rotary_encoder.py

#!/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 BELOW

	    """

        self.pi = pi
        self.gpioA = gpioA
        self.gpioB = gpioB
        self.callback = callback

        self.levA = 0
        self.levB = 0
        self.lastSeq = 2

        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      
            seq = (self.levA^self.levB) + (self.levA<<1)
            if ((seq-self.lastSeq==1)or(seq-self.lastSeq==-3)):
                self.callback(1)
            elif ((seq-self.lastSeq==-1)or(seq-self.lastSeq==3)):
                self.callback(-1)
            self.lastSeq=seq
         

    def cancel(self):

        """
        Cancel the rotary encoder decoder.
        """

        self.cbA.cancel()
        self.cbB.cancel()

#EXAMPLE:

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, 9, 11, callback)

    time.sleep(5)

    decoder.cancel()

    pi.stop()