Program ultrasonic range
sensor in autonomous mode
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Program ultrasonic range
sensor in autonomous mode
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Performance Objective: Given the components of a
VEX robotics design system program an ultrasonic
range sensor in autonomous mode to have the robot
travel forward until it is 12 inches from the wall.
Enabling Objectives:
explain the purpose of an ultrasonic range sensor
explain how an ultrasonic range sensor operates
draw a flow chart for using an ultrasonic range sensor
program an ultrasonic range sensor
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Ultrasonic range sensor
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An ultrasonic range sensor enables a robot to detect
obstacles in its path by utilizing the propagation of
high-frequency sound waves
The sensor emits a sound wave, which bounces off a
reflective surface and returns to the sensor
Then, using the amount of time it takes for the wave
to return to the sensor, the distance to the object can
be computed
The distance is returned as a distance in inches
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Sound waves
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The beam pattern
coming from the
ultrasonic sensor
looks like the
images to the right
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Sound waves
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The sensitivity of the sensor depends on
the objects’ surfaces that are detected
by the emitted sound waves
For example, a reflective surface may
produce a different reading than a nonreflective surface
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Verifying the sensor
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Plug the sensor into two digital ports
Vex Ultrasonic Sensors are labeled with
reference to the sensor, so the input cable
coming from the sensor should be connected
as a digital output on the robot controller
Open easyC and download the Ultrasonic test
file
Move the robot and notice the change in value
of the sensor
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Program the ultrasonic
ranger sensor
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The Start command tells
the ultrasonic sensor to
start recording sound
waves
The Get command allows
you to store the
feedback from the
sensor into a variable
The Stop command tells
the ultrasonic sensor to
stop recording
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Program the ultrasonic
ranger sensor
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Program a VEX robot equipped with an
ultrasonic range sensor to move forward
until the robot is 12 inches from a wall
Draw the flow chart of a program that
can complete the above task
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Program the ultrasonic
ranger sensor
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Open a new competition project and
configure the microcontroller for the
ultrasonic ranger finder
Add a variable for the ultrasonic range
sensor
Insert an appropriate driving mode block
into the operator tab
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Program the ultrasonic
ranger sensor
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Insert a block to start
the ultrasonic range
sensor
Insert a block to get the
ultrasonic variable value
NOTE: The wire from the sensor labeled output is the
interrupt port in the program, and the wire labeled
input on the sensor is the output port in the program
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Program the ultrasonic
ranger sensor
Insert a while loop to run while the
ultrasonic sensor is greater than 16
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In the while loop get the ultrasonic
variable value again
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Insert the appropriate motor blocks
to make the robot move forward
NOTE: Because of processing speed in
the microcontroller, you must add
four inches to the distance you
want the robot to stop when the
motors are running at full speed (to
stop the robot at 12 inches, the
sensor must read until 16 inches)
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Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Program the ultrasonic
ranger sensor
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After the while loop
insert blocks to stop
the motors, if you do
not stop the motors
they will continue to
run even if the
sensor is no longer
greater than the
value in the if
statement
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode
Test time
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Download your code and test it to see if the robot
stops 12 inches from the wall
If it does, show your instructor!
If the robot does not stop correctly, go back through
the lesson and double check your code
For more technical information on the ultrasonic range
sensor visit:
http://www.vexforum.com/wiki/index.php/Ultrasonic
_Range_Finder
Available at: www.etcurr.com
Lesson 3.4 – Program Ultrasonic Range Sensor in Autonomous Mode