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 -- int32

Returns the currently measured weight in grams.

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 -- bool

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 -- uint8
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.

The range for the averaging is 1-40.

The default value is 4.

BrickletLoadCell.get_moving_average
Function ID:

9

Request:

empty payload

Response:
  • average -- uint8

Returns the length moving average as set by set_moving_average.

BrickletLoadCell.calibrate
Function ID:

13

Request:
  • weight -- uint32
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 in grams.

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 -- uint8
  • gain -- uint8
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 default rate is 10Hz and the default gain is 128x.

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

  • 0: 10hz, for rate
  • 1: 80hz, for rate
  • 0: 128x, for gain
  • 1: 64x, for gain
  • 2: 32x, for gain
BrickletLoadCell.get_configuration
Function ID:

16

Request:

empty payload

Response:
  • rate -- uint8
  • gain -- uint8

Returns the configuration as set by set_configuration.

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

  • 0: 10hz, for rate
  • 1: 80hz, for rate
  • 0: 128x, for gain
  • 1: 64x, for gain
  • 2: 32x, for gain
BrickletLoadCell.get_identity
Function ID:

255

Request:

empty payload

Response:
  • uid -- char[8]
  • connected_uid -- char[8]
  • position -- char
  • hardware_version -- uint8[3]
  • firmware_version -- uint8[3]
  • device_identifier -- uint16

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

Callback Configuration Functions

BrickletLoadCell.set_weight_callback_period
Function ID:

2

Request:
  • period -- uint32
Response:

no response

Sets the period in ms 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.

The default value is 0.

BrickletLoadCell.get_weight_callback_period
Function ID:

3

Request:

empty payload

Response:
  • period -- uint32

Returns the period as set by set_weight_callback_period.

BrickletLoadCell.set_weight_callback_threshold
Function ID:

4

Request:
  • option -- char
  • min -- int32
  • max -- int32
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 default value is ('x', 0, 0).

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

  • x: off, for option
  • o: outside, for option
  • i: inside, for option
  • <: smaller, for option
  • >: greater, for option
BrickletLoadCell.get_weight_callback_threshold
Function ID:

5

Request:

empty payload

Response:
  • option -- char
  • min -- int32
  • max -- int32

Returns the threshold as set by set_weight_callback_threshold.

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

  • x: off, for option
  • o: outside, for option
  • i: inside, for option
  • <: smaller, for option
  • >: greater, for option
BrickletLoadCell.set_debounce_period
Function ID:

6

Request:
  • debounce -- uint32
Response:

no response

Sets the period in ms with which the threshold callback

is triggered, if the threshold

keeps being reached.

The default value is 100.

BrickletLoadCell.get_debounce_period
Function ID:

7

Request:

empty payload

Response:
  • debounce -- uint32

Returns the debounce period as set by set_debounce_period.

Callbacks

BrickletLoadCell.CALLBACK_WEIGHT
Function ID:

17

Response:
  • weight -- int32

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 -- int32

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.