from machine import Pin, PWM, time_pulse_us
import time

trig = Pin(15, Pin.OUT)
echo = Pin(14, Pin.IN)
buzzer = PWM(Pin(16))

NGUONG = 30  # cm

def do_khoang_cach():
    trig.low()
    time.sleep_us(2)
    trig.high()
    time.sleep_us(10)
    trig.low()

    thoi_gian = time_pulse_us(echo, 1, 30000)  # đo độ rộng xung Echo

    if thoi_gian < 0:
        return None

    khoang_cach = thoi_gian * 0.0343 / 2
    return khoang_cach

while True:
    kc = do_khoang_cach()

    if kc is not None:
        print("Khoang cach:", round(kc, 2), "cm")

        if kc < NGUONG:
            buzzer.freq(1000)
            buzzer.duty_u16(30000)   # buzzer kêu liên tục
        else:
            buzzer.duty_u16(0)       # buzzer tắt
    else:
        print("Khong do duoc")
        buzzer.duty_u16(0)

    time.sleep(0.1)