Modbus - Load Cell Bricklet – Tinkerforge

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# Modbus - Load Cell Bricklet

Note

This Bricklet is currently in the prototype stage and the software/hardware as well as the documentation is in an incomplete state.

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 `CALLBACK_WEIGHT` 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:

  - value -- uint8

  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.

`BrickletLoadCell.``get_configuration`

  Function ID: | 16
  Request: | empty payload

  Response:

  - rate -- uint8
  - gain -- uint8

  Returns the configuration as set by `set_configuration`.

`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.

  `CALLBACK_WEIGHT` 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).

`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`.

`BrickletLoadCell.``set_debounce_period`

  Function ID: | 6

  Request:

  - debounce -- uint32

  Response: | no response

  Sets the period in ms with which the threshold callback

  - `CALLBACK_WEIGHT_REACHED`

  is triggered, if the threshold

  - `set_weight_callback_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.

  `CALLBACK_WEIGHT` 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`.

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