ROBOTC
Reference
Ultrasonic Rangefinder Overview
The Ultrasonic Rangefinder, pictured left, is
used to detect objects at a distance, without the
need for the robot to actually contact them. The
Ultrasonic Rangefinder uses sound pulses to
measure distance, in a similar way to how bats
or submarines find their way around. By emitting
an ultrasonic pulse and timing how long it takes
to hear an echo, the Ultrasonic Rangefinder can
accurately estimate how far away the object is.
The Ultrasonic Rangefinder for VEX
This sensor is most often used in obstacle
detection. It can detect objects at a range
of up to 255 inches (approximately 647
centimeters), but this range can be limited
in certain environments. Since the Ultrasonic
Rangefinder relies on sound waves, any
surfaces that absorb or deflect sound, such as
cushioned surfaces or sharp angles.
When wiring the Ultrasonic Rangefinder to the
Cortex, both wires are plugged into adjacent
digital sensor ports. For the sensor to work
properly, the “INPUT” wire must be in the
lower numbered slot, and the “OUTPUT” wire
in the higher numbered slot. For example, one
Example of an Ultrasonic Rangefinder attachment working configuration is having the “INPUT”
wire in digital port 8, and the “OUTPUT” wire
in digital port 9.
Note: The units that the Ultrasonic Rangefinder uses (inches, centimeters, etc.) are controlled by the
user in the “Motors and Sensors Setup” window.
© Carnegie Mellon Robotics Academy / For use with VEX robotics systems Ultrasonic Rangefinder • 1
ROBOTC
Reference
Ultrasonic Rangefinder
Natural Language Sample Code
Move Forward Until Near
This code has the robot move forward until the Ultrasonic Rangefinder sees an object within 20 units.
task main ()
{
robotType(recbot); //Specifies the robot type
forward(63); // Move forward at speed 63.
untilSonarLessThan(20, dgtl8); // Wait for the Ultrasonic
//Rangefinder in digital ports
//8 and 9 to see an object
//within 20 units
stop(); // Stop.
}
Move Backward Until Far
This code has the robot move backward until the Ultrasonic Rangefinder sees that the object is greater
than 20 units away.
task main ()
{
robotType(recbot); //Specifies the robot type
backward(63); // Move backward at speed 63.
untilSonarGreaterThan(20, dgtl8); // Wait for the Ultrasonic
//Rangefinder in digital
//ports 8 and 9 to see an
//object greater than 20
//units away
stop(); // Stop.
}
© Carnegie Mellon Robotics Academy / For use with VEX robotics systems Ultrasonic Rangefinder • 2
