pigpio code for wateproof ultrasonic sensor

pigpio_ultrasonic.py

#!/usr/bin/python 

#  By Dan-in-CA 11/2018
#  Updated 3/21/2019

from __future__ import print_function, division
from time import sleep
import pigpio

pi = pigpio.pi()

# Define GPIO pins to use on Pi (BMC numbering)
pin_trigger = 23
pin_echo = 24

start = None
prev = 0
max_dif = 10
distance = None
verbose = False

# Speed of sound in cm/ms at temperature (changed from cm/s)
temperature = 24
sound_speed = 33.1 + (0.0006*temperature)

#  Set pin modes and output level
pi.set_mode(pin_trigger, pigpio.OUTPUT)
pi.write(pin_trigger, 0)
pi.set_mode(pin_echo, pigpio.INPUT)


def calc(gpio, level, tick):
    """
    Callback function to handle distance calculation.
    """
    global start, prev, distance
    if level == 1: #  Start of echo pulse
        start = tick
    if start and level == 0: #  If start has a value and echo pulse ended        
        echo = pigpio.tickDiff(start, tick) # Length of echo pulse in microseconds
        if verbose:
            print("echo: ", echo)
        dist = round(((echo / 1000) * sound_speed)/2, 1)
        if not abs(prev - dist) > max_dif: #### May want to make this user setable
            distance = dist
        prev = dist
        start = None
    return


def measure():
    """
    Send a pulse and time the echo.
    """
    pi.gpio_trigger(pin_trigger, 10, 1) #  Send a 10 microsecond pulse on the trigger pin
    cb = pi.callback(pin_echo, pigpio.EITHER_EDGE, calc) #  Catch the echo pulse and pass timing to calc callback function
    sleep(0.1)
    cb.cancel()
    if verbose and distance:
        print("distance: ", distance)
    return distance    


if __name__ == '__main__':  
    verbose = True
    while True:
        measure()
        sleep(1)