0. Calculate the offset by measuring the distance to a known distance and set it again.

request/laser_range_finder_v2_bricklet/<UID>/get_offset_calibration
Response payload:
 
  • offset -- int

Returns the offset value as set by request/laser_range_finder_v2_bricklet/<UID>/set_offset_calibration.

request/laser_range_finder_v2_bricklet/<UID>/get_spitfp_error_count
Response payload:
 
  • error_count_ack_checksum -- int
  • error_count_message_checksum -- int
  • error_count_frame -- int
  • error_count_overflow -- int

Returns the error count for the communication between Brick and Bricklet.

The errors are divided into

  • ACK checksum errors,
  • message checksum errors,
  • framing errors and
  • overflow errors.

The errors counts are for errors that occur on the Bricklet side. All Bricks have a similar function that returns the errors on the Brick side.

request/laser_range_finder_v2_bricklet/<UID>/set_bootloader_mode
Request payload:
 
  • mode -- int (has symbols)
Response payload:
 
  • status -- int (has symbols)

Sets the bootloader mode and returns the status after the requested mode change was instigated.

You can change from bootloader mode to firmware mode and vice versa. A change from bootloader mode to firmware mode will only take place if the entry function, device identifier and CRC are present and correct.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

The following symbols are available for this function:

for mode:

  • "Bootloader" = 0
  • "Firmware" = 1
  • "BootloaderWaitForReboot" = 2
  • "FirmwareWaitForReboot" = 3
  • "FirmwareWaitForEraseAndReboot" = 4

for status:

  • "OK" = 0
  • "InvalidMode" = 1
  • "NoChange" = 2
  • "EntryFunctionNotPresent" = 3
  • "DeviceIdentifierIncorrect" = 4
  • "CRCMismatch" = 5
request/laser_range_finder_v2_bricklet/<UID>/get_bootloader_mode
Response payload:
 
  • mode -- int (has symbols)

Returns the current bootloader mode, see request/laser_range_finder_v2_bricklet/<UID>/set_bootloader_mode.

The following symbols are available for this function:

for mode:

  • "Bootloader" = 0
  • "Firmware" = 1
  • "BootloaderWaitForReboot" = 2
  • "FirmwareWaitForReboot" = 3
  • "FirmwareWaitForEraseAndReboot" = 4
request/laser_range_finder_v2_bricklet/<UID>/set_write_firmware_pointer
Request payload:
 
  • pointer -- int

Sets the firmware pointer for request/laser_range_finder_v2_bricklet/<UID>/write_firmware. The pointer has to be increased by chunks of size 64. The data is written to flash every 4 chunks (which equals to one page of size 256).

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

request/laser_range_finder_v2_bricklet/<UID>/write_firmware
Request payload:
 
  • data -- [int,... (x64)]
Response payload:
 
  • status -- int

Writes 64 Bytes of firmware at the position as written by request/laser_range_finder_v2_bricklet/<UID>/set_write_firmware_pointer before. The firmware is written to flash every 4 chunks.

You can only write firmware in bootloader mode.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

request/laser_range_finder_v2_bricklet/<UID>/set_status_led_config
Request payload:
 
  • config -- int (has symbols)

Sets the status LED configuration. By default the LED shows communication traffic between Brick and Bricklet, it flickers once for every 10 received data packets.

You can also turn the LED permanently on/off or show a heartbeat.

If the Bricklet is in bootloader mode, the LED is will show heartbeat by default.

The following symbols are available for this function:

for config:

  • "Off" = 0
  • "On" = 1
  • "ShowHeartbeat" = 2
  • "ShowStatus" = 3
request/laser_range_finder_v2_bricklet/<UID>/get_status_led_config
Response payload:
 
  • config -- int (has symbols)

Returns the configuration as set by request/laser_range_finder_v2_bricklet/<UID>/set_status_led_config

The following symbols are available for this function:

for config:

  • "Off" = 0
  • "On" = 1
  • "ShowHeartbeat" = 2
  • "ShowStatus" = 3
request/laser_range_finder_v2_bricklet/<UID>/get_chip_temperature
Response payload:
 
  • temperature -- int

Returns the temperature in °C 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 bad accuracy. Practically it is only useful as an indicator for temperature changes.

request/laser_range_finder_v2_bricklet/<UID>/reset

Calling this function will reset the Bricklet. All configurations will be lost.

After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

request/laser_range_finder_v2_bricklet/<UID>/write_uid
Request payload:
 
  • uid -- int

Writes a new UID into flash. If you want to set a new UID you have to decode the Base58 encoded UID string into an integer first.

We recommend that you use Brick Viewer to change the UID.

request/laser_range_finder_v2_bricklet/<UID>/read_uid
Response payload:
 
  • uid -- int

Returns the current UID as an integer. Encode as Base58 to get the usual string version.

request/laser_range_finder_v2_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 2.0's name in a human readable form.

Callback Configuration Functions

request/laser_range_finder_v2_bricklet/<UID>/set_distance_callback_configuration
Request payload:
 
  • period -- int
  • value_has_to_change -- bool
  • option -- string (has symbols)
  • min -- int
  • max -- int

The period in ms is the period with which the register/laser_range_finder_v2_bricklet/<UID>/distance callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

It is furthermore possible to constrain the callback with thresholds.

The option-parameter together with min/max sets a threshold for the register/laser_range_finder_v2_bricklet/<UID>/distance callback.

The following options are possible:

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

If the option is set to 'x' (threshold turned off) the callback is triggered with the fixed period.

The default value is (0, false, '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_v2_bricklet/<UID>/get_distance_callback_configuration
Response payload:
 
  • period -- int
  • value_has_to_change -- bool
  • option -- string (has symbols)
  • min -- int
  • max -- int

Returns the callback configuration as set by request/laser_range_finder_v2_bricklet/<UID>/set_distance_callback_configuration.

The following symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'
request/laser_range_finder_v2_bricklet/<UID>/set_velocity_callback_configuration
Request payload:
 
  • period -- int
  • value_has_to_change -- bool
  • option -- string (has symbols)
  • min -- int
  • max -- int

The period in ms is the period with which the register/laser_range_finder_v2_bricklet/<UID>/velocity callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

It is furthermore possible to constrain the callback with thresholds.

The option-parameter together with min/max sets a threshold for the register/laser_range_finder_v2_bricklet/<UID>/velocity callback.

The following options are possible:

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

If the option is set to 'x' (threshold turned off) the callback is triggered with the fixed period.

The default value is (0, false, '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_v2_bricklet/<UID>/get_velocity_callback_configuration
Response payload:
 
  • period -- int
  • value_has_to_change -- bool
  • option -- string (has symbols)
  • min -- int
  • max -- int

Returns the callback configuration as set by request/laser_range_finder_v2_bricklet/<UID>/set_velocity_callback_configuration.

The following symbols are available for this function:

for option:

  • "Off" = 'x'
  • "Outside" = 'o'
  • "Inside" = 'i'
  • "Smaller" = '<'
  • "Greater" = '>'

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_v2_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_v2_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_v2_bricklet/<UID>/distance[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically according to the configuration set by request/laser_range_finder_v2_bricklet/<UID>/set_distance_callback_configuration.

The callback payload is the same as request/laser_range_finder_v2_bricklet/<UID>/get_distance.

register/laser_range_finder_v2_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_v2_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_v2_bricklet/<UID>/velocity[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically according to the configuration set by request/laser_range_finder_v2_bricklet/<UID>/set_velocity_callback_configuration.

The callback payload is the same as request/laser_range_finder_v2_bricklet/<UID>/get_velocity.