Control a USB light via software

Question

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 1

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.

Answer 2

Maybe you can tell the USB controller to cut off power to the USB port. I've seen this option on the power saving settings on my PC.

Answer 3

Your best bet is probably to buy something like an FTDI interface cable, available from Digi-Key for $20. That gives you +5, ground, and four wires you can switch high or low under software control. The software's easiest if you use the thing as a logic-level serial port with rx/tx/rts/cts. The manufacturer part number is TTL-232R-5V-WE (go to digikey.com and type that number into the part search box). Digi-Key has links to the manufacturer data sheets and web site.

Answer 4

I'm going to use my PL-2303-based USB/serial bridge and an ATtiny2313 microcontroller running a USB stack--possibly USBtiny. It'll work like this:

• The USB light is attached directly to the microcontroller--not the computer
• An app/driver controls the microcontroller via USB
• The microcontroller sets the voltage for the USB light

I'll look into wiring it so there are some resistors on some outputs so I can set the light to different brightnesses, and if I want to do patterns or anything, I'll do them in software.

Answer 5

Would it be possible to rewire the usb connector so that instead of being connected to VCC the power of the usb light would be connected to the data of the usb port?

Then maybe you could control that and specify if it was 0 or 5 volts.

Not sure if that's even possible, I know nothing about usb.