The Ultrasonic Sensor can measure the distance to an object in front of it. It does this by sending out sound waves and measuring how long it takes the sound to reflect back to the sensor. The sound frequency is too high for you to hear (“ultrasonic”).

You can measure the distance to an object in either inches or centimetres. You could use this, for example, to make your robot stop a certain distance from a wall.

You can also use the Ultrasonic Sensor to detect whether another ultrasonic sensor nearby is operating. For example, you could use this to detect the presence of another robot that is using an ultrasonic sensor nearby. In this “listen only” mode, the sensor listens for sound signals but does not send them.

Ultrasonic Sensor Data

The Ultrasonic Sensor can give the following data:

Data	Type	Range	Notes
Distance in Centimetres	Numeric	0 to 255	Distance to object in centimetres.
Distance in Inches	Numeric	0 to 100	Distance to object in inches.
Ultrasound Detected	Logic	True/False	True if another ultrasonic sensor is detected.

Tips and Tricks

•	The Ultrasonic Sensor works best to detect objects with hard surfaces that reflect sound well. Soft objects, such as cloth, may absorb the sound waves and not be detected. Objects with rounded or angled surfaces are also harder to detect.
•	The sensor cannot detect objects that are very close to the sensor (closer than about 3 cm or 1.5 inches).
•	The sensor has a wide “field of view” and may detect a closer object off to the side instead of a farther object straight ahead.

Examples Using the Ultrasonic Sensor

Some examples of how you can use the Ultrasonic Sensor in your program are shown below.

Example 1: Stop a Certain Distance before a Wall

This program makes a robot drive forward until the Ultrasonic Sensor detects something closer than 10 inches, then the robot is stopped. The program uses the Wait block in the Ultrasonic Sensor - Compare – Distance Inches mode to wait for the detected distance to become less than 10 inches. If the Ultrasonic Sensor is facing forward, the robot will stop about 10 inches before a wall.

Tips and Tricks

Remember to use the On mode of the Move Steering block when you want to drive while waiting for a sensor.

Example 2: Sound an Alarm when an Object is Detected Nearby

This program has the robot make a sound whenever the Ultrasonic Sensor detects an object closer than 50 centimetres away. The program uses a Switch with the Ultrasonic Sensor - Compare – Distance Centimetres mode to test whether the distance detected is less than 50 centimetres. If so, the Switch plays a tone. The Switch is repeated in a loop so that the test is repeated continuously.

Tips and Tricks

While running this program, try moving objects around in front of the sensor to experiment with how wide the sensor’s “field of view” is.

Example 3: Gradually Slow Down Before Reaching an Object

This program makes a robot gradually slow down and then stop about 10 cm away from anything it detects in front of it. The closer it gets to the object, the slower it will drive.

The program uses the Ultrasonic Sensor block in the Measure – Distance Centimetres mode to get a distance measurement and get the resulting number on a data wire. A Mathematics block then subtracts 10 from the distance, and the result is wired to the Power input of a Move Steering block. Shorter distances result in lower power, and when the distance reaches 10 cm, the power will be zero, and the robot will stop. The process is repeated in a loop so that the motor power is adjusted continuously based on new distance measurements.

Tips and Tricks

You can also try moving the object while this program is running. The robot will continuously adjust its speed.

Ultrasonic Sensor Blocks and Modes

The table below shows all of the programming blocks and modes that you can use with the Ultrasonic Sensor. The Distance modes have sub-modes that let you choose between centimetres and inches.

Block	Mode	Use
Wait	Ultrasonic Sensor - Compare – Distance	Wait for the distance to reach a certain value.
Wait	Ultrasonic Sensor - Compare – Presence	Wait, in “listen only” mode, for an ultrasonic signal to be detected.
Wait	Ultrasonic Sensor - Change – Distance	Wait for the distance to change by a certain amount.
Loop	Ultrasonic Sensor - Compare - Distance	Repeat a sequence of blocks until the distance reaches a certain value.
Loop	Ultrasonic Sensor – Compare - Presence	Repeat a sequence of blocks until an ultrasonic signal is detected, in “listen only” mode.
Loop	Ultrasonic Sensor – Change - Distance	Repeat a sequence of blocks until the distance changes by a certain amount.
Switch	Ultrasonic Sensor – Compare - Distance	Choose between two sequences of blocks based on the distance.
Switch	Ultrasonic Sensor – Compare - Presence	Choose between two sequences of blocks based on whether an ultrasonic signal is detected in “listen only” mode.
Ultrasonic Sensor	Measure – Distance	Measure the distance and get the result on a Numeric data wire.
Ultrasonic Sensor	Measure – Presence	Listen for other ultrasonic signals in “listen only” mode, and get the result on a Logic data wire.
Ultrasonic Sensor	Compare – Distance	Compare the distance to a threshold, and get the result on a Logic data wire.
Ultrasonic Sensor	Compare – Presence	Listen for other ultrasonic signals in “listen only” mode, and get the result on a Logic data wire.
Ultrasonic Sensor	Advanced	Similar to Measure – Distance, but with the option to make only a single sound ping.
Data Logging		See Data Logging.