# Exercise 13(a)
from machine import Pin, time_pulse_us
from time import sleep_ms,sleep_us

# Define the GPIO lines needed
echo_pin = Pin(18, Pin.IN)
trig_pin = Pin(19, Pin.OUT)

# Ensure the trigger line is zero to begin with
trig_pin.value(0)
sleep_us(10) 

while True:
    trig_pin.value(1)  # signal to output pulses
    sleep_us(10)       # only need a short burst of pulses
    trig_pin.value(0)  # signal to stop pulses

    # determine how long before an echo signal is received
    pulse_duration = time_pulse_us(echo_pin, 1, 1000000)  # Wait for a LOW pulse, 1s timeout
    
    if pulse_duration > -1:
        echo_duration = pulse_duration/2
    
        # calculate the distance in cms
        object_distance = 341 * (echo_duration/1000000)*100
        print(f' The object is {object_distance:.1f} cms away')

    sleep_ms(500)  # no need to update the readings too frequently