import machine
from machine import Pin,PWM
from time import sleep_us,sleep
buzzer = Pin(4, Pin.OUT)
buzzer_pwm=PWM(buzzer)
echo = Pin(18,Pin.IN)
trig = Pin(5,Pin.OUT)
while True :
    trig.value(0)
    sleep_us(2)
    trig.value(1)
    sleep_us(10)
    trig.value(0)
    x = machine.time_pulse_us(echo,1)
    distance = (0.034*x)/2
    print('distance', distance, 'cm' )
    if distance <=50 :
        buzzer_pwm.freq
        buzzer_pwm.duty(100)
    else :
        buzzer_pwm.duty(0)
        sleep(1)