Python - Hall Effect Bricklet – Tinkerforge

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# Python - Hall Effect Bricklet

This is the description of the Python API bindings for the Hall Effect Bricklet. General information and technical specifications for the Hall Effect 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 to your UID

    from tinkerforge.ip_connection import IPConnection
    from tinkerforge.bricklet_hall_effect import HallEffect

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

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

        # Get current edge count of encoder without reset
        edge_count = he.get_edge_count(False)

        print('EdgeCount: ' + str(edge_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 to your UID

    from tinkerforge.ip_connection import IPConnection
    from tinkerforge.bricklet_hall_effect import HallEffect

    # Callback function for edge count callback
    def cb_edge_count(edge_count, value):
        print('EdgeCount: ' + str(edge_count))

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

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

        # Set Period for edge_count callback to 0.05s (50ms)
        # Note: The edge_count callback is only called every 50ms if the
        #       edge_count has changed since the last call!
        he.set_edge_count_callback_period(50)

        # Register edge count callback to function cb_edge_count
        he.register_callback(he.CALLBACK_EDGE_COUNT, cb_edge_count)

        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.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

`HallEffect`(uid, ipcon)

  Parameters:

  - uid -- string
  - ipcon -- IPConnection

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

      hall_effect = HallEffect("YOUR_DEVICE_UID", ipcon)

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

`HallEffect.``get_value`()

  Return type: | bool

  Returns true if a magnetic field of 35 Gauss (3.5mT) or greater is detected.

`HallEffect.``get_edge_count`(reset_counter)

  Parameters: | reset_counter -- bool
  Return type: | int

  Returns the current value of the edge counter. You can configure edge type (rising, falling, both) that is counted with `set_edge_count_config()`.

  If you set the reset counter to true, the count is set back to 0 directly after it is read.

### Advanced Functions

`HallEffect.``set_edge_count_config`(edge_type, debounce)

  Parameters:

  - edge_type -- int
  - debounce -- int

  Return type: | None

  The edge type parameter configures if rising edges, falling edges or both are counted. Possible edge types are:

  - 0 = rising (default)
  - 1 = falling
  - 2 = both

  A magnetic field of 35 Gauss (3.5mT) or greater causes a falling edge and a magnetic field of 25 Gauss (2.5mT) or smaller causes a rising edge.

  If a magnet comes near the Bricklet the signal goes low (falling edge), if a magnet is removed from the vicinity the signal goes high (rising edge).

  The debounce time is given in ms.

  Configuring an edge counter resets its value to 0.

  If you don't know what any of this means, just leave it at default. The default configuration is very likely OK for you.

  Default values: 0 (edge type) and 100ms (debounce time)

  The following constants are available for this function:

  - HallEffect.EDGE_TYPE_RISING = 0
  - HallEffect.EDGE_TYPE_FALLING = 1
  - HallEffect.EDGE_TYPE_BOTH = 2

`HallEffect.``get_edge_count_config`()

  Return type: | (int, int)

  Returns the edge type and debounce time as set by `set_edge_count_config()`.

  The following constants are available for this function:

  - HallEffect.EDGE_TYPE_RISING = 0
  - HallEffect.EDGE_TYPE_FALLING = 1
  - HallEffect.EDGE_TYPE_BOTH = 2

  The returned namedtuple has the variables `edge_type` and `debounce`.

`HallEffect.``get_api_version`()

  Return type: | [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.

`HallEffect.``get_response_expected`(function_id)

  Parameters: | function_id -- int
  Return 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.

  See `set_response_expected()` for the list of function ID constants available for this function.

`HallEffect.``set_response_expected`(function_id, response_expected)

  Parameters:

  - function_id -- int
  - response_expected -- bool

  Return type: | 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:

  - HallEffect.FUNCTION_SET_EDGE_COUNT_CONFIG = 3
  - HallEffect.FUNCTION_SET_EDGE_INTERRUPT = 5
  - HallEffect.FUNCTION_SET_EDGE_COUNT_CALLBACK_PERIOD = 7

`HallEffect.``set_response_expected_all`(response_expected)

  Parameters: | response_expected -- bool
  Return type: | None

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

`HallEffect.``get_identity`()

  Return type: | (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 here. There is also a constant for the device identifier of this Bricklet.

  The returned namedtuple has the variables `uid`, `connected_uid`, `position`, `hardware_version`, `firmware_version` and `device_identifier`.

### Callback Configuration Functions

`HallEffect.``register_callback`(id, callback)

  Parameters:

  - id -- int
  - callback -- callable

  Return type: | None

  Registers a callback with ID id to the function callback. The available IDs with corresponding function signatures are listed below.

`HallEffect.``set_edge_interrupt`(edges)

  Parameters: | edges -- int
  Return type: | None

  Sets the number of edges until an interrupt is invoked.

  If edges is set to n, an interrupt is invoked for every n-th detected edge.

  If edges is set to 0, the interrupt is disabled.

  Default value is 0.

`HallEffect.``get_edge_interrupt`()

  Return type: | int

  Returns the edges as set by `set_edge_interrupt()`.

`HallEffect.``set_edge_count_callback_period`(period)

  Parameters: | period -- int
  Return type: | None

  Sets the period in ms with which the `CALLBACK_EDGE_COUNT` callback is triggered periodically. A value of 0 turns the callback off.

  `CALLBACK_EDGE_COUNT` is only triggered if the edge count has changed since the last triggering.

  The default value is 0.

`HallEffect.``get_edge_count_callback_period`()

  Return type: | int

  Returns the period as set by `set_edge_count_callback_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)

    hall_effect.register_callback(HallEffect.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.

`HallEffect.``CALLBACK_EDGE_COUNT`

  Parameters:

  - count -- int
  - value -- bool

  This callback is triggered periodically with the period that is set by `set_edge_count_callback_period()`. The parameters are the current count and the current value (see `get_value()` and `get_edge_count()`).

  `CALLBACK_EDGE_COUNT` is only triggered if the count or value changed since the last triggering.

### Constants

`HallEffect.``DEVICE_IDENTIFIER`

  This constant is used to identify a Hall Effect Bricklet.

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

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