from utime import sleep_us
from machine import Pin, time_pulse_us


class Ultrasonic:
    def __init__(self, tPin, ePin):
        # Init trigger pin (out)
        self.trigger = Pin(tPin, Pin.OUT)
        self.trigger.low()

        # Init echo pin (in)
        self.echo = Pin(ePin, Pin.IN)

    def distance_in_cm(self):
        # Send a 10us pulse.
        self.trigger.high()
        sleep_us(10)
        self.trigger.low()

        try:
            time = time_pulse_us(self.echo, 1, 29000)
        except OSError:
            return None

        # Calc the duration of the recieved pulse, divide the result by
        # 2 (round-trip) and divide it by 29 (the speed of sound is
        # 340 m/s and that is 29 us/cm).
        dist_in_cm = (time / 2.0) / 29

        return dist_in_cm