Ultrasonic Rangefinder

Robots 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 (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 ​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());
    }
  

Run the program and observe the "Front range" value in the ​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 here