MQTT - Linear Poti Bricklet

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

setup:
    # Get current position
    subscribe to tinkerforge/response/linear_poti_bricklet/XYZ/get_position
    publish '' to tinkerforge/request/linear_poti_bricklet/XYZ/get_position

Callback

Download (example-callback.txt)

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# Change XYZ to the UID of your Linear Poti Bricklet

setup:
    # Handle incoming position callbacks
    subscribe to tinkerforge/callback/linear_poti_bricklet/XYZ/position
    publish '{"register": true}' to tinkerforge/register/linear_poti_bricklet/XYZ/position # Register position callback
    
    # Set period for position callback to 0.05s (50ms)
    # Note: The position callback is only called every 0.05 seconds
    #       if the position has changed since the last call!
    publish '{"period": 50}' to tinkerforge/request/linear_poti_bricklet/XYZ/set_position_callback_period

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/linear_poti_bricklet/<UID>/get_position
Request:
  • empty payload
Response:
  • position – Type: int, Range: [0 to 216 - 1]

Returns the position of the linear potentiometer. The value is between 0 (slider down) and 100 (slider up).

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

Advanced Functions

request/linear_poti_bricklet/<UID>/get_analog_value
Request:
  • empty payload
Response:
  • value – Type: int, Range: [0 to 216 - 1]

Returns the value as read by a 12-bit analog-to-digital converter. The value is between 0 and 4095.

Note

The value returned by request/linear_poti_bricklet/<UID>/get_position is averaged over several samples to yield less noise, while request/linear_poti_bricklet/<UID>/get_analog_value gives back raw unfiltered analog values. The only reason to use request/linear_poti_bricklet/<UID>/get_analog_value is, if you need the full resolution of the analog-to-digital converter.

If you want the analog value periodically, it is recommended to use the register/linear_poti_bricklet/<UID>/analog_value callback and set the period with request/linear_poti_bricklet/<UID>/set_analog_value_callback_period.

request/linear_poti_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
  • hardware_version – Type: [int, ...], Length: 3, Range: [0 to 255]
  • firmware_version – Type: [int, ...], Length: 3, 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' 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 Linear Poti's name in a human readable form.

Callback Configuration Functions

request/linear_poti_bricklet/<UID>/set_position_callback_period
Request:
  • period – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
Response:
  • no response

Sets the period with which the register/linear_poti_bricklet/<UID>/position callback is triggered periodically. A value of 0 turns the callback off.

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

request/linear_poti_bricklet/<UID>/get_position_callback_period
Request:
  • empty payload
Response:
  • period – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0

Returns the period as set by request/linear_poti_bricklet/<UID>/set_position_callback_period.

request/linear_poti_bricklet/<UID>/set_analog_value_callback_period
Request:
  • period – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
Response:
  • no response

Sets the period with which the register/linear_poti_bricklet/<UID>/analog_value callback is triggered periodically. A value of 0 turns the callback off.

The register/linear_poti_bricklet/<UID>/analog_value callback is only triggered if the analog value has changed since the last triggering.

request/linear_poti_bricklet/<UID>/get_analog_value_callback_period
Request:
  • empty payload
Response:
  • period – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0

Returns the period as set by request/linear_poti_bricklet/<UID>/set_analog_value_callback_period.

request/linear_poti_bricklet/<UID>/set_position_callback_threshold
Request:
  • option – Type: char, Range: See symbols, Default: "x"
  • min – Type: int, Range: [0 to 216 - 1]
  • max – Type: int, Range: [0 to 216 - 1]
Response:
  • no response

Sets the thresholds for the register/linear_poti_bricklet/<UID>/position_reached callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the position is outside the min and max values
'i' Callback is triggered when the position is inside the min and max values
'<' Callback is triggered when the position is smaller than the min value (max is ignored)
'>' Callback is triggered when the position 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/linear_poti_bricklet/<UID>/get_position_callback_threshold
Request:
  • empty payload
Response:
  • option – Type: char, Range: See symbols, Default: "x"
  • min – Type: int, Range: [0 to 216 - 1]
  • max – Type: int, Range: [0 to 216 - 1]

Returns the threshold as set by request/linear_poti_bricklet/<UID>/set_position_callback_threshold.

The following symbols are available for this function:

For option:

  • "Off" = "x"
  • "Outside" = "o"
  • "Inside" = "i"
  • "Smaller" = "<"
  • "Greater" = ">"
request/linear_poti_bricklet/<UID>/set_analog_value_callback_threshold
Request:
  • option – Type: char, Range: See symbols, Default: "x"
  • min – Type: int, Range: [0 to 216 - 1]
  • max – Type: int, Range: [0 to 216 - 1]
Response:
  • no response

Sets the thresholds for the register/linear_poti_bricklet/<UID>/analog_value_reached callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the analog value is outside the min and max values
'i' Callback is triggered when the analog value is inside the min and max values
'<' Callback is triggered when the analog value is smaller than the min value (max is ignored)
'>' Callback is triggered when the analog 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/linear_poti_bricklet/<UID>/get_analog_value_callback_threshold
Request:
  • empty payload
Response:
  • option – Type: char, Range: See symbols, Default: "x"
  • min – Type: int, Range: [0 to 216 - 1]
  • max – Type: int, Range: [0 to 216 - 1]

Returns the threshold as set by request/linear_poti_bricklet/<UID>/set_analog_value_callback_threshold.

The following symbols are available for this function:

For option:

  • "Off" = "x"
  • "Outside" = "o"
  • "Inside" = "i"
  • "Smaller" = "<"
  • "Greater" = ">"
request/linear_poti_bricklet/<UID>/set_debounce_period
Request:
  • debounce – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 100
Response:
  • no response

Sets the period with which the threshold callbacks

are triggered, if the thresholds

keep being reached.

request/linear_poti_bricklet/<UID>/get_debounce_period
Request:
  • empty payload
Response:
  • debounce – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 100

Returns the debounce period as set by request/linear_poti_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/linear_poti_bricklet/<UID>/position
Register Request:
  • register – Type: bool
Callback Response:
  • position – Type: int, Range: [0 to 216 - 1]

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

This callback is triggered periodically with the period that is set by request/linear_poti_bricklet/<UID>/set_position_callback_period. The callback payload is the position of the linear potentiometer.

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

register/linear_poti_bricklet/<UID>/analog_value
Register Request:
  • register – Type: bool
Callback Response:
  • value – Type: int, Range: [0 to 216 - 1]

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

This callback is triggered periodically with the period that is set by request/linear_poti_bricklet/<UID>/set_analog_value_callback_period. The callback payload is the analog value of the Linear Potentiometer.

The register/linear_poti_bricklet/<UID>/analog_value callback is only triggered if the position has changed since the last triggering.

register/linear_poti_bricklet/<UID>/position_reached
Register Request:
  • register – Type: bool
Callback Response:
  • position – Type: int, Range: [0 to 216 - 1]

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

This callback is triggered when the threshold as set by request/linear_poti_bricklet/<UID>/set_position_callback_threshold is reached. The callback payload is the position of the linear potentiometer.

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

register/linear_poti_bricklet/<UID>/analog_value_reached
Register Request:
  • register – Type: bool
Callback Response:
  • value – Type: int, Range: [0 to 216 - 1]

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

This callback is triggered when the threshold as set by request/linear_poti_bricklet/<UID>/set_analog_value_callback_threshold is reached. The callback payload is the analog value of the linear potentiometer.

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