The 486 that [someyob] is restoring had the Turbo button, but sadly there was just a simple LED to show whether or not it was engaged.

Running out of GPIO pins? Learn how to connect multiple buttons to just one Arduino pin using clever wiring and resistor techniques. Perfect for compact projects, keyboards, or when using small ...

The output can be digital (in several formats) or analog. The radio takes serial (I2C) commands, and the Arduino converts the user interface so that you can control it.