from machine import Pin, PWM
import time

trigger = Pin(4, Pin.OUT)
echo = Pin(3, Pin.IN)

def measure_distance():
    
    trigger.value(1)
    time.sleep_us(10)
    trigger.value(0)

    while echo.value() == 0:
        pass

    start_time = time.ticks_us()

   
    while echo.value() == 1:
        pass

    end_time = time.ticks_us()

   
    duration = time.ticks_diff(end_time, start_time)

    distance_cm = duration / 58.0

    return distance_cm

while True:
    distance_cm = measure_distance()
    print("Distance in CM:", distance_cm)
    

    if distance_cm < 100:
        print("Present")
        
    else:
        print("Absent")

    time.sleep(1)