== Ultrasonic Rangefinder

Robots need to sense the environment around them, particularly when driving autonomously.  Ultrasonic sensors are like the sonar used by bats.  [[Image(UltrasonicSensor.jpg,right,250px,margin=10)]] 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 (about 1125 ft/s) through air, we can use the echo delay to calculate distance to the object was that reflected the sound.  You can read more about ultrasonic sensors on [https://wpilib.screenstepslive.com/s/currentCS/m/java/l/599715-ultrasonic-sensors-measuring-robot-distance-to-a-surface ScreenStepsLive]

Ultrasonic sensors are connected to the RoboRIO using DIO ports.  In the example below, a sensor's Ping and Echo wires are connected to DIO1 and DIO0.

Create another program using the !TimedRobot java template and name it !UltrasonicTest. Modify the auto-generated template 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 
  {{{
    // Sensor is connected to DIO1, DIO0
    f_ultrasonic = new Ultrasonic(1,0);
    // Start sensor continuously pinging
    f_ultrasonic.setAutomaticMode(true);
  }}}
* in robotPeriodic() read and display the range 
  {{{
    if (f_ultrasonic.isRangeValid()) {
       SmartDashboard.putNumber("Front range", f_ultrasonic.getRangeInches());
    }
  }}}

Build and Deploy the program to your robot as you did in the [wiki:ControlSystems/SoftwareTeam/Training/GettingStarted/XboxController previous example] 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.

Extra Credit: explore more advanced ultrasonic sample program [wiki:ControlSystems/SampleCode/Ultrasonic here]