Python - Rotary Encoder Bricklet

This is the description of the Python API bindings for the Rotary Encoder Bricklet. General information and technical specifications for the Rotary Encoder Bricklet are summarized in its hardware description.

An installation guide for the Python API bindings is part of their general description.

Examples

The example code below is Public Domain (CC0 1.0).

Simple

Download (example_simple.py)

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#!/usr/bin/env python
# -*- coding: utf-8 -*-

HOST = "localhost"
PORT = 4223
UID = "XYZ" # Change XYZ to the UID of your Rotary Encoder Bricklet

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_rotary_encoder import BrickletRotaryEncoder

if __name__ == "__main__":
    ipcon = IPConnection() # Create IP connection
    re = BrickletRotaryEncoder(UID, ipcon) # Create device object

    ipcon.connect(HOST, PORT) # Connect to brickd
    # Don't use device before ipcon is connected

    # Get current count without reset
    count = re.get_count(False)
    print("Count: " + str(count))

    raw_input("Press key to exit\n") # Use input() in Python 3
    ipcon.disconnect()

Callback

Download (example_callback.py)

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#!/usr/bin/env python
# -*- coding: utf-8 -*-

HOST = "localhost"
PORT = 4223
UID = "XYZ" # Change XYZ to the UID of your Rotary Encoder Bricklet

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_rotary_encoder import BrickletRotaryEncoder

# Callback function for count callback
def cb_count(count):
    print("Count: " + str(count))

if __name__ == "__main__":
    ipcon = IPConnection() # Create IP connection
    re = BrickletRotaryEncoder(UID, ipcon) # Create device object

    ipcon.connect(HOST, PORT) # Connect to brickd
    # Don't use device before ipcon is connected

    # Register count callback to function cb_count
    re.register_callback(re.CALLBACK_COUNT, cb_count)

    # Set period for count callback to 0.05s (50ms)
    # Note: The count callback is only called every 0.05 seconds
    #       if the count has changed since the last call!
    re.set_count_callback_period(50)

    raw_input("Press key to exit\n") # Use input() in Python 3
    ipcon.disconnect()

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.NOT_ADDED = -6 (unused since Python bindings version 2.0.0)
  • Error.ALREADY_CONNECTED = -7
  • Error.NOT_CONNECTED = -8
  • Error.INVALID_PARAMETER = -9
  • Error.NOT_SUPPORTED = -10
  • Error.UNKNOWN_ERROR_CODE = -11
  • Error.STREAM_OUT_OF_SYNC = -12
  • Error.INVALID_UID = -13
  • Error.NON_ASCII_CHAR_IN_SECRET = -14

All methods listed below are thread-safe.

Basic Functions

BrickletRotaryEncoder(uid, ipcon)
Parameters:
  • uid – Type: str
  • ipcon – Type: IPConnection
Returns:
  • rotary_encoder – Type: BrickletRotaryEncoder

Creates an object with the unique device ID uid:

rotary_encoder = BrickletRotaryEncoder("YOUR_DEVICE_UID", ipcon)

This object can then be used after the IP Connection is connected (see examples above).

BrickletRotaryEncoder.get_count(reset)
Parameters:
  • reset – Type: bool
Returns:
  • count – Type: int, Range: [-231 to 231 - 1]

Returns the current count of the encoder. If you set reset to true, the count is set back to 0 directly after the current count is read.

The encoder has 24 steps per rotation

Turning the encoder to the left decrements the counter, so a negative count is possible.

BrickletRotaryEncoder.is_pressed()
Returns:
  • pressed – Type: bool

Returns true if the button is pressed and false otherwise.

It is recommended to use the CALLBACK_PRESSED and CALLBACK_RELEASED callbacks to handle the button.

Advanced Functions

BrickletRotaryEncoder.get_api_version()
Returns:
  • api_version – Type: [int, ...], Length: 3, Range: [0 to 255]

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.

BrickletRotaryEncoder.get_response_expected(function_id)
Parameters:
  • function_id – Type: int, Range: See constants
Returns:
  • response_expected – Type: 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 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.

The following constants are available for this function:

For function_id:

  • BrickletRotaryEncoder.FUNCTION_SET_COUNT_CALLBACK_PERIOD = 2
  • BrickletRotaryEncoder.FUNCTION_SET_COUNT_CALLBACK_THRESHOLD = 4
  • BrickletRotaryEncoder.FUNCTION_SET_DEBOUNCE_PERIOD = 6
BrickletRotaryEncoder.set_response_expected(function_id, response_expected)
Parameters:
  • function_id – Type: int, Range: See constants
  • response_expected – Type: bool
Returns:
  • 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.

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 constants are available for this function:

For function_id:

  • BrickletRotaryEncoder.FUNCTION_SET_COUNT_CALLBACK_PERIOD = 2
  • BrickletRotaryEncoder.FUNCTION_SET_COUNT_CALLBACK_THRESHOLD = 4
  • BrickletRotaryEncoder.FUNCTION_SET_DEBOUNCE_PERIOD = 6
BrickletRotaryEncoder.set_response_expected_all(response_expected)
Parameters:
  • response_expected – Type: bool
Returns:
  • None

Changes the response expected flag for all setter and callback configuration functions of this device at once.

BrickletRotaryEncoder.get_identity()
Return Object:
  • uid – Type: str, Length: up to 8
  • connected_uid – Type: str, Length: up to 8
  • position – Type: chr
  • 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]

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. There is also a constant for the device identifier of this Bricklet.

Callback Configuration Functions

BrickletRotaryEncoder.register_callback(callback_id, function)
Parameters:
  • callback_id – Type: int
  • function – Type: callable
Returns:
  • None

Registers the given function with the given callback_id.

The available callback IDs with corresponding function signatures are listed below.

BrickletRotaryEncoder.set_count_callback_period(period)
Parameters:
  • period – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
Returns:
  • None

Sets the period with which the CALLBACK_COUNT callback is triggered periodically. A value of 0 turns the callback off.

The CALLBACK_COUNT callback is only triggered if the count has changed since the last triggering.

BrickletRotaryEncoder.get_count_callback_period()
Returns:
  • period – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0

Returns the period as set by set_count_callback_period().

BrickletRotaryEncoder.set_count_callback_threshold(option, min, max)
Parameters:
  • option – Type: chr, Range: See constants, Default: "x"
  • min – Type: int, Range: [-231 to 231 - 1]
  • max – Type: int, Range: [-231 to 231 - 1]
Returns:
  • None

Sets the thresholds for the CALLBACK_COUNT_REACHED callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the count is outside the min and max values
'i' Callback is triggered when the count is inside the min and max values
'<' Callback is triggered when the count is smaller than the min value (max is ignored)
'>' Callback is triggered when the count is greater than the min value (max is ignored)

The default value is ('x', 0, 0).

The following constants are available for this function:

For option:

  • BrickletRotaryEncoder.THRESHOLD_OPTION_OFF = "x"
  • BrickletRotaryEncoder.THRESHOLD_OPTION_OUTSIDE = "o"
  • BrickletRotaryEncoder.THRESHOLD_OPTION_INSIDE = "i"
  • BrickletRotaryEncoder.THRESHOLD_OPTION_SMALLER = "<"
  • BrickletRotaryEncoder.THRESHOLD_OPTION_GREATER = ">"
BrickletRotaryEncoder.get_count_callback_threshold()
Return Object:
  • option – Type: chr, Range: See constants, Default: "x"
  • min – Type: int, Range: [-231 to 231 - 1]
  • max – Type: int, Range: [-231 to 231 - 1]

Returns the threshold as set by set_count_callback_threshold().

The following constants are available for this function:

For option:

  • BrickletRotaryEncoder.THRESHOLD_OPTION_OFF = "x"
  • BrickletRotaryEncoder.THRESHOLD_OPTION_OUTSIDE = "o"
  • BrickletRotaryEncoder.THRESHOLD_OPTION_INSIDE = "i"
  • BrickletRotaryEncoder.THRESHOLD_OPTION_SMALLER = "<"
  • BrickletRotaryEncoder.THRESHOLD_OPTION_GREATER = ">"
BrickletRotaryEncoder.set_debounce_period(debounce)
Parameters:
  • debounce – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 100
Returns:
  • None

Sets the period with which the threshold callback

is triggered, if the thresholds

keeps being reached.

BrickletRotaryEncoder.get_debounce_period()
Returns:
  • debounce – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 100

Returns the debounce period as set by set_debounce_period().

Callbacks

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

def my_callback(param):
    print(param)

rotary_encoder.register_callback(BrickletRotaryEncoder.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.

BrickletRotaryEncoder.CALLBACK_COUNT
Callback Parameters:
  • count – Type: int, Range: [-231 to 231 - 1]

This callback is triggered periodically with the period that is set by set_count_callback_period(). The parameter is the count of the encoder.

The CALLBACK_COUNT callback is only triggered if the count has changed since the last triggering.

BrickletRotaryEncoder.CALLBACK_COUNT_REACHED
Callback Parameters:
  • count – Type: int, Range: [-231 to 231 - 1]

This callback is triggered when the threshold as set by set_count_callback_threshold() is reached. The parameter is the count of the encoder.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by set_debounce_period().

BrickletRotaryEncoder.CALLBACK_PRESSED
Callback Parameters:
  • no parameters

This callback is triggered when the button is pressed.

BrickletRotaryEncoder.CALLBACK_RELEASED
Callback Parameters:
  • no parameters

This callback is triggered when the button is released.

Constants

BrickletRotaryEncoder.DEVICE_IDENTIFIER

This constant is used to identify a Rotary Encoder Bricklet.

The get_identity() function and the IPConnection.CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.

BrickletRotaryEncoder.DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Rotary Encoder Bricklet.