As you fly from airport to airport, you are required to "check in" with Air Traffic Control to get permission to taxi, land, etc. This is done via a bank of electronics collectively called the radio stack.
From top to bottom, On a Cessna 172, you have two COMM/NAV radio beacons, a ADF (Automatic Direction Finder), and a DME. The ADF is a radio compass and gives the relative bearing using a navigation beacon. A DME stands for Direction Measuring Equipment and provides the plit groundspeed and time-to-station (ie distance) readouts by differentiation.
Simulator Requirements:
20x 7Segment displays for the each of the two COMM/NAV units. However the first digit is always a 1 so that can be fixed and not interfaced to a pic. This reduces the number down to 4 per frequency or 32. It might be possible to reduce the number of digits still further depending on the offical allowable frequnecy range. (Please change this to suit and add the source for checking.) Eight switches is required along with two rotary encoders for each of the comm/nav compnents.
Short componetn list
Comm/NAV compent (Multiply by 2 for the pai of Comm/NAV)
16x 7Segment Displays
2x rotary encoders to change the frequencies
2x push buttons for swapping between selected and standby frequencies
2x toggle switches for activivating the comm/nav.
2x rotary switch ( setting the volume of the audio from the navigation beacon.
ADF is probably the smallest compnent of the radio stack. 6x 7segment displays are used. One
Other instruments need to be Documented