dial.py

#! /usr/bin/python3
import time
import threading
import RPi.GPIO as GPIO

class Dial (threading.Thread):
  def __init__(self, threadID, name):
    threading.Thread.__init__(self)
    self.threadID = threadID
    self.name = name

    # BCM pin numbering!
    GPIO.setmode(GPIO.BCM)
    GPIO.setup([17, 18], direction=GPIO.IN, pull_up_down=GPIO.PUD_UP)
    self.direction = 0

  def __del__(self):
    GPIO.cleanup()

  def get_direction(self):
    # Pickup the direction and zero it, so we only get it once
    return_val = self.direction
    self.direction = 0
    return return_val

  def run(self):
    while True:
      # We only need to check for an interrupt on one pin
      # because we can simply test the value of the other to
      # work out which direction the dial was turned.
      # We cannot modify the global direction variable because
      # it is processed afterwards, so it would not be thread safe
      GPIO.wait_for_edge(17, GPIO.FALLING)
      new_direction = GPIO.input(18)
      if not new_direction:
        new_direction = -1

      # Save the new_direction
      self.direction = new_direction

      # Debounce period
      time.sleep(0.3)