Python - Compass Bricklet

This is the description of the Python API bindings for the Compass Bricklet. General information and technical specifications for the Compass 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 Compass Bricklet

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_compass import BrickletCompass

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

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

    # Get current heading
    heading = c.get_heading()
    print("Heading: " + str(heading/10.0) + " °")

    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 Compass Bricklet

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_compass import BrickletCompass

# Callback function for heading callback
def cb_heading(heading):
    print("Heading: " + str(heading/10.0) + " °")

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

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

    # Register heading callback to function cb_heading
    c.register_callback(c.CALLBACK_HEADING, cb_heading)

    # Set period for heading callback to 0.1s (100ms) without a threshold
    c.set_heading_callback_configuration(100, False, "x", 0, 0)

    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

BrickletCompass(uid, ipcon)
Parameters:
  • uid -- string
  • ipcon -- IPConnection

Creates an object with the unique device ID uid:

compass = BrickletCompass("YOUR_DEVICE_UID", ipcon)

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

BrickletCompass.get_heading()
Return type:int

Returns the heading in 1/10 degree (north = 0 degree, east = 90 degree).

Alternatively you can use get_magnetic_flux_density() and calculate the heading with heading = atan2(y, x) * 180 / PI.

If you want to get the value periodically, it is recommended to use the CALLBACK_HEADING callback. You can set the callback configuration with set_heading_callback_configuration().

BrickletCompass.get_magnetic_flux_density()
Return type:(int, int, int)

Returns the magnetic flux density (magnetic induction) for all three axis in 1/10 mG (milli Gauss).

If you want to get the value periodically, it is recommended to use the CALLBACK_MAGNETIC_FLUX_DENSITY callback. You can set the callback configuration with set_magnetic_flux_density_callback_configuration().

The returned namedtuple has the variables x, y and z.

BrickletCompass.set_configuration(data_rate, background_calibration)
Parameters:
  • data_rate -- int
  • background_calibration -- bool
Return type:

None

Configures the data rate and background calibration.

  • Data Rate: Sets the data rate that is used by the magnetometer. The lower the data rate, the lower is the noise on the data.
  • Background Calibration: Set to true to enable the background calibration and false to turn it off. If the background calibration is enabled the sensing polarity is flipped once per second to automatically calculate and remove offset that is caused by temperature changes. This polarity flipping takes about 20ms. This means that once a second you will not get new data for a period of 20ms. We highly recommend that you keep the background calibration enabled and only disable it if the 20ms off-time is a problem in your application.

Default values: Data rate of 100Hz and background calibration enabled.

The following constants are available for this function:

  • BrickletCompass.DATA_RATE_100HZ = 0
  • BrickletCompass.DATA_RATE_200HZ = 1
  • BrickletCompass.DATA_RATE_400HZ = 2
  • BrickletCompass.DATA_RATE_600HZ = 3
BrickletCompass.get_configuration()
Return type:(int, bool)

Returns the configuration as set by set_configuration().

The following constants are available for this function:

  • BrickletCompass.DATA_RATE_100HZ = 0
  • BrickletCompass.DATA_RATE_200HZ = 1
  • BrickletCompass.DATA_RATE_400HZ = 2
  • BrickletCompass.DATA_RATE_600HZ = 3

The returned namedtuple has the variables data_rate and background_calibration.

Advanced Functions

BrickletCompass.set_calibration(offset, gain)
Parameters:
  • offset -- [int, int, int]
  • gain -- [int, int, int]
Return type:

None

Sets offset and gain for each of the three axes.

The Bricklet is factory calibrated. If you want to re-calibrate the Bricklet we recommend that you do the calibration through Brick Viewer.

The calibration is saved in non-volatile memory and only has to be done once.

BrickletCompass.get_calibration()
Return type:([int, int, int], [int, int, int])

Returns the calibration parameters as set by set_calibration().

The returned namedtuple has the variables offset and gain.

BrickletCompass.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.

BrickletCompass.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.

The following constants are available for this function:

  • BrickletCompass.FUNCTION_SET_HEADING_CALLBACK_CONFIGURATION = 2
  • BrickletCompass.FUNCTION_SET_MAGNETIC_FLUX_DENSITY_CALLBACK_CONFIGURATION = 6
  • BrickletCompass.FUNCTION_SET_CONFIGURATION = 9
  • BrickletCompass.FUNCTION_SET_CALIBRATION = 11
  • BrickletCompass.FUNCTION_SET_WRITE_FIRMWARE_POINTER = 237
  • BrickletCompass.FUNCTION_SET_STATUS_LED_CONFIG = 239
  • BrickletCompass.FUNCTION_RESET = 243
  • BrickletCompass.FUNCTION_WRITE_UID = 248
BrickletCompass.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.

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:

  • BrickletCompass.FUNCTION_SET_HEADING_CALLBACK_CONFIGURATION = 2
  • BrickletCompass.FUNCTION_SET_MAGNETIC_FLUX_DENSITY_CALLBACK_CONFIGURATION = 6
  • BrickletCompass.FUNCTION_SET_CONFIGURATION = 9
  • BrickletCompass.FUNCTION_SET_CALIBRATION = 11
  • BrickletCompass.FUNCTION_SET_WRITE_FIRMWARE_POINTER = 237
  • BrickletCompass.FUNCTION_SET_STATUS_LED_CONFIG = 239
  • BrickletCompass.FUNCTION_RESET = 243
  • BrickletCompass.FUNCTION_WRITE_UID = 248
BrickletCompass.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.

BrickletCompass.get_spitfp_error_count()
Return type:(int, int, int, int)

Returns the error count for the communication between Brick and Bricklet.

The errors are divided into

  • ACK checksum errors,
  • message checksum errors,
  • framing errors and
  • overflow errors.

The errors counts are for errors that occur on the Bricklet side. All Bricks have a similar function that returns the errors on the Brick side.

The returned namedtuple has the variables error_count_ack_checksum, error_count_message_checksum, error_count_frame and error_count_overflow.

BrickletCompass.set_bootloader_mode(mode)
Parameters:mode -- int
Return type:int

Sets the bootloader mode and returns the status after the requested mode change was instigated.

You can change from bootloader mode to firmware mode and vice versa. A change from bootloader mode to firmware mode will only take place if the entry function, device identifier and CRC are present and correct.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

The following constants are available for this function:

  • BrickletCompass.BOOTLOADER_MODE_BOOTLOADER = 0
  • BrickletCompass.BOOTLOADER_MODE_FIRMWARE = 1
  • BrickletCompass.BOOTLOADER_MODE_BOOTLOADER_WAIT_FOR_REBOOT = 2
  • BrickletCompass.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_REBOOT = 3
  • BrickletCompass.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_ERASE_AND_REBOOT = 4
  • BrickletCompass.BOOTLOADER_STATUS_OK = 0
  • BrickletCompass.BOOTLOADER_STATUS_INVALID_MODE = 1
  • BrickletCompass.BOOTLOADER_STATUS_NO_CHANGE = 2
  • BrickletCompass.BOOTLOADER_STATUS_ENTRY_FUNCTION_NOT_PRESENT = 3
  • BrickletCompass.BOOTLOADER_STATUS_DEVICE_IDENTIFIER_INCORRECT = 4
  • BrickletCompass.BOOTLOADER_STATUS_CRC_MISMATCH = 5
BrickletCompass.get_bootloader_mode()
Return type:int

Returns the current bootloader mode, see set_bootloader_mode().

The following constants are available for this function:

  • BrickletCompass.BOOTLOADER_MODE_BOOTLOADER = 0
  • BrickletCompass.BOOTLOADER_MODE_FIRMWARE = 1
  • BrickletCompass.BOOTLOADER_MODE_BOOTLOADER_WAIT_FOR_REBOOT = 2
  • BrickletCompass.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_REBOOT = 3
  • BrickletCompass.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_ERASE_AND_REBOOT = 4
BrickletCompass.set_write_firmware_pointer(pointer)
Parameters:pointer -- int
Return type:None

Sets the firmware pointer for write_firmware(). The pointer has to be increased by chunks of size 64. The data is written to flash every 4 chunks (which equals to one page of size 256).

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

BrickletCompass.write_firmware(data)
Parameters:data -- [int, int, ..61x.., int]
Return type:int

Writes 64 Bytes of firmware at the position as written by set_write_firmware_pointer() before. The firmware is written to flash every 4 chunks.

You can only write firmware in bootloader mode.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

BrickletCompass.set_status_led_config(config)
Parameters:config -- int
Return type:None

Sets the status LED configuration. By default the LED shows communication traffic between Brick and Bricklet, it flickers once for every 10 received data packets.

You can also turn the LED permanently on/off or show a heartbeat.

If the Bricklet is in bootloader mode, the LED is will show heartbeat by default.

The following constants are available for this function:

  • BrickletCompass.STATUS_LED_CONFIG_OFF = 0
  • BrickletCompass.STATUS_LED_CONFIG_ON = 1
  • BrickletCompass.STATUS_LED_CONFIG_SHOW_HEARTBEAT = 2
  • BrickletCompass.STATUS_LED_CONFIG_SHOW_STATUS = 3
BrickletCompass.get_status_led_config()
Return type:int

Returns the configuration as set by set_status_led_config()

The following constants are available for this function:

  • BrickletCompass.STATUS_LED_CONFIG_OFF = 0
  • BrickletCompass.STATUS_LED_CONFIG_ON = 1
  • BrickletCompass.STATUS_LED_CONFIG_SHOW_HEARTBEAT = 2
  • BrickletCompass.STATUS_LED_CONFIG_SHOW_STATUS = 3
BrickletCompass.get_chip_temperature()
Return type:int

Returns the temperature in °C as measured inside the microcontroller. The value returned is not the ambient temperature!

The temperature is only proportional to the real temperature and it has bad accuracy. Practically it is only useful as an indicator for temperature changes.

BrickletCompass.reset()
Return type:None

Calling this function will reset the Bricklet. All configurations will be lost.

After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

BrickletCompass.write_uid(uid)
Parameters:uid -- int
Return type:None

Writes a new UID into flash. If you want to set a new UID you have to decode the Base58 encoded UID string into an integer first.

We recommend that you use Brick Viewer to change the UID.

BrickletCompass.read_uid()
Return type:int

Returns the current UID as an integer. Encode as Base58 to get the usual string version.

BrickletCompass.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

BrickletCompass.register_callback(callback_id, function)
Parameters:
  • callback_id -- int
  • function -- callable
Return type:

None

Registers the given function with the given callback_id.

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

BrickletCompass.set_heading_callback_configuration(period, value_has_to_change, option, min, max)
Parameters:
  • period -- int
  • value_has_to_change -- bool
  • option -- chr
  • min -- int
  • max -- int
Return type:

None

The period in ms is the period with which the CALLBACK_HEADING callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

It is furthermore possible to constrain the callback with thresholds.

The option-parameter together with min/max sets a threshold for the CALLBACK_HEADING callback.

The following options are possible:

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

If the option is set to 'x' (threshold turned off) the callback is triggered with the fixed period.

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

The following constants are available for this function:

  • BrickletCompass.THRESHOLD_OPTION_OFF = 'x'
  • BrickletCompass.THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletCompass.THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletCompass.THRESHOLD_OPTION_SMALLER = '<'
  • BrickletCompass.THRESHOLD_OPTION_GREATER = '>'
BrickletCompass.get_heading_callback_configuration()
Return type:(int, bool, chr, int, int)

Returns the callback configuration as set by set_heading_callback_configuration().

The following constants are available for this function:

  • BrickletCompass.THRESHOLD_OPTION_OFF = 'x'
  • BrickletCompass.THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletCompass.THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletCompass.THRESHOLD_OPTION_SMALLER = '<'
  • BrickletCompass.THRESHOLD_OPTION_GREATER = '>'

The returned namedtuple has the variables period, value_has_to_change, option, min and max.

BrickletCompass.set_magnetic_flux_density_callback_configuration(period, value_has_to_change)
Parameters:
  • period -- int
  • value_has_to_change -- bool
Return type:

None

The period in ms is the period with which the CALLBACK_MAGNETIC_FLUX_DENSITY callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

The default value is (0, false).

BrickletCompass.get_magnetic_flux_density_callback_configuration()
Return type:(int, bool)

Returns the callback configuration as set by set_magnetic_flux_density_callback_configuration().

The returned namedtuple has the variables period and value_has_to_change.

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)

compass.register_callback(BrickletCompass.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.

BrickletCompass.CALLBACK_HEADING
Parameters:heading -- int

This callback is triggered periodically according to the configuration set by set_heading_callback_configuration().

The parameter is the same as get_heading().

BrickletCompass.CALLBACK_MAGNETIC_FLUX_DENSITY
Parameters:
  • x -- int
  • y -- int
  • z -- int

This callback is triggered periodically according to the configuration set by set_magnetic_flux_density_callback_configuration().

The parameters are the same as get_magnetic_flux_density().

Constants

BrickletCompass.DEVICE_IDENTIFIER

This constant is used to identify a Compass 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.

BrickletCompass.DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Compass Bricklet.