Specifications / Modbus Protocol / API / Bricklets (Discontinued) / Load Cell Bricklet

Modbus - Load Cell Bricklet¶

This is the description of the Modbus protocol for the Load Cell Bricklet. General information and technical specifications for the Load Cell Bricklet are summarized in its hardware description.

API¶

A general description of the Modbus protocol structure can be found here.

Basic Functions¶

BrickletLoadCell.get_weight¶

Function ID:	1
Request:	empty payload
Response:	weight – Type: int32, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1]

Returns the currently measured weight.

If you want to get the weight periodically, it is recommended to use the CALLBACK_WEIGHT callback and set the period with set_weight_callback_period.

BrickletLoadCell.led_on¶

Function ID:	10
Request:	empty payload
Response:	no response

Turns the LED on.

BrickletLoadCell.led_off¶

Function ID:	11
Request:	empty payload
Response:	no response

Turns the LED off.

BrickletLoadCell.is_led_on¶

Function ID:	12
Request:	empty payload
Response:	on – Type: bool, Default: false

Returns true if the led is on, false otherwise.

BrickletLoadCell.tare¶

Function ID:	14
Request:	empty payload
Response:	no response

Sets the currently measured weight as tare weight.

Advanced Functions¶

BrickletLoadCell.set_moving_average¶

Function ID:	8
Request:	average – Type: uint8, Range: [1 to 40], Default: 4
Response:	no response

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.

BrickletLoadCell.get_moving_average¶

Function ID:	9
Request:	empty payload
Response:	average – Type: uint8, Range: [1 to 40], Default: 4

Returns the length moving average as set by set_moving_average.

BrickletLoadCell.calibrate¶

Function ID:	13
Request:	weight – Type: uint32, Unit: 1 g, Range: [0 to 2³² - 1]
Response:	no response

To calibrate your Load Cell Bricklet 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 EEPROM 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.

BrickletLoadCell.set_configuration¶

Function ID:	15
Request:	rate – Type: uint8, Range: See meanings, Default: 0 gain – Type: uint8, Range: See meanings, Default: 0
Response:	no response

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 configuration is saved in the EEPROM of the Bricklet and only needs to be done once.

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

The following meanings are defined for the elements of this function:

For rate:

0 = 10Hz
1 = 80Hz

For gain:

0 = 128x
1 = 64x
2 = 32x

BrickletLoadCell.get_configuration¶

Function ID:	16
Request:	empty payload
Response:	rate – Type: uint8, Range: See meanings, Default: 0 gain – Type: uint8, Range: See meanings, Default: 0

Returns the configuration as set by set_configuration.

The following meanings are defined for the elements of this function:

For rate:

0 = 10Hz
1 = 80Hz

For gain:

0 = 128x
1 = 64x
2 = 32x

BrickletLoadCell.get_identity¶

Function ID:	255
Request:	empty payload
Response:	uid – Type: char[8] connected_uid – Type: char[8] position – Type: char, Range: ['a' to 'h', 'z'] hardware_version – Type: uint8[3] 0: major – Type: uint8, Range: [0 to 255] 1: minor – Type: uint8, Range: [0 to 255] 2: revision – Type: uint8, Range: [0 to 255] firmware_version – Type: uint8[3] 0: major – Type: uint8, Range: [0 to 255] 1: minor – Type: uint8, Range: [0 to 255] 2: revision – Type: uint8, Range: [0 to 255] device_identifier – Type: uint16, 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.

Callback Configuration Functions¶

BrickletLoadCell.set_weight_callback_period¶

Function ID:	2
Request:	period – Type: uint32, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0
Response:	no response

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

The CALLBACK_WEIGHT callback is only triggered if the weight has changed since the last triggering.

BrickletLoadCell.get_weight_callback_period¶

Function ID:	3
Request:	empty payload
Response:	period – Type: uint32, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 0

Returns the period as set by set_weight_callback_period.

BrickletLoadCell.set_weight_callback_threshold¶

Function ID:	4
Request:	option – Type: char, Range: See meanings, Default: 'x' min – Type: int32, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1], Default: 0 max – Type: int32, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1], Default: 0
Response:	no response

Sets the thresholds for the CALLBACK_WEIGHT_REACHED callback.

The following options are possible:

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

The following meanings are defined for the elements of this function:

For option:

'x' = Off
'o' = Outside
'i' = Inside
'<' = Smaller
'>' = Greater

BrickletLoadCell.get_weight_callback_threshold¶

Function ID:	5
Request:	empty payload
Response:	option – Type: char, Range: See meanings, Default: 'x' min – Type: int32, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1], Default: 0 max – Type: int32, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1], Default: 0

Returns the threshold as set by set_weight_callback_threshold.

The following meanings are defined for the elements of this function:

For option:

'x' = Off
'o' = Outside
'i' = Inside
'<' = Smaller
'>' = Greater

BrickletLoadCell.set_debounce_period¶

Function ID:	6
Request:	debounce – Type: uint32, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 100
Response:	no response

Sets the period with which the threshold callback

CALLBACK_WEIGHT_REACHED

is triggered, if the threshold

set_weight_callback_threshold

keeps being reached.

BrickletLoadCell.get_debounce_period¶

Function ID:	7
Request:	empty payload
Response:	debounce – Type: uint32, Unit: 1 ms, Range: [0 to 2³² - 1], Default: 100

Returns the debounce period as set by set_debounce_period.

Callbacks¶

BrickletLoadCell.CALLBACK_WEIGHT¶

Function ID:	17
Response:	weight – Type: int32, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1]

This callback is triggered periodically with the period that is set by set_weight_callback_period. The response value is the weight as measured by the load cell.

The CALLBACK_WEIGHT callback is only triggered if the weight has changed since the last triggering.

BrickletLoadCell.CALLBACK_WEIGHT_REACHED¶

Function ID:	18
Response:	weight – Type: int32, Unit: 1 g, Range: [-2³¹ to 2³¹ - 1]

This callback is triggered when the threshold as set by set_weight_callback_threshold is reached. The response value is the weight as measured by the load cell.

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