MATLAB/Octave - Multi Touch Bricklet

This is the description of the MATLAB/Octave API bindings for the Multi Touch Bricklet. General information and technical specifications for the Multi Touch Bricklet are summarized in its hardware description.

An installation guide for the MATLAB/Octave API bindings is part of their general description.

Examples

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

Simple (MATLAB)

Download (matlab_example_simple.m)

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function matlab_example_simple()
    import com.tinkerforge.IPConnection;
    import com.tinkerforge.BrickletMultiTouch;

    HOST = 'localhost';
    PORT = 4223;
    UID = 'XYZ'; % Change XYZ to the UID of your Multi Touch Bricklet

    ipcon = IPConnection(); % Create IP connection
    mt = handle(BrickletMultiTouch(UID, ipcon), 'CallbackProperties'); % Create device object

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

    % Get current touch state
    state = mt.getTouchState();
    s = '';

    if bitand(state, bitshift(1, 12))
        s = strcat(s, 'In proximity, ');
    end

    if (bitand(state, hex2dec('FFF'))) == 0
        s = strcat(s, 'No electrodes touched');
    else
        s = strcat(s, 'Electrodes ');
        for i = 0:11
            if bitand(state, bitshift(1, i))
                s = strcat(s, num2str(i));
                s = strcat(s, ' ');
            end
        end
        s = strcat(s, 'touched');
    end

    disp(s);

    input('Press key to exit\n', 's');
    ipcon.disconnect();
end

Callback (MATLAB)

Download (matlab_example_callback.m)

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function matlab_example_callback()
    import com.tinkerforge.IPConnection;
    import com.tinkerforge.BrickletMultiTouch;

    HOST = 'localhost';
    PORT = 4223;
    UID = 'XYZ'; % Change XYZ to the UID of your Multi Touch Bricklet

    ipcon = IPConnection(); % Create IP connection
    mt = handle(BrickletMultiTouch(UID, ipcon), 'CallbackProperties'); % Create device object

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

    % Register touch state callback to function cb_touch_state
    set(mt, 'TouchStateCallback', @(h, e) cb_touch_state(e));

    input('Press key to exit\n', 's');
    ipcon.disconnect();
end

% Callback function for touch state callback
function cb_touch_state(e)
    s = '';

    if bitand(e.state, bitshift(1, 12))
        s = strcat(s, 'In proximity, ');
    end

    if (bitand(e.state, hex2dec('FFF'))) == 0
        s = strcat(s, 'No electrodes touched');
    else
        s = strcat(s, 'Electrodes ');
        for i = 0:11
            if bitand(e.state, bitshift(1, i))
                s = strcat(s, num2str(i));
                s = strcat(s, ' ');
            end
        end
        s = strcat(s, 'touched');
    end

    disp(s);
end

Simple (Octave)

Download (octave_example_simple.m)

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function octave_example_simple()
    more off;

    HOST = "localhost";
    PORT = 4223;
    UID = "XYZ"; % Change XYZ to the UID of your Multi Touch Bricklet

    ipcon = javaObject("com.tinkerforge.IPConnection"); % Create IP connection
    mt = javaObject("com.tinkerforge.BrickletMultiTouch", UID, ipcon); % Create device object

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

    % Get current touch state
    state = mt.getTouchState();
    s = "";

    if bitand(state, bitshift(1, 12))
        s = strcat(s, "In proximity, ");
    end

    if (bitand(state, hex2dec("FFF"))) == 0
        s = strcat(s, "No electrodes touched");
    else
        s = strcat(s, "Electrodes ");
        for i = 0:11
            if bitand(state, bitshift(1, i))
                s = strcat(s, num2str(i));
                s = strcat(s, " ");
            end
        end
        s = strcat(s, "touched");
    end

    disp(s);

    input("Press key to exit\n", "s");
    ipcon.disconnect();
end

Callback (Octave)

Download (octave_example_callback.m)

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function octave_example_callback()
    more off;

    HOST = "localhost";
    PORT = 4223;
    UID = "XYZ"; % Change XYZ to the UID of your Multi Touch Bricklet

    ipcon = javaObject("com.tinkerforge.IPConnection"); % Create IP connection
    mt = javaObject("com.tinkerforge.BrickletMultiTouch", UID, ipcon); % Create device object

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

    % Register touch state callback to function cb_touch_state
    mt.addTouchStateCallback(@cb_touch_state);

    input("Press key to exit\n", "s");
    ipcon.disconnect();
end

% Callback function for touch state callback
function cb_touch_state(e)
    s = "";

    if bitand(e.state, bitshift(1, 12))
        s = strcat(s, "In proximity, ");
    end

    if (bitand(e.state, hex2dec("FFF"))) == 0
        s = strcat(s, "No electrodes touched");
    else
        s = strcat(s, "Electrodes ");
        for i = 0:11
            if bitand(e.state, bitshift(1, i))
                s = strcat(s, num2str(i));
                s = strcat(s, " ");
            end
        end
        s = strcat(s, "touched");
    end

    disp(s);
end

API

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.

Basic Functions

public class BrickletMultiTouch(String uid, IPConnection ipcon)

Creates an object with the unique device ID uid.

In MATLAB:

import com.tinkerforge.BrickletMultiTouch;

multiTouch = BrickletMultiTouch('YOUR_DEVICE_UID', ipcon);

In Octave:

multiTouch = java_new("com.tinkerforge.BrickletMultiTouch", "YOUR_DEVICE_UID", ipcon);

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

public int getTouchState()

Returns the current touch state. The state is given as a bitfield.

Bits 0 to 11 represent the 12 electrodes and bit 12 represents the proximity.

If an electrode is touched, the corresponding bit is true. If a hand or similar is in proximity to the electrodes, bit 12 is true.

Example: The state 4103 = 0x1007 = 0b1000000000111 means that electrodes 0, 1 and 2 are touched and that something is in the proximity of the electrodes.

The proximity is activated with a distance of 1-2cm. An electrode is already counted as touched if a finger is nearly touching the electrode. This means that you can put a piece of paper or foil or similar on top of a electrode to build a touch panel with a professional look.

public void recalibrate()

Recalibrates the electrodes. Call this function whenever you changed or moved you electrodes.

public void setElectrodeConfig(int enabledElectrodes)

Enables/disables electrodes with a bitfield (see getTouchState()).

True enables the electrode, false disables the electrode. A disabled electrode will always return false as its state. If you don't need all electrodes you can disable the electrodes that are not needed.

It is recommended that you disable the proximity bit (bit 12) if the proximity feature is not needed. This will reduce the amount of traffic that is produced by the TouchStateCallback callback.

Disabling electrodes will also reduce power consumption.

Default: 8191 = 0x1FFF = 0b1111111111111 (all electrodes enabled)

public int getElectrodeConfig()

Returns the electrode configuration, as set by setElectrodeConfig().

public void setElectrodeSensitivity(short sensitivity)

Sets the sensitivity of the electrodes. An electrode with a high sensitivity will register a touch earlier then an electrode with a low sensitivity.

If you build a big electrode you might need to decrease the sensitivity, since the area that can be charged will get bigger. If you want to be able to activate an electrode from further away you need to increase the sensitivity.

After a new sensitivity is set, you likely want to call recalibrate() to calibrate the electrodes with the newly defined sensitivity.

The valid sensitivity value range is 5-201.

The default sensitivity value is 181.

public short getElectrodeSensitivity()

Returns the current sensitivity, as set by setElectrodeSensitivity().

Advanced Functions

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 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.

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 callback 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:

  • BrickletMultiTouch.FUNCTION_RECALIBRATE = 2
  • BrickletMultiTouch.FUNCTION_SET_ELECTRODE_CONFIG = 3
  • BrickletMultiTouch.FUNCTION_SET_ELECTRODE_SENSITIVITY = 6
public void setResponseExpectedAll(boolean responseExpected)

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

public BrickletMultiTouch.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.

Callbacks

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 my_callback(e)
    fprintf('Parameter: %s\n', e.param);
end

set(device, 'ExampleCallback', @(h, e) my_callback(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 my_callback(e)
    fprintf("Parameter: %s\n", e.param);
end

device.addExampleCallback(@my_callback);

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.

public callback BrickletMultiTouch.TouchStateCallback
Parameters:state -- int

Returns the current touch state, see getTouchState() for information about the state.

This callback is triggered every time the touch state changes.

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 addTouchStateCallback() function. An added callback function can be removed with the removeTouchStateCallback() function.

Constants

public static final int BrickletMultiTouch.DEVICE_IDENTIFIER

This constant is used to identify a Multi Touch 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.

public static final String BrickletMultiTouch.DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Multi Touch Bricklet.