rotary_encoder.py

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#!/usr/bin/env python
 
import pigpio
 
class decoder:
 
   """Class to decode mechanical rotary encoder pulses."""
 
   def __init__(self, pi, gpioA, gpioB, callback):
 
      """
      Instantiate the class with the pi and gpios connected to
      rotary encoder contacts A and B.  The common contact
      should be connected to ground.  The callback is
      called when the rotary encoder is turned.  It takes
      one parameter which is +1 for clockwise and -1 for
      counterclockwise.
 
      EXAMPLE
 
      import time
      import pigpio
 
      import rotary_encoder
 
      pos = 0
 
      def callback(way):
 
         global pos
 
         pos += way
 
         print("pos={}".format(pos))
 
      pi = pigpio.pi()
 
      decoder = rotary_encoder.decoder(pi, 7, 8, callback)
 
      time.sleep(300)
 
      decoder.cancel()
 
      pi.stop()
 
      """
 
      self.pi = pi
      self.gpioA = gpioA
      self.gpioB = gpioB
      self.callback = callback
 
      self.levA = 0
      self.levB = 0
 
      self.lastGpio = None
 
      self.pi.set_mode(gpioA, pigpio.INPUT)
      self.pi.set_mode(gpioB, pigpio.INPUT)
 
      self.pi.set_pull_up_down(gpioA, pigpio.PUD_UP)
      self.pi.set_pull_up_down(gpioB, pigpio.PUD_UP)
 
      self.cbA = self.pi.callback(gpioA, pigpio.EITHER_EDGE, self._pulse)
      self.cbB = self.pi.callback(gpioB, pigpio.EITHER_EDGE, self._pulse)
 
   def _pulse(self, gpio, level, tick):
 
      """
      Decode the rotary encoder pulse.
 
                   +---------+         +---------+      0
                   |         |         |         |
         A         |         |         |         |
                   |         |         |         |
         +---------+         +---------+         +----- 1
 
             +---------+         +---------+            0
             |         |         |         |
         B   |         |         |         |
             |         |         |         |
         ----+         +---------+         +---------+  1
      """
 
      if gpio == self.gpioA:
         self.levA = level
      else:
         self.levB = level;
 
      if gpio != self.lastGpio: # debounce
         self.lastGpio = gpio
 
         if   gpio == self.gpioA and level == 1:
            if self.levB == 1:
               self.callback(1)
         elif gpio == self.gpioB and level == 1:
            if self.levA == 1:
               self.callback(-1)
 
   def cancel(self):
 
      """
      Cancel the rotary encoder decoder.
      """
 
      self.cbA.cancel()
      self.cbB.cancel()
 
if __name__ == "__main__":
 
   import time
   import pigpio
 
   import rotary_encoder
 
   pos = 0
 
   def callback(way):
 
      global pos
 
      pos += way
 
      print("pos={}".format(pos))
 
   pi = pigpio.pi()
 
   decoder = rotary_encoder.decoder(pi, 7, 8, callback)
 
   time.sleep(300)
 
   decoder.cancel()
 
   pi.stop()