Control a USB light via software
I have a little USB-powered light. I'd like to be able to turn it on and off with software. I'll be attaching it to a Linux computer. I have an Atmel ATtiny2313 from a previous project, but I'd rather do this with a simple hack than repurpose my microcontroller.
Is this possible? I suspect this can't be done as the computer won't talk to a device without some kind of USB-compliant firmware?
I found this question, which has a comment suggesting that the OP use an LM317 voltage regulator to change the voltage of the USB out. I don't think this is applicable to me, but thought I'd mention it.
Update:
Looks like I could maybe put USBtiny on my microcontroller, then I could wire it up to the light, then I could write an app to control the controller. Sounds like a lot of work, though. I'd rather do a simple hack, but I lack experience with USB.
Answer
I don't think it is possible, because the power (Vcc) line on USB is always-on--it is not intended to be a control line.
Unless your USB light already provides a way to control itself via USB data, you are out of luck. I do not recommend trying to change the voltage of the USB power line.