For accurate display management it is important that each display unit monitor (LCD) is controlled by the appropriate aircraft power bus.
This allows for correct simulation and power monitor (on/off) output behaviour. Avionics software such as ProSimA320 and Jeehell FMGS are able to manage the screen displays but this is done at a software level. This can be unrealistic – for example, in an aircraft cold and dark state, although the flight deck is unpowered the displays will display a certain black hue (due to the nature of LCDs) giving the impression that they are still powered. The backlight of the LCD can also leak from the display edges, again misrepresenting the simulation.
There are several challenges when trying to achieve correct display power management. A relay can be used to power and logically switch each LCD, but there remains a significant issue with Windows and program desktop arrangement. When the LCDs are powered off, they present themselves in a disconnected state to Windows because they are hot plug (HDMI, DVI, DisplayPort) devices. When the displays are turned on again program window arrangement can be disjointed and not in its original multi-desktop position.
There are several ways to overcome this issue – the hot plug event can be muted with hardware or software modification – blocking pin 19 on the HDMI male connector (this did not work for me), writing your own custom firmware to the LCD (although this can be dangerous and may brick your device), or using an EDID emulator to ‘fake’ the display to Windows.
There are large variety of pass-through EDID emulators on the market – an unpowered LCD can be connected and it will maintain a virtual monitor state with Windows. The NVIDIA Quadro line of video cards also come with a built in EDID manager. When your LCDs are connected, the EDID settings and configuration can be written to a file. Windows can maintain the multi-screen desktop by reading the EDID file and ignores all hot plug disconnect events.
It was determined using an NVIDIA Quadro video card and the EDID manager were the safest and best solution which could be integrated into the simulator. There are a variety of Quadro video cards (some low cost) with multiple video outputs which helped with this decision.
Each LCD (12 VDC) power source can now be individually managed by a relay with correct desktop management and electrical BUS state. With failure triggering the displays will also power off accurately simulating the correct display unit state.
In the ProSimA320-System application the relays controlling the LCDs are assigned the appropriate bus under CONFIGURATION – ELECTRICAL – GATES.
Display Unit BUS Equipment List
CAPT PFD – AC ESS
CAPT ND – SHED
F/O PFD – AC2
F/O ND – AC2
Upper ECAM DU – AC ESS
Lower ECAM DU – AC2
The upper and lower ECAM (simulated on one monitor) power can be simultaneously assigned to two relays, one switching AC ESS and the other AC2. The 12V supply should be supplied in parallel. This allows the monitor to remain on, but software dimming provides the illusion that one monitor is shut down (AC1, AC ESS, AC2 failure).