JavaScript - Load Cell Bricklet – Tinkerforge

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# JavaScript - Load Cell Bricklet

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.

## Examples

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

### Simple (Node.js)

Download (ExampleSimple.js)

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    var Tinkerforge = require('tinkerforge');

    var HOST = 'localhost';
    var PORT = 4223;
    var UID = 'XYZ'; // Change to your UID

    var ipcon = new Tinkerforge.IPConnection(); // Create IP connection
    var lc = new Tinkerforge.BrickletLoadCell(UID, ipcon); // Create device object

    ipcon.connect(HOST, PORT,
        function(error) {
            console.log('Error: '+error);
        }
    ); // Connect to brickd

    // Don't use device before ipcon is connected
    ipcon.on(Tinkerforge.IPConnection.CALLBACK_CONNECTED,
        function(connectReason) {
            // Get current weight (unit is g)
            lc.getWeight(
                function(weight) {
                    console.log('Weight: '+weight/1000+' kg');
                },
                function(error) {
                    console.log('Error: '+error);
                }
            );
        }
    );

    console.log("Press any key to exit ...");
    process.stdin.on('data',
        function(data) {
            ipcon.disconnect();
            process.exit(0);
        }
    );

### Callback (Node.js)

Download (ExampleCallback.js)

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    var Tinkerforge = require('tinkerforge');

    var HOST = 'localhost';
    var PORT = 4223;
    var UID = 'XYZ'; // Change to your UID

    var ipcon = new Tinkerforge.IPConnection(); // Create IP connection
    var lc = new Tinkerforge.BrickletLoadCell(UID, ipcon); // Create device object

    ipcon.connect(HOST, PORT,
        function(error) {
            console.log('Error: '+error);
        }
    ); // Connect to brickd
    // Don't use device before ipcon is connected

    ipcon.on(Tinkerforge.IPConnection.CALLBACK_CONNECTED,
        function(connectReason) {
            // 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);
        }
    );

    // Register position callback
    lc.on(Tinkerforge.BrickletLoadCell.CALLBACK_WEIGHT,
        // Callback function for weight callback (parameter has unit g)
        function(weight) {
            console.log('Weight: '+weight/1000+' kg');
        }
    );

    console.log("Press any key to exit ...");
    process.stdin.on('data',
        function(data) {
            ipcon.disconnect();
            process.exit(0);
        }
    );

### Threshold (Node.js)

Download (ExampleThreshold.js)

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    var Tinkerforge = require('tinkerforge');

    var HOST = 'localhost';
    var PORT = 4223;
    var UID = 'XYZ'; // Change to your UID

    var ipcon = new Tinkerforge.IPConnection(); // Create IP connection
    var lc = new Tinkerforge.BrickletLoadCell(UID, ipcon); // Create device object

    ipcon.connect(HOST, PORT,
        function(error) {
            console.log('Error: '+error);
        }
    ); // Connect to brickd
    // Don't use device before ipcon is connected

    ipcon.on(Tinkerforge.IPConnection.CALLBACK_CONNECTED,
        function(connectReason) {
            // Get threshold callbacks with a debounce time of 10 seconds (10000ms)
            lc.setDebouncePeriod(10000);
            // Configure threshold for "greater than 200 g"
            lc.setWeightCallbackThreshold('>', 200, 0);
        }
    );

    // Register threshold reached callback to function cb_reached
    lc.on(Tinkerforge.BrickletLoadCell.CALLBACK_WEIGHT_REACHED,
        // Callback for weight greater than 200 g
        function(weight) {
            console.log('Weight: ' +weight/1000 + ' kg.');
        }
    );

    console.log("Press any key to exit ...");
    process.stdin.on('data',
        function(data) {
            ipcon.disconnect();
            process.exit(0);
        }
    );

### Simple (HTML)

Download (ExampleSimple.html), Test (ExampleSimple.html)

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    <!DOCTYPE html>
    <html>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <head>
            <title>Tinkerforge | JavaScript Example</title>
        </head>
        <body>
            <div style="text-align:center;">
                <h1>Load Cell Bricklet Simple Example</h1>
                <p>
                    <input value="localhost" id="host" type="text" size="20">:
                    <input value="4280" id="port" type="text" size="5">,
                    <input value="uid" id="uid" type="text" size="5">
                    <input value="Start Example" id="start" type="button" onclick="startExample();">
                </p>
                <p>
                    <textarea id="text" cols="80" rows="24" style="resize:none;"
                              >Press "Start Example" to begin ...</textarea>
                </p>
            <div>
            <script src="./Tinkerforge.js" type='text/javascript'></script>
            <script type='text/javascript'>
                var ipcon;
                var textArea = document.getElementById("text");
                function startExample() {
                    textArea.value = "";
                    var HOST = document.getElementById("host").value;
                    var PORT = parseInt(document.getElementById("port").value);
                    var UID = document.getElementById("uid").value;
                    if(ipcon !== undefined) {
                        ipcon.disconnect();
                    }
                    ipcon = new Tinkerforge.IPConnection(); // Create IP connection
                    var lc = new Tinkerforge.BrickletLoadCell(UID, ipcon); // Create device object
                    ipcon.connect(HOST, PORT,
                        function(error) {
                            textArea.value += 'Error: '+error+ '\n';
                        }
                    ); // Connect to brickd
                    // Don't use device before ipcon is connected

                    ipcon.on(Tinkerforge.IPConnection.CALLBACK_CONNECTED,
                        function(connectReason) {
                            // Get current weight (unit is g)
                            lc.getWeight(
                                function(weight) {
                                    textArea.value += 'Weight: '+weight/1000+' kg\n';
                                },
                                function(error) {
                                    textArea.value += 'Error: '+error+'\n';
                                }
                            );
                        }
                    );
                }
            </script>
        </body>
    </html>

### Callback (HTML)

Download (ExampleCallback.html), Test (ExampleCallback.html)

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    <!DOCTYPE html>
    <html>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <head>
            <title>Tinkerforge | JavaScript Example</title>
        </head>
        <body>
            <div style="text-align:center;">
                <h1>Load Cell Bricklet Callback Example</h1>
                <p>
                    <input value="localhost" id="host" type="text" size="20">:
                    <input value="4280" id="port" type="text" size="5">,
                    <input value="uid" id="uid" type="text" size="5">
                    <input value="Start Example" id="start" type="button" onclick="startExample();">
                </p>
                <p>
                    <textarea id="text" cols="80" rows="24" style="resize:none;"
                              >Press "Start Example" to begin ...</textarea>
                </p>
            <div>
            <script src="./Tinkerforge.js" type='text/javascript'></script>
            <script type='text/javascript'>
                var ipcon;
                var textArea = document.getElementById("text");
                function startExample() {
                    textArea.value = "";
                    var HOST = document.getElementById("host").value;
                    var PORT = parseInt(document.getElementById("port").value);
                    var UID = document.getElementById("uid").value;
                    if(ipcon !== undefined) {
                        ipcon.disconnect();
                    }
                    ipcon = new Tinkerforge.IPConnection(); // Create IP connection
                    var lc = new Tinkerforge.BrickletLoadCell(UID, ipcon); // Create device object
                    ipcon.connect(HOST, PORT,
                        function(error) {
                            textArea.value += 'Error: '+error+ '\n';
                        }
                    ); // Connect to brickd
                    // Don't use device before ipcon is connected

                    ipcon.on(Tinkerforge.IPConnection.CALLBACK_CONNECTED,
                        function(connectReason) {
                            // 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!
                            al.setWeightCallbackPeriod(1000);
                        }
                    );
                    // Register position callback
                    lc.on(Tinkerforge.BrickletLoadCell.CALLBACK_WEIGHT,
                        // Callback function for weight callback (parameter has unit g)
                        function(weight) {
                            textArea.value += 'Weight: '+weight/1000+' kg';
                            textArea.value += '\n';
                            textArea.scrollTop = textArea.scrollHeight;
                        }
                    );
                }
            </script>
        </body>
    </html>

### Threshold (HTML)

Download (ExampleThreshold.html), Test (ExampleThreshold.html)

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    <!DOCTYPE html>
    <html>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <head>
            <title>Tinkerforge | JavaScript Example</title>
        </head>
        <body>
            <div style="text-align:center;">
                <h1>Load Cell Bricklet Threshold Example</h1>
                <p>
                    <input value="localhost" id="host" type="text" size="20">:
                    <input value="4280" id="port" type="text" size="5">,
                    <input value="uid" id="uid" type="text" size="5">
                    <input value="Start Example" id="start" type="button" onclick="startExample();">
                </p>
                <p>
                    <textarea id="text" cols="80" rows="24" style="resize:none;"
                              >Press "Start Example" to begin ...</textarea>
                </p>
            <div>
            <script src="./Tinkerforge.js" type='text/javascript'></script>
            <script type='text/javascript'>
                var ipcon;
                var textArea = document.getElementById("text");
                function startExample() {
                    textArea.value = "";
                    var HOST = document.getElementById("host").value;
                    var PORT = parseInt(document.getElementById("port").value);
                    var UID = document.getElementById("uid").value;
                    if(ipcon !== undefined) {
                        ipcon.disconnect();
                    }
                    ipcon = new Tinkerforge.IPConnection(); // Create IP connection
                    var lc = new Tinkerforge.BrickletLoadCell(UID, ipcon); // Create device object
                    ipcon.connect(HOST, PORT,
                        function(error) {
                            textArea.value += 'Error: '+error+ '\n';
                        }
                    ); // Connect to brickd
                    // Don't use device before ipcon is connected

                    ipcon.on(Tinkerforge.IPConnection.CALLBACK_CONNECTED,
                        function(connectReason) {
                            // Get threshold callbacks with a debounce time of 10 seconds (10000ms)
                            lc.setDebouncePeriod(10000);
                            // Configure threshold for "greater than 200 g" (unit is g)
                            lc.setWeightCallbackThreshold('>', 200, 0);
                        }
                    );
                    // Register threshold reached callback to function cb_reached
                    lc.on(Tinkerforge.BrickletLoadCell.CALLBACK_WEIGHT_REACHED,
                        // Callback for weight greater than 200 g
                        function(weight) {
                            textArea.value += 'Weight ' +weight/1000 + ' kg.\n';
                            textArea.value += '\n';
                            textArea.scrollTop = textArea.scrollHeight;
                        }
                    );
                }
            </script>
        </body>
    </html>

## API

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:

- IPConnection.ERROR_ALREADY_CONNECTED = 11
- IPConnection.ERROR_NOT_CONNECTED = 12
- IPConnection.ERROR_CONNECT_FAILED = 13
- IPConnection.ERROR_INVALID_FUNCTION_ID = 21
- IPConnection.ERROR_TIMEOUT = 31
- IPConnection.ERROR_INVALID_PARAMETER = 41
- IPConnection.ERROR_FUNCTION_NOT_SUPPORTED = 42
- IPConnection.ERROR_UNKNOWN_ERROR = 43

The namespace for the JavaScript bindings is `Tinkerforge.*`.

### Basic Functions

new `BrickletLoadCell`(uid, ipcon)

  Parameters:

  - uid -- string
  - ipcon -- IPConnection

  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).

`BrickletLoadCell.``getWeight`([returnCallback][, errorCallback])

  Callback:

  - weight -- int

  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()`.

`BrickletLoadCell.``ledOn`([returnCallback][, errorCallback])

  Callback: | undefined

  Turns the LED on.

`BrickletLoadCell.``ledOff`([returnCallback][, errorCallback])

  Callback: | undefined

  Turns the LED off.

`BrickletLoadCell.``isLEDOn`([returnCallback][, errorCallback])

  Callback:

  - value -- int

  Returns true if the led is on, false otherwise.

`BrickletLoadCell.``tare`([returnCallback][, errorCallback])

  Callback: | undefined

  Sets the currently measured weight as tare weight.

### Advanced Functions

`BrickletLoadCell.``setMovingAverage`(average[, returnCallback][, errorCallback])

  Parameters:

  - average -- int

  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.

`BrickletLoadCell.``getMovingAverage`([returnCallback][, errorCallback])

  Callback:

  - average -- int

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

`BrickletLoadCell.``calibrate`(weight[, returnCallback][, errorCallback])

  Parameters:

  - weight -- int

  Callback: | undefined

  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.

`BrickletLoadCell.``setConfiguration`(rate, gain[, returnCallback][, errorCallback])

  Parameters:

  - rate -- int
  - gain -- int

  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:

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

`BrickletLoadCell.``getConfiguration`([returnCallback][, errorCallback])

  Callback:

  - rate -- int
  - gain -- int

  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

`BrickletLoadCell.``getAPIVersion`()

  Return type: | [int, int, int]

  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.

`BrickletLoadCell.``getResponseExpected`(functionId[, errorCallback])

  Parameters:

  - functionId -- int

  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.

`BrickletLoadCell.``setResponseExpected`(functionId, responseExpected[, errorCallback])

  Parameters:

  - functionId -- int
  - responseExpected -- boolean

  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:

  - 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

`BrickletLoadCell.``setResponseExpectedAll`(responseExpected)

  Parameters:

  - responseExpected -- boolean

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

`BrickletLoadCell.``getIdentity`([returnCallback][, errorCallback])

  Callback:

  - uid -- string
  - connectedUid -- string
  - position -- char
  - hardwareVersion -- [int, int, int]
  - firmwareVersion -- [int, int, int]
  - deviceIdentifier -- int

  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.

### Callback Configuration Functions

`BrickletLoadCell.``on`(id, callback)

  Parameters:

  - id -- int
  - callback -- function

  Registers a callback with ID id to the function callback. The available IDs with corresponding function signatures are listed below.

`BrickletLoadCell.``setWeightCallbackPeriod`(period[, returnCallback][, errorCallback])

  Parameters:

  - period -- int

  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.

`BrickletLoadCell.``getWeightCallbackPeriod`([returnCallback][, errorCallback])

  Callback:

  - period -- int

  Returns the period as set by `setWeightCallbackPeriod()`.

`BrickletLoadCell.``setWeightCallbackThreshold`(option, min, max[, returnCallback][, errorCallback])

  Parameters:

  - option -- char
  - min -- int
  - max -- int

  Callback: | undefined

  Sets the thresholds for the `CALLBACK_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 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 = '>'

`BrickletLoadCell.``getWeightCallbackThreshold`([returnCallback][, errorCallback])

  Callback:

  - option -- char
  - min -- int
  - max -- int

  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 = '>'

`BrickletLoadCell.``setDebouncePeriod`(debounce[, returnCallback][, errorCallback])

  Parameters:

  - debounce -- int

  Callback: | undefined

  Sets the period in ms with which the threshold callback

  - `CALLBACK_WEIGHT_REACHED`

  is triggered, if the threshold

  - `setWeightCallbackThreshold()`

  keeps being reached.

  The default value is 100.

`BrickletLoadCell.``getDebouncePeriod`([returnCallback][, errorCallback])

  Callback:

  - debounce -- int

  Returns the debounce period as set by `setDebouncePeriod()`.

### Callbacks

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.

`BrickletLoadCell.``CALLBACK_WEIGHT`

  Parameters:

  - weight -- int

  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.

`BrickletLoadCell.``CALLBACK_WEIGHT_REACHED`

  Parameters:

  - weight -- int

  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()`.

### Constants

`BrickletLoadCell.``DEVICE_IDENTIFIER`

  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.

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