Software / API Bindings / MQTT / API Reference and Examples / Bricklets / Laser Range Finder Bricklet 2.0

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).

Simple¶

Download (example-simple.txt)

# Change XYZ to the UID of your Laser Range Finder Bricklet 2.0

setup:
    # Turn laser on and wait 250ms for very first measurement to be ready
    publish '{"enable": true}' to tinkerforge/request/laser_range_finder_v2_bricklet/XYZ/set_enable

    wait for 0.25s

    # Get current distance
    subscribe to tinkerforge/response/laser_range_finder_v2_bricklet/XYZ/get_distance
    publish '' to tinkerforge/request/laser_range_finder_v2_bricklet/XYZ/get_distance

cleanup:
    # If you are done, run this to clean up
    # Turn laser off
    publish '{"enable": false}' to tinkerforge/request/laser_range_finder_v2_bricklet/XYZ/set_enable

Callback¶

Download (example-callback.txt)

# Change XYZ to the UID of your Laser Range Finder Bricklet 2.0

setup:
    # Turn laser on and wait 250ms for very first measurement to be ready
    publish '{"enable": true}' to tinkerforge/request/laser_range_finder_v2_bricklet/XYZ/set_enable

    wait for 0.25s

    # Handle incoming distance callbacks
    subscribe to tinkerforge/callback/laser_range_finder_v2_bricklet/XYZ/distance
    publish '{"register": true}' to tinkerforge/register/laser_range_finder_v2_bricklet/XYZ/distance # Register distance callback

    # Set period for distance callback to 0.2s (200ms) without a threshold
    publish '{"period": 200, "value_has_to_change": false, "option": "off", "min": 0, "max": 0}' to tinkerforge/request/laser_range_finder_v2_bricklet/XYZ/set_distance_callback_configuration

cleanup:
    # If you are done, run this to clean up
    # Turn laser off
    publish '{"enable": false}' to tinkerforge/request/laser_range_finder_v2_bricklet/XYZ/set_enable

Threshold¶

Download (example-threshold.txt)

# Change XYZ to the UID of your Laser Range Finder Bricklet 2.0

setup:
    # Turn laser on and wait 250ms for very first measurement to be ready
    publish '{"enable": true}' to tinkerforge/request/laser_range_finder_v2_bricklet/XYZ/set_enable

    wait for 0.25s

    # Handle incoming distance callbacks
    subscribe to tinkerforge/callback/laser_range_finder_v2_bricklet/XYZ/distance
    publish '{"register": true}' to tinkerforge/register/laser_range_finder_v2_bricklet/XYZ/distance # Register distance callback

    # Configure threshold for distance "greater than 20 cm"
    # with a debounce period of 1s (1000ms)
    publish '{"period": 1000, "value_has_to_change": false, "option": "greater", "min": 20, "max": 0}' to tinkerforge/request/laser_range_finder_v2_bricklet/XYZ/set_distance_callback_configuration

cleanup:
    # If you are done, run this to clean up
    # Turn laser off
    publish '{"enable": false}' to tinkerforge/request/laser_range_finder_v2_bricklet/XYZ/set_enable

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 member _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¶

Request:	empty payload
Response:	distance – Type: int, Unit: 1 cm, Range: [0 to 4000]

Returns the measured distance.

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¶

Request:	empty payload
Response:	velocity – Type: int, Unit: 1 cm/s, Range: [-12800 to 12700]

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:	enable – Type: bool, Default: false
Response:	no response

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¶

Request:	empty payload
Response:	enable – Type: bool, Default: false

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:	acquisition_count – Type: int, Range: [1 to 255], Default: 128 enable_quick_termination – Type: bool, Default: false threshold_value – Type: int, Range: [0 to 255], Default: 0 measurement_frequency – Type: int, Unit: 1 Hz, Range: [0, 10 to 500], Default: 0
Response:	no response

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 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¶

Request:	empty payload
Response:	acquisition_count – Type: int, Range: [1 to 255], Default: 128 enable_quick_termination – Type: bool, Default: false threshold_value – Type: int, Range: [0 to 255], Default: 0 measurement_frequency – Type: int, Unit: 1 Hz, Range: [0, 10 to 500], Default: 0

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:	config – Type: int, Range: See symbols, Default: 3
Response:	no response

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

The following symbols are available for this function:

For config:

"off" = 0
"on" = 1
"show_heartbeat" = 2
"show_distance" = 3

request/laser_range_finder_v2_bricklet/<UID>/get_distance_led_config¶

Request:	empty payload
Response:	config – Type: int, Range: See symbols, Default: 3

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
"show_heartbeat" = 2
"show_distance" = 3

Advanced Functions¶

request/laser_range_finder_v2_bricklet/<UID>/set_moving_average¶

Request:	distance_average_length – Type: int, Range: [0 to 255], Default: 10 velocity_average_length – Type: int, Range: [0 to 255], Default: 10
Response:	no response

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.

request/laser_range_finder_v2_bricklet/<UID>/get_moving_average¶

Request:	empty payload
Response:	distance_average_length – Type: int, Range: [0 to 255], Default: 10 velocity_average_length – Type: int, Range: [0 to 255], Default: 10

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:	offset – Type: int, Unit: 1 cm, Range: [-2¹⁵ to 28767]
Response:	no response

The offset is 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¶

Request:	empty payload
Response:	offset – Type: int, Unit: 1 cm, Range: [-2¹⁵ to 28767]

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¶

Request:	empty payload
Response:	error_count_ack_checksum – Type: int, Range: [0 to 2³² - 1] error_count_message_checksum – Type: int, Range: [0 to 2³² - 1] error_count_frame – Type: int, Range: [0 to 2³² - 1] error_count_overflow – Type: int, Range: [0 to 2³² - 1]

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_status_led_config¶

Request:	config – Type: int, Range: See symbols, Default: 3
Response:	no response

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
"show_heartbeat" = 2
"show_status" = 3

request/laser_range_finder_v2_bricklet/<UID>/get_status_led_config¶

Request:	empty payload
Response:	config – Type: int, Range: See symbols, Default: 3

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
"show_heartbeat" = 2
"show_status" = 3

request/laser_range_finder_v2_bricklet/<UID>/get_chip_temperature¶

Request:	empty payload
Response:	temperature – Type: int, Unit: 1 °C, Range: [-2¹⁵ to 2¹⁵ - 1]

Returns the temperature 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¶

Request:	empty payload
Response:	no response

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>/get_identity¶

Request:

empty payload

Response:

uid – Type: string, Length: up to 8
connected_uid – Type: string, Length: up to 8
position – Type: char, Range: ["a" to "h", "z"]
hardware_version – Type: [int, ...], Length: 3

0: major – Type: int, Range: [0 to 255]
1: minor – Type: int, Range: [0 to 255]
2: revision – Type: int, Range: [0 to 255]

firmware_version – Type: [int, ...], Length: 3

0: major – Type: int, Range: [0 to 255]
1: minor – Type: int, Range: [0 to 255]
2: revision – Type: int, Range: [0 to 255]

device_identifier – Type: int, Range: [0 to 2¹⁶ - 1]
_display_name – Type: 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', 'd', 'e', 'f', 'g' or 'h' (Bricklet Port). A Bricklet connected to an Isolator Bricklet is always at position 'z'.

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:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: false option – Type: char, Range: See symbols, Default: "x" min – Type: int, Unit: 1 cm, Range: [-2¹⁵ to 2¹⁵ - 1], Default: 0 max – Type: int, Unit: 1 cm, Range: [-2¹⁵ to 2¹⁵ - 1], Default: 0
Response:	no response

The period 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 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¶

Request:	empty payload
Response:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: false option – Type: char, Range: See symbols, Default: "x" min – Type: int, Unit: 1 cm, Range: [-2¹⁵ to 2¹⁵ - 1], Default: 0 max – Type: int, Unit: 1 cm, Range: [-2¹⁵ to 2¹⁵ - 1], Default: 0

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:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: false option – Type: char, Range: See symbols, Default: "x" min – Type: int, Unit: 1 cm/s, Range: [-2¹⁵ to 2¹⁵ - 1], Default: 0 max – Type: int, Unit: 1 cm/s, Range: [-2¹⁵ to 2¹⁵ - 1], Default: 0
Response:	no response

The period 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 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 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¶

Request:	empty payload
Response:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: false option – Type: char, Range: See symbols, Default: "x" min – Type: int, Unit: 1 cm/s, Range: [-2¹⁵ to 2¹⁵ - 1], Default: 0 max – Type: int, Unit: 1 cm/s, Range: [-2¹⁵ to 2¹⁵ - 1], Default: 0

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¶

Register Request:	register – Type: bool
Callback Response:	distance – Type: int, Unit: 1 cm, Range: [0 to 4000]

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¶

Register Request:	register – Type: bool
Callback Response:	velocity – Type: int, Unit: 1 cm/s, Range: [-12800 to 12700]

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.

Internal Functions¶

Internal functions are used for maintenance tasks such as flashing a new firmware of changing the UID of a Bricklet. These task should be performed using Brick Viewer instead of using the internal functions directly.

request/laser_range_finder_v2_bricklet/<UID>/set_bootloader_mode¶

Request:	mode – Type: int, Range: See symbols
Response:	status – Type: int, Range: See 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
"bootloader_wait_for_reboot" = 2
"firmware_wait_for_reboot" = 3
"firmware_wait_for_erase_and_reboot" = 4

For status:

"ok" = 0
"invalid_mode" = 1
"no_change" = 2
"entry_function_not_present" = 3
"device_identifier_incorrect" = 4
"crc_mismatch" = 5

request/laser_range_finder_v2_bricklet/<UID>/get_bootloader_mode¶

Request:	empty payload
Response:	mode – Type: int, Range: See 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
"bootloader_wait_for_reboot" = 2
"firmware_wait_for_reboot" = 3
"firmware_wait_for_erase_and_reboot" = 4

request/laser_range_finder_v2_bricklet/<UID>/set_write_firmware_pointer¶

Request:	pointer – Type: int, Unit: 1 B, Range: [0 to 2³² - 1]
Response:	no response

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:	data – Type: [int, ...], Length: 64, Range: [0 to 255]
Response:	status – Type: int, Range: [0 to 255]

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>/write_uid¶

Request:	uid – Type: int, Range: [0 to 2³² - 1]
Response:	no response

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¶

Request:	empty payload
Response:	uid – Type: int, Range: [0 to 2³² - 1]

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