Python - LCD 16x2 Bricklet – Tinkerforge

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# Python - LCD 16x2 Bricklet

This is the description of the Python API bindings for the LCD 16x2 Bricklet. General information and technical specifications for the LCD 16x2 Bricklet are summarized in its hardware description.

An installation guide for the Python API bindings is part of their general description.

## Examples

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

### Hello World

Download (example_hello_world.py)

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    #!/usr/bin/env python
    # -*- coding: utf-8 -*-

    HOST = "localhost"
    PORT = 4223
    UID = "XYZ" # Change to your UID

    from tinkerforge.ip_connection import IPConnection
    from tinkerforge.bricklet_lcd_16x2 import LCD16x2

    if __name__ == "__main__":
        ipcon = IPConnection() # Create IP connection
        lcd = LCD16x2(UID, ipcon) # Create device object

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

        # Turn backlight on
        lcd.backlight_on()

        # Write "Hello World"
        lcd.write_line(0, 0, 'Hello World')

        raw_input('Press key to exit\n') # Use input() in Python 3
        ipcon.disconnect()

### Button Callbacks

Download (example_button_callbacks.py)

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    #!/usr/bin/env python
    # -*- coding: utf-8 -*-

    HOST = "localhost"
    PORT = 4223
    UID = "XYZ" # Change to your UID

    from tinkerforge.ip_connection import IPConnection
    from tinkerforge.bricklet_lcd_16x2 import LCD16x2

    # Callback functions for button status
    def cb_pressed(i):
        print('Pressed: ' + str(i))

    def cb_released(i):
        print('Released: ' + str(i))

    if __name__ == "__main__":
        ipcon = IPConnection() # Create IP connection
        lcd = LCD16x2(UID, ipcon) # Create device object

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

        # Register button status callbacks to cb_pressed and cb_released
        lcd.register_callback(lcd.CALLBACK_BUTTON_PRESSED, cb_pressed)
        lcd.register_callback(lcd.CALLBACK_BUTTON_RELEASED, cb_released)

        raw_input('Press key to exit\n') # Use input() in Python 3
        ipcon.disconnect()

### Unicode

Download (example_unicode.py)

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    #!/usr/bin/env python
    # -*- coding: utf-8 -*-

    HOST = "localhost"
    PORT = 4223
    UID = "6mJ" # Change to your UID

    import sys
    import types
    from tinkerforge.ip_connection import IPConnection
    from tinkerforge.bricklet_lcd_16x2 import LCD16x2

    # Maps a Python string to the LCD charset
    def unicode_to_ks0066u(string):
        if sys.hexversion < 0x03000000:
            byte = lambda x: chr(x)
            ks0066u = ''

            if type(string) != types.UnicodeType:
                code_points = unicode(string, 'UTF-8')
            else:
                code_points = string
        else:
            byte = lambda x: bytes([x])
            ks0066u = bytes()
            code_points = string

        for code_point in code_points:
            code_point = ord(code_point)

            # ASCII subset from JIS X 0201
            if code_point >= 0x0020 and code_point <= 0x007e:
                # The LCD charset doesn't include '\' and '~', use similar characters instead
                mapping = {
                    0x005c : byte(0xa4), # REVERSE SOLIDUS maps to HALFWIDTH IDEOGRAPHIC COMMA
                    0x007e : byte(0x2d)  # TILDE maps to HYPHEN-MINUS
                }

                try:
                    c = mapping[code_point]
                except KeyError:
                    c = byte(code_point)
            # Katakana subset from JIS X 0201
            elif code_point >= 0xff61 and code_point <= 0xff9f:
                c = byte(code_point - 0xfec0)
            # Special characters
            else:
                mapping = {
                    0x00a5 : byte(0x5c), # YEN SIGN
                    0x2192 : byte(0x7e), # RIGHTWARDS ARROW
                    0x2190 : byte(0x7f), # LEFTWARDS ARROW
                    0x00b0 : byte(0xdf), # DEGREE SIGN maps to KATAKANA SEMI-VOICED SOUND MARK
                    0x03b1 : byte(0xe0), # GREEK SMALL LETTER ALPHA
                    0x00c4 : byte(0xe1), # LATIN CAPITAL LETTER A WITH DIAERESIS
                    0x00e4 : byte(0xe1), # LATIN SMALL LETTER A WITH DIAERESIS
                    0x00df : byte(0xe2), # LATIN SMALL LETTER SHARP S
                    0x03b5 : byte(0xe3), # GREEK SMALL LETTER EPSILON
                    0x00b5 : byte(0xe4), # MICRO SIGN
                    0x03bc : byte(0xe4), # GREEK SMALL LETTER MU
                    0x03c2 : byte(0xe5), # GREEK SMALL LETTER FINAL SIGMA
                    0x03c1 : byte(0xe6), # GREEK SMALL LETTER RHO
                    0x221a : byte(0xe8), # SQUARE ROOT
                    0x00b9 : byte(0xe9), # SUPERSCRIPT ONE maps to SUPERSCRIPT (minus) ONE
                    0x00a4 : byte(0xeb), # CURRENCY SIGN
                    0x00a2 : byte(0xec), # CENT SIGN
                    0x2c60 : byte(0xed), # LATIN CAPITAL LETTER L WITH DOUBLE BAR
                    0x00f1 : byte(0xee), # LATIN SMALL LETTER N WITH TILDE
                    0x00d6 : byte(0xef), # LATIN CAPITAL LETTER O WITH DIAERESIS
                    0x00f6 : byte(0xef), # LATIN SMALL LETTER O WITH DIAERESIS
                    0x03f4 : byte(0xf2), # GREEK CAPITAL THETA SYMBOL
                    0x221e : byte(0xf3), # INFINITY
                    0x03a9 : byte(0xf4), # GREEK CAPITAL LETTER OMEGA
                    0x00dc : byte(0xf5), # LATIN CAPITAL LETTER U WITH DIAERESIS
                    0x00fc : byte(0xf5), # LATIN SMALL LETTER U WITH DIAERESIS
                    0x03a3 : byte(0xf6), # GREEK CAPITAL LETTER SIGMA
                    0x03c0 : byte(0xf7), # GREEK SMALL LETTER PI
                    0x0304 : byte(0xf8), # COMBINING MACRON
                    0x00f7 : byte(0xfd), # DIVISION SIGN
                    0x25a0 : byte(0xff)  # BLACK SQUARE
                }

                try:
                    c = mapping[code_point]
                except KeyError:
                    c = byte(0xff) # BLACK SQUARE

            # Special handling for 'x' followed by COMBINING MACRON
            if c == byte(0xf8):
                if len(ks0066u) == 0 or not ks0066u.endswith(byte(0x78)):
                    c = byte(0xff) # BLACK SQUARE

                if len(ks0066u) > 0:
                    ks0066u = ks0066u[:-1]

            ks0066u += c

        return ks0066u

    if __name__ == "__main__":
        ipcon = IPConnection() # Create IP connection
        lcd = LCD16x2(UID, ipcon) # Create device object

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

        # Turn backlight on
        lcd.backlight_on()

        # Write a string using the unicode_to_ks0066u function to map to the LCD charset
        lcd.write_line(0, 0, unicode_to_ks0066u('Stromstärke: 5µA'))

        # Write a string directly including characters from the LCD charset
        lcd.write_line(1, 0, b'Drehzahl: 1000s\xe9')

        raw_input('Press key to exit\n') # Use input() in Python 3
        ipcon.disconnect()

## API

Generally, every method of the Python bindings can throw an `tinkerforge.ip_connection.Error` exception that has a `value` and a `description` property. `value` can have different values:

- Error.TIMEOUT = -1
- Error.ALREADY_CONNECTED = -7
- Error.NOT_CONNECTED = -8
- Error.INVALID_PARAMETER = -9
- Error.NOT_SUPPORTED = -10
- Error.UNKNOWN_ERROR_CODE = -11

All methods listed below are thread-safe.

### Basic Functions

`LCD16x2`(uid, ipcon)

  Parameters:

  - uid -- string
  - ipcon -- IPConnection

  Creates an object with the unique device ID `uid`:

      lcd_16x2 = LCD16x2("YOUR_DEVICE_UID", ipcon)

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

`LCD16x2.``write_line`(line, position, text)

  Parameters:

  - line -- int
  - position -- int
  - text -- str

  Return type: | None

  Writes text to a specific line (0 to 1) with a specific position (0 to 15). The text can have a maximum of 16 characters.

  For example: (0, 5, "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.

`LCD16x2.``clear_display`()

  Return type: | None

  Deletes all characters from the display.

`LCD16x2.``backlight_on`()

  Return type: | None

  Turns the backlight on.

`LCD16x2.``backlight_off`()

  Return type: | None

  Turns the backlight off.

`LCD16x2.``is_backlight_on`()

  Return type: | bool

  Returns true if the backlight is on and false otherwise.

### Advanced Functions

`LCD16x2.``set_config`(cursor, blinking)

  Parameters:

  - cursor -- bool
  - blinking -- bool

  Return type: | None

  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 `write_line()`.

  The default is (false, false).

`LCD16x2.``get_config`()

  Return type: | (bool, bool)

  Returns the configuration as set by `set_config()`.

  The returned namedtuple has the variables `cursor` and `blinking`.

`LCD16x2.``is_button_pressed`(button)

  Parameters: | button -- int
  Return type: | bool

  Returns true if the button (0 to 2) is pressed. If you want to react on button presses and releases it is recommended to use the `CALLBACK_BUTTON_PRESSED` and `CALLBACK_BUTTON_RELEASED` callbacks.

`LCD16x2.``set_custom_character`(index, character)

  Parameters:

  - index -- int
  - character -- [int, int, int, int, int, int, int, int]

  Return type: | None

  The LCD 16x2 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 `write_line()` by using the characters with the byte representation 8 to 15.

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

`LCD16x2.``get_custom_character`(index)

  Parameters: | index -- int
  Return type: | [int, int, int, int, int, int, int, int]

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

  New in version 2.0.1 (Plugin).

`LCD16x2.``get_api_version`()

  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.

`LCD16x2.``get_response_expected`(function_id)

  Parameters: | function_id -- int
  Return type: | bool

  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 `set_response_expected()`. 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 `set_response_expected()` for the list of function ID constants available for this function.

`LCD16x2.``set_response_expected`(function_id, response_expected)

  Parameters:

  - function_id -- int
  - response_expected -- bool

  Return type: | None

  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:

  - LCD16x2.FUNCTION_WRITE_LINE = 1
  - LCD16x2.FUNCTION_CLEAR_DISPLAY = 2
  - LCD16x2.FUNCTION_BACKLIGHT_ON = 3
  - LCD16x2.FUNCTION_BACKLIGHT_OFF = 4
  - LCD16x2.FUNCTION_SET_CONFIG = 6
  - LCD16x2.FUNCTION_SET_CUSTOM_CHARACTER = 11

`LCD16x2.``set_response_expected_all`(response_expected)

  Parameters: | response_expected -- bool
  Return type: | None

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

`LCD16x2.``get_identity`()

  Return type: | (str, str, chr, [int, int, int], [int, int, int], 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.

  The returned namedtuple has the variables `uid`, `connected_uid`, `position`, `hardware_version`, `firmware_version` and `device_identifier`.

### Callback Configuration Functions

`LCD16x2.``register_callback`(id, callback)

  Parameters:

  - id -- int
  - callback -- callable

  Return type: | None

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

### Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the `register_callback()` function of the device object. The first parameter is the callback ID and the second parameter the callback function:

    def my_callback(param):
        print(param)

    lcd_16x2.register_callback(LCD16x2.CALLBACK_EXAMPLE, my_callback)

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.

`LCD16x2.``CALLBACK_BUTTON_PRESSED`

  Parameters: | button -- int

  This callback is triggered when a button is pressed. The parameter is the number of the button (0 to 2).

`LCD16x2.``CALLBACK_BUTTON_RELEASED`

  Parameters: | button -- int

  This callback is triggered when a button is released. The parameter is the number of the button (0 to 2).

### Constants

`LCD16x2.``DEVICE_IDENTIFIER`

  This constant is used to identify a LCD 16x2 Bricklet.

  The `get_identity()` 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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