11. MOVEMotor line follower 4

11.1. Add thick line following: follow_thick_line function

Add code to follow a wide thick black track.

Define follow_thick_line(drive_time=20)

Base this on the thin line following code.

Modify the if and elif code to keep the buggy over the black track.

When both line sensors are over white (not(black_left) and not(black_right)), the buggy spins to try to make just one sensor over black.

When the left sensor is over black but the right is over white (black_left and not(black_right)), the buggy turns to the left to try to get the right line sensor back over black.

When the right sensor is over black but the left is over white (black_right and not(black_left)), the buggy turns to the right to try to get the left line sensor back over black.

When both line sensors are over black (black_left and black_right), the buggy goes forward.

def follow_thick_line(drive_time=20):
    left_sensor = line_sensor.line_sensor_read('left')
    right_sensor = line_sensor.line_sensor_read('right')
    black_left = left_sensor + CHANGETHRESHOLD < left_sensor_start
    black_right = right_sensor + CHANGETHRESHOLD < right_sensor_start
    if not(black_left) and not(black_right):
        display.show(' ')
        both_indicators()
        buggy.left_motor(-MAXTURN)
        buggy.right_motor(-MAXTURN)
    elif black_left and not(black_right):
        display.show(Image.ARROW_W)
        left_indicator()
        buggy.left_motor(MINTURN)
        buggy.right_motor(MAXTURN)
    elif black_right and not(black_left):
        display.show(Image.ARROW_E)
        right_indicator()
        buggy.left_motor(MAXTURN)
        buggy.right_motor(MINTURN)
    else:
        display.show(Image.ARROW_N)
        head_lights()
        buggy.left_motor(MAXSPEED)
        buggy.right_motor(MAXSPEED)
    sleep(drive_time)

---

11.2. Thick or thin line following flag

Add to the section of code where the constants are set, to include a boolean variable, thin_line_follow_flag, which is True if the buggy follows a thin line or False if the buggy follows a thick line.

Set thin_line_follow_flag = True to cause thin line following as the default.

thin_line_follow_flag = True

---

11.3. Set thick or thin line following flag using buttons

Add button pressing to change the line following mode.

Use the A button to set the buggy to follow a thin line by setting thin_line_follow_flag to True.

Use the B button to set the buggy to follow a thick line by setting thin_line_follow_flag to False.

Add the if-else block to set the line following mode based on the value of the thin_line_follow_flag.

while True:
    if button_a.is_pressed() and not button_b.is_pressed():
        display.scroll('A', delay=100)
        thin_line_follow_flag = True
    elif button_b.is_pressed() and not button_a.is_pressed():
        display.scroll('B', delay=100)
        thin_line_follow_flag = False
    if thin_line_follow_flag:
        follow_thin_line(MOTORTIME)
    else:
        follow_thick_line(MOTORTIME)

---

11.4. Version 4 Line following code in full

The code below will follow both the thin line track that goes between the line sensors or the thick line track that both sensors sit over.

from microbit import *
import music
from neopixel import NeoPixel as leds
import MOVEMotor


buggy = MOVEMotor.MOVEMotorMotors()
buggy.stop()
line_sensor = MOVEMotor.MOVEMotorLineSensors()
line_sensor.line_sensor_calibrate()
left_sensor_start = line_sensor.line_sensor_read('left')
right_sensor_start = line_sensor.line_sensor_read('right')
distance_sensor = MOVEMotor.MOVEMotorDistanceSensors()

thin_line_follow_flag = True
CHANGETHRESHOLD = 40
MAXSPEED = 1
MINTURN = -1
MAXTURN = 1
MOTORTIME = 20
SPINTIME = 800
# Set up the Neopixels on pin8 with a length of 4 pixels
NUM_PIXELS = 4
LED_PIN = pin8
buggy_lights = leds(LED_PIN, NUM_PIXELS)
DULL_WHITE = (20, 20, 20)
DULL_YELLOW = (35, 25, 0)
DULL_RED = (20, 0, 0)

def rear_lights():
    buggy_lights[2] = DULL_RED
    buggy_lights[3] = DULL_RED

def front_lights(left, right):
    buggy_lights[0] = left
    buggy_lights[1] = right
    rear_lights()
    buggy_lights.show()

def head_lights():
    front_lights(DULL_WHITE, DULL_WHITE)

def left_indicator():
    front_lights(DULL_YELLOW, DULL_WHITE)

def right_indicator():
    front_lights(DULL_WHITE, DULL_YELLOW)

def both_indicators():
    front_lights(DULL_YELLOW, DULL_YELLOW)

def police_siren():
    for i in range(3):
        for freq in range(1500, 1760, 16):
            music.pitch(freq, 30, wait=False)
            sleep(20)
        for freq in range(1760, 1500, -16):
            music.pitch(freq, 30, wait=False)
            sleep(20)

def follow_thin_line(drive_time=20):
    left_sensor = line_sensor.line_sensor_read('left')
    right_sensor = line_sensor.line_sensor_read('right')
    black_left = left_sensor + CHANGETHRESHOLD < left_sensor_start
    black_right = right_sensor + CHANGETHRESHOLD < right_sensor_start
    if not(black_left) and not(black_right):
        display.show(Image.ARROW_N)
        head_lights()
        buggy.left_motor(MAXSPEED)
        buggy.right_motor(MAXSPEED)
    elif black_left and not(black_right):
        display.show(Image.ARROW_W)
        left_indicator()
        buggy.left_motor(MINTURN)
        buggy.right_motor(MAXTURN)
    elif black_right and not(black_left):
        display.show(Image.ARROW_E)
        right_indicator()
        buggy.left_motor(MAXTURN)
        buggy.right_motor(MINTURN)
    else:
        display.show(' ')
        both_indicators()
        buggy.left_motor(MAXTURN)
        buggy.right_motor(-MAXTURN)
    sleep(drive_time)

def follow_thick_line(drive_time=20):
    left_sensor = line_sensor.line_sensor_read('left')
    right_sensor = line_sensor.line_sensor_read('right')
    black_left = left_sensor + CHANGETHRESHOLD < left_sensor_start
    black_right = right_sensor + CHANGETHRESHOLD < right_sensor_start
    if not(black_left) and not(black_right):
        display.show(' ')
        both_indicators()
        buggy.left_motor(-MAXTURN)
        buggy.right_motor(-MAXTURN)
    elif black_left and not(black_right):
        display.show(Image.ARROW_W)
        left_indicator()
        buggy.left_motor(MINTURN)
        buggy.right_motor(MAXTURN)
    elif black_right and not(black_left):
        display.show(Image.ARROW_E)
        right_indicator()
        buggy.left_motor(MAXTURN)
        buggy.right_motor(MINTURN)
    else:
        display.show(Image.ARROW_N)
        head_lights()
        buggy.left_motor(MAXSPEED)
        buggy.right_motor(MAXSPEED)
    sleep(drive_time)

def spin_from_obstacle(spin_time=800):
    display.show(' ')
    both_indicators()
    buggy.left_motor(MAXTURN)
    buggy.right_motor(-MAXTURN)
    sleep(spin_time)

def start_buggy():
    left_sensor = line_sensor.line_sensor_read('left')
    right_sensor = line_sensor.line_sensor_read('right')
    display.scroll('L' + str(left_sensor), delay=60)
    display.scroll('R' + str(right_sensor), delay=60)
    head_lights()
    police_siren()
    both_indicators()

start_buggy()
while True:
    if button_a.is_pressed() and not button_b.is_pressed():
        display.scroll('A', delay=100)
        thin_line_follow_flag = True
    elif button_b.is_pressed() and not button_a.is_pressed():
        display.scroll('B', delay=100)
        thin_line_follow_flag = False
    if thin_line_follow_flag:
        follow_thin_line(MOTORTIME)
    else:
        follow_thick_line(MOTORTIME)
    # check for obstacle and spin and go back
    if distance_sensor.distance() < 10:
        spin_from_obstacle(SPINTIME)
    buggy.stop()
    sleep(10)

---

Tasks

1. Set up a thin line track and a thick line track and switch the buggy from one track to the other using button pressing.

2. Use the track templates to create identically shaped thin and thick tracks and time the buggy on each to find out which track it is better at following.