title: Controlling simple relay switch via USB
body: <p>I'm looking to control a mains powered light from a simple relay switch connected via USB to the computer.</p>
  
  <p>The relay switch isn't even a USB device, it's just a simple switch that requires the USB voltage to turn it on. When the voltage drops below a threshold, the switch will turn the light off.</p>
  
  <p>My problem is that I can't control the power output of a USB port. I'm happy to do it using any language on Windows or Linux (but preferably Java because I'm used to it).</p>