sonar_trigger_echo.py

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#!/usr/bin/env python

import time

import pigpio

class ranger:
   """
   This class encapsulates a type of acoustic ranger.  In particular
   the type of ranger with separate trigger and echo pins.

   A pulse on the trigger initiates the sonar ping and shortly
   afterwards a sonar pulse is transmitted and the echo pin
   goes high.  The echo pins stays high until a sonar echo is
   received (or the response times-out).  The time between
   the high and low edges indicates the sonar round trip time.
   """

   def __init__(self, pi, trigger, echo):
      """
      The class is instantiated with the Pi to use and the
      gpios connected to the trigger and echo pins.
      """
      self.pi    = pi
      self._trig = trigger
      self._echo = echo

      self._ping = False
      self._high = None
      self._time = None

      self._triggered = False

      self._trig_mode = pi.get_mode(self._trig)
      self._echo_mode = pi.get_mode(self._echo)

      pi.set_mode(self._trig, pigpio.OUTPUT)
      pi.set_mode(self._echo, pigpio.INPUT)

      self._cb = pi.callback(self._trig, pigpio.EITHER_EDGE, self._cbf)
      self._cb = pi.callback(self._echo, pigpio.EITHER_EDGE, self._cbf)

      self._inited = True

   def _cbf(self, gpio, level, tick):
      if gpio == self._trig:
         if level == 0: # trigger sent
            self._triggered = True
            self._high = None
      else:
         if self._triggered:
            if level == 1:
               self._high = tick
            else:
               if self._high is not None:
                  self._time = tick - self._high
                  self._high = None
                  self._ping = True

   def read(self):
      """
      Triggers a reading.  The returned reading is the number
      of microseconds for the sonar round-trip.

      round trip cms = round trip time / 1000000.0 * 34030
      """
      if self._inited:
         self._ping = False
         self.pi.gpio_trigger(self._trig)
         start = time.time()
         while not self._ping:
            if (time.time()-start) > 5.0:
               return 20000
            time.sleep(0.001)
         return self._time
      else:
         return None

   def cancel(self):
      """
      Cancels the ranger and returns the gpios to their
      original mode.
      """
      if self._inited:
         self._inited = False
         self._cb.cancel()
         self.pi.set_mode(self._trig, self._trig_mode)
         self.pi.set_mode(self._echo, self._echo_mode)

if __name__ == "__main__":

   import time

   import pigpio

   import sonar_trigger_echo

   pi = pigpio.pi()

   sonar = sonar_trigger_echo.ranger(pi, 23, 18)

   end = time.time() + 600.0

   r = 1
   while time.time() < end:

      print("{} {}".format(r, sonar.read()))
      r += 1
      time.sleep(0.03)

   sonar.cancel()

   pi.stop()