Keypad v1.0

Connects a matrix keypad to a receiver. Characters are displayed on an LCD and sent via USB (with USART). While typing, you can switch between uppercase and lowercase letters and numbers. The implementation supports character deletion.

For code documentation see projects website.

Physical components

• Arduino UNO board with ATmega328P - the core of the device, communicates with outer devices via USB, other similar devices might also work
• matrix keypad - used for device control
• LCD HD44780 16x2 - displays the text written by the user
• I2C converter for LCD - ensures communication conversion between the board and the LCD

Features

• displaying typed characters on the LCD and sending them via USB
  • the last two lines of text are shown on the LCD
  • characters are sent via USB one by one
• when pressed repeatedly, the currently selected letter is displayed at the cursor position
• customizable key mapping (in the source code)
• customizable macro functions for the A, B, C, D buttons, default configurations are as follows:
• toggling between uppercase and lowercase letters and numbers
  • uppercase/lowercase toggled with A
  • numbers toggled with B
  • when transitioning from uppercase letters to numbers and back, uppercase letters are maintained
• scrolling on the LCD
  • scrolling on the display is possible using C
  • scrolling does not affect the transmitted data and is not equivalent to \n; it is purely visual
• deleting characters using D
• the LED lights up while any key is being pressed

Wiring diagram

Possible improvements

Overall project improvements

• More keyboard modes and improved indication (e.g., using multiple differently colored LEDs).
• On-the-fly key mapping configuration. Entering a menu where the user can click to choose which letters they want on the keys.
• On/Off button.
• Placing the device in a compact enclosure, approximately 9x12 cm.
• Bluetooth, Wi-Fi connectivity to the computer, enabling text input from virtually anywhere.
• Linking with a PC to use the device as a full-fledged keyboard. Currently, I only display its output in a terminal monitoring the serial link.
• Mouse cursor control mode. The keypad has enough buttons for it, and we could even support diagonal movement.

Code improvements

• Extract key mapping to a config file.
• Get rid of active waiting, instead rely on interrupts.

Acknowledgments

The communication between the Arduino UNO board and LCD via I2C is managed by the library HD44780_PCF8574 by Matiasus.