Program Line Follower in
Autonomous Mode
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Program Line Follower in
Autonomous Mode






Performance Objective: Given the components of a
VEX robotics design system program a line follower in
autonomous mode to have the robot move forward
and follow a white line on a gray mat.
Enabling Objectives:
explain the purpose of a line follower
explain how a line follower operates
draw a flow chart for using a line follower
program a line follower
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Line follower




A line tracker mostly consists of an infrared light
sensor and an infrared LED
The line follow functions by illuminating a surface with
infrared light; the sensor then picks up the reflected
infrared radiation and, based on its intensity,
determines the reflectivity of the surface in question
Lightly colored surfaces will reflect more light than
dark surfaces; therefore, lightly colored surfaces will
appear brighter to the sensor
This allows the sensor to detect a dark line on a light
surface, or a light line on a dark surface
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Line follower



An efficient way to follow a line is using
three sensors
The three sensors are lined up beside
each other
The center line follower is designed to be
on the line being followed, while the
outside sensors are detecting the surface
beside the line
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Line follower logic
1

2
3
The logic behind using three sensors is this: if
sensors 1 and 3 are dark and sensor 2 is light,
then go straight; if sensors 1 and 2 are dark
while sensor 3 is light, turn right; if sensors 2
and 3 are dark, and sensor 1 is light, turn left
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Line follower logic



Three sensors are best when there are
crossing lines
All three sensors will be reading the
same color, you know to turn a direction
when this happens
Using this logic, two sensors will work to
follow a line that does not cross another
line
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Verify the sensor





Plug the three sensors into analog ports
Open easyC and download the line follower test code
The test code is only written for one sensor, you can
add the two additional get blocks to be able to read
the other two sensors, you also need to define two
new variables
Place the robot on a gray mat and notice the value of
the sensors (> 700)
Place the robot on a white surface and notice the
value of the sensors (< 500)
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Program the line follower


Program a VEX robot equipped with a
line following kit to move forward and
follow a white line on a gray mat
Draw the flow chart of a program that
can complete the above task according
to the logic explained earlier
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Program the line follower



Open a new competition project and
configure the microcontroller for the
three line following sensors
Add a variable for each line following
sensor
Insert an appropriate driving mode block
into the operator tab
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Program the line follower


Insert a while loop
where 1==1
Insert the get
analog input block
for each line
follower
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Program the line follower

Insert an If statement to
move the robot forward
if both outside sensors
are dark and the middle
sensor is light
NOTE: When using the
line follower kit, you will
want to move slower,
therefore insert a user
value of 60 or -60 when
programming the motors
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Program the line follower

Insert an Else-If statement to correct the
robot if it starts to veer off the line towards
the right
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Program the line follower

For correction when the robot veers off of
the line, insert an Else-If statement to
correct the positioning
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Test your code



Build and download your code
Run the code with the Competition
Switch Simulator
The robot should slowly move forward
following a line, correcting itself if it
starts to veer to one side or the other
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode
Show it off!



If your code works, show it to your instructor
If the robot does not run correctly, go back
through the lesson and double check your
code
For more technical data on the line follower
visit:
http://www.vexforum.com/wiki/index.php/Lin
e_Follower
Available at: www.etcurr.com
Lesson 3.6 – Program Line Follower in Autonomous Mode