Electronic Jumper for Power Switching

I was curious if it was possible to remove the physical jumper that controls which source of power the arduino board uses and replace it by an electronic switch. My electronic experience isn't that great so I was hoping I could get some insight here from the gurus.

One note. We will be powering the arduino board via an external power supply and connecting a wire to the 5V pin instead of using the wall wart. So, if we use the 5V pin and connect that to comparator and the other side to ground and if pin is high (ie. pin V > 0 V) short the power supply side of the pins for selecting the power source. Would that work? If that works, the other problem I can't figure out how to solve is, getting a power line from the USB side to do the same. Is there anyway to access the voltage line?\

Thanks fillalph


sure you can replace the header with an SPDT slide switch...

the other part of your post is a little confusing.. can you post a diagram? Sometime language falls short at describing a complex circuit well.