Controlling simple relay switch via USB

controlsdeviceperipheralspower-managementusb

I'm looking to control a mains powered light from a simple relay switch connected via USB to the computer.

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.

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).

Best Answer

Unfortunately, in most cases you cannot control the power supply to the USB port. The power supply is usually hardwired through, and not switchable in software. You can send a reset to a USB device, but that won't work in your case.

There are a number of projects on instructables that do similar to what you describe, but unfortunately they seem to either be quite complicated or require expensive parts.

EDIT: There is actually a product currently in the news which would do want you want, but it doesn't appear to be shipping yet: http://www.pwrusb.com/

EDIT (again): Apparently you can do this with some usb hubs. This post sugggests the Linksys USB2HUB4 is one that works.

EDIT (and again): Apparently there are a number of similar questions, but there don't seem to be any more useful answers:

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