Shell - Load Cell Bricklet

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

An installation guide for the Shell API bindings is part of their general description.

Examples

The example code below is Public Domain (CC0 1.0).

Simple

Download (example-simple.sh)

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#!/bin/sh
# Connects to localhost:4223 by default, use --host and --port to change this

uid=XYZ # Change XYZ to the UID of your Load Cell Bricklet

# Get current weight
tinkerforge call load-cell-bricklet $uid get-weight

Callback

Download (example-callback.sh)

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#!/bin/sh
# Connects to localhost:4223 by default, use --host and --port to change this

uid=XYZ # Change XYZ to the UID of your Load Cell Bricklet

# Handle incoming weight callbacks
tinkerforge dispatch load-cell-bricklet $uid weight &

# Set period for weight callback to 1s (1000ms)
# Note: The weight callback is only called every second
#       if the weight has changed since the last call!
tinkerforge call load-cell-bricklet $uid set-weight-callback-period 1000

echo "Press key to exit"; read dummy

kill -- -$$ # Stop callback dispatch in background

Threshold

Download (example-threshold.sh)

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#!/bin/sh
# Connects to localhost:4223 by default, use --host and --port to change this

uid=XYZ # Change XYZ to the UID of your Load Cell Bricklet

# Get threshold callbacks with a debounce time of 1 second (1000ms)
tinkerforge call load-cell-bricklet $uid set-debounce-period 1000

# Handle incoming weight reached callbacks
tinkerforge dispatch load-cell-bricklet $uid weight-reached &

# Configure threshold for weight "greater than 200 g"
tinkerforge call load-cell-bricklet $uid set-weight-callback-threshold threshold-option-greater 200 0

echo "Press key to exit"; read dummy

kill -- -$$ # Stop callback dispatch in background

API

Possible exit codes for all tinkerforge commands are:

  • 1: interrupted (ctrl+c)
  • 2: syntax error
  • 21: Python 2.5 or newer is required
  • 22: Python argparse module is missing
  • 23: socket error
  • 24: other exception
  • 25: invalid placeholder in format string
  • 26: authentication error
  • 201: timeout occurred
  • 209: invalid argument value
  • 210: function is not supported
  • 211: unknown error

Command Structure

The common options of the call and dispatch commands are documented here. The specific command structure is shown below.

tinkerforge call load-cell-bricklet [<option>..] <uid> <function> [<argument>..]
Parameters:
  • <uid> -- string
  • <function> -- string

The call command is used to call a function of the Load Cell Bricklet. It can take several options:

  • --help shows help for the specific call command and exits
  • --list-functions shows a list of known functions of the Load Cell Bricklet and exits
tinkerforge dispatch load-cell-bricklet [<option>..] <uid> <callback>
Parameters:
  • <uid> -- string
  • <callback> -- string

The dispatch command is used to dispatch a callback of the Load Cell Bricklet. It can take several options:

  • --help shows help for the specific dispatch command and exits
  • --list-callbacks shows a list of known callbacks of the Load Cell Bricklet and exits
tinkerforge call load-cell-bricklet <uid> <function> [<option>..] [<argument>..]
Parameters:
  • <uid> -- string
  • <function> -- string

The <function> to be called can take different options depending of its kind. All functions can take the following options:

  • --help shows help for the specific function and exits

Getter functions can take the following options:

  • --execute <command> shell command line to execute for each incoming response (see section about output formatting for details)

Setter functions can take the following options:

  • --expect-response requests response and waits for it

The --expect-response option for setter functions allows to detect timeouts and other error conditions calls of setters as well. The device will then send a response for this purpose. If this option is not given for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

tinkerforge dispatch load-cell-bricklet <uid> <callback> [<option>..]
Parameters:
  • <uid> -- string
  • <callback> -- string

The <callback> to be dispatched can take several options:

  • --help shows help for the specific callback and exits
  • --execute <command> shell command line to execute for each incoming response (see section about output formatting for details)

Basic Functions

tinkerforge call load-cell-bricklet <uid> get-weight
Output:
  • weight -- int

Returns the currently measured weight in grams.

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

tinkerforge call load-cell-bricklet <uid> led-on
Output:no output

Turns the LED on.

tinkerforge call load-cell-bricklet <uid> led-off
Output:no output

Turns the LED off.

tinkerforge call load-cell-bricklet <uid> is-led-on
Output:
  • on -- bool

Returns true if the led is on, false otherwise.

tinkerforge call load-cell-bricklet <uid> tare
Output:no output

Sets the currently measured weight as tare weight.

Advanced Functions

tinkerforge call load-cell-bricklet <uid> set-moving-average <average>
Parameters:
  • <average> -- int
Output:

no output

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.

tinkerforge call load-cell-bricklet <uid> get-moving-average
Output:
  • average -- int

Returns the length moving average as set by set-moving-average.

tinkerforge call load-cell-bricklet <uid> calibrate <weight>
Parameters:
  • <weight> -- int
Output:

no output

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.

tinkerforge call load-cell-bricklet <uid> set-configuration <rate> <gain>
Parameters:
  • <rate> -- int (has symbols)
  • <gain> -- int (has symbols)
Output:

no output

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 symbols are available for this function:

  • rate-10hz = 0, for <rate>
  • rate-80hz = 1, for <rate>
  • gain-128x = 0, for <gain>
  • gain-64x = 1, for <gain>
  • gain-32x = 2, for <gain>
tinkerforge call load-cell-bricklet <uid> get-configuration
Output:
  • rate -- int (has symbols)
  • gain -- int (has symbols)

Returns the configuration as set by set-configuration.

The following symbols are available for this function:

  • rate-10hz = 0, for rate
  • rate-80hz = 1, for rate
  • gain-128x = 0, for gain
  • gain-64x = 1, for gain
  • gain-32x = 2, for gain
tinkerforge call load-cell-bricklet <uid> get-identity
Output:
  • uid -- string
  • connected-uid -- string
  • position -- char
  • hardware-version -- int,int,int
  • firmware-version -- int,int,int
  • device-identifier -- int (has symbols)

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

tinkerforge call load-cell-bricklet <uid> set-weight-callback-period <period>
Parameters:
  • <period> -- int
Output:

no output

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

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

The default value is 0.

tinkerforge call load-cell-bricklet <uid> get-weight-callback-period
Output:
  • period -- int

Returns the period as set by set-weight-callback-period.

tinkerforge call load-cell-bricklet <uid> set-weight-callback-threshold <option> <min> <max>
Parameters:
  • <option> -- char (has symbols)
  • <min> -- int
  • <max> -- int
Output:

no output

Sets the thresholds for the 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 symbols are available for this function:

  • threshold-option-off = x, for <option>
  • threshold-option-outside = o, for <option>
  • threshold-option-inside = i, for <option>
  • threshold-option-smaller = <, for <option>
  • threshold-option-greater = >, for <option>
tinkerforge call load-cell-bricklet <uid> get-weight-callback-threshold
Output:
  • option -- char (has symbols)
  • min -- int
  • max -- int

Returns the threshold as set by set-weight-callback-threshold.

The following symbols are available for this function:

  • threshold-option-off = x, for option
  • threshold-option-outside = o, for option
  • threshold-option-inside = i, for option
  • threshold-option-smaller = <, for option
  • threshold-option-greater = >, for option
tinkerforge call load-cell-bricklet <uid> set-debounce-period <debounce>
Parameters:
  • <debounce> -- int
Output:

no output

Sets the period in ms with which the threshold callback

is triggered, if the threshold

keeps being reached.

The default value is 100.

tinkerforge call load-cell-bricklet <uid> get-debounce-period
Output:
  • debounce -- int

Returns the debounce period as set by set-debounce-period.

Callbacks

Callbacks can be used to receive time critical or recurring data from the device:

tinkerforge dispatch load-cell-bricklet <uid> example

The available callbacks 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.

tinkerforge dispatch load-cell-bricklet <uid> weight
Output:
  • weight -- int

This callback is triggered periodically with the period that is set by set-weight-callback-period. The parameter is the weight as measured by the load cell.

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

tinkerforge dispatch load-cell-bricklet <uid> weight-reached
Output:
  • weight -- int

This callback is triggered when the threshold as set by set-weight-callback-threshold is reached. The parameter 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.