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 XYZ to the UID of your Hall Effect Bricklet

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_hall_effect import BrickletHallEffect

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

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

    # Get current edge count without reset
    count = he.get_edge_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 Hall Effect Bricklet

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_hall_effect import BrickletHallEffect

# Callback function for edge count callback
def cb_edge_count(count, value):
    print("Count: " + str(count))

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

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

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

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

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

API

Generally, every function 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 functions listed below are thread-safe.

Basic Functions

BrickletHallEffect(uid, ipcon)
Parameters:
  • uid – Type: str
  • ipcon – Type: IPConnection
Returns:
  • hall_effect – Type: BrickletHallEffect

Creates an object with the unique device ID uid:

hall_effect = BrickletHallEffect("YOUR_DEVICE_UID", ipcon)

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

BrickletHallEffect.get_value()
Returns:
  • value – Type: bool

Returns true if a magnetic field of 3.5 millitesla or greater is detected.

BrickletHallEffect.get_edge_count(reset_counter)
Parameters:
  • reset_counter – Type: bool
Returns:
  • count – Type: int, Range: [0 to 232 - 1]

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

BrickletHallEffect.set_edge_count_config(edge_type, debounce)
Parameters:
  • edge_type – Type: int, Range: See constants, Default: 0
  • debounce – Type: int, Unit: 1 ms, Range: [0 to 255], Default: 100
Returns:
  • None

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

  • 0 = rising
  • 1 = falling
  • 2 = both

A magnetic field of 3.5 millitesla or greater causes a falling edge and a magnetic field of 2.5 millitesla 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).

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.

The following constants are available for this function:

For edge_type:

  • BrickletHallEffect.EDGE_TYPE_RISING = 0
  • BrickletHallEffect.EDGE_TYPE_FALLING = 1
  • BrickletHallEffect.EDGE_TYPE_BOTH = 2
BrickletHallEffect.get_edge_count_config()
Return Object:
  • edge_type – Type: int, Range: See constants, Default: 0
  • debounce – Type: int, Unit: 1 ms, Range: [0 to 255], Default: 100

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

The following constants are available for this function:

For edge_type:

  • BrickletHallEffect.EDGE_TYPE_RISING = 0
  • BrickletHallEffect.EDGE_TYPE_FALLING = 1
  • BrickletHallEffect.EDGE_TYPE_BOTH = 2
BrickletHallEffect.get_identity()
Return Object:
  • uid – Type: str, Length: up to 8
  • connected_uid – Type: str, Length: up to 8
  • position – Type: chr, Range: ["a" to "h", "i", "z"]
  • hardware_version – Type: [int, ...], Length: 3
    • 0: major – Type: int, Range: [0 to 255]
    • 1: minor – Type: int, Range: [0 to 255]
    • 2: revision – Type: int, Range: [0 to 255]
  • firmware_version – Type: [int, ...], Length: 3
    • 0: major – Type: int, Range: [0 to 255]
    • 1: minor – Type: int, Range: [0 to 255]
    • 2: revision – Type: int, 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', 'd', 'e', 'f', 'g' or 'h' (Bricklet Port). The Raspberry Pi HAT (Zero) Brick is always at position 'i' and the Bricklet connected to an Isolator Bricklet is always as position 'z'.

The device identifier numbers can be found here. There is also a constant for the device identifier of this Bricklet.

Callback Configuration Functions

BrickletHallEffect.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.

BrickletHallEffect.set_edge_interrupt(edges)
Parameters:
  • edges – Type: int, Range: [0 to 232 - 1], Default: 0
Returns:
  • 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.

BrickletHallEffect.get_edge_interrupt()
Returns:
  • edges – Type: int, Range: [0 to 232 - 1], Default: 0

Returns the edges as set by set_edge_interrupt().

BrickletHallEffect.set_edge_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_EDGE_COUNT callback is triggered periodically. A value of 0 turns the callback off.

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

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

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(BrickletHallEffect.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.

BrickletHallEffect.CALLBACK_EDGE_COUNT
Callback Parameters:
  • count – Type: int, Range: [0 to 232 - 1]
  • value – Type: 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()).

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

Virtual Functions

Virtual functions don't communicate with the device itself, but operate only on the API bindings device object. They can be called without the corresponding IP Connection object being connected.

BrickletHallEffect.get_api_version()
Return Object:
  • api_version – Type: [int, ...], Length: 3
    • 0: major – Type: int, Range: [0 to 255]
    • 1: minor – Type: int, Range: [0 to 255]
    • 2: revision – Type: int, Range: [0 to 255]

Returns the version of the API definition 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.

BrickletHallEffect.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:

  • BrickletHallEffect.FUNCTION_SET_EDGE_COUNT_CONFIG = 3
  • BrickletHallEffect.FUNCTION_SET_EDGE_INTERRUPT = 5
  • BrickletHallEffect.FUNCTION_SET_EDGE_COUNT_CALLBACK_PERIOD = 7
BrickletHallEffect.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:

  • BrickletHallEffect.FUNCTION_SET_EDGE_COUNT_CONFIG = 3
  • BrickletHallEffect.FUNCTION_SET_EDGE_INTERRUPT = 5
  • BrickletHallEffect.FUNCTION_SET_EDGE_COUNT_CALLBACK_PERIOD = 7
BrickletHallEffect.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.

Constants

BrickletHallEffect.DEVICE_IDENTIFIER

This constant is used to identify a Hall Effect 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.

BrickletHallEffect.DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Hall Effect Bricklet.