A driver library and expansion board for controlling a 5-wire 4-phase stepper motor via the I2C interface.

[leezisheng]

The Bus Unipolar Stepper Motor Expansion Board is a module designed to control multiple unipolar stepper motors (e.g., 5-wire 4-phase stepper motors like 28BYJ48, 35BYJ46, 35BY412L) via the I2C serial communication interface. Key features include:

• Compact Design: Compatible with XIAO series and Adafruit Qt Py series main control boards, or usable as a standalone module.
• I2C Interface: Supports daisy-chaining with stackable expansion. Four address bits allow theoretical cascading of up to 16 driver boards.
• Onboard Power Indicators: LEDs for motor power and PWM expansion chip power.
• Power Protection: Supports power input via terminal blocks or Type-C port with reverse-polarity protection.
• Stable Power Regulation: Utilizes two 220μF solid-state capacitors for lower ESR, higher frequency performance, and longer lifespan compared to aluminum electrolytic capacitors.
• Broad Compatibility: Drives various 5-wire 4-phase unipolar stepper motors (e.g., 28BYJ-48) at 5V–24V. ULN2003 Darlington array provides 500mA per channel (2.5A total per chip).
• Multiple Driving Modes: Supports single-step, full-step, and half-step modes, with per-channel LED indicators.

This expansion board combines a compact footprint (directly attachable to XIAO mainboards or standalone use) with ULN2003 drivers (500mA/channel, 2.5A total) for 5-wire 4-phase steppers (5–24V input). Dual solid capacitors ensure stable power, while reverse-polarity protection and visual status LEDs enhance reliability in stacked configurations.

We provide MicroPython sample code with robust error handling for multi-motor independent control.
Bus Stepper Motor Driver

Main Features

• Independent Multi-Motor Control: A single PCA9685 chip supports up to 2 stepper motors (each motor occupies 4 PWM channels). Each motor can independently set direction, speed, drive mode, and motion mode.
• Flexible Motion Modes: Supports continuous motion (motor keeps rotating until manually stopped) and step motion (precisely controls motor to rotate a specified number of steps before stopping).
• Three Drive Modes: Single-phase drive (low power consumption, lower torque), dual-phase drive (high torque, suitable for heavy loads), and half-step drive (higher resolution, smoother motion).
• Hardware Optimization: Uses micropython.native decorator to improve execution efficiency of critical functions.
• Non-Blocking Control: Timer interrupts drive step pulses, reducing program blocking.

File Description

Core Software Design Concept

By integrating the PCA9685 PWM control chip with the RZ7899 motor driver chip, we can control DC motors. The program communicates with the PCA9685 via I²C to generate PWM signals, controlling motor speed, direction. The classes PCA9685 and BusDCMotor are designed:

• The PCA9685 class is responsible for controlling the generation of waveform frequency and duty cycle for different PWM channels.
• The BusDCMotor class encapsulates the control of DC motors, adjusting speed and direction using PWM duty cycles.

pca9685.py

This file implements control over the PCA9685 chip, allowing for the setting of PWM frequency, controlling the duty cycle of PWM waveforms, and driving servos or other devices using PWM signals.

Main Class

PCA9685:

• This class provides control over the PCA9685 chip, enabling the setting and retrieval of PWM frequencies and controlling the duty cycle of PWM waveforms.

  Methods:

  • reset(): Resets the PCA9685 module, restoring default settings.
  • freq(freq: float): Sets or retrieves the PWM frequency of the PCA9685.
  • pwm(index: int, on: int, off: int): Sets or retrieves the PWM signal for the specified channel.
  • duty(index: int, value: int, invert: bool = False): Sets the duty cycle for the specified channel and provides an option to invert the signal.

bus_step_motor.py

This file controls DC motors. The PWM signals generated by the PCA9685 chip allow for control of the speed and direction of up to 4 DC motors.

Main Class

BusStepMotor:

• Controls 5-wire, 4-phase stepper motors (such as 28BYJ-48), supporting three drive modes and two motion modes.

  Methods:

  • __init__(pca9685: PCA9685, motor_count: int = 2): Initializes the stepper motor control class.
  • _next_step(motor_id: int): Computes and updates the stepper motor state for the specified motor.
  • _start_timer(motor_id: int, speed: int): Starts a timer and sets a callback function to control continuous motor motion.
  • _stop_timer(motor_id: int): Stops the timer for the specified motor, stopping its motion.
  • start_continuous_motion(motor_id: int, direction: int, driver_mode: int, speed: int): Starts continuous motion for a motor.
  • stop_continuous_motion(motor_id: int): Stops the continuous motion of a motor.
  • start_step_motion(motor_id: int, direction: int, driver_mode: int, speed: int, steps: int): Starts step motion, rotating a motor for a specified number of steps.

  Attributes:

  • pca9685 (PCA9685): Instance of the PCA9685 chip that controls PWM signal output.
  • motor_count (int): Number of stepper motors controlled, with a maximum of 4.
  • timers (list): List storing the timers for each motor.
  • steps (list): List storing the target steps for each motor.
  • step_counters (list): List storing the current step counters for each motor.
  • directions (list): List storing the movement direction of each motor (forward or backward).
  • driver_modes (list): List storing the drive mode of each motor (single-phase, dual-phase, or half-step drive).
  • speeds (list): List storing the speed of each motor (controlling the pulse frequency of the driver output).

  Class Variables:

  • DRIVER_MODE_SINGLE (int): Constant value for the single-phase drive mode.
  • DRIVER_MODE_DOUBLE (int): Constant value for the dual-phase drive mode.
  • DRIVER_MODE_HALF_STEP (int): Constant value for the half-step drive mode.
  • FORWARD (int): Constant value for the forward direction of the stepper motor.
  • BACKWARD (int): Constant value for the backward direction of the stepper motor.
  • PHASES (dict): A dictionary containing phase sequences for different drive modes.

The channel drive sequence under different drive modes is shown in the table below:

Step	Single-phase (A+/A-/B+/B-)	Dual-phase (A+/A-/B+/B-)	Half-step (A+/A-/B+/B-)	Torque Characteristics
1	[1, 0, 0, 0]	[1, 1, 0, 0]	[1, 0, 0, 0]	Single:★☆☆ Dual:★★★ Half:★☆☆
2	[0, 1, 0, 0]	[0, 1, 1, 0]	[1, 0, 1, 0]	Single:★☆☆ Dual:★★☆ Half:★★★
3	[0, 0, 1, 0]	[0, 0, 1, 1]	[0, 0, 1, 0]	Single:★☆☆ Dual:★★★ Half:★☆☆
4	[0, 0, 0, 1]	[1, 0, 0, 1]	[0, 0, 1, 1]	Single:★☆☆ Dual:★★☆ Half:★★★
5	-	-	[0, 0, 0, 1]	Half-step:★☆☆
6	-	-	[0, 1, 0, 1]	Half-step:★★★
7	-	-	[0, 1, 0, 0]	Half-step:★☆☆
8	-	-	[1, 1, 0, 0]	Half-step:★★★

Phase Notation:

• 1: Active
• 0: Inactive
  Torque Levels:
• ★☆☆: Low
• ★★☆: Medium
• ★★★: High

Key Features

• Control Forward/Reverse and Speed: Adjust the PWM duty cycle to control the speed of the motor. The direction can also be set using a direction flag.
• Control up to 4 Motors: The class supports controlling up to four motors. By controlling multiple PWM channels, independent control of multiple motors is achievable.
• Motor Stop Function: The motor can be stopped by setting the PWM signal to 0, halting the motor's movement.

How to Use

Install Dependencies

Before running the example program, ensure that your environment has the necessary modules like machine and time. You can install dependencies via the MicroPython package manager.
Save the two files to your main folder and import them as follows:

# 导入硬件相关模块
from machine import Pin, I2C
# 导入时间相关模块
import time
# 导入自定义模块
from pca9685 import PCA9685
# 导入直流电机控制模块
from bus_step_motor import BusStepMotor

Usage Example

# Python env   : MicroPython v1.23.0 on Raspberry Pi Pico
# -*- coding: utf-8 -*-
# @Time    : 2025/1/19 上午10:57
# @Author  : 李清水
# @File    : main.py
# @Description : 总线步进电机扩展板示例程序

# ======================================== 导入相关模块 =========================================

# 导入硬件相关模块
from machine import Pin, I2C
# 导入时间相关模块
import time
# 导入自定义模块
from pca9685 import PCA9685
# 导入直流电机控制模块
from bus_step_motor import BusStepMotor

# ======================================== 全局变量 ============================================

# 外置PWM扩展芯片地址
PCA9685_ADDR = 0

# ======================================== 功能函数 ============================================

# ======================================== 自定义类 ============================================

# ======================================== 初始化配置 ==========================================

# 上电延时3s
time.sleep(3)
# 打印调试消息
print("FreakStudio: Using PCA9685 to control step motor")

# 创建硬件I2C的实例，使用I2C1外设，时钟频率为400KHz，SDA引脚为6，SCL引脚为7
i2c = I2C(id=1, sda=Pin(6), scl=Pin(7), freq=400000)

# 开始扫描I2C总线上的设备，返回从机地址的列表
devices_list = i2c.scan()
print('START I2C SCANNER')

# 若devices_list为空，则没有设备连接到I2C总线上
if len(devices_list) == 0:
    print("No i2c device !")
# 若非空，则打印从机设备地址
else:
    print('i2c devices found:', len(devices_list))
    # 遍历从机设备地址列表
    for device in devices_list:
        # 判断地址是否在0x40到0x4F之间，如果是，则为PCA9685芯片地址
        if 0x40 <= device <= 0x4F:
            print("PCA9685 I2C hexadecimal address: ", hex(device))
            PCA9685_ADDR = device

# 创建PCA9685实例，使用I2C0外设
pca9685 = PCA9685(i2c, PCA9685_ADDR)

# 创建步进电机实例，使用PCA9685实例，电机数量为4
bus_step_motor = BusStepMotor(pca9685, 4)

# ========================================  主程序  ===========================================

# 开启步进电机连续运动模式：电机编号为1，方向为正转，驱动模式为单相驱动，速度为10
bus_step_motor.start_continuous_motion(1, BusStepMotor.FORWARD, BusStepMotor.DRIVER_MODE_SINGLE, 10)
# 延时10s
time.sleep(10)
# 停止步进电机连续运动模式
bus_step_motor.stop_continuous_motion(1)

# 开启步进电机步进运动模式：电机编号为1，方向为正转，驱动模式为单相驱动，速度为10，步数为10
bus_step_motor.start_step_motion(1, 1, 0, 100, 1000)

Notes

• Power Requirements: Ensure that the stepper motor receives sufficient power to support multiple motors running simultaneously. Insufficient power voltage may cause the motor to fail to start or operate unstably.
• I2C Communication Stability: Since multiple motors share the PCA9685 chip via the I2C bus, ensure the stability of the I2C communication lines to avoid signal interference or communication loss.
• PWM Frequency Settings: When setting the PWM frequency, ensure it is suitable for the type of motor being controlled. An excessively high PWM frequency may cause the motor to overheat or reduce efficiency.

Conclusion

This example program provides a basic framework for driving unipolar stepper motors using the I2C bus. You can adjust motor control parameters as needed to develop more complex control logic.

Contact the Developer

• For any inquiries or assistance, feel free to contact the developer at [email protected].

License

This project is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).

This project includes code originally licensed under the MIT License (for pca9685.py) and modified code licensed under the Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0) (for bus_dc_motor.py).

MIT License:

• pca9685.py: Originally published by Adafruit and licensed under the MIT License.

CC BY-NC 4.0 License:

• bus_step_motor.py: Extensions by leeqingshui and licensed under the CC BY-NC 4.0 License.