Project Black Screen

[Desdichado]

I'm looking for a device that will sit inline on a vga cable and allow me, with the press of a button, to switch back and forth from displaying whatever's coming down the cable to displaying just a black screen. I've seen this done in classrooms, but I can't seem to find a device that will do it. I guess as a fall-back plan, something like this shouldn't be too hard to make. Anyone seen one of these?

 

[yaric]

If you press the power button it'll go black on any monitor...