MQTT - Load Cell Bricklet¶

Simple¶

Download (example-simple.txt)

1# Change XYZ to the UID of your Load Cell Bricklet
2
3setup:
4    # Get current weight
5    subscribe to tinkerforge/response/load_cell_bricklet/XYZ/get_weight
6    publish '' to tinkerforge/request/load_cell_bricklet/XYZ/get_weight

Callback¶

Download (example-callback.txt)

 1# Change XYZ to the UID of your Load Cell Bricklet
 2
 3setup:
 4    # Handle incoming weight callbacks
 5    subscribe to tinkerforge/callback/load_cell_bricklet/XYZ/weight
 6    publish '{"register": true}' to tinkerforge/register/load_cell_bricklet/XYZ/weight # Register weight callback
 7
 8    # Set period for weight callback to 1s (1000ms)
 9    # Note: The weight callback is only called every second
10    #       if the weight has changed since the last call!
11    publish '{"period": 1000}' to tinkerforge/request/load_cell_bricklet/XYZ/set_weight_callback_period

Threshold¶

Download (example-threshold.txt)

 1# Change XYZ to the UID of your Load Cell Bricklet
 2
 3setup:
 4    # Get threshold callbacks with a debounce time of 1 second (1000ms)
 5    publish '{"debounce": 1000}' to tinkerforge/request/load_cell_bricklet/XYZ/set_debounce_period
 6
 7    # Handle incoming weight reached callbacks
 8    subscribe to tinkerforge/callback/load_cell_bricklet/XYZ/weight_reached
 9    publish '{"register": true}' to tinkerforge/register/load_cell_bricklet/XYZ/weight_reached # Register weight_reached callback
10
11    # Configure threshold for weight "greater than 200 g"
12    publish '{"option": "greater", "min": 200, "max": 0}' to tinkerforge/request/load_cell_bricklet/XYZ/set_weight_callback_threshold

Basic Functions¶

request/load_cell_bricklet/<UID>/get_weight¶

Request:	empty payload
Response:	weight – Type: int, 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 register/load_cell_bricklet/<UID>/weight() callback and set the period with request/load_cell_bricklet/<UID>/set_weight_callback_period().

request/load_cell_bricklet/<UID>/led_on¶

Request:	empty payload
Response:	no response

Turns the LED on.

request/load_cell_bricklet/<UID>/led_off¶

Request:	empty payload
Response:	no response

Turns the LED off.

request/load_cell_bricklet/<UID>/is_led_on¶

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

Returns true if the led is on, false otherwise.

request/load_cell_bricklet/<UID>/tare¶

Request:	empty payload
Response:	no response

Sets the currently measured weight as tare weight.

Advanced Functions¶

request/load_cell_bricklet/<UID>/set_moving_average¶

Request:	average – Type: int, 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.

request/load_cell_bricklet/<UID>/get_moving_average¶

Request:	empty payload
Response:	average – Type: int, Range: [1 to 40], Default: 4

Returns the length moving average as set by request/load_cell_bricklet/<UID>/set_moving_average().

request/load_cell_bricklet/<UID>/calibrate¶

Request:	weight – Type: int, 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.

request/load_cell_bricklet/<UID>/set_configuration¶

Request:	rate – Type: int, Range: See symbols, Default: 0 gain – Type: int, Range: See symbols, 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 request/load_cell_bricklet/<UID>/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 symbols are available for this function:

For rate:

• "10hz" = 0

• "80hz" = 1

For gain:

• "128x" = 0

• "64x" = 1

• "32x" = 2

request/load_cell_bricklet/<UID>/get_configuration¶

Request:	empty payload
Response:	rate – Type: int, Range: See symbols, Default: 0 gain – Type: int, Range: See symbols, Default: 0

Returns the configuration as set by request/load_cell_bricklet/<UID>/set_configuration().

The following symbols are available for this function:

For rate:

• "10hz" = 0

• "80hz" = 1

For gain:

• "128x" = 0

• "64x" = 1

• "32x" = 2

request/load_cell_bricklet/<UID>/get_identity¶

Request:

empty payload

Response:

uid – Type: string, Length: up to 8 connected_uid – Type: string, Length: up to 8 position – Type: char, 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] _display_name – Type: string

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. If symbolic output is not disabled, the device identifier is mapped to the corresponding name in the format used in topics.

The display name contains the Load Cell's name in a human readable form.

Callback Configuration Functions¶

request/load_cell_bricklet/<UID>/set_weight_callback_period¶

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

Sets the period with which the register/load_cell_bricklet/<UID>/weight() callback is triggered periodically. A value of 0 turns the callback off.

The register/load_cell_bricklet/<UID>/weight() callback is only triggered if the weight has changed since the last triggering.

request/load_cell_bricklet/<UID>/get_weight_callback_period¶

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

Returns the period as set by request/load_cell_bricklet/<UID>/set_weight_callback_period().

request/load_cell_bricklet/<UID>/set_weight_callback_threshold¶

Request:	option – Type: char, Range: See symbols, 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
Response:	no response

Sets the thresholds for the register/load_cell_bricklet/<UID>/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 symbols are available for this function:

For option:

• "off" = "x"

• "outside" = "o"

• "inside" = "i"

• "smaller" = "<"

• "greater" = ">"

request/load_cell_bricklet/<UID>/get_weight_callback_threshold¶

Request:	empty payload
Response:	option – Type: char, Range: See symbols, 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 threshold as set by request/load_cell_bricklet/<UID>/set_weight_callback_threshold().

The following symbols are available for this function:

For option:

• "off" = "x"

• "outside" = "o"

• "inside" = "i"

• "smaller" = "<"

• "greater" = ">"

request/load_cell_bricklet/<UID>/set_debounce_period¶

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

Sets the period with which the threshold callback

• register/load_cell_bricklet/<UID>/weight_reached()

is triggered, if the threshold

• request/load_cell_bricklet/<UID>/set_weight_callback_threshold()

keeps being reached.

request/load_cell_bricklet/<UID>/get_debounce_period¶

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

Returns the debounce period as set by request/load_cell_bricklet/<UID>/set_debounce_period().

Callbacks¶

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the corresponding .../register/... topic and an optional suffix. This suffix can be used to deregister the callback later.

register/load_cell_bricklet/<UID>/weight¶

Register Request:	register – Type: bool
Callback Response:	weight – Type: int, Unit: 1 g, Range: [-231 to 231 - 1]

A callback can be registered for this event by publishing to the .../register/load_cell_bricklet/<UID>/weight[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/load_cell_bricklet/<UID>/weight[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically with the period that is set by request/load_cell_bricklet/<UID>/set_weight_callback_period(). The callback payload is the weight as measured by the load cell.

The register/load_cell_bricklet/<UID>/weight() callback is only triggered if the weight has changed since the last triggering.

register/load_cell_bricklet/<UID>/weight_reached¶

Register Request:	register – Type: bool
Callback Response:	weight – Type: int, Unit: 1 g, Range: [-231 to 231 - 1]

A callback can be registered for this event by publishing to the .../register/load_cell_bricklet/<UID>/weight_reached[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/load_cell_bricklet/<UID>/weight_reached[/<SUFFIX>] topic for each registered suffix.

This callback is triggered when the threshold as set by request/load_cell_bricklet/<UID>/set_weight_callback_threshold() is reached. The callback payload 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 request/load_cell_bricklet/<UID>/set_debounce_period().