Ruby - LCD 20x4 Bricklet

This is the description of the Ruby 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 Ruby 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.rb)

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#!/usr/bin/env ruby
# -*- ruby encoding: utf-8 -*-

require 'tinkerforge/ip_connection'
require 'tinkerforge/bricklet_lcd_20x4'

include Tinkerforge

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

ipcon = IPConnection.new # Create IP connection
lcd = BrickletLCD20x4.new 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'

puts 'Press key to exit'
$stdin.gets
ipcon.disconnect

Button Callback

Download (example_button_callback.rb)

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#!/usr/bin/env ruby
# -*- ruby encoding: utf-8 -*-

require 'tinkerforge/ip_connection'
require 'tinkerforge/bricklet_lcd_20x4'

include Tinkerforge

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

ipcon = IPConnection.new # Create IP connection
lcd = BrickletLCD20x4.new UID, ipcon # Create device object

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

# Register button pressed callback
lcd.register_callback(BrickletLCD20x4::CALLBACK_BUTTON_PRESSED) do |button|
  puts "Button Pressed: #{button}"
end

# Register button released callback
lcd.register_callback(BrickletLCD20x4::CALLBACK_BUTTON_RELEASED) do |button|
  puts "Button Released: #{button}"
end

puts 'Press key to exit'
$stdin.gets
ipcon.disconnect

Unicode

Download (example_unicode.rb)

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#!/usr/bin/env ruby
# -*- ruby encoding: utf-8 -*-

require 'tinkerforge/ip_connection'
require 'tinkerforge/bricklet_lcd_20x4'

include Tinkerforge

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

def unicode_to_ks0066u(string)
  ks0066u = ''

  string.each_codepoint do |codepoint|
    # ASCII subset from JIS X 0201
    if codepoint >= 0x0020 and codepoint <= 0x007e
      # The LCD charset doesn't include '\' and '~', use similar characters instead
      mapping = {
        0x005c => 0xa4.chr, # REVERSE SOLIDUS maps to IDEOGRAPHIC COMMA
        0x007e => 0x2d.chr  # TILDE maps to HYPHEN-MINUS
      }

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

      if mapping.has_key? codepoint
        c = mapping[codepoint]
      else
        c = 0xff.chr # BLACK SQUARE
      end
    end

    # Special handling for 'x' followed by COMBINING MACRON
    if c == 0xf8.chr
      if ks0066u.length == 0 or not ks0066u[-1, 1] == 0x78.chr
        c = 0xff.chr # BLACK SQUARE
      end

      if ks0066u.length > 0
        ks0066u = ks0066u[0..-2]
      end
    end

    ks0066u += c
  end

  ks0066u
end

ipcon = IPConnection.new # Create IP connection
lcd = BrickletLCD20x4.new 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: 17µA')
lcd.write_line 1, 0, unicode_to_ks0066u('Temperatur:  23°C')

# Write a string directly including characters from the LCD charset
lcd.write_line 2, 0, "Drehzahl:   750min\xe9"

puts 'Press key to exit'
$stdin.gets
ipcon.disconnect

API

All methods listed below are thread-safe.

Basic Functions

BrickletLCD20x4::new(uid, ipcon) → lcd_20x4
Parameters:
  • uid -- str
  • ipcon -- IPConnection

Creates an object with the unique device ID uid:

lcd_20x4 = BrickletLCD20x4.new 'YOUR_DEVICE_UID', ipcon

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

BrickletLCD20x4#write_line(line, position, text) → nil
Parameters:
  • line -- int
  • position -- int
  • text -- str

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.

BrickletLCD20x4#clear_display → nil

Deletes all characters from the display.

BrickletLCD20x4#backlight_on → nil

Turns the backlight on.

BrickletLCD20x4#backlight_off → nil

Turns the backlight off.

BrickletLCD20x4#is_backlight_on → bool

Returns true if the backlight is on and false otherwise.

Advanced Functions

BrickletLCD20x4#set_config(cursor, blinking) → nil
Parameters:
  • cursor -- bool
  • blinking -- bool

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).

BrickletLCD20x4#get_config → [bool, bool]

Returns the configuration as set by #set_config.

The returned array has the values cursor and blinking.

BrickletLCD20x4#is_button_pressed(button) → bool
Parameters:button -- int

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 ::CALLBACK_BUTTON_PRESSED and ::CALLBACK_BUTTON_RELEASED callbacks.

BrickletLCD20x4#set_custom_character(index, character) → nil
Parameters:
  • index -- int
  • character -- [int, int, ..5x.., int]

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 #write_line 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).

BrickletLCD20x4#get_custom_character(index) → [int, int, ..5x.., int]
Parameters:index -- int

Returns the custom character for a given index, as set with #set_custom_character.

New in version 2.0.1 (Plugin).

BrickletLCD20x4#set_default_text(line, text) → nil
Parameters:
  • line -- int
  • text -- str

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 #set_default_text_counter.

New in version 2.0.2 (Plugin).

BrickletLCD20x4#get_default_text(line) → str
Parameters:line -- int

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

New in version 2.0.2 (Plugin).

BrickletLCD20x4#set_default_text_counter(counter) → nil
Parameters:counter -- int

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 #set_default_text) 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 #set_default_text_counter 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).

BrickletLCD20x4#get_default_text_counter → int

Returns the current value of the default text counter.

New in version 2.0.2 (Plugin).

BrickletLCD20x4#get_api_version → [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.

BrickletLCD20x4#get_response_expected(function_id) → bool
Parameters:function_id -- int

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.

BrickletLCD20x4#set_response_expected(function_id, response_expected) → nil
Parameters:
  • function_id -- int
  • response_expected -- bool

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
BrickletLCD20x4#set_response_expected_all(response_expected) → nil
Parameters:response_expected -- bool

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

BrickletLCD20x4#get_identity → [str, str, str, [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 array has the values uid, connected_uid, position, hardware_version, firmware_version and device_identifier.

Callback Configuration Functions

BrickletLCD20x4#register_callback(callback_id) { |param [, ...]| block } → nil
Parameters:callback_id -- int

Registers the given block with the given callback_id.

The available callback 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 is a block:

lcd_20x4.register_callback BrickletLCD20x4::CALLBACK_EXAMPLE, do |param|
  puts "#{param}"
end

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.

BrickletLCD20x4::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 or 0 to 3 since hardware version 1.2).

BrickletLCD20x4::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 or 0 to 3 since hardware version 1.2).

Constants

BrickletLCD20x4::DEVICE_IDENTIFIER

This constant is used to identify a LCD 20x4 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.

BrickletLCD20x4::DEVICE_DISPLAY_NAME

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