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.

Solution 1

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.

Solution 2

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.

Solution 3

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.

Solution 4

I guess this could be possible using the computer's ability to switch on/off the USB ports to save battery. After a surprissingly short search I found another question regarding that:

Controlling a USB power supply (on/off) with linux

Though I have not tried it. Please let us know if it worked!

View more solutions

Comments

[Justin Force]

But can I manipulate the data output from the computer and use that as input to a transistor or microcontroller? Then I can control whether to let the 5V through to the light. I just don't know if I can manipulate the data pins on the USB port if the device on the other end isn't a legitimate USB device.

[Hamish Grubijan]

+1 DigiKey is a damn good resource for serious electrical/computer engineering.

[Justin Force]

This looks cool. I think that my current USB/serial bridge may be able to help me here. I have a [PL-2303 ](prolific.com.tw/eng/products.asp?id=59) USB/serial adapter. Think that'll do it?

[Justin Force]

I appreciate your suggestion and +1 it, but it doesn't really answer my question. Thanks for the DigiKey and FTDI tips, though! I especially appreciate the part number.

[Patrick Szalapski]

So you would shunt the data lines on the usb port to your own microcontroller? I suppose there is a way, but then you'd have to learn the USB hardware layer and how to write a driver for it.

[Justin Force]

I considered this, but I doubt I'll be able to talk to the data wire of the USB port if the device at the other end isn't doing USB communication. I also know very little about USB. I think I'll know quite a bit by the end of this project, though. :)

[Justin Force]

Yeah! I think you're mostly right, but USBtiny should fit on my microcontroller, and should fill this role for me. I'm probably going to learn the USB hardware layer anyway for fun.

[Admin]

How to do this in Windows 8, 10?

[Patrick]

You can use, for example, PyFtdi to control the signals.