Shell - LCD 20x4 Bricklet

This is the description of the Shell 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 Shell 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.sh)

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#!/bin/sh
# Connects to localhost:4223 by default, use --host and --port to change this

uid=XYZ # Change XYZ to the UID of your LCD 20x4 Bricklet

# Turn backlight on
tinkerforge call lcd-20x4-bricklet $uid backlight-on

# Write "Hello World"
tinkerforge call lcd-20x4-bricklet $uid write-line 0 0 "Hello World"

Button Callback

Download (example-button-callback.sh)

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#!/bin/sh
# Connects to localhost:4223 by default, use --host and --port to change this

uid=XYZ # Change XYZ to the UID of your LCD 20x4 Bricklet

# Handle incoming button pressed callbacks
tinkerforge dispatch lcd-20x4-bricklet $uid button-pressed &

# Handle incoming button released callbacks
tinkerforge dispatch lcd-20x4-bricklet $uid button-released &

echo "Press key to exit"; read dummy

kill -- -$$ # Stop callback dispatch in background

Unicode

Download (example-unicode.sh)

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#!/bin/sh
# Connects to localhost:4223 by default, use --host and --port to change this

uid=XYZ # Change XYZ to the UID of your LCD 20x4 Bricklet

# Turn backlight on
tinkerforge call lcd-20x4-bricklet $uid backlight-on

# Write some strings using sed to map to the LCD charset
# Note: This assumes that the shell supports UTF-8
tinkerforge call lcd-20x4-bricklet $uid write-line 0 0\
 "`echo 'Stromstärke: 17µA' | sed 'y/\o134~¥→←°αÄäßεµςρ√¹¤¢ⱠñÖöϴ∞ΩÜüΣπ÷■/\o244\o55\o134\o176\o177\o337\o340\o341\o341\o342\o343\o344\o345\o346\o350\o351\o353\o354\o355\o356\o357\o357\o362\o363\o364\o365\o365\o366\o367\o375\o377/'`"
tinkerforge call lcd-20x4-bricklet $uid write-line 1 0\
 "`echo 'Temperatur:  23°C' | sed 'y/\o134~¥→←°αÄäßεµςρ√¹¤¢ⱠñÖöϴ∞ΩÜüΣπ÷■/\o244\o55\o134\o176\o177\o337\o340\o341\o341\o342\o343\o344\o345\o346\o350\o351\o353\o354\o355\o356\o357\o357\o362\o363\o364\o365\o365\o366\o367\o375\o377/'`"

# Write a string directly including characters from the LCD charset
tinkerforge call lcd-20x4-bricklet $uid write-line 2 0\
 "`printf 'Drehzahl:   750min\xe9'`"

API

Possible exit codes for all tinkerforge commands are:

  • 1: interrupted (ctrl+c)
  • 2: syntax error
  • 21: Python 2.5 or newer is required
  • 22: Python argparse module is missing
  • 23: socket error
  • 24: other exception
  • 25: invalid placeholder in format string
  • 26: authentication error
  • 201: timeout occurred
  • 209: invalid argument value
  • 210: function is not supported
  • 211: unknown error

Command Structure

The common options of the call and dispatch commands are documented here. The specific command structure is shown below.

tinkerforge call lcd-20x4-bricklet [<option>..] <uid> <function> [<argument>..]
Parameters:
  • <uid> -- string
  • <function> -- string

The call command is used to call a function of the LCD 20x4 Bricklet. It can take several options:

  • --help shows help for the specific call command and exits
  • --list-functions shows a list of known functions of the LCD 20x4 Bricklet and exits
tinkerforge dispatch lcd-20x4-bricklet [<option>..] <uid> <callback>
Parameters:
  • <uid> -- string
  • <callback> -- string

The dispatch command is used to dispatch a callback of the LCD 20x4 Bricklet. It can take several options:

  • --help shows help for the specific dispatch command and exits
  • --list-callbacks shows a list of known callbacks of the LCD 20x4 Bricklet and exits
tinkerforge call lcd-20x4-bricklet <uid> <function> [<option>..] [<argument>..]
Parameters:
  • <uid> -- string
  • <function> -- string

The <function> to be called can take different options depending of its kind. All functions can take the following options:

  • --help shows help for the specific function and exits

Getter functions can take the following options:

  • --execute <command> shell command line to execute for each incoming response (see section about output formatting for details)

Setter functions can take the following options:

  • --expect-response requests response and waits for it

The --expect-response option for setter functions allows to detect timeouts and other error conditions calls of setters as well. The device will then send a response for this purpose. If this option is not given for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

tinkerforge dispatch lcd-20x4-bricklet <uid> <callback> [<option>..]
Parameters:
  • <uid> -- string
  • <callback> -- string

The <callback> to be dispatched can take several options:

  • --help shows help for the specific callback and exits
  • --execute <command> shell command line to execute for each incoming response (see section about output formatting for details)

Basic Functions

tinkerforge call lcd-20x4-bricklet <uid> write-line <line> <position> <text>
Parameters:
  • <line> -- int
  • <position> -- int
  • <text> -- string
Output:

no output

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.

tinkerforge call lcd-20x4-bricklet <uid> clear-display
Output:no output

Deletes all characters from the display.

tinkerforge call lcd-20x4-bricklet <uid> backlight-on
Output:no output

Turns the backlight on.

tinkerforge call lcd-20x4-bricklet <uid> backlight-off
Output:no output

Turns the backlight off.

tinkerforge call lcd-20x4-bricklet <uid> is-backlight-on
Output:
  • backlight -- bool

Returns true if the backlight is on and false otherwise.

Advanced Functions

tinkerforge call lcd-20x4-bricklet <uid> set-config <cursor> <blinking>
Parameters:
  • <cursor> -- bool
  • <blinking> -- bool
Output:

no output

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).

tinkerforge call lcd-20x4-bricklet <uid> get-config
Output:
  • cursor -- bool
  • blinking -- bool

Returns the configuration as set by set-config.

tinkerforge call lcd-20x4-bricklet <uid> is-button-pressed <button>
Parameters:
  • <button> -- int
Output:
  • pressed -- 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 button-pressed and button-released callbacks.

tinkerforge call lcd-20x4-bricklet <uid> set-custom-character <index> <character>
Parameters:
  • <index> -- int
  • <character> -- int,int,..5x..,int
Output:

no output

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).

tinkerforge call lcd-20x4-bricklet <uid> get-custom-character <index>
Parameters:
  • <index> -- int
Output:
  • character -- 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).

tinkerforge call lcd-20x4-bricklet <uid> set-default-text <line> <text>
Parameters:
  • <line> -- int
  • <text> -- string
Output:

no output

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).

tinkerforge call lcd-20x4-bricklet <uid> get-default-text <line>
Parameters:
  • <line> -- int
Output:
  • text -- string

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

New in version 2.0.2 (Plugin).

tinkerforge call lcd-20x4-bricklet <uid> set-default-text-counter <counter>
Parameters:
  • <counter> -- int
Output:

no output

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).

tinkerforge call lcd-20x4-bricklet <uid> get-default-text-counter
Output:
  • counter -- int

Returns the current value of the default text counter.

New in version 2.0.2 (Plugin).

tinkerforge call lcd-20x4-bricklet <uid> get-identity
Output:
  • uid -- string
  • connected-uid -- string
  • position -- char
  • hardware-version -- int,int,int
  • firmware-version -- int,int,int
  • device-identifier -- int (has symbols)

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

Callbacks

Callbacks can be used to receive time critical or recurring data from the device:

tinkerforge dispatch lcd-20x4-bricklet <uid> example

The available callbacks 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.

tinkerforge dispatch lcd-20x4-bricklet <uid> button-pressed
Output:
  • 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).

tinkerforge dispatch lcd-20x4-bricklet <uid> button-released
Output:
  • 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).