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 MATLAB/Octave 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 MATLAB/Octave API bindings is part of their general description.
The example code below is Public Domain (CC0 1.0).
Generally, every method of the MATLAB bindings that returns a value can throw a TimeoutException. This exception gets thrown if the device did not respond. If a cable based connection is used, it is unlikely that this exception gets thrown (assuming nobody unplugs the device). However, if a wireless connection is used, timeouts will occur if the distance to the device gets too big.
Beside the TimeoutException there is also a NotConnectedException that is thrown if a method needs to communicate with the device while the IP Connection is not connected.
Since the MATLAB bindings are based on Java and Java does not support multiple return values and return by reference is not possible for primitive types, we use small classes that only consist of member variables. The member variables of the returned objects are described in the corresponding method descriptions.
The package for all Brick/Bricklet bindings and the IP Connection is com.tinkerforge.*
All methods listed below are thread-safe.
Creates an object with the unique device ID uid.
In MATLAB:
import com.tinkerforge.BrickletLoadCell;
loadCell = BrickletLoadCell('YOUR_DEVICE_UID', ipcon);
In Octave:
loadCell = java_new("com.tinkerforge.BrickletLoadCell", "YOUR_DEVICE_UID", ipcon);
This object can then be used after the IP Connection is connected (see examples above).
Returns the currently measured weight in grams.
If you want to get the weight periodically, it is recommended to use the callback WeightCallback and set the period with setWeightCallbackPeriod().
Turns the LED on.
Turns the LED off.
Returns true if the led is on, false otherwise.
Sets the currently measured weight as tare weight.
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.
Returns the length moving average as set by setMovingAverage().
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.
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:
Returns the configuration as set by setConfiguration().
The following constants are available for this function:
The returned object has the public member variables short rate and short gain.
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.
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.
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:
Changes the response expected flag for all setter and callback configuration functions of this device at once.
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.
The returned object has the public member variables String uid, String connectedUid, char position, short[] hardwareVersion, short[] firmwareVersion and int deviceIdentifier.
Sets the period in ms with which the WeightCallback callback is triggered periodically. A value of 0 turns the callback off.
WeightCallback is only triggered if the weight has changed since the last triggering.
The default value is 0.
Returns the period as set by setWeightCallbackPeriod().
Sets the thresholds for the WeightReachedCallback 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 constants are available for this function:
Returns the threshold as set by setWeightCallbackThreshold().
The following constants are available for this function:
The returned object has the public member variables char option, short min and short max.
Sets the period in ms with which the threshold callback
is triggered, if the threshold
keeps being reached.
The default value is 100.
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 "set" function of MATLAB. The parameters consist of the IP Connection object, the callback name and the callback function. For example, it looks like this in MATLAB:
function cb_example(e)
fprintf('Parameter: %s\n', e.param);
end
set(device, 'ExampleCallback', @(h, e) cb_example(e));
Due to a difference in the Octave Java support the "set" function cannot be used in Octave. The registration is done with "add*Callback" functions of the device object. It looks like this in Octave:
function cb_example(e)
fprintf("Parameter: %s\n", e.param);
end
device.addExampleCallback(@cb_example);
It is possible to add several callbacks and to remove them with the corresponding "remove*Callback" function.
The parameters of the callback are passed to the callback function as fields of the structure e, which is derived from the java.util.EventObject class. The available callback names with corresponding structure fields 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: | weight -- long |
---|
This callback is triggered periodically with the period that is set by setWeightCallbackPeriod(). The parameter is the weight as measured by the load cell.
WeightCallback is only triggered if the weight has changed since the last triggering.
In MATLAB the set() function can be used to register a callback function to this callback.
In Octave a callback function can be added to this callback using the addWeightCallback() function. An added callback function can be removed with the removeWeightCallback() function.
Parameters: | weight -- short |
---|
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().
In MATLAB the set() function can be used to register a callback function to this callback.
In Octave a callback function can be added to this callback using the addWeightReachedCallback() function. An added callback function can be removed with the removeWeightReachedCallback() function.
This constant is used to identify a Load Cell Bricklet.
The getIdentity() function and the EnumerateCallback callback of the IP Connection have a deviceIdentifier parameter to specify the Brick's or Bricklet's type.