Checking on MCU and their use, gave me the opportunity to create Autopilot Units. Controlling all AP and some Radio settings just like in real aircraft’s, makes flying with a simulator even more exciting!
Microchip PIC micro controllers with USB capability can be configured as a virtual COM port device. This make interfacing with a PC very easy. 

The need of a program between the COM ports and the flight sim made me create a program called APNAVI. It reads all FS variables and sends them to the units via the COM ports. Then it scans inputs on both FS and the units. Changes in settings are copied the other way.

APNAVI, written in VB6, can be downloaded here as a reference.

Both units have LCD screens for the convenience of setting values, debugging and configuration of internal values. Click on the drawing below to see it detailed.

Most LED’s and buttons are controlled by I2C-IO, 8 channel extenders.
The rotary knobs in both units are like encoders. They are self made with IR LED’s / IR Transistor OPTO couplers, so they are endlessly turn able.

The AP unit was created around a PIC18F4550 Micro controller. The Radio unit has a PIC18F14K50 micro controller.
Both units are equipped with a boot loader so, programmable by USB!!

Recently I created a way in the Radio unit to set the barometric pressure.