This encoder has 5 pins named A (output 1), B (output 2), C (central, GND) and two pins for the pushbutton.
The connection to the Master Card is very easy: simply connect the pin A and B to two consecutive inputs of the Master Card (1 and 2 for instance) and the pin C to the GND of the same group of the M. Card inputs where pins A and B are connected: you don't need nothing else !
Since I don't have the chance to make a dual rotary encoder for the NAV1/NAV2 frequency selector, I thought I could have used the pushbutton to set alternatively the decimal part of the frequency or the "hundreds" part of it.
Same thing for the ALT selector (pushing the button means to set the altitude with increment/decrement of 1000 feet per detent), for the HDG/CRS selector the button activates the increment/decrement of 10 degree per detent.
The keyboard to select the various functions of the autopilot is a simple group of buttons connected to the Master Card inputs.
The software took the biggest part of this work, spending many hours to fly studying the "behaviour" of the autopilot implemented in different ATR panels.
Mainly the program dialogs with FS using FSUIPC, while the connection with the Master Card is made using a DLL (IOCDLL.DLL) included with the Master Card software.
Note that IOCDLL.DLL is no longer supported by Opencockpits but I found it useful since I can read
all the inputs (and drive outputs).
The encoders and Master Card inputs are read every 10 ms with a light impact on the CPU load.
The next page will show you some pic of the module.