MQTT - Line Bricklet

This is the description of the MQTT API bindings for the Line Bricklet. General information and technical specifications for the Line 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 Line Bricklet

setup:
    # Get current reflectivity
    subscribe to tinkerforge/response/line_bricklet/XYZ/get_reflectivity
    publish '' to tinkerforge/request/line_bricklet/XYZ/get_reflectivity

Callback

Download (example-callback.txt)

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# Change XYZ to the UID of your Line Bricklet

setup:
    # Handle incoming reflectivity callbacks
    subscribe to tinkerforge/callback/line_bricklet/XYZ/reflectivity
    publish '{"register": true}' to tinkerforge/register/line_bricklet/XYZ/reflectivity # Register reflectivity callback
    
    # Set period for reflectivity callback to 1s (1000ms)
    # Note: The reflectivity callback is only called every second
    #       if the reflectivity has changed since the last call!
    publish '{"period": 1000}' to tinkerforge/request/line_bricklet/XYZ/set_reflectivity_callback_period

Threshold

Download (example-threshold.txt)

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# Change XYZ to the UID of your Line Bricklet

setup:
    # Get threshold callbacks with a debounce time of 1 second (1000ms)
    publish '{"debounce": 1000}' to tinkerforge/request/line_bricklet/XYZ/set_debounce_period
    
    # Handle incoming reflectivity reached callbacks
    subscribe to tinkerforge/callback/line_bricklet/XYZ/reflectivity_reached
    publish '{"register": true}' to tinkerforge/register/line_bricklet/XYZ/reflectivity_reached # Register reflectivity_reached callback
    
    # Configure threshold for reflectivity "greater than 2000"
    publish '{"option": "greater", "min": 2000, "max": 0}' to tinkerforge/request/line_bricklet/XYZ/set_reflectivity_callback_threshold

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/line_bricklet/<UID>/get_reflectivity
Response payload:
 
  • reflectivity -- int

Returns the currently measured reflectivity. The reflectivity is a value between 0 (not reflective) and 4095 (very reflective).

Usually black has a low reflectivity while white has a high reflectivity.

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

Advanced Functions

request/line_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 Line's name in a human readable form.

Callback Configuration Functions

request/line_bricklet/<UID>/set_reflectivity_callback_period
Request payload:
 
  • period -- int

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

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

The default value is 0.

request/line_bricklet/<UID>/get_reflectivity_callback_period
Response payload:
 
  • period -- int

Returns the period as set by request/line_bricklet/<UID>/set_reflectivity_callback_period.

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

Sets the thresholds for the register/line_bricklet/<UID>/reflectivity_reached callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the reflectivity is outside the min and max values
'i' Callback is triggered when the reflectivity is inside the min and max values
'<' Callback is triggered when the reflectivity is smaller than the min value (max is ignored)
'>' Callback is triggered when the reflectivity 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/line_bricklet/<UID>/get_reflectivity_callback_threshold
Response payload:
 
  • option -- string (has symbols)
  • min -- int
  • max -- int

Returns the threshold as set by request/line_bricklet/<UID>/set_reflectivity_callback_threshold.

The following symbols are available for this function:

for option:

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

Sets the period in ms with which the threshold callback

is triggered, if the threshold

keeps being reached.

The default value is 100.

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

Returns the debounce period as set by request/line_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/line_bricklet/<UID>/reflectivity
Request payload:
 
  • register -- bool
Response payload:
 
  • reflectivity -- int

A callback can be registered for this event by publishing to the .../register/line_bricklet/<UID>/reflectivity[/<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/line_bricklet/<UID>/reflectivity[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/line_bricklet/<UID>/set_reflectivity_callback_period. The callback payload is the reflectivity of the sensor.

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

register/line_bricklet/<UID>/reflectivity_reached
Request payload:
 
  • register -- bool
Response payload:
 
  • reflectivity -- int

A callback can be registered for this event by publishing to the .../register/line_bricklet/<UID>/reflectivity_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/line_bricklet/<UID>/reflectivity_reached[/<SUFFIX>] topic for each registered suffix.

This callback is triggered when the threshold as set by request/line_bricklet/<UID>/set_reflectivity_callback_threshold is reached. The callback payload is the reflectivity of the sensor.

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