from machine import Pin,PWM
import time
buzzer = Pin(14,Pin.OUT)
pwm = PWM(buzzer,freq=1000,duty=900)

while True:
    # 频率递增循环
    for i in range(300, 701):  # 从 300Hz 到 700Hz
        pwm.freq(i)
        time.sleep_ms(10)
    time.sleep(5) 

pwm.deinit()