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:breadcrumbs: <a href="../../index.html">Home</a> / <a href="../../index.html#software-python">Software</a> / Python - Linear Poti Bricklet

.. |device_identifier_constant| replace:: There is also a :ref:`constant <linear_poti_bricklet_python_constants>` for the device identifier of this Bricklet.

.. _linear_poti_bricklet_python:

Python - Linear Poti Bricklet
=============================

This is the description of the :ref:`Python API bindings <api_bindings_python>` for the :ref:`Linear Poti Bricklet <linear_poti_bricklet>`. General information and technical
specifications for the Linear Poti Bricklet are summarized in its :ref:`hardware description
<linear_poti_bricklet_description>`.

An :ref:`installation guide <api_bindings_python_install>` for the Python API
bindings is part of their general description.

.. _linear_poti_bricklet_python_examples:


Examples
--------

The example code below is `Public Domain (CC0 1.0)
<http://creativecommons.org/publicdomain/zero/1.0/>`__.

Simple
^^^^^^

`Download (example_simple.py) <https://github.com/Tinkerforge/linear-poti-bricklet/raw/master/software/examples/python/example_simple.py>`__

.. literalinclude:: LinearPoti_Bricklet_Python_example_simple.py
 :language: python
 :linenos:
 :tab-width: 4

Callback
^^^^^^^^

`Download (example_callback.py) <https://github.com/Tinkerforge/linear-poti-bricklet/raw/master/software/examples/python/example_callback.py>`__

.. literalinclude:: LinearPoti_Bricklet_Python_example_callback.py
 :language: python
 :linenos:
 :tab-width: 4

.. _linear_poti_bricklet_python_api:

API
---

Generally, every method of the Python bindings can throw an
``tinkerforge.ip_connection.Error`` exception that has a ``value`` and a
``description`` property. ``value`` can have different values:

* Error.TIMEOUT = -1
* Error.ALREADY_CONNECTED = -7
* Error.NOT_CONNECTED = -8
* Error.INVALID_PARAMETER = -9
* Error.NOT_SUPPORTED = -10
* Error.UNKNOWN_ERROR_CODE = -11

All methods listed below are thread-safe.




Basic Functions
^^^^^^^^^^^^^^^


.. py:function:: LinearPoti(uid, ipcon)

 :param uid: string
 :param ipcon: IPConnection

 Creates an object with the unique device ID ``uid``:

 .. code-block:: python

    linear_poti = LinearPoti("YOUR_DEVICE_UID", ipcon)

 This object can then be used after the IP Connection is connected
 (see examples :ref:`above <linear_poti_bricklet_python_examples>`).


.. py:function:: LinearPoti.get_position()

 :rtype: int

 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
 callback :py:attr:`CALLBACK_POSITION <LinearPoti.CALLBACK_POSITION>` and set the period with 
 :py:func:`set_position_callback_period() <LinearPoti.set_position_callback_period>`.
 


Advanced Functions
^^^^^^^^^^^^^^^^^^

.. py:function:: LinearPoti.get_analog_value()

 :rtype: int

 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 :py:func:`get_position() <LinearPoti.get_position>` is averaged over several samples
  to yield less noise, while :py:func:`get_analog_value() <LinearPoti.get_analog_value>` gives back raw
  unfiltered analog values. The only reason to use :py:func:`get_analog_value() <LinearPoti.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 
 callback :py:attr:`CALLBACK_ANALOG_VALUE <LinearPoti.CALLBACK_ANALOG_VALUE>` and set the period with 
 :py:func:`set_analog_value_callback_period() <LinearPoti.set_analog_value_callback_period>`.
 
.. py:function:: LinearPoti.get_api_version()

 :rtype: [int, int, int]

 Returns the version of the API definition (major, minor, revision) implemented
 by this API bindings. This is neither the release version of this API bindings
 nor does it tell you anything about the represented Brick or Bricklet.
 
.. py:function:: LinearPoti.get_response_expected(function_id)

 :param function_id: int
 :rtype: bool

 Returns the response expected flag for the function specified by the function
 ID parameter. It is *true* if the function is expected to send a response,
 *false* otherwise.
 
 For getter functions this is enabled by default and cannot be disabled,
 because those functions will always send a response. For callback configuration
 functions it is enabled by default too, but can be disabled by
 :py:func:`set_response_expected() <LinearPoti.set_response_expected>`. For setter functions it is disabled by default
 and can be enabled.
 
 Enabling the response expected flag for a setter function allows to detect
 timeouts and other error conditions calls of this setter as well. The
 device will then send a response for this purpose. If this flag is disabled for
 a setter function then no response is send and errors are silently ignored,
 because they cannot be detected.
 
 See :py:func:`set_response_expected() <LinearPoti.set_response_expected>`
 for the list of function ID constants available for this function.
 
.. py:function:: LinearPoti.set_response_expected(function_id, response_expected)

 :param function_id: int
 :param response_expected: bool
 :rtype: None

 Changes the response expected flag of the function specified by the
 function ID parameter. This flag can only be changed for setter (default value:
 *false*) and callback configuration functions (default value: *true*). For
 getter functions it is always enabled and callbacks it is always disabled.
 
 Enabling the response expected flag for a setter function allows to detect
 timeouts and other error conditions calls of this setter as well. The
 device will then send a response for this purpose. If this flag is disabled for
 a setter function then no response is send and errors are silently ignored,
 because they cannot be detected.
 
 The following function ID constants are available for this function:
 
 * LinearPoti.FUNCTION_SET_POSITION_CALLBACK_PERIOD = 3
 * LinearPoti.FUNCTION_SET_ANALOG_VALUE_CALLBACK_PERIOD = 5
 * LinearPoti.FUNCTION_SET_POSITION_CALLBACK_THRESHOLD = 7
 * LinearPoti.FUNCTION_SET_ANALOG_VALUE_CALLBACK_THRESHOLD = 9
 * LinearPoti.FUNCTION_SET_DEBOUNCE_PERIOD = 11
 
.. py:function:: LinearPoti.set_response_expected_all(response_expected)

 :param response_expected: bool
 :rtype: None

 Changes the response expected flag for all setter and callback configuration
 functions of this device at once.
 
.. py:function:: LinearPoti.get_identity()

 :rtype: (str, str, chr, [int, int, int], [int, int, int], int)

 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 :ref:`here <device_identifier>`.
 |device_identifier_constant|
 
 The returned namedtuple has the variables ``uid``, ``connected_uid``, ``position``, ``hardware_version``, ``firmware_version`` and ``device_identifier``.



Callback Configuration Functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


.. py:function:: LinearPoti.register_callback(id, callback)

 :param id: int
 :param callback: callable
 :rtype: None

 Registers a callback with ID *id* to the function *callback*. The available
 IDs with corresponding function signatures are listed
 :ref:`below <linear_poti_bricklet_python_callbacks>`.


.. py:function:: LinearPoti.set_position_callback_period(period)

 :param period: int
 :rtype: None

 Sets the period in ms with which the :py:attr:`CALLBACK_POSITION <LinearPoti.CALLBACK_POSITION>` callback is triggered
 periodically. A value of 0 turns the callback off.
 
 :py:attr:`CALLBACK_POSITION <LinearPoti.CALLBACK_POSITION>` is only triggered if the position has changed since the
 last triggering.
 
 The default value is 0.
 
.. py:function:: LinearPoti.get_position_callback_period()

 :rtype: int

 Returns the period as set by :py:func:`set_position_callback_period() <LinearPoti.set_position_callback_period>`.
 
.. py:function:: LinearPoti.set_analog_value_callback_period(period)

 :param period: int
 :rtype: None

 Sets the period in ms with which the :py:attr:`CALLBACK_ANALOG_VALUE <LinearPoti.CALLBACK_ANALOG_VALUE>` callback is triggered
 periodically. A value of 0 turns the callback off.
 
 :py:attr:`CALLBACK_ANALOG_VALUE <LinearPoti.CALLBACK_ANALOG_VALUE>` is only triggered if the analog value has changed since the
 last triggering.
 
 The default value is 0.
 
.. py:function:: LinearPoti.get_analog_value_callback_period()

 :rtype: int

 Returns the period as set by :py:func:`set_analog_value_callback_period() <LinearPoti.set_analog_value_callback_period>`.
 
.. py:function:: LinearPoti.set_position_callback_threshold(option, min, max)

 :param option: chr
 :param min: int
 :param max: int
 :rtype: None

 Sets the thresholds for the :py:attr:`CALLBACK_POSITION_REACHED <LinearPoti.CALLBACK_POSITION_REACHED>` callback. 
 
 The following options are possible:
 
 .. csv-table::
  :header: "Option", "Description"
  :widths: 10, 100
 
  "'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 constants are available for this function:
 
 * LinearPoti.THRESHOLD_OPTION_OFF = 'x'
 * LinearPoti.THRESHOLD_OPTION_OUTSIDE = 'o'
 * LinearPoti.THRESHOLD_OPTION_INSIDE = 'i'
 * LinearPoti.THRESHOLD_OPTION_SMALLER = '<'
 * LinearPoti.THRESHOLD_OPTION_GREATER = '>'
 
.. py:function:: LinearPoti.get_position_callback_threshold()

 :rtype: (chr, int, int)

 Returns the threshold as set by :py:func:`set_position_callback_threshold() <LinearPoti.set_position_callback_threshold>`.
 
 The following constants are available for this function:
 
 * LinearPoti.THRESHOLD_OPTION_OFF = 'x'
 * LinearPoti.THRESHOLD_OPTION_OUTSIDE = 'o'
 * LinearPoti.THRESHOLD_OPTION_INSIDE = 'i'
 * LinearPoti.THRESHOLD_OPTION_SMALLER = '<'
 * LinearPoti.THRESHOLD_OPTION_GREATER = '>'
 
 The returned namedtuple has the variables ``option``, ``min`` and ``max``.

.. py:function:: LinearPoti.set_analog_value_callback_threshold(option, min, max)

 :param option: chr
 :param min: int
 :param max: int
 :rtype: None

 Sets the thresholds for the :py:attr:`CALLBACK_ANALOG_VALUE_REACHED <LinearPoti.CALLBACK_ANALOG_VALUE_REACHED>` callback. 
 
 The following options are possible:
 
 .. csv-table::
  :header: "Option", "Description"
  :widths: 10, 100
 
  "'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 constants are available for this function:
 
 * LinearPoti.THRESHOLD_OPTION_OFF = 'x'
 * LinearPoti.THRESHOLD_OPTION_OUTSIDE = 'o'
 * LinearPoti.THRESHOLD_OPTION_INSIDE = 'i'
 * LinearPoti.THRESHOLD_OPTION_SMALLER = '<'
 * LinearPoti.THRESHOLD_OPTION_GREATER = '>'
 
.. py:function:: LinearPoti.get_analog_value_callback_threshold()

 :rtype: (chr, int, int)

 Returns the threshold as set by :py:func:`set_analog_value_callback_threshold() <LinearPoti.set_analog_value_callback_threshold>`.
 
 The following constants are available for this function:
 
 * LinearPoti.THRESHOLD_OPTION_OFF = 'x'
 * LinearPoti.THRESHOLD_OPTION_OUTSIDE = 'o'
 * LinearPoti.THRESHOLD_OPTION_INSIDE = 'i'
 * LinearPoti.THRESHOLD_OPTION_SMALLER = '<'
 * LinearPoti.THRESHOLD_OPTION_GREATER = '>'
 
 The returned namedtuple has the variables ``option``, ``min`` and ``max``.

.. py:function:: LinearPoti.set_debounce_period(debounce)

 :param debounce: int
 :rtype: None

 Sets the period in ms with which the threshold callbacks
 
 * :py:attr:`CALLBACK_POSITION_REACHED <LinearPoti.CALLBACK_POSITION_REACHED>`,
 * :py:attr:`CALLBACK_ANALOG_VALUE_REACHED <LinearPoti.CALLBACK_ANALOG_VALUE_REACHED>`
 
 are triggered, if the thresholds
 
 * :py:func:`set_position_callback_threshold() <LinearPoti.set_position_callback_threshold>`,
 * :py:func:`set_analog_value_callback_threshold() <LinearPoti.set_analog_value_callback_threshold>`
 
 keep being reached.
 
 The default value is 100.
 
.. py:function:: LinearPoti.get_debounce_period()

 :rtype: int

 Returns the debounce period as set by :py:func:`set_debounce_period() <LinearPoti.set_debounce_period>`.
 


.. _linear_poti_bricklet_python_callbacks:

Callbacks
^^^^^^^^^

Callbacks can be registered to receive
time critical or recurring data from the device. The registration is done
with the :py:func:`register_callback() <LinearPoti.register_callback>` function of
the device object. The first parameter is the callback ID and the second
parameter the callback function:

.. code-block:: python

    def my_callback(param):
        print(param)

    linear_poti.register_callback(LinearPoti.CALLBACK_EXAMPLE, my_callback)

The available constants with inherent number and type of parameters are
described below.

.. 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.

.. py:attribute:: LinearPoti.CALLBACK_POSITION

 :param position: int


 This callback is triggered periodically with the period that is set by
 :py:func:`set_position_callback_period() <LinearPoti.set_position_callback_period>`. The parameter is the position of the
 Linear Potentiometer.
 
 :py:attr:`CALLBACK_POSITION <LinearPoti.CALLBACK_POSITION>` is only triggered if the position has changed since the
 last triggering.
 
.. py:attribute:: LinearPoti.CALLBACK_ANALOG_VALUE

 :param value: int


 This callback is triggered periodically with the period that is set by
 :py:func:`set_analog_value_callback_period() <LinearPoti.set_analog_value_callback_period>`. The parameter is the analog value of the
 Linear Potentiometer.
 
 :py:attr:`CALLBACK_ANALOG_VALUE <LinearPoti.CALLBACK_ANALOG_VALUE>` is only triggered if the position has changed since the
 last triggering.
 
.. py:attribute:: LinearPoti.CALLBACK_POSITION_REACHED

 :param position: int


 This callback is triggered when the threshold as set by
 :py:func:`set_position_callback_threshold() <LinearPoti.set_position_callback_threshold>` is reached.
 The parameter is the position of the Linear Potentiometer.
 
 If the threshold keeps being reached, the callback is triggered periodically
 with the period as set by :py:func:`set_debounce_period() <LinearPoti.set_debounce_period>`.
 
.. py:attribute:: LinearPoti.CALLBACK_ANALOG_VALUE_REACHED

 :param value: int


 This callback is triggered when the threshold as set by
 :py:func:`set_analog_value_callback_threshold() <LinearPoti.set_analog_value_callback_threshold>` is reached.
 The parameter 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 :py:func:`set_debounce_period() <LinearPoti.set_debounce_period>`.
 


.. _linear_poti_bricklet_python_constants:

Constants
^^^^^^^^^

.. py:attribute:: LinearPoti.DEVICE_IDENTIFIER

 This constant is used to identify a Linear Poti Bricklet.

 The :py:func:`get_identity() <LinearPoti.get_identity>` function and the
 :py:attr:`CALLBACK_ENUMERATE <IPConnection.CALLBACK_ENUMERATE>`
 callback of the IP Connection have a ``device_identifier`` parameter to specify
 the Brick's or Bricklet's type.

