Line Tracking

This project will use the Grayscale module to make the PiCar-X move forward along a line. Use dark-colored tape to make a line as straight as possible, and not too curved. Some experimenting might be needed if the PiCar-X is derailed.

Run the Code

cd /home/pi/picar-x/example
sudo python3 minecart_plus.py

After running the code, PiCar-X will move forward along a line.

Code

Note

You can Modify/Reset/Copy/Run/Stop the code below. But before that, you need to go to source code path like picar-x/example. After modifying the code, you can run it directly to see the effect.

from picarx import Picarx


if __name__=='__main__':
    try:
        px = Picarx()
        # px = Picarx(grayscale_pins=['A0', 'A1', 'A2'])
        px_power = 10
        while True:
            gm_val_list = px.get_grayscale_data()
            print("gm_val_list:",gm_val_list)
            gm_status = px.get_line_status(gm_val_list)
            print("gm_status:",gm_status)

            if gm_status == 'forward':
                print(1)
                px.forward(px_power)

            elif gm_status == 'left':
                px.set_dir_servo_angle(12)
                px.forward(px_power)

            elif gm_status == 'right':
                px.set_dir_servo_angle(-12)
                px.forward(px_power)
            else:
                px.set_dir_servo_angle(0)
                px.stop()
    finally:
        px.stop()

How it works?

The grayscale sensor module grayscale_module is also imported in the picarx module, and we can use some of these methods to detect black lines.

The function to detect the black line looks like this:

• get_grayscale_data(): This method directly outputs the readings of the three sensors, from right to left. The brighter the area, the larger the value obtained.

• get_line_status(): get_line_status(): This method will generate an action based on the values detected by the three probes. There are four types of actions: forward , left , right , and stop.

The trigger conditions for these actions are as follows: A value is assigned by default in the module as the threshold for detecting black or white. When the detection values of the three probes are all greater than the threshold, it means that the probes are sensing the color white, and no black line is detected, which makes the get_line_status() to generate a return value of stop.

• If the right (and the first) probe detects a black line, right is returned;

• If the middle probe detects a black line, return forward;

• If the left probe detects a black line, left is returned.