Are you worrying about how to handle your old iPhone? Most people give it to children to use it as iPod touch or personal gaming system. Here's a genius application I'm using while I'm driving, I always driving as pilot a plane now.
Let me guide you how to make your own head up display.
Refer the instruction to make you own cardboard base to fit your smartphone.
Install Navigation or Driving Assistant App.
Turn by Turn Navigation : Hudway or Navier.
Navigation Map : Sygic or Garmin
Speedometer : Speedometer or Awesome HUD
OBD : Torque or EOBD
3. Order Head Up Display combiner (glass) via Amazon and assembly it with your cardboard base.