Raspberry Pi in the sky: How to build this awesome $115 airplane tracker

If you've ever looked up at a plane and wondered where it's headed, this simple project is for you. Thanks to cheap, miniaturized electronics, you can now build a receiver that connects to your smartphone and shows details about all the aircraft in the sky around you. It takes less than an hour and costs about $115.
The device receives and decodes ADS-B, a data broadcast from aircraft that transmits a callsign, location, altitude, speed and a few other bits of information. If you live near an ai