5. Selection in the Event Loop

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from microbit import *
import music

while True:
    if button_a.is_pressed():
        music.pitch(440, 200)
        sleep(500)
        music.pitch(440, 200)
        sleep(500)

Note

Here the micro:bit is constantly checking button A. When it detects a press it will execute the indented code underneath.

music.pitch(440, 200) plays a tone at 440 Hz (the note A4) for 200 milliseconds. You can change the number to get a higher or lower pitch.

Notice the indentation: the if statement is indented to indicate that it belongs to the while loop. The music.pitch() and sleep() calls are indented again to indicate that they belong to the if statement.

This indentation is very important in Python as it dictates the structure of the code/program.

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from microbit import *
import music

while True:
    if button_a.is_pressed():
        music.pitch(440, 200)
        sleep(500)
    music.pitch(440, 200)
    sleep(500)

Note

With a slight change to the program, we see completely different behaviour from the micro:bit.

In this case the micro:bit will beep all the time because the last two lines (music.pitch() and sleep()) belong to the while loop, not the if statement. This means that on every loop / iteration those lines will always run.

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from microbit import *
import music

while True:
    # Reads an analog signal from pin 1 (e.g. IR distance sensor)
    # A low reading (close to 0) means an obstacle is detected
    if pin1.read_analog() < 100:
        music.pitch(440, 200)
        sleep(200)

Note

Connect an IR distance sensor to pin 1 and GND/3V on the edge connector. pin1.read_analog() returns a value from 0 to 1023. A low value means an obstacle is close. Inside the loop we check the sensor value every single iteration.

Before you run this program, have a guess at what the micro:bit does when running it.

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from microbit import *
import music

# Set the threshold for what counts as a "loud" sound (0-255)
microphone.set_threshold(SoundEvent.LOUD, 150)

while True:
    if microphone.was_event(SoundEvent.LOUD):
        music.pitch(440, 200)
        sleep(500)

    sleep(300)

Note

microphone.set_threshold(SoundEvent.LOUD, 150) sets the sensitivity — higher values mean only very loud sounds will trigger it. microphone.was_event(SoundEvent.LOUD) checks whether a loud sound occurred since the last time it was called, and clears the history each time — similar to resetting the sensor each loop.

Note: The built-in microphone is only available on the micro:bit V2.

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from microbit import *
import music

light_threshold = 150

while True:
    if display.read_light_level() > light_threshold:
        # Bright light detected — play a high-pitched tone
        music.pitch(1000, 200)
        sleep(500)

    sleep(500)

Note

The micro:bit uses its LED display to read ambient light levels via display.read_light_level(), which returns a value from 0 (dark) to 255 (bright). The threshold value can be adjusted to suit your environment.

Unlike the Edison which has separate left and right light sensors, the micro:bit has a single combined light sensor through the display. Two different pitches could be used to simulate different responses — try changing the frequency passed to music.pitch().

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from microbit import *
import random
import music

while True:
    num = random.randint(1, 4)

    if num == 1:
        display.scroll("F")   # Forward
        music.pitch(440, 300)
    elif num == 2:
        display.scroll("B")   # Backward
        music.pitch(330, 300)
    elif num == 3:
        display.scroll("L")   # Left
        music.pitch(550, 300)
    elif num == 4:
        display.scroll("R")   # Right
        music.pitch(660, 300)

    sleep(1500)