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 JavaScript 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 JavaScript API bindings is part of their general description.
The example code below is Public Domain (CC0 1.0).
Generally, every method of the JavaScript bindings can take two optional parameters, returnCallback and errorCallback. These are two user defined callback functions. The returnCallback is called with the return values as parameters, if the method returns something. The errorCallback is called with an error code in case of an error. The error code can be one of the following values:
The namespace for the JavaScript bindings is Tinkerforge.*.
Parameters: |
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Creates an object with the unique device ID uid:
var loadCell = new BrickletLoadCell("YOUR_DEVICE_UID", ipcon);
This object can then be used after the IP Connection is connected (see examples above).
Callback: |
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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 CALLBACK_WEIGHT and set the period with setWeightCallbackPeriod().
Callback: | undefined |
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Turns the LED on.
Callback: | undefined |
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Turns the LED off.
Callback: |
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Returns true if the led is on, false otherwise.
Callback: | undefined |
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Sets the currently measured weight as tare weight.
Parameters: |
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Callback: | undefined |
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.
Callback: |
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Returns the length moving average as set by setMovingAverage().
Parameters: |
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Callback: | undefined |
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.
Parameters: |
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Callback: | undefined |
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 setMovingAverage()) 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 constants are available for this function:
Callback: |
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Returns the configuration as set by setConfiguration().
The following constants are available for this function:
Return type: | [int, int, int] |
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Returns the version of the API definition (major, minor, revision) implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.
Parameters: |
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Return type: | boolean |
Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.
For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For callback configuration functions it is enabled by default too, but can be disabled by setResponseExpected(). For setter functions it is disabled by default and can be enabled.
Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.
See setResponseExpected() for the list of function ID constants available for this function.
Parameters: |
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Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and callback configuration functions (default value: true). For getter functions it is always enabled and callbacks it is always disabled.
Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.
The following function ID constants are available for this function:
Parameters: |
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Changes the response expected flag for all setter and callback configuration functions of this device at once.
Callback: |
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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. There is also a constant for the device identifier of this Bricklet.
Parameters: |
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Registers a callback with ID id to the function callback. The available IDs with corresponding function signatures are listed below.
Parameters: |
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Callback: | undefined |
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.
Callback: |
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Returns the period as set by setWeightCallbackPeriod().
Parameters: |
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Callback: | undefined |
Sets the thresholds for the CALLBACK_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 constants are available for this function:
Callback: |
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Returns the threshold as set by setWeightCallbackThreshold().
The following constants are available for this function:
Parameters: |
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Callback: | undefined |
Sets the period in ms with which the threshold callback
is triggered, if the threshold
keeps being reached.
The default value is 100.
Callback: |
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Returns the debounce period as set by setDebouncePeriod().
Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the on() function of the device object. The first parameter is the callback ID and the second parameter the callback function:
loadCell.on(BrickletLoadCell.CALLBACK_EXAMPLE,
function (param) {
console.log(param);
}
);
The available constants with inherent number and type of parameters 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.
Parameters: |
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This callback is triggered periodically with the period that is set by setWeightCallbackPeriod(). The parameter is the weight as measured by the load cell.
CALLBACK_WEIGHT is only triggered if the weight has changed since the last triggering.
Parameters: |
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This callback is triggered when the threshold as set by setWeightCallbackThreshold() 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 setDebouncePeriod().
This constant is used to identify a Load Cell Bricklet.
The getIdentity() function and the CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.