10. MOVEMotor line follower 3

10.1. Adding lights and sound: import modules

Use the LEDs and buzzer.

Import the music module to use the buzzer.

Import the neopixel module so it can be referred to simply as leds.

For different forms of module importing see:

• https://www.w3schools.com/python/ref_keyword_import.asp

• https://www.w3schools.com/python/ref_keyword_as.asp

• https://www.w3schools.com/python/ref_keyword_from.asp

import music
from neopixel import NeoPixel as leds

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10.2. Adding lights and sound: set up lights

Set up the Neopixels on pin8 with a length of 4 pixels using the neopixel syntax.

The constants, LED_PIN and NUM_PIXELS, are used to help remember the neopixel syntax.

It would be just as easy to use lights = leds(pin8, 4).

Add constants for the LED colours to use. These have the RGB values for the colours. The ones chosen are subtle. They avoid using the full brightness values that can go as high 255.

LED_PIN = pin8
NUM_PIXELS = 4
lights = leds(LED_PIN, NUM_PIXELS)
DULL_WHITE = (20, 20, 20)
DULL_YELLOW = (35, 25, 0)
DULL_RED = (20, 0, 0)

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10.3. Adding lights and sound: lights functions

Define rear_lights() so that it sets the rear lights (index 2 and 3) to red.

Define front_lights(left, right) so that it keeps reuses the rear lights and sets the front left and front right lights (index 0 and 1) to the colours passed in place of the left and right parameters.

Define head_lights(), left_indicator(), right_indicator(), both_indicators(), so that they use front_lights(left, right) and specify the front lights to use for each.

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

def front_lights(left, right):
    lights[0] = left
    lights[1] = right
    rear_lights()
    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)

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10.4. Adding lights and sound: police siren function

Set up the police_siren() function so that it makes a siren for a short time.

Use the music.pitch method for playing the siren sounds.

music.pitch(frequency, duration=-1, pin=microbit.pin0, wait=True)

Plays a pitch at the integer frequency given for the specified number of milliseconds.

If the frequency is set to 440 and the duration to 1000 then a standard concert A note is played for one second.

Note that only one pitch can be played on one pin at any one time.

If wait is set to True, this function is blocking and must be completed before going on to the rest of the code.

If duration is negative the pitch is played continuously until either the blocking call is interrupted or, in the case of a background call, a new frequency is set or stop is called (see below).

Use the music.pitch method in a for-loop in which pith frequency goes up in steps before going down in a second for-loop and then repeated.

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

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10.5. Adding lights and sound: start_buggy function

Define the start_buggy() function below to be used before the while True loop.

Get the line sensor readings and display them to make sure that the buggy was over a consistent white surface to start off.

Turn on front and rear lights using head_lights().

Play the police siren.

Turn on both front indicators as warning lights to place the buggy on a thin line track.

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()

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10.6. Adding lights and sound: add lights to line following and spin

Add lights to the line following and spin functions.

For follow_thin_line, display arrows to indicate the direction the buggy will go and adjust the front lights depending on whether the buggy will go forward, turn or spin.

For spin_from_obstacle, clear the display and show both front indicators.

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

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10.7. Version 3 Code for thin line following with lights and sound

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()

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

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

def front_lights(left, right):
    lights[0] = left
    lights[1] = right
    rear_lights()
    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)
            sleep(20)
        for freq in range(1760, 1500, -16):
            music.pitch(freq, 30)
            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 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:
    follow_thin_line(MOTORTIME)
    # check for obstacle and spin and go back
    if distance_sensor.distance() < 10:
        spin_from_obstacle(SPINTIME)
    buggy.stop()
    sleep(10)

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Tasks

1. Add siren sounds when the buggy spins to avoid an obstacle.

2. Add a beep sound when the buggy turns left or right.

3. Add constants for different LED colours and use them when the buggy spins around.