Modbus - 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 Modbus protocol for the Laser Range Finder Bricklet. General information and technical specifications for the Laser Range Finder Bricklet are summarized in its hardware description.

API

A general description of the Modbus protocol structure can be found here.

Basic Functions

BrickletLaserRangeFinder.get_distance
Function ID:

1

Request:

empty payload

Response:
  • distance -- uint16

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
Function ID:

2

Request:

empty payload

Response:
  • velocity -- int16

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
Function ID:

15

Request:
  • mode -- uint8
Response:

no response

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).

BrickletLaserRangeFinder.get_mode
Function ID:

16

Request:

empty payload

Response:
  • mode -- uint8

Returns the mode as set by set_mode.

BrickletLaserRangeFinder.enable_laser
Function ID:17
Request:empty payload
Response:no response

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
Function ID:18
Request:empty payload
Response:no response

Deactivates the laser of the LIDAR.

BrickletLaserRangeFinder.is_laser_enabled
Function ID:

19

Request:

empty payload

Response:
  • laser_enabled -- bool

Returns true if the laser is enabled, false otherwise.

Advanced Functions

BrickletLaserRangeFinder.set_moving_average
Function ID:

13

Request:
  • distance_average_length -- uint8
  • velocity_average_length -- uint8
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.

The range for the averaging is 0-30.

The default value is 10.

BrickletLaserRangeFinder.get_moving_average
Function ID:

14

Request:

empty payload

Response:
  • distance_average_length -- uint8
  • velocity_average_length -- uint8

Returns the length moving average as set by set_moving_average.

BrickletLaserRangeFinder.get_identity
Function ID:

255

Request:

empty payload

Response:
  • uid -- char[8]
  • connected_uid -- char[8]
  • position -- char
  • hardware_version -- uint8[3]
  • firmware_version -- uint8[3]
  • device_identifier -- uint16

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

Callback Configuration Functions

BrickletLaserRangeFinder.set_distance_callback_period
Function ID:

3

Request:
  • period -- uint32
Response:

no response

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
Function ID:

4

Request:

empty payload

Response:
  • period -- uint32

Returns the period as set by set_distance_callback_period.

BrickletLaserRangeFinder.set_velocity_callback_period
Function ID:

5

Request:
  • period -- uint32
Response:

no response

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
Function ID:

6

Request:

empty payload

Response:
  • period -- uint32

Returns the period as set by set_velocity_callback_period.

BrickletLaserRangeFinder.set_distance_callback_threshold
Function ID:

7

Request:
  • option -- char
  • min -- uint16
  • max -- uint16
Response:

no response

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).

BrickletLaserRangeFinder.get_distance_callback_threshold
Function ID:

8

Request:

empty payload

Response:
  • option -- char
  • min -- uint16
  • max -- uint16

Returns the threshold as set by set_distance_callback_threshold.

BrickletLaserRangeFinder.set_velocity_callback_threshold
Function ID:

9

Request:
  • option -- char
  • min -- int16
  • max -- int16
Response:

no response

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).

BrickletLaserRangeFinder.get_velocity_callback_threshold
Function ID:

10

Request:

empty payload

Response:
  • option -- char
  • min -- int16
  • max -- int16

Returns the threshold as set by set_velocity_callback_threshold.

BrickletLaserRangeFinder.set_debounce_period
Function ID:

11

Request:
  • debounce -- uint32
Response:

no response

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
Function ID:

12

Request:

empty payload

Response:
  • debounce -- uint32

Returns the debounce period as set by set_debounce_period.

Callbacks

BrickletLaserRangeFinder.CALLBACK_DISTANCE
Function ID:

20

Response:
  • distance -- uint16

This callback is triggered periodically with the period that is set by set_distance_callback_period. The response value 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
Function ID:

21

Response:
  • velocity -- int16

This callback is triggered periodically with the period that is set by set_velocity_callback_period. The response value 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
Function ID:

22

Response:
  • distance -- uint16

This callback is triggered when the threshold as set by set_distance_callback_threshold is reached. The response value 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
Function ID:

23

Response:
  • velocity -- int16

This callback is triggered when the threshold as set by set_velocity_callback_threshold is reached. The response value 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.

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