Perl - LCD 20x4 Bricklet

This is the description of the Perl 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 Perl 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.pl)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
#!/usr/bin/perl

use strict;
use Tinkerforge::IPConnection;
use Tinkerforge::BrickletLCD20x4;

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

my $ipcon = Tinkerforge::IPConnection->new(); # Create IP connection
my $lcd = Tinkerforge::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");

print "Press key to exit\n";
<STDIN>;
$ipcon->disconnect();

Button Callback

Download (example_button_callback.pl)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
#!/usr/bin/perl

use strict;
use Tinkerforge::IPConnection;
use Tinkerforge::BrickletLCD20x4;

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

# Callback subroutine for button pressed callback
sub cb_button_pressed
{
    my ($button) = @_;

    print "Button Pressed: $button\n";
}

# Callback subroutine for button released callback
sub cb_button_released
{
    my ($button) = @_;

    print "Button Released: $button\n";
}

my $ipcon = Tinkerforge::IPConnection->new(); # Create IP connection
my $lcd = Tinkerforge::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 to subroutine cb_button_pressed
$lcd->register_callback($lcd->CALLBACK_BUTTON_PRESSED, 'cb_button_pressed');

# Register button released callback to subroutine cb_button_released
$lcd->register_callback($lcd->CALLBACK_BUTTON_RELEASED, 'cb_button_released');

print "Press key to exit\n";
<STDIN>;
$ipcon->disconnect();

API

Generally, every subroutine of the Perl bindings can report an error as Tinkerforge::Error object via croak(). The object has a get_code() and a get_message() subroutine. There are different error code:

  • Error->ALREADY_CONNECTED = 11
  • Error->NOT_CONNECTED = 12
  • Error->CONNECT_FAILED = 13
  • Error->INVALID_FUNCTION_ID = 21
  • Error->TIMEOUT = 31
  • Error->INVALID_PARAMETER = 41
  • Error->FUNCTION_NOT_SUPPORTED = 42
  • Error->UNKNOWN_ERROR = 43

All methods listed below are thread-safe.

Basic Functions

BrickletLCD20x4->new($uid, $ipcon)
Parameters:
  • $uid -- string
  • $ipcon -- IPConnection
Return type:

BrickletLCD20x4

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)
Parameters:
  • $line -- int
  • $position -- int
  • $text -- string
Return type:

undef

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()
Return type:undef

Deletes all characters from the display.

BrickletLCD20x4->backlight_on()
Return type:undef

Turns the backlight on.

BrickletLCD20x4->backlight_off()
Return type:undef

Turns the backlight off.

BrickletLCD20x4->is_backlight_on()
Return type:bool

Returns true if the backlight is on and false otherwise.

Advanced Functions

BrickletLCD20x4->set_config($cursor, $blinking)
Parameters:
  • $cursor -- bool
  • $blinking -- bool
Return type:

undef

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()
Return type:[bool, bool]

Returns the configuration as set by set_config().

The returned array contains the elements cursor and blinking.

BrickletLCD20x4->is_button_pressed($button)
Parameters:$button -- int
Return type:bool

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)
Parameters:
  • $index -- int
  • @character -- [int, int, ..5x.., int]
Return type:

undef

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($index)
Parameters:$index -- int
Return type:[int, int, ..5x.., 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)
Parameters:
  • $line -- int
  • $text -- string
Return type:

undef

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($line)
Parameters:$line -- int
Return type:string

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($counter)
Parameters:$counter -- int
Return type:undef

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()
Return type:int

Returns the current value of the default text counter.

New in version 2.0.2 (Plugin).

BrickletLCD20x4->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.

BrickletLCD20x4->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.

BrickletLCD20x4->set_response_expected($function_id, $response_expected)
Parameters:
  • $function_id -- int
  • $response_expected -- bool
Return type:

undef

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($response_expected)
Parameters:$response_expected -- bool
Return type:undef

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

BrickletLCD20x4->get_identity()
Return type:[string, string, char, [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 contains the elements uid, connected_uid, position, hardware_version, firmware_version and device_identifier.

Callback Configuration Functions

BrickletLCD20x4->register_callback($id, $callback)
Parameters:
  • $id -- int
  • $callback -- string
Return type:

undef

Registers the given $function name 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 the callback function name:

sub my_callback
{
    print "@_[0]";
}

$lcd_20x4->register_callback(BrickletLCD20x4->CALLBACK_EXAMPLE, 'my_callback')

The callback function will be called from an internal thread of the IP Connection. In contrast to many other programming languages, variables are not automatically shared between threads in Perl. If you want to share a global variable between a callback function and the rest for your program it has to be marked as :shared. See the documentation of the threads::shared Perl module for more details.

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.