Ok, sorry again about the vagueness. I attached a simple diagram. Basically, I want to be able to zero the sensor at time t1, so that it will use the distance d1 as "zero". Over the time interval t1 - t2, the sensor will be continuously measuring the distance d. If that distance changes at any time over that interval (so that d2 > d1), I want the controller to turn on an LED.
The sensor I'm looking at is this: http://www.acroname.com/products/R146-GP2D120.html
My understanding is that it continuously measures distance, and the output signal is a voltage which relates to that distance.
So my questions are: (1) Can I hook up this sensor to an arduino, and will it properly read the voltage output from the sensor? (2) Can I code the controller so that if there is any deviation in that voltage, a light will be switched on?