In this project, an Arduino Leonardo was setup to be a line following robot. The chassis, sensors, and code were all designed/constructed/written from scratch. A simple binary controller allows the robot to use the underside IR sensors to track the black line. It can handle curves, straight lines, right-angle turns, small radius turns, and acute-angle turns.
Using the robot
course_run.mp4
The source file line_follower.ino is composed of a typical setup()/loop() configuration found on all Arduino devices, written in C++.
Outside of these, we initialise some key global variables, and define the driver code:
- ir_current: An array to store the current IR sensor readings. It has two elements representing the left (
ir_current[0]) and right (ir_current[1]) sensors. - ir_max: An array to store the maximum IR sensor readings. This is set during the automated calibration and remains constant.
- button_value: A variable to hold the state of the off-board button
- go: A boolean variable that determines whether the robot is in calibration or tracking mode. It's controlled by the on-board button, hence the callback function.
- ir_cutoff: A percentage multiplier that controls the robots' sensitivity to ir_max.
- steady_state_speed: A constant representing the speed of the motors during the steady state when going in a straight line. Keep in mind that the motors are mounted in reverse, so this value is negative.
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Calibration: The code includes a calibration routine triggered by pressing the off-board button. The calibration() function performs a sweeping operation of the IR sensors to determine the maximum sensor readings. It adjusts the motor speeds during the sweeping process and stores the maximum IR sensor values. A cut-off threshold is then applied to the stored maximum values for calibration. The robot will roughly rotate back and fourth
$180^o$ . This makes sure it sweeps the brightest and darkest portions of the line. The whole calibration process is automated this way. -
irSweep: This performs the sweeping operation of the IR sensors and updates the maximum IR sensor readings.
The setup() function initializes the pin modes, serial communication, and assigns the button callback.
The loop() function is responsible for the main program logic. It continuously checks the "go" variable to determine if the robot should be moving. If go = true, the code turns on the IR emitter and reads the IR sensor values. Based on the sensor readings, it adjusts the motor speeds to follow the line.
Normally we would seperate the control system code into its own function, but its a simple binary controller so it's appropriate to leave it as-is.
The value of go is controlled by the onboard button, hence the callback function.
If go = false the motors are set to zero speed, and the robot enters calibration mode. In this mode, we can press the off-board button to start the automated calibration process.
Simply upload the code to your Arduino Leonardo and you're set.
Remember to download the prismino.h library in the Arduino IDE.
For details on the used parts, visit the Prisme kit for the base parts, and the Prisme extensions for other parts. Note, these webpages are in french.
The chassis was made arbitrarily, feel free to get creative, or derive from my work in the images folder.
The track is also found there.
All of the videos are also found in the videos folder.
The calibration of the robot is seen here: