This software is for an arduino pro micro (atmega32u4). It acts as an USB keyboard and converts impulses from a rotary disk into digits transmitted via USB to any software supporting keyboard.
impulse contact (nsi) is connected to pin 10 and nsa to pin 9. nsa get closed as soon disk is revolved. nsi starts generating impulses as soon disk is released and rotates back.
Needs only 3 wires, for nsi, nsa and 1x ground to the 2 switches. internal pull-up is used for pin 9 and 10.
Uses TimerOne library. https://code.google.com/archive/p/arduino-timerone/downloads Search for how-to tutorials if it is your first arduino library you install.
If you connect it to your computer (OS does not matter, as long it supports USB HID), you might get an error message. This is for the programming serial line, also implemented on that USB device. You can ignore that, after ..9 seconds rotary disk keyboard should be ready.
And if you think twice, impulse dialing is digital dialing. since 1913 (or so)