Software / API Bindings / Python / API Reference and Examples / Bricklets / Load Cell Bricklet 2.0

Python - Load Cell Bricklet 2.0¶

This is the description of the Python API bindings for the Load Cell Bricklet 2.0. General information and technical specifications for the Load Cell Bricklet 2.0 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)

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

HOST = "localhost"
PORT = 4223
UID = "XYZ" # Change XYZ to the UID of your Load Cell Bricklet 2.0

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_load_cell_v2 import BrickletLoadCellV2

if __name__ == "__main__":
    ipcon = IPConnection() # Create IP connection
    lc = BrickletLoadCellV2(UID, ipcon) # Create device object

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

    # Get current weight
    weight = lc.get_weight()
    print("Weight: " + str(weight) + " g")

    input("Press key to exit\n") # Use raw_input() in Python 2
    ipcon.disconnect()

Callback¶

Download (example_callback.py)

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

HOST = "localhost"
PORT = 4223
UID = "XYZ" # Change XYZ to the UID of your Load Cell Bricklet 2.0

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_load_cell_v2 import BrickletLoadCellV2

# Callback function for weight callback
def cb_weight(weight):
    print("Weight: " + str(weight) + " g")

if __name__ == "__main__":
    ipcon = IPConnection() # Create IP connection
    lc = BrickletLoadCellV2(UID, ipcon) # Create device object

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

    # Register weight callback to function cb_weight
    lc.register_callback(lc.CALLBACK_WEIGHT, cb_weight)

    # Set period for weight callback to 1s (1000ms) without a threshold
    lc.set_weight_callback_configuration(1000, False, "x", 0, 0)

    input("Press key to exit\n") # Use raw_input() in Python 2
    ipcon.disconnect()

Threshold¶

Download (example_threshold.py)

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

HOST = "localhost"
PORT = 4223
UID = "XYZ" # Change XYZ to the UID of your Load Cell Bricklet 2.0

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_load_cell_v2 import BrickletLoadCellV2

# Callback function for weight callback
def cb_weight(weight):
    print("Weight: " + str(weight) + " g")

if __name__ == "__main__":
    ipcon = IPConnection() # Create IP connection
    lc = BrickletLoadCellV2(UID, ipcon) # Create device object

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

    # Register weight callback to function cb_weight
    lc.register_callback(lc.CALLBACK_WEIGHT, cb_weight)

    # Configure threshold for weight "greater than 200 g"
    # with a debounce period of 1s (1000ms)
    lc.set_weight_callback_configuration(1000, False, ">", 200, 0)

    input("Press key to exit\n") # Use raw_input() in Python 2
    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
Error.WRONG_DEVICE_TYPE = -15
Error.DEVICE_REPLACED = -16
Error.WRONG_RESPONSE_LENGTH = -17

All functions listed below are thread-safe.

Basic Functions¶

BrickletLoadCellV2(uid, ipcon)¶

Parameters:	uid – Type: str ipcon – Type: IPConnection
Returns:	load_cell_v2 – Type: BrickletLoadCellV2

Creates an object with the unique device ID uid:

load_cell_v2 = BrickletLoadCellV2("YOUR_DEVICE_UID", ipcon)

This object can then be used after the IP Connection is connected.

BrickletLoadCellV2.get_weight()¶

Returns:	weight – Type: int, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1]

Returns the currently measured weight.

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

BrickletLoadCellV2.set_info_led_config(config)¶

Parameters:	config – Type: int, Range: See constants, Default: 0
Returns:	None

Configures the info LED to be either turned off, turned on, or blink in heartbeat mode.

The following constants are available for this function:

For config:

BrickletLoadCellV2.INFO_LED_CONFIG_OFF = 0
BrickletLoadCellV2.INFO_LED_CONFIG_ON = 1
BrickletLoadCellV2.INFO_LED_CONFIG_SHOW_HEARTBEAT = 2

BrickletLoadCellV2.get_info_led_config()¶

Returns:	config – Type: int, Range: See constants, Default: 0

Returns the LED configuration as set by set_info_led_config()

The following constants are available for this function:

For config:

BrickletLoadCellV2.INFO_LED_CONFIG_OFF = 0
BrickletLoadCellV2.INFO_LED_CONFIG_ON = 1
BrickletLoadCellV2.INFO_LED_CONFIG_SHOW_HEARTBEAT = 2

BrickletLoadCellV2.tare()¶

Returns:	None

Sets the currently measured weight as tare weight.

Advanced Functions¶

BrickletLoadCellV2.set_moving_average(average)¶

Parameters:	average – Type: int, Range: [1 to 100], Default: 4
Returns:	None

Sets the length of a moving averaging for the weight value.

Setting the length to 1 will turn the averaging off. With less averaging, there is more noise on the data.

BrickletLoadCellV2.get_moving_average()¶

Returns:	average – Type: int, Range: [1 to 100], Default: 4

Returns the length moving average as set by set_moving_average().

BrickletLoadCellV2.calibrate(weight)¶

Parameters:	weight – Type: int, Unit: 1 g, Range: [0 to 2³² - 1]
Returns:	None

To calibrate your Load Cell Bricklet 2.0 you have to

empty the scale and call this function with 0 and
add a known weight to the scale and call this function with the weight.

The calibration is saved in the flash of the Bricklet and only needs to be done once.

We recommend to use the Brick Viewer for calibration, you don't need to call this function in your source code.

BrickletLoadCellV2.set_configuration(rate, gain)¶

Parameters:	rate – Type: int, Range: See constants, Default: 0 gain – Type: int, Range: See constants, Default: 0
Returns:	None

The measurement rate and gain are configurable.

The rate can be either 10Hz or 80Hz. A faster rate will produce more noise. It is additionally possible to add a moving average (see set_moving_average()) to the measurements.

The gain can be 128x, 64x or 32x. It represents a measurement range of ±20mV, ±40mV and ±80mV respectively. The Load Cell Bricklet uses an excitation voltage of 5V and most load cells use an output of 2mV/V. That means the voltage range is ±15mV for most load cells (i.e. gain of 128x is best). If you don't know what all of this means you should keep it at 128x, it will most likely be correct.

The following constants are available for this function:

For rate:

BrickletLoadCellV2.RATE_10HZ = 0
BrickletLoadCellV2.RATE_80HZ = 1

For gain:

BrickletLoadCellV2.GAIN_128X = 0
BrickletLoadCellV2.GAIN_64X = 1
BrickletLoadCellV2.GAIN_32X = 2

BrickletLoadCellV2.get_configuration()¶

Return Object:	rate – Type: int, Range: See constants, Default: 0 gain – Type: int, Range: See constants, Default: 0

Returns the configuration as set by set_configuration().

The following constants are available for this function:

For rate:

BrickletLoadCellV2.RATE_10HZ = 0
BrickletLoadCellV2.RATE_80HZ = 1

For gain:

BrickletLoadCellV2.GAIN_128X = 0
BrickletLoadCellV2.GAIN_64X = 1
BrickletLoadCellV2.GAIN_32X = 2

BrickletLoadCellV2.get_spitfp_error_count()¶

Return Object:	error_count_ack_checksum – Type: int, Range: [0 to 2³² - 1] error_count_message_checksum – Type: int, Range: [0 to 2³² - 1] error_count_frame – Type: int, Range: [0 to 2³² - 1] error_count_overflow – Type: int, Range: [0 to 2³² - 1]

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.

BrickletLoadCellV2.set_status_led_config(config)¶

Parameters:	config – Type: int, Range: See constants, Default: 3
Returns:	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:

For config:

BrickletLoadCellV2.STATUS_LED_CONFIG_OFF = 0
BrickletLoadCellV2.STATUS_LED_CONFIG_ON = 1
BrickletLoadCellV2.STATUS_LED_CONFIG_SHOW_HEARTBEAT = 2
BrickletLoadCellV2.STATUS_LED_CONFIG_SHOW_STATUS = 3

BrickletLoadCellV2.get_status_led_config()¶

Returns:	config – Type: int, Range: See constants, Default: 3

Returns the configuration as set by set_status_led_config()

The following constants are available for this function:

For config:

BrickletLoadCellV2.STATUS_LED_CONFIG_OFF = 0
BrickletLoadCellV2.STATUS_LED_CONFIG_ON = 1
BrickletLoadCellV2.STATUS_LED_CONFIG_SHOW_HEARTBEAT = 2
BrickletLoadCellV2.STATUS_LED_CONFIG_SHOW_STATUS = 3

BrickletLoadCellV2.get_chip_temperature()¶

Returns:	temperature – Type: int, Unit: 1 °C, Range: [-2¹⁵ to 2¹⁵ - 1]

Returns the temperature 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.

BrickletLoadCellV2.reset()¶

Returns:	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!

BrickletLoadCellV2.get_identity()¶

Return Object:

Return Object:	uid – Type: str, Length: up to 8 connected_uid – Type: str, Length: up to 8 position – Type: chr, Range: ["a" to "h", "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]

uid – Type: str, Length: up to 8
connected_uid – Type: str, Length: up to 8
position – Type: chr, Range: ["a" to "h", "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). A Bricklet connected to an Isolator Bricklet is always at 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¶

BrickletLoadCellV2.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.

BrickletLoadCellV2.set_weight_callback_configuration(period, value_has_to_change, option, min, max)¶

Parameters:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: False option – Type: chr, Range: See constants, Default: "x" min – Type: int, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1], Default: 0 max – Type: int, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1], Default: 0
Returns:	None

The period is the period with which the CALLBACK_WEIGHT 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_WEIGHT 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 following constants are available for this function:

For option:

BrickletLoadCellV2.THRESHOLD_OPTION_OFF = "x"
BrickletLoadCellV2.THRESHOLD_OPTION_OUTSIDE = "o"
BrickletLoadCellV2.THRESHOLD_OPTION_INSIDE = "i"
BrickletLoadCellV2.THRESHOLD_OPTION_SMALLER = "<"
BrickletLoadCellV2.THRESHOLD_OPTION_GREATER = ">"

BrickletLoadCellV2.get_weight_callback_configuration()¶

Return Object:	period – Type: int, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0 value_has_to_change – Type: bool, Default: False option – Type: chr, Range: See constants, Default: "x" min – Type: int, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1], Default: 0 max – Type: int, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1], Default: 0

Returns the callback configuration as set by set_weight_callback_configuration().

The following constants are available for this function:

For option:

BrickletLoadCellV2.THRESHOLD_OPTION_OFF = "x"
BrickletLoadCellV2.THRESHOLD_OPTION_OUTSIDE = "o"
BrickletLoadCellV2.THRESHOLD_OPTION_INSIDE = "i"
BrickletLoadCellV2.THRESHOLD_OPTION_SMALLER = "<"
BrickletLoadCellV2.THRESHOLD_OPTION_GREATER = ">"

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)

load_cell_v2.register_callback(BrickletLoadCellV2.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.

BrickletLoadCellV2.CALLBACK_WEIGHT¶

Callback Parameters:	weight – Type: int, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1]

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

The parameter is the same as get_weight().

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.

BrickletLoadCellV2.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.

BrickletLoadCellV2.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 sent and errors are silently ignored, because they cannot be detected.

The following constants are available for this function:

For function_id:

BrickletLoadCellV2.FUNCTION_SET_WEIGHT_CALLBACK_CONFIGURATION = 2
BrickletLoadCellV2.FUNCTION_SET_MOVING_AVERAGE = 5
BrickletLoadCellV2.FUNCTION_SET_INFO_LED_CONFIG = 7
BrickletLoadCellV2.FUNCTION_CALIBRATE = 9
BrickletLoadCellV2.FUNCTION_TARE = 10
BrickletLoadCellV2.FUNCTION_SET_CONFIGURATION = 11
BrickletLoadCellV2.FUNCTION_SET_WRITE_FIRMWARE_POINTER = 237
BrickletLoadCellV2.FUNCTION_SET_STATUS_LED_CONFIG = 239
BrickletLoadCellV2.FUNCTION_RESET = 243
BrickletLoadCellV2.FUNCTION_WRITE_UID = 248

BrickletLoadCellV2.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.

The following constants are available for this function:

For function_id:

BrickletLoadCellV2.FUNCTION_SET_WEIGHT_CALLBACK_CONFIGURATION = 2
BrickletLoadCellV2.FUNCTION_SET_MOVING_AVERAGE = 5
BrickletLoadCellV2.FUNCTION_SET_INFO_LED_CONFIG = 7
BrickletLoadCellV2.FUNCTION_CALIBRATE = 9
BrickletLoadCellV2.FUNCTION_TARE = 10
BrickletLoadCellV2.FUNCTION_SET_CONFIGURATION = 11
BrickletLoadCellV2.FUNCTION_SET_WRITE_FIRMWARE_POINTER = 237
BrickletLoadCellV2.FUNCTION_SET_STATUS_LED_CONFIG = 239
BrickletLoadCellV2.FUNCTION_RESET = 243
BrickletLoadCellV2.FUNCTION_WRITE_UID = 248

BrickletLoadCellV2.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.

Internal Functions¶

Internal functions are used for maintenance tasks such as flashing a new firmware of changing the UID of a Bricklet. These task should be performed using Brick Viewer instead of using the internal functions directly.

BrickletLoadCellV2.set_bootloader_mode(mode)¶

Parameters:	mode – Type: int, Range: See constants
Returns:	status – Type: int, Range: See constants

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:

For mode:

BrickletLoadCellV2.BOOTLOADER_MODE_BOOTLOADER = 0
BrickletLoadCellV2.BOOTLOADER_MODE_FIRMWARE = 1
BrickletLoadCellV2.BOOTLOADER_MODE_BOOTLOADER_WAIT_FOR_REBOOT = 2
BrickletLoadCellV2.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_REBOOT = 3
BrickletLoadCellV2.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_ERASE_AND_REBOOT = 4

For status:

BrickletLoadCellV2.BOOTLOADER_STATUS_OK = 0
BrickletLoadCellV2.BOOTLOADER_STATUS_INVALID_MODE = 1
BrickletLoadCellV2.BOOTLOADER_STATUS_NO_CHANGE = 2
BrickletLoadCellV2.BOOTLOADER_STATUS_ENTRY_FUNCTION_NOT_PRESENT = 3
BrickletLoadCellV2.BOOTLOADER_STATUS_DEVICE_IDENTIFIER_INCORRECT = 4
BrickletLoadCellV2.BOOTLOADER_STATUS_CRC_MISMATCH = 5

BrickletLoadCellV2.get_bootloader_mode()¶

Returns:	mode – Type: int, Range: See constants

Returns the current bootloader mode, see set_bootloader_mode().

The following constants are available for this function:

For mode:

BrickletLoadCellV2.BOOTLOADER_MODE_BOOTLOADER = 0
BrickletLoadCellV2.BOOTLOADER_MODE_FIRMWARE = 1
BrickletLoadCellV2.BOOTLOADER_MODE_BOOTLOADER_WAIT_FOR_REBOOT = 2
BrickletLoadCellV2.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_REBOOT = 3
BrickletLoadCellV2.BOOTLOADER_MODE_FIRMWARE_WAIT_FOR_ERASE_AND_REBOOT = 4

BrickletLoadCellV2.set_write_firmware_pointer(pointer)¶

Parameters:	pointer – Type: int, Unit: 1 B, Range: [0 to 2³² - 1]
Returns:	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.

BrickletLoadCellV2.write_firmware(data)¶

Parameters:	data – Type: [int, ...], Length: 64, Range: [0 to 255]
Returns:	status – Type: int, Range: [0 to 255]

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.

BrickletLoadCellV2.write_uid(uid)¶

Parameters:	uid – Type: int, Range: [0 to 2³² - 1]
Returns:	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.

BrickletLoadCellV2.read_uid()¶

Returns:	uid – Type: int, Range: [0 to 2³² - 1]

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

Constants¶

BrickletLoadCellV2.DEVICE_IDENTIFIER¶

This constant is used to identify a Load Cell Bricklet 2.0.

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.

BrickletLoadCellV2.DEVICE_DISPLAY_NAME¶: This constant represents the human readable name of a Load Cell Bricklet 2.0.