Keyboard and Mouse Control | Arduino Documentation | Arduino Documentation
Simple keyboard using the tone() function | Arduino Documentation | Arduino Documentation
Arduino Keypad
4x4 Matrix Keyboard 4*4 Keypad Array Module Key Button Membrane Switch with LED MCU Control Panel Board Pad DIY Kit For Arduino|Integrated Circuits| - AliExpress
Analog Button for Arduino Keyboard Electronic Simulate Five Key | eBay
Lekce 7 - Arduino - Membránová klávesnice a její programování