Right I’ve found a solution for laptops not detecting a projector (in certain circumstances). It isn’t pretty, but maybe an electrical engineer can pick this up and show how to make a compatible plug to get this working. More after the break…

The situation: small theatre with a projector. It’s a fair way to the projector so the vga signal is sent down UTP network cable, with a pc on the ’shop floor’. I need to run a long cable out to the stage for the laptop. Their pc has a ‘Y’ splitter out from its video card with one connection into the back of a monitor, the other into a signal booster to run it over the UTP.

Plug my laptop into the signal booster instead, nothing. Now when I plug my laptop directly into other projectors via a VGA lead you get windows detecting new hardware (with that beepy noise) and everything works ok. This just would not connect. Not just my laptop too, their new laptop did the same thing. Eventually after lots of head scratching we got it working.

laptop>-----long cable--->y splitter> ----> monitor
                                    v
                                    signal booster
                                    v
                                    UTP Cable
                                    v
                                    Projector

The long vga cable does not need to be in there if you don’t need it, but it must be at that point, putting it after the y splitter gives ghosting on the screen image.

When used with a monitor through the splitter, the laptop actually detects a display there and (I assume) turns on that video output.

Weirdly this still works if the monitor is switched off. It also still works of the monitor is switched off AND the power lead is removed. I can only postulate from that there is some kind of link between 2 pins on the vga connector that creating a circuit (even if that is off) tells the laptop there is a display connected.

In that case it may be possible to build a small adapter that hooks up those pins and could just be placed in between the laptop and projector. Any electrical engineers out there interested at looking into that?

There’s plenty of postings from people saying “i go and do a lot of presentations and every now and then i find one that doesn’t work with my laptop”. Definately a product there waiting to get built.