from machine import Pin, PWM
from hcsr04 import HCSR04
from time import *

buzzer = PWM(Pin(12, Pin.OUT)) #Check the pin #. Some pins cannot support PWM.
ultrasonic = HCSR04(trigger_pin=18, echo_pin=19, echo_timeout_us=1000000)

def buzz(frequency, duration):
    buzzer.freq(frequency)
    buzzer.duty(512) # 0 to 1023, 512 is half volume
    sleep(duration) 

buzz(1, 0.2)   #Mute for 0.2s

while True:
    distance = ultrasonic.distance_cm() 
    print('Distance:', distance, 'cm')
    if 5 < distance < 200:
        buzz(440, distance/200)
        buzz(1, distance/200)