The Arduino uses a shift register to interact with the keyboard’s 8×10 matrix, and the sketch translates any serial data it receives into the keypresses the clone is expecting.

[Peter] chose the Arduino Nano. However, the LK200 was more than just a keyboard for communicating with the terminal, it also housed a speaker and LEDs which the terminal used to communicate with ...

To make that actually work, Robofun paired an Arduino board with some capacitive controllers for the base, and connected that to a Raspberry Pi that linked the keyboard to the TV.