Saturday, January 11, 2014

VGA Dummy Plug - so that’s what it’s called…

Way back in a GSD post Some Notes for a Certain Project I was struggling to come up with a solution to make a “headless” system but that still supported dual-monitor displays when remote connecting.

Example: Dual-head video card on system. Two desktop displays (dual monitor) present. Primary display to be used for performing system maintenance activities when remote attached to the system. Secondary display output is fed to a public video display for the running output…like an information power-point display perhaps.

Obviously we don’t want to show the public what we are doing when servicing the system, but we don’t want to leave the box with a monitor, keyboard, or mouse where it is placed.

What it turns out I was looking for is a pretty well-know piece of hardware hack called a VGA Dummy plug.

By using a few resistors plugged into a VGA plug, it can mimic the resistance provided by a monitor, thus allowing you not to have an actual monitor attached, but tricking the Windows OS into thinking a physical monitor is present. Clever. DVI versions also exist.

Here are some links for the curious. Note any product links are for reference only and not any way a GSD endorsement of the vendor or product offered.

FYI…I’ve been told that the concept also works if you take a spare VGA cable lying around that was used and cut it and join the right cable pairs together. The resistance of the wires alone may be sufficient to allow it to work saving you a trip down to the local RadioShack parts depot for a VGA plug and resistors. Not nearly as pretty but can do in a pinch.

Know we both know.

And for what its worth, my testing of a VGA Dummy plug found it worked perfectly for the particular application I needed it for on XP/Win7.


Claus V.

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