== Ultrasonic Rangefinder

Robots often need to sense the environment around them, particularly when driving autonomously.  Ultrasonic sensors are like the sonar used by bats.  They emit a chirp of sound and measure the time it takes to hear an echo of that chirp.  The longer the time, the further the sound traveled.  Since sound travels at a particular speed through air, we can use the echo delay to calculate how far away the object was that reflected the sound.  You can read more about ultrasonic sensors [https://wpilib.screenstepslive.com/s/currentCS/m/java/l/599715-ultrasonic-sensors-measuring-robot-distance-to-a-surface here]

Create another program using the !TimedRobot java template and name it !UltrasonicTest. Modify the generated code as follows:
* import the Ultrasonic class {{{ import edu.wpi.first.wpilibj.Ultrasonic; }}}
* declare a ultrasonic variable in the Robot class {{{ private Ultrasonic f_ultrasonic; }}}
* in robotInit() instantiate an ultrasonic object and set it to start automatically ranging 
  {{{
    f_ultrasonic = new Ultrasonic(1,0);
    f_ultrasonic.setAutomaticMode(true);
  }}}
* in robotPeriodic() read and display the range 
  {{{
    if (f_ultrasonic.isRangeValid()) {
       SmartDashboard.putNumber("Front range", f_ultrasonic.getRangeInches());
    }
  }}}

Run the program and observe the "Front range" value in the [https://wpilib.screenstepslive.com/s/currentCS/m/java/l/599724-displaying-data-on-the-ds-dashboard-overview Smart Dashboard] as you move the robot towards and away from the wall.

Notice that the measurements aren't always perfect; the sensor may receive echos from multiple surfaces.