To verify that the encoder disc design would work, I started with a single-bit of the eventual 3-bit encoder and just the one stepper motor.

In this first pass, I didn't have any LM393s in my parts bin. So while I awaited delivery, I used an op-amp (LM386) and a 2N2222 transistor to get the digital input needed for the microcontroller. Above the pycom microcontroller is a DRV8825 for the stepper motor.

DEFAULT_SPEED = 100

enc0 = Pin('P3', mode=Pin.IN)
step_pin = Pin('P11', mode=Pin.OUT),
dir_pin = Pin('P12', mode=Pin.OUT)

# turn the stepper motor n degrees
def turnKnob(degrees, cw=True, speed=DEFAULT_SPEED):

    # set direction
    dir_pin.value(0 if cw else 1)

    # adjust for the 5:1 planetary gear reduction
    steps = int(degrees * (1036/360))
    delay = 1 / speed

    # create a pulse for each step needed
    for i in range(0, steps):
        step_pin.value(0)
        time.sleep(0.0001)
        step_pin.value(1)
        time.sleep(0.0001)
        step_pin.value(0)
        # time between pulses sets speed
        # short delay, faster rotation
        # longer delay, slower rotation
        time.sleep(delay)

# run until the encoder hits a slot
def runUntil(cw=True, speed=DEFAULT_SPEED):

    while enc0.value() != 0:
        turnKnob(1, cw, speed)

This snippet turns the stepper motor until a slot in the encoder disk triggers the IR/photodiode comparator