Tool-activated shopvac for dust collection? A relay for activating a shopvac for dust collection when a tool is started Answered
Some expensive shopvacs can be "tool activated", meaning that the shopvac hose can be attached to the dust port of chop saw, sander, router table, etc, and the shopvac turned on or energized when a relay device detects that the attached tool is drawing power. It saves trips between the shopvac and the tool, making automatic dust collection at the point of dust generation more practical.
Off the shelf solutions are $50 to $80, usually consisting of a short extension cord with two outlet sockets. A power draw on one outlet energizes the other. The theory is simple enough that I can't think of a good excuse for why it couldn't be done with stock components.