USB killswitch turns off your home entertainment bling automatically

Finally, the USB port on the back of your television can be tapped for something useful. [Don] is using this add-on device to automatically cut the power to his Ambilight clone. Initially, he got tired of unplugging the power adapter each time he shut off the television, so he added a switch. But laziness overcame him and he decided he needed an automatic method. After probing around on the connections available, he established that the serial interface (normally used for servicing the device) was not of any use, but the USB port is. He measured the voltage of the power bus to be 5V when the TV is on, and 0.15V when it is off. He whipped up the circuit you see above which uses the USB connection to trigger a relay, connecting power to his Ambilight clone when the television comes on, and disconnecting it when the set is switched off.

Our dream has always been an XBMC capable device that can Velcro to the back of a TV, and be powered from that USB port. Unfortunately the Beagle Board hasn’t yet made it to a stable level when running XBMC. Our next hope is the AppleTV 2, which can run XBMC but would require some hacking to get it working off of the USB port, raising concerns about how much current it would draw at 5V.


  1. macegr says:

    Probably wouldn’t want your entire media PC to go through a hard poweroff with the TV anyway. Using it to turn off the LEDs is a great idea though.

  2. slurm says:

    simple master slave power outlet would have done the same. and could even switch more devices

  3. Mental2k says:

    Could the ras pi deal with xbmc? Use one of the GPIO ports to trigger a safe powerdown of the device.

  4. Adam Outler says:

    i wish i could use 1 from the mobile version of this site… good work… 1.

  5. Adam Outler says:

    plus 1… darnit. why did it remove the plus?

  6. rasz says:

    doesnt running XBMC on appleTV2 require some serious hacking EVERY time you boot it?

  7. Decius says:

    How many USB boards are able to utilize a CPU that’s equivalent to the first generation Xbox’s Intel Celeron Pentium 3 733MHz that must also run on only… 5V…

    I don’t think hard shutdowns effect flash storage as much as a conventional spinning hard disks would if said device was powered by the TV’s USB Port.

  8. Bernhard says:
  9. Scorp-D says:

    What is the difference between this, and USB powersavers like this one:

    • Eirinn says:

      AFAIK nothing.

      Just remember when using USB power off devices like these to set your BIOS to turning off power to the USB ports when OFF – else it wont work (most computers today allows power on the USB ports when the computer is off).

  10. Brian says:

    How hard would it be to re purpose this design to turn a power strip on/off? I am thinking add a female usb port to a power strip and a relay which triggers the power strip on/off depending on the signal coming from the TV. This would be great for my entertainment system as i can keep all my power drawing devices like amps, subs, consoles, etc. connected to a single powerstrip that would turn off with the tv.

    • Marc says:

      Look up PowerSwitch Tail. It’s an off the shelf part which could help you do just that.

    • Victor says:

      Did you finally make any progress on your project? I have similar need and are looking around to find a ready to use solution. I have very limited space can barely contain a wall mount outlet, so the PowerSwitch Tail is not an option for me. I am thinking somehow mode the wall mount outlet to be triggered by the TV USB output.

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