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 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.
The example code below is Public Domain (CC0 1.0).
Possible exit codes for all tinkerforge commands are:
The common options of the call and dispatch commands are documented here. The specific command structure is shown below.
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The call command is used to call a function of the Load Cell Bricklet. It can take several options:
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The dispatch command is used to dispatch a callback of the Load Cell Bricklet. It can take several options:
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The <function> to be called can take different options depending of its kind. All functions can take the following options:
Getter functions can take the following options:
Setter functions can take the following options:
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.
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The <callback> to be dispatched can take several options:
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Returns the currently measured weight in grams.
If you want to get the weight periodically, it is recommended to use the callback weight and set the period with set-weight-callback-period.
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Turns the LED on.
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Turns the LED off.
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Returns true if the led is on, false otherwise.
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Sets the currently measured weight as tare weight.
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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.
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Returns the length moving average as set by set-moving-average.
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Output: | no output |
To calibrate your Load Cell Bricklet you have to
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.
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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:
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Returns the configuration as set by set-configuration.
The following symbols are available for this function:
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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.
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Output: | no output |
Sets the period in ms with which the weight callback is triggered periodically. A value of 0 turns the callback off.
weight is only triggered if the weight has changed since the last triggering.
The default value is 0.
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Returns the period as set by set-weight-callback-period.
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Output: | no output |
Sets the thresholds for the weight-reached callback.
The following options are possible:
Option | Description |
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'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:
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Returns the threshold as set by set-weight-callback-threshold.
The following symbols are available for this function:
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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.
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Returns the debounce period as set by set-debounce-period.
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.
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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.
weight is only triggered if the weight has changed since the last triggering.
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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.