CD controlled lawn mower
 

[Oliver Nash] was enlisted by his parents to fix their robotic lawn mower. They owned a Robomow which happily navigated their yard to keep the grass at a nice level. These robots rely on a perimeter wire with a special signal running through it to ensure they are inside of the mowing area. Confronted by a dead perimeter module, [Oliver] ordered a new unit and disassembled the old module to study the components. He also measured the signal generated by the replacement unit. In the end he was able to produce a replica of the signal using audio software, burn it to a CD, and playback the recording using the perimeter wire. It’s a bit of a zany idea but it worked.

http://hackaday.com/2010/06/26/cd-co...ed-lawn-mower/