Objective: Learn how to implement a "too close" trigger using an ultrasonic sensor connected to an Arduino board that is connected to a Linkbot robot.

Overview: As in the previous "Ultrasonic 2a" activity, the pre-placed code blocks initialize an ultrasonic sensor, but the program then uses a "while" loop to keep reading the sensor as long as the distance read is greater than 3 inches. Or to put it another way, it keeps reading the sensor until the distance is less than or equal to 3. Then the loop stops. Although this code is more complicated than the previous "2a" example, it does allow us to record the distance each time and then display the final distance. (Note that we insert a half-second delay in the loop so that the sensor doesn't get overloaded with too many readings in too short a time.) After you try running the code, modify it as directed in the Problem Statement.