import time
from machine import Pin, time_pulse_us

TRIG_PIN = 5
ECHO_PIN = 18
BUZZER_PIN = 4

trig = Pin(TRIG_PIN, Pin.OUT)
echo = Pin(ECHO_PIN, Pin.IN)
buzzer = Pin(BUZZER_PIN, Pin.OUT)

def get_distance():
    trig.value(0)
    time.sleep_us(2)

    trig.value(1)
    time.sleep_us(10)
    trig.value(0)

    duration = time_pulse_us(echo, 1, 30000)

    if duration < 0:
        return None

    return duration * 0.0343 / 2

print("Ultrasonic obstacle alert system started.")

while True:
    distance = get_distance()

    if distance is None:
        buzzer.value(0)
        print("No echo received")

    else:
        print("Distance: {:.1f} cm".format(distance))

        if distance < 15:
            buzzer.value(1)
            print("BUZZER ON - Obstacle too close!")
        else:
            buzzer.value(0)
            print("BUZZER OFF - Clear path")

    time.sleep(1)