print('Distance Sensor')
import machine, time
from machine import Pin
from time import sleep

class HCSR04:
    """
    Driver to use the untrasonic sensor HC-SR04.
    The sensor range is between 2cm and 4m.
    The timeouts received listening to echo pin are converted to
    OSError('Out of range')
    """
# echo_timeout_us is based in chip range limit (400cm)
    def __init__(self, trigger_pin, echo_pin, echo_timeout_us=500*2*30):
        """
        trigger_pin: Output pin to send pulses
        echo_pin: Readonly pin to measure the distance. The pin should be
        protected with 1k resistor
        echo_timeout_us: Timeout in microseconds to listen to echo pin.
        By default is based in sensor limit range (4m)
        """
        self.echo_timeout_us = echo_timeout_us
        # Init trigger pin (out)
        self.trigger = Pin(trigger_pin, mode=Pin.OUT, pull=None)
        self.trigger.value(0)
        # Init echo pin (in)
        self.echo = Pin(echo_pin, mode=Pin.IN, pull=None)

    def _send_pulse_and_wait(self):
        """
        Send the pulse to trigger and listen on echo pin.
        We use the method `machine.time_pulse_us()` to get the microseconds
        until the echo is received.
        """
        self.trigger.value(0) # Stabilize the sensor
        time.sleep_us(5)
        self.trigger.value(1)
        # Send a 10us pulse.
        time.sleep_us(10)
        self.trigger.value(0)

        try:
            pulse_time = machine.time_pulse_us(self.echo, 1,self.echo_timeout_us)
            return pulse_time
        except OSError as ex:
            if ex.args[0] == 110: # 110 = ETIMEDOUT
                raise OSError('Out of range')
            raise ex

    def distance_cm(self):
        pulse_time = self._send_pulse_and_wait()
        cms = (pulse_time / 2) / 29.1
        return cms

sensor = HCSR04(trigger_pin=5, echo_pin=17, echo_timeout_us=30000)
while True:
    distance = sensor.distance_cm()
    print('Distance:', distance, 'cm')
    sleep(1)


# distance = V x t
# V= sound speed in air 343.2m/s -> 0.0342 cm/micro-second -> 1/29.1
# in 1cm -> 29.1 micro-second
# t = time in micro-second

# 2 -> for both sended and reflected signal time