Java - Load Cell Bricklet

This is the description of the Java 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 Java API bindings is part of their general description.

Examples

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

Simple

Download (ExampleSimple.java)

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import com.tinkerforge.IPConnection;
import com.tinkerforge.BrickletLoadCell;

public class ExampleSimple {
    private static final String HOST = "localhost";
    private static final int PORT = 4223;

    // Change XYZ to the UID of your Load Cell Bricklet
    private static final String UID = "XYZ";

    // Note: To make the example code cleaner we do not handle exceptions. Exceptions
    //       you might normally want to catch are described in the documentation
    public static void main(String args[]) throws Exception {
        IPConnection ipcon = new IPConnection(); // Create IP connection
        BrickletLoadCell lc = new BrickletLoadCell(UID, ipcon); // Create device object

        ipcon.connect(HOST, PORT); // Connect to brickd
        // Don't use device before ipcon is connected

        // Get current weight
        int weight = lc.getWeight(); // Can throw com.tinkerforge.TimeoutException
        System.out.println("Weight: " + weight + " g");

        System.out.println("Press key to exit"); System.in.read();
        ipcon.disconnect();
    }
}

Callback

Download (ExampleCallback.java)

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import com.tinkerforge.IPConnection;
import com.tinkerforge.BrickletLoadCell;

public class ExampleCallback {
    private static final String HOST = "localhost";
    private static final int PORT = 4223;

    // Change XYZ to the UID of your Load Cell Bricklet
    private static final String UID = "XYZ";

    // Note: To make the example code cleaner we do not handle exceptions. Exceptions
    //       you might normally want to catch are described in the documentation
    public static void main(String args[]) throws Exception {
        IPConnection ipcon = new IPConnection(); // Create IP connection
        BrickletLoadCell lc = new BrickletLoadCell(UID, ipcon); // Create device object

        ipcon.connect(HOST, PORT); // Connect to brickd
        // Don't use device before ipcon is connected

        // Add weight listener
        lc.addWeightListener(new BrickletLoadCell.WeightListener() {
            public void weight(int weight) {
                System.out.println("Weight: " + weight + " g");
            }
        });

        // 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!
        lc.setWeightCallbackPeriod(1000);

        System.out.println("Press key to exit"); System.in.read();
        ipcon.disconnect();
    }
}

Threshold

Download (ExampleThreshold.java)

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import com.tinkerforge.IPConnection;
import com.tinkerforge.BrickletLoadCell;

public class ExampleThreshold {
    private static final String HOST = "localhost";
    private static final int PORT = 4223;

    // Change XYZ to the UID of your Load Cell Bricklet
    private static final String UID = "XYZ";

    // Note: To make the example code cleaner we do not handle exceptions. Exceptions
    //       you might normally want to catch are described in the documentation
    public static void main(String args[]) throws Exception {
        IPConnection ipcon = new IPConnection(); // Create IP connection
        BrickletLoadCell lc = new BrickletLoadCell(UID, ipcon); // Create device object

        ipcon.connect(HOST, PORT); // Connect to brickd
        // Don't use device before ipcon is connected

        // Get threshold callbacks with a debounce time of 1 second (1000ms)
        lc.setDebouncePeriod(1000);

        // Add weight reached listener
        lc.addWeightReachedListener(new BrickletLoadCell.WeightReachedListener() {
            public void weightReached(int weight) {
                System.out.println("Weight: " + weight + " g");
            }
        });

        // Configure threshold for weight "greater than 200 g"
        lc.setWeightCallbackThreshold('>', 200, 0);

        System.out.println("Press key to exit"); System.in.read();
        ipcon.disconnect();
    }
}

API

Generally, every method of the Java 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 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.

Basic Functions

public class BrickletLoadCell(String uid, IPConnection ipcon)

Creates an object with the unique device ID uid:

BrickletLoadCell loadCell = new BrickletLoadCell("YOUR_DEVICE_UID", ipcon);

This object can then be used after the IP Connection is connected (see examples above).

public int getWeight()

Returns the currently measured weight in grams.

If you want to get the weight periodically, it is recommended to use the WeightListener listener and set the period with setWeightCallbackPeriod().

public void ledOn()

Turns the LED on.

public void ledOff()

Turns the LED off.

public boolean isLEDOn()

Returns true if the led is on, false otherwise.

public void tare()

Sets the currently measured weight as tare weight.

Advanced Functions

public void setMovingAverage(short average)

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.

public short getMovingAverage()

Returns the length moving average as set by setMovingAverage().

public void calibrate(long weight)

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.

public void setConfiguration(short rate, short gain)

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:

  • BrickletLoadCell.RATE_10HZ = 0
  • BrickletLoadCell.RATE_80HZ = 1
  • BrickletLoadCell.GAIN_128X = 0
  • BrickletLoadCell.GAIN_64X = 1
  • BrickletLoadCell.GAIN_32X = 2
public BrickletLoadCell.Configuration getConfiguration()

Returns the configuration as set by setConfiguration().

The following constants are available for this function:

  • BrickletLoadCell.RATE_10HZ = 0
  • BrickletLoadCell.RATE_80HZ = 1
  • BrickletLoadCell.GAIN_128X = 0
  • BrickletLoadCell.GAIN_64X = 1
  • BrickletLoadCell.GAIN_32X = 2

The returned object has the public member variables short rate and short gain.

public short[] getAPIVersion()

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.

public boolean getResponseExpected(short functionId)

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 listener 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.

public void setResponseExpected(short functionId, boolean responseExpected)

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 listener configuration functions (default value: true). For getter functions it is always 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.

The following function ID constants are available for this function:

  • BrickletLoadCell.FUNCTION_SET_WEIGHT_CALLBACK_PERIOD = 2
  • BrickletLoadCell.FUNCTION_SET_WEIGHT_CALLBACK_THRESHOLD = 4
  • BrickletLoadCell.FUNCTION_SET_DEBOUNCE_PERIOD = 6
  • BrickletLoadCell.FUNCTION_SET_MOVING_AVERAGE = 8
  • BrickletLoadCell.FUNCTION_LED_ON = 10
  • BrickletLoadCell.FUNCTION_LED_OFF = 11
  • BrickletLoadCell.FUNCTION_CALIBRATE = 13
  • BrickletLoadCell.FUNCTION_TARE = 14
  • BrickletLoadCell.FUNCTION_SET_CONFIGURATION = 15
public void setResponseExpectedAll(boolean responseExpected)

Changes the response expected flag for all setter and listener configuration functions of this device at once.

public BrickletLoadCell.Identity getIdentity()

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.

Listener Configuration Functions

public void setWeightCallbackPeriod(long period)

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

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

The default value is 0.

public long getWeightCallbackPeriod()

Returns the period as set by setWeightCallbackPeriod().

public void setWeightCallbackThreshold(char option, int min, int max)

Sets the thresholds for the WeightReachedListener listener.

The following options are possible:

Option Description
'x' Listener is turned off
'o' Listener is triggered when the weight is outside the min and max values
'i' Listener is triggered when the weight is inside the min and max values
'<' Listener is triggered when the weight is smaller than the min value (max is ignored)
'>' Listener 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:

  • BrickletLoadCell.THRESHOLD_OPTION_OFF = 'x'
  • BrickletLoadCell.THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletLoadCell.THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletLoadCell.THRESHOLD_OPTION_SMALLER = '<'
  • BrickletLoadCell.THRESHOLD_OPTION_GREATER = '>'
public BrickletLoadCell.WeightCallbackThreshold getWeightCallbackThreshold()

Returns the threshold as set by setWeightCallbackThreshold().

The following constants are available for this function:

  • BrickletLoadCell.THRESHOLD_OPTION_OFF = 'x'
  • BrickletLoadCell.THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletLoadCell.THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletLoadCell.THRESHOLD_OPTION_SMALLER = '<'
  • BrickletLoadCell.THRESHOLD_OPTION_GREATER = '>'

The returned object has the public member variables char option, int min and int max.

public void setDebouncePeriod(long debounce)

Sets the period in ms with which the threshold listener

  • WeightReachedListener

is triggered, if the threshold

keeps being reached.

The default value is 100.

public long getDebouncePeriod()

Returns the debounce period as set by setDebouncePeriod().

Listeners

Listeners can be registered to receive time critical or recurring data from the device. The registration is done with add*Listener() functions of the device object.

The parameter is a listener class object, for example:

device.addExampleListener(new BrickletLoadCell.ExampleListener() {
    public void property(int value) {
        System.out.println("Value: " + value);
    }
});

The available listener classes with inherent methods to be overwritten are described below. It is possible to add several listeners and to remove them with the corresponding remove*Listener() function.

Note

Using listeners 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.

public class BrickletLoadCell.WeightListener()

This listener can be added with the addWeightListener() function. An added listener can be removed with the removeWeightListener() function.

public void weight(int weight)

This listener is triggered periodically with the period that is set by setWeightCallbackPeriod(). The parameter is the weight as measured by the load cell.

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

public class BrickletLoadCell.WeightReachedListener()

This listener can be added with the addWeightReachedListener() function. An added listener can be removed with the removeWeightReachedListener() function.

public void weightReached(int weight)

This listener 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 listener is triggered periodically with the period as set by setDebouncePeriod().

Constants

public static final int BrickletLoadCell.DEVICE_IDENTIFIER

This constant is used to identify a Load Cell Bricklet.

The getIdentity() function and the IPConnection.EnumerateListener listener of the IP Connection have a deviceIdentifier parameter to specify the Brick's or Bricklet's type.

public static final String BrickletLoadCell.DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Load Cell Bricklet.