from machine import PWM, Pin
from utime import sleep

buzzer = PWM(Pin(7))
for f in (262, 330, 392, 523):  # C E G C
    buzzer.freq(f)
    buzzer.duty_u16(32768)   # 50% duty
    print("Playing", f)
    sleep(0.4)
buzzer.duty_u16(0)