Turn a USB device on/off

I'm certain this will have been answered before but when I search I just find lots of questions about powering the ardunio itself - so apologies in advance for creating a duplicate question.

I have a simple usb device (it's a police siren similar to this.) I want to be able to turn it on and off via an Arduino Duemilanove. I've split the usb cable and connected it to the 5v and gnd lines on the arduino which works fine, but moving it to a high digital pin doesn't work, presumably due to lack of voltage from the pin.

I'm leaning towards the idea that I need to buy a relay and control it with the digital pin but I thought I'd seek some advice from you guys before I spend any money.


Probably lack of current rather than voltage. The Arduino pins can only drive 40 mA maximum. To control hardware that needs more than that you will need a relay or a transistor. If you chose a relay, be sure to get one with a 5v coil that requires 30 mA or less.

In that case I'll have a look at ordering something like this



Bulluk: moving it to a high digital pin doesn't work

Bear in mind that this attempt may have blown the digital pin you were using.

@Pete I must have got lucky and the digital pin must be sound as the relay I discussed with John has got me working

Thanks to both for your help :)