MATLAB/Octave - LCD 20x4 Bricklet

This is the description of the MATLAB/Octave API bindings for the LCD 20x4 Bricklet. General information and technical specifications for the LCD 20x4 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).

Hello World (MATLAB)

Download (matlab_example_hello_world.m)

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function matlab_example_hello_world()
    import com.tinkerforge.IPConnection;
    import com.tinkerforge.BrickletLCD20x4;

    HOST = 'localhost';
    PORT = 4223;
    UID = 'XYZ'; % Change XYZ to the UID of your LCD 20x4 Bricklet

    ipcon = IPConnection(); % Create IP connection
    lcd = handle(BrickletLCD20x4(UID, ipcon), 'CallbackProperties'); % Create device object

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

    % Turn backlight on
    lcd.backlightOn();

    % Write "Hello World"
    lcd.writeLine(0, 0, 'Hello World');

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

Button Callback (MATLAB)

Download (matlab_example_button_callback.m)

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function matlab_example_button_callback()
    import com.tinkerforge.IPConnection;
    import com.tinkerforge.BrickletLCD20x4;

    HOST = 'localhost';
    PORT = 4223;
    UID = 'XYZ'; % Change XYZ to the UID of your LCD 20x4 Bricklet

    ipcon = IPConnection(); % Create IP connection
    lcd = handle(BrickletLCD20x4(UID, ipcon), 'CallbackProperties'); % Create device object

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

    % Register button pressed callback to function cb_button_pressed
    set(lcd, 'ButtonPressedCallback', @(h, e) cb_button_pressed(e));

    % Register button released callback to function cb_button_released
    set(lcd, 'ButtonReleasedCallback', @(h, e) cb_button_released(e));

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

% Callback function for button pressed callback
function cb_button_pressed(e)
    fprintf('Button Pressed: %i\n', e.button);
end

% Callback function for button released callback
function cb_button_released(e)
    fprintf('Button Released: %i\n', e.button);
end

Hello World (Octave)

Download (octave_example_hello_world.m)

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function octave_example_hello_world()
    more off;

    HOST = "localhost";
    PORT = 4223;
    UID = "XYZ"; % Change XYZ to the UID of your LCD 20x4 Bricklet

    ipcon = javaObject("com.tinkerforge.IPConnection"); % Create IP connection
    lcd = javaObject("com.tinkerforge.BrickletLCD20x4", UID, ipcon); % Create device object

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

    % Turn backlight on
    lcd.backlightOn();

    % Write "Hello World"
    lcd.writeLine(0, 0, "Hello World");

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

Button Callback (Octave)

Download (octave_example_button_callback.m)

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function octave_example_button_callback()
    more off;

    HOST = "localhost";
    PORT = 4223;
    UID = "XYZ"; % Change XYZ to the UID of your LCD 20x4 Bricklet

    ipcon = javaObject("com.tinkerforge.IPConnection"); % Create IP connection
    lcd = javaObject("com.tinkerforge.BrickletLCD20x4", UID, ipcon); % Create device object

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

    % Register button pressed callback to function cb_button_pressed
    lcd.addButtonPressedCallback(@cb_button_pressed);

    % Register button released callback to function cb_button_released
    lcd.addButtonReleasedCallback(@cb_button_released);

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

% Callback function for button pressed callback
function cb_button_pressed(e)
    fprintf("Button Pressed: %d\n", java2int(e.button));
end

% Callback function for button released callback
function cb_button_released(e)
    fprintf("Button Released: %d\n", java2int(e.button));
end

function int = java2int(value)
    if compare_versions(version(), "3.8", "<=")
        int = value.intValue();
    else
        int = value;
    end
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 BrickletLCD20x4(String uid, IPConnection ipcon)

Creates an object with the unique device ID uid.

In MATLAB:

import com.tinkerforge.BrickletLCD20x4;

lcd20x4 = BrickletLCD20x4('YOUR_DEVICE_UID', ipcon);

In Octave:

lcd20x4 = java_new("com.tinkerforge.BrickletLCD20x4", "YOUR_DEVICE_UID", ipcon);

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

public void writeLine(short line, short position, String text)

Writes text to a specific line (0 to 3) with a specific position (0 to 19). The text can have a maximum of 20 characters.

For example: (0, 7, "Hello") will write Hello in the middle of the first line of the display.

The display uses a special charset that includes all ASCII characters except backslash and tilde. The LCD charset also includes several other non-ASCII characters, see the charset specification for details. The Unicode example above shows how to specify non-ASCII characters and how to translate from Unicode to the LCD charset.

public void clearDisplay()

Deletes all characters from the display.

public void backlightOn()

Turns the backlight on.

public void backlightOff()

Turns the backlight off.

public boolean isBacklightOn()

Returns true if the backlight is on and false otherwise.

Advanced Functions

public void setConfig(boolean cursor, boolean blinking)

Configures if the cursor (shown as "_") should be visible and if it should be blinking (shown as a blinking block). The cursor position is one character behind the the last text written with writeLine().

The default is (false, false).

public BrickletLCD20x4.Config getConfig()

Returns the configuration as set by setConfig().

The returned object has the public member variables boolean cursor and boolean blinking.

public boolean isButtonPressed(short button)

Returns true if the button (0 to 2 or 0 to 3 since hardware version 1.2) is pressed.

If you want to react on button presses and releases it is recommended to use the ButtonPressedCallback and ButtonReleasedCallback callbacks.

public void setCustomCharacter(short index, short[] character)

The LCD 20x4 Bricklet can store up to 8 custom characters. The characters consist of 5x8 pixels and can be addressed with the index 0-7. To describe the pixels, the first 5 bits of 8 bytes are used. For example, to make a custom character "H", you should transfer the following:

  • character[0] = 0b00010001 (decimal value 17)
  • character[1] = 0b00010001 (decimal value 17)
  • character[2] = 0b00010001 (decimal value 17)
  • character[3] = 0b00011111 (decimal value 31)
  • character[4] = 0b00010001 (decimal value 17)
  • character[5] = 0b00010001 (decimal value 17)
  • character[6] = 0b00010001 (decimal value 17)
  • character[7] = 0b00000000 (decimal value 0)

The characters can later be written with writeLine() by using the characters with the byte representation 8 ("x08") to 15 ("x0F").

You can play around with the custom characters in Brick Viewer version since 2.0.1.

Custom characters are stored by the LCD in RAM, so they have to be set after each startup.

New in version 2.0.1 (Plugin).

public short[] getCustomCharacter(short index)

Returns the custom character for a given index, as set with setCustomCharacter().

New in version 2.0.1 (Plugin).

public void setDefaultText(short line, String text)

Sets the default text for lines 0-3. The max number of characters per line is 20.

The default text is shown on the LCD, if the default text counter expires, see setDefaultTextCounter().

New in version 2.0.2 (Plugin).

public String getDefaultText(short line)

Returns the default text for a given line (0-3) as set by setDefaultText().

New in version 2.0.2 (Plugin).

public void setDefaultTextCounter(int counter)

Sets the default text counter in ms. This counter is decremented each ms by the LCD firmware. If the counter reaches 0, the default text (see setDefaultText()) is shown on the LCD.

This functionality can be used to show a default text if the controlling program crashes or the connection is interrupted.

A possible approach is to call setDefaultTextCounter() every minute with the parameter 1000*60*2 (2 minutes). In this case the default text will be shown no later than 2 minutes after the controlling program crashes.

A negative counter turns the default text functionality off.

The default is -1.

New in version 2.0.2 (Plugin).

public int getDefaultTextCounter()

Returns the current value of the default text counter.

New in version 2.0.2 (Plugin).

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:

  • BrickletLCD20x4.FUNCTION_WRITE_LINE = 1
  • BrickletLCD20x4.FUNCTION_CLEAR_DISPLAY = 2
  • BrickletLCD20x4.FUNCTION_BACKLIGHT_ON = 3
  • BrickletLCD20x4.FUNCTION_BACKLIGHT_OFF = 4
  • BrickletLCD20x4.FUNCTION_SET_CONFIG = 6
  • BrickletLCD20x4.FUNCTION_SET_CUSTOM_CHARACTER = 11
  • BrickletLCD20x4.FUNCTION_SET_DEFAULT_TEXT = 13
  • BrickletLCD20x4.FUNCTION_SET_DEFAULT_TEXT_COUNTER = 15
public void setResponseExpectedAll(boolean responseExpected)

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

public BrickletLCD20x4.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 BrickletLCD20x4.ButtonPressedCallback
Parameters:button -- short

This callback is triggered when a button is pressed. The parameter is the number of the button (0 to 2 or 0 to 3 since hardware version 1.2).

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 addButtonPressedCallback() function. An added callback function can be removed with the removeButtonPressedCallback() function.

public callback BrickletLCD20x4.ButtonReleasedCallback
Parameters:button -- short

This callback is triggered when a button is released. The parameter is the number of the button (0 to 2 or 0 to 3 since hardware version 1.2).

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 addButtonReleasedCallback() function. An added callback function can be removed with the removeButtonReleasedCallback() function.

Constants

public static final int BrickletLCD20x4.DEVICE_IDENTIFIER

This constant is used to identify a LCD 20x4 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 BrickletLCD20x4.DEVICE_DISPLAY_NAME

This constant represents the human readable name of a LCD 20x4 Bricklet.