import machine, time  
from machine import Pin

def HCSR04(trigger_pin, echo_pin):
  trigger = Pin(trigger_pin, mode=Pin.OUT, pull=None)
  trigger.value(0)
  echo = Pin(echo_pin, mode=Pin.IN, pull=None)
  return trigger,echo

def _send_pulse_and_wait(trigger,echo):
    trigger.value(0)
    time.sleep_us(5)
    trigger.value(1)
    time.sleep_us(10)
    trigger.value(0)

    echo_timeout_us=500*2*30

    pulse_time = machine.time_pulse_us(echo, 1,echo_timeout_us)
    return pulse_time


def distance_cm(trigger,echo):
    pulse_time = _send_pulse_and_wait(trigger,echo)
    cms = (pulse_time / 2) / 29.1
    return cms

trigger,echo = HCSR04(trigger_pin=5, echo_pin=21)

while True:
    distance = distance_cm(trigger,echo)
    print('Distance:', distance, 'cm')
    time.sleep(1)