Rotary_Encoder

Hall Effect Based

Hardware

• Encoder (Amazon)
  • Type: AB bidirectional incremental magnetic Hall encoder
  • Line speed: 12 pulse per revolution)
  • Supply voltage: DC3.3/5V
  • Basic function: comes with pull-up shaping resistor, direct connection of single chip microcomputer
  • Interface type: PH2.0 with connecting cable
  • Output signal type: square wave AB phase
  • Response frequency: 100KH
  • Magnetic ring trigger series: 24 poles (12 pairs poles)
    

Waveform

Implementation for MicroPython on Raspberry Pi Pico

• We use 2 independent (interrupt) events [Rising A, Rising B] and 4 pin states [High A, Low A, High B, Low B]
  • MicroPython identifies rising event as 8
  • Obviously, high pin state is 1 and low is 0
  • Since we have two irq pins, we can right-shift the second pin's event identifier to 4
  • When two sets of identifiers combine, we have 4 events [8, 5, 9, 4]
    • Rising A and High B can be combined together, the new combined identifier is 9
      • Rising A, Low or High B = 8 or 9
      • Rising B, Low or High B = 4 (8>>1) or 5 ((8>>1)+1)
    • But Rising A and Low A cannot be together
  • Look at the waveform, we will only encounter combined events [8, 5] when rotates clockwisely or encounter [9, 4] when counter-clockwisely
  • Combined event 9 will not follow 8 normally, only 5 follows 8. Otherwise, rotation direction reversesing happens
    • We now have a EED (Event Expectation Dict) and ERR [ERRor dict]

      EED = {8:5, 5:8, 9:4, 4:9} # Expectation
      ERR = {8:5, 5:5, 9:9, 4:9} # when direction reversed, we need reset OldEvent to a default value
      if NewEvent == EED[OldEvent]:  # New event is as expected
          if   NewEvent ==  8: print('CW')
          elif NewEvent ==  4: print('CCW')
          OldEvent = NewEvent
      else:                         # New event is unexpected, reset beginning event
          OldEvent = ERR[NewEvent]  # We reset old event because of direction reversing.