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Andrew Pollock


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Thursday, 04 June 2009

Software controlling the power to USB Woot! lights

I've had a few enquiries from my blog post about trying to control dumb USB-powered lights.

I thought I'd just write something up to save myself replying to any more emails.

Yes, it's doable. Finding a USB hub that will do it is another story. From my own research, I found someone else who was doing something with USB-powered devices (I can't remember what now), and he had been using a what is now a Linksys ProConnect USB 4-Port Hub USB 2.0

I'd first tried a couple of random cheap hubs from Fry's with no success (fortunately I was able to return them) before I determined that the Linksys one would definitely work. The downside of the Linksys hub is it requires external power. It was also one of the more expensive USB hubs on the market.

One of my co-workers, who is an Electrical Engineer by education, said that the USB spec requires the functionality that I wanted, but most chip manufacturers had cut a corner in the interests of cost saving. The Linksys hub uses an NEC chipset. Every other hub that I could get my hands on had a Genesys Logic chipset, and did not work. You can tell if you've got a winner by the output of lsusb -v. If the hub characteristics include "Per-port power switching", you're in business.

To do the actual port powering on and off, I'm using a setuid-root hub-ctrl, wrapped with a small shell script, which has the USB ID of the hub and the port number the lights are plugged into hard-coded in it.

In my searching, I found also that it may be possible to do with Python, but I did not invest the time trying to find out.

[23:20] [tech] [permalink]