Play a Scale

Welcome to the Scale Lab

In this lab, you will use a loop to play many tones in order from low to high. This is called playing a scale — just like you do on a piano!

Why Use a Loop?

Playing a scale means playing many tones, each a little higher than the last. You could write out each tone one by one, but that would be a very long program! A loop lets you play all the tones in just a few lines of code.

Playing a Scale With a Loop

This program starts at a very low pitch of 30 Hz and steps up through 64 tones. Each new tone is 10% higher than the last.

from machine import Pin, PWM  # import Pin and PWM classes
from utime import sleep        # import sleep to pause between notes

SPEAKER_PIN = 16               # GPIO pin connected to the speaker

# Create a PWM object on the speaker pin
speaker = PWM(Pin(SPEAKER_PIN))

def play_tone(frequency):
    """Turn on the speaker at the given frequency."""
    speaker.duty_u16(1000)     # turn the sound on
    speaker.freq(frequency)    # set the pitch
    sleep(0.3)                 # hold the note for 0.3 seconds

def be_quiet():
    """Turn the speaker off."""
    speaker.duty_u16(0)        # set duty cycle to 0 to silence the speaker

freq = 30                      # start at 30 Hz (very low)

for i in range(64):            # repeat 64 times
    print(freq)                # print the current frequency
    play_tone(freq)            # play the tone
    freq = int(freq * 1.1)     # increase frequency by 10%

# Turn off the speaker when the scale is done
speaker.duty_u16(0)

What Each Line Does

1. def play_tone(frequency): — defines a function that plays one tone at the given pitch.
2. speaker.duty_u16(1000) — turns the speaker on.
3. speaker.freq(frequency) — sets the pitch to the value passed in.
4. sleep(0.3) — holds the note for 0.3 seconds.
5. freq = 30 — starts the scale at a very low pitch of 30 Hz.
6. for i in range(64): — repeats the loop body 64 times.
7. freq = int(freq * 1.1) — makes the next frequency 10% higher than the current one.

Key Idea

Notice that the frequencies printed to the console are not evenly spaced — the gaps get bigger as the pitch goes up. This is how human hearing works: we hear pitch differences as ratios, not as fixed steps.

How the Frequency Changes

Look at this line from the program:

freq = int(freq * 1.1)

This line takes the current frequency and multiplies it by 1.1. That makes the next tone 10% higher than the last one.

This is called a geometric or multiplicative step. It matches how musical notes are spaced. On a piano, each note is about 6% higher than the one before it.

Experiments

1. Change the line freq = int(freq * 1.1) to freq = freq + 100. Now every tone is exactly 100 Hz higher than the last. Run the program. Does it sound like a regular musical scale, or does it sound odd? Why?
2. Change the multiplier from 1.1 to 1.06 to get closer to real musical note spacing. How does it sound now?
3. Change range(64) to range(12). Now only play 12 notes. How many octaves do you hear?

Monty's Tip

The print(freq) line shows you the current frequency in the console as the scale plays. Watch the numbers and compare them to what you hear!

Great Work!

You just used a loop to play a whole scale! Next, you will use a list of exact note frequencies to play a real song.