To measure long distances you probably need to use a laser beam, and calculate the time the light beam travels back and forth from an object. www.philohome.com/sensors/lasersensor.htm
If you do some research and look at what others have done successfully in the past, like the ARPA autonomous vehicle contest, you'll see that everyone uses some combination of lasers and video cameras with image analysis to do what you want. Lasers are potentially dangerous in populated areas, even at low power levels and image analysis is very difficult.
None of this is just available for purchase "ready to go" and none of the pieces are cheap.
Comments
*what* do you want to sense long distance?
sound, light, EMF ... ?
Everyone's glad to help out, but we need to know more.
- Howard
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Don't worry. Be happy
None of this is just available for purchase "ready to go" and none of the pieces are cheap.