The MCDU push buttons are configured in a keyboard matrix, or grid setup. The keyboard (and other OEM equipment with extensive input requirements) can be interfaced to a board and software which supports matrix wiring configuration.

The Airbus MCDU requires inputs for a 10 x 8 grid (see pinout schematics here), and analog support for a potentiometer (screen dimmer).

Once connected in matrix configuration to your interface board, software must be developed to translate the key presses to the avionics API. Alternatively, the matrix keyboard can be connected to a universal joystick board and each keyboard switch can be configured in the avionics suite as joystick push buttons.

For the Soarbywire Airbus A320 setup, the MCDU outputs are connected to a 50P IDC ribbon cable and interfaced to a Arduino Leonardo R3 ATmega32U4. This board is low cost (clones are available on eBay) and has the sufficient inputs for the matrix configuration and analog input for the potentiometer.

An appropriate joystick software to use is MMJoy2. Ensure you upload the appropriate firmware which supports 128 pushbuttons (69 is required for the MCDU which older firmware may not support).

Configure the rows and columns accordingly:

Once the hardware has been configured enter the avionics joystick button configuration program (FMGS_Config for Jeehell FMGS) to individually assign each switch.

A common LCD used for the MCDU is the Innolux Display model AT058TN52 V.3 (5.6″). Place the screen behind a thick tinted glass to simulate a CRT display.

To complete the setup connect the annunciator bulbs (FAIL, FMGC, MENU, MCDU) to your output board, and the LCD power to a relay for realistic bus (MCDU 1 – AC ESS SHED, MCDU 2 – AC2) operation.