The upcoming brief Python scripts will showcase the fundamental functionality of the Raspberry Pi Pico board. These presume that one or more binary input or output circuits are connected externally. You can activate each one by pasting the program into code.py on the CIRCUITRY drive provided by the board. The text is available for copying from this page, or the files are downloadable from the CircuitPython sample code folder on this website.
Sample A4988 Stepper Driver Circuit
A4988 Stepper Driver Demo
Direct download: a4988_demo.py.
# a4988.py
#
# Raspberry Pi Pico - stepper motor driver support
#
# This module provides a class for controlling an Allegro 4988 stepper motor
# driver. This device can drive one bipolar stepper motor up to 2A per coil
# using microstepping current control.
# A typical usage requires two digital outputs. The defaults assumes a Pololu
# A4988 stepper driver has been wired up to the Pico as follows:
#
# Pico pin 21, GPIO16 -> DIR
# Pico pin 22, GPIO17 -> STEP
# any Pico GND -> GND
# A4988 carrier board: https://www.pololu.com/product/1182
# This implementation bit-bangs the step line and so is limited to about 1000
# steps/sec as a result of CircuitPython execution speed. This solution is is
# only suitable for low-speed stepper motion.
# Likely a better long-term solution will be to use the RP2040 programmable IO
# peripheral (PIO) to cycle the step output.
################################################################
# CircuitPython module documentation:
# time https://circuitpython.readthedocs.io/en/latest/shared-bindings/time/index.html
# board https://circuitpython.readthedocs.io/en/latest/shared-bindings/board/index.html
# digitalio https://circuitpython.readthedocs.io/en/latest/shared-bindings/digitalio/index.html
#
# Driver lifecycle documentation:
# https://circuitpython.readthedocs.io/en/latest/docs/design_guide.html#lifetime-and-contextmanagers
#
################################################################################
# load standard Python modules
import time
# load the CircuitPython hardware definition module for pin definitions
import board
# load the CircuitPython GPIO support
import digitalio
#--------------------------------------------------------------------------------
class A4988:
def __init__(self, DIR=board.GP16, STEP=board.GP17):
"""This class represents an A4988 stepper motor driver. It uses two output pins
for direction and step control signals."""
self._dir = digitalio.DigitalInOut(DIR)
self._step = digitalio.DigitalInOut(STEP)
self._dir.direction = digitalio.Direction.OUTPUT
self._step.direction = digitalio.Direction.OUTPUT
self._dir.value = False
self._step.value = False
def step(self, forward=True):
"""Emit one step pulse, with an optional direction flag."""
self._dir.value = forward
# Create a short pulse on the step pin. Note that CircuitPython is slow
# enough that normal execution delay is sufficient without actually
# sleeping.
self._step.value = True
# time.sleep(1e-6)
self._step.value = False
def move_sync(self, steps, speed=1000.0):
"""Move the stepper motor the signed number of steps forward or backward at the
speed specified in steps per second. N.B. this function will not return
until the move is done, so it is not compatible with asynchronous event
loops.
"""
self._dir.value = (steps >= 0)
time_per_step = 1.0 / speed
for count in range(abs(steps)):
self._step.value = True
# time.sleep(1e-6)
self._step.value = False
time.sleep(time_per_step)
def deinit(self):
"""Manage resource release as part of object lifecycle."""
self._dir.deinit()
self._step.deinit()
self._dir = None
self._step = None
def __enter__(self):
return self
def __exit__(self):
# Automatically deinitializes the hardware when exiting a context.
self.deinit()
#--------------------------------------------------------------------------------
# Stepper motor demonstration.
stepper = A4988()
print("Starting stepper motor test.")
speed = 200
while True:
print(f"Speed: {speed} steps/sec.")
stepper.move_sync(800, speed)
time.sleep(1.0)
stepper.move_sync(-800, speed)
time.sleep(1.0)
speed *= 1.2
if speed > 2000:
speed = 100
Source: Raspberry Pi Pico Stepper Motor Examples
