OpenFlexure stage controller

A standalone controller for an OpenFlexure Delta Stage — part of an open two-photon microscope project. Three rotary encoders drive three stepper motors through the mainboard, with live position feedback on an LCD. No PC required.

Ingredients

BeeHive boards:

Other components:

How it works

The OpenFlexure Delta Stage moves its sample with three actuators in a delta geometry. Here, three rotary encoders act as the manual interface: turning an encoder feeds counts to the mainboard, which converts them into delta-stage movement coordinates and drives the three 28BYJ-48 stepper motors accordingly.

Position and status are shown live on an HD44780 LCD over I2C, so the whole controller works without a PC — USB serial is optional for logging or remote control. The same approach simplifies to cartesian stages: with a cartesian geometry the coordinate conversion collapses to one encoder per axis driving one motor.

Wiring

• Each rotary encoder DB to a mainboard data line (A/B channels), plus power and ground.
• Each 28BYJ-48 driver to mainboard data lines for its motor; motor power from the appropriate rail.
• HD44780 LCD (I2C backpack) to the mainboard I2C data lines (SDA/SCL), plus power and ground.
• Optional USB serial to a host PC.

Code

Controlled via MicroPython. A minimal encoder-to-motor skeleton (coordinate conversion omitted):

# TODO: pins/addresses are placeholders; add the delta-stage coordinate maths
#       and your stepper stepping routine.
from machine import Pin, I2C
import time

# Three encoders (A/B per axis)
enc = [(Pin(4, Pin.IN), Pin(5, Pin.IN)),
       (Pin(12, Pin.IN), Pin(13, Pin.IN)),
       (Pin(14, Pin.IN), Pin(15, Pin.IN))]

lcd_i2c = I2C(0, scl=Pin(22), sda=Pin(21))   # HD44780 via I2C backpack
pos = [0, 0, 0]

def read_delta(i):
    # TODO: quadrature decode to +1 / -1 / 0
    return 0

def to_stage_coords(pos):
    # TODO: delta-stage geometry; for a cartesian stage this is the identity
    return pos

def drive_motors(target):
    # TODO: step each 28BYJ-48 towards target
    pass

def show(coords):
    # TODO: write coords to the HD44780 over I2C
    pass

while True:
    for i in range(3):
        pos[i] += read_delta(i)
    coords = to_stage_coords(pos)
    drive_motors(coords)
    show(coords)
    time.sleep_ms(5)

Results / notes

The controller gives a self-contained, PC-free way to drive an OpenFlexure Delta Stage from three rotary encoders, with live LCD feedback. It reduces to a simple one-encoder-per-axis controller for cartesian stages.