MicroPython HC-SR04 on a Pico with a driver module

# The same ranger with a driver: hcsr04.py, in the next tab, does the
# trigger and the timing, so the loop only asks for the distance.
import time
from hcsr04 import HCSR04

sonar = HCSR04(trig=19, echo=18)

while True:
    d = sonar.distance_cm()
    print("distance: %.1f cm" % d if d is not None else "nothing in range")
    time.sleep_ms(500)

# hcsr04.py: an HC-SR04 ultrasonic ranger.
# A 20 us pulse on TRIG sends a burst of sound; ECHO stays high for as long
# as the sound took to get there and back.
from machine import Pin, time_pulse_us
import time

class HCSR04:
    def __init__(self, trig, echo):
        self.trig = Pin(trig, Pin.OUT, value=0)
        self.echo = Pin(echo, Pin.IN)

    def distance_cm(self):
        self.trig.value(1)
        time.sleep_us(20)                         # 20 us: the datasheet asks for at least 10
        self.trig.value(0)
        us = time_pulse_us(self.echo, 1, 30000)   # 30 ms is about 5 m
        if us < 0:
            return None                           # no echo: nothing in range
        return us * 0.0343 / 2                    # sound: 343 m/s, there and back