1. Forward Until Near
Stop when near a wall

2. NXT Ultrasonic Sensors

3. NXT Ultrasonic Sensors
How does the Ultrasonic Sensor detect distance?
The ultrasonic Sensor sends out a high-frequency sound pulse and times how long it takes for the echo of the sound to be reflected back. Since the speed of sound is known, the sensor uses rate and time to calculate the distance.

4. Forward Until Near Program

5. Motor Block One Details

6. Ultrasonic Block Two Details

7. Motor Block Three Details

8. Test Your Robot
Stop when near a wall

9. Backward Until Far
Back away from the wall until a specified distance is achieved

10. Backward until Far Ultrasonic Block Two Details
Wait for the Ultrasonic Sensor on Port 4 to get a Far reading
Far = Ultrasonic Sensor value > Threshold value

11. Test Your Robot
Back away from the wall until a specified distance is achieved