使用PCA9685模块驱动舵机的方法

前言

你是否曾遇到过直接使用树莓派引脚输出PWM控制舵机时，舵机出现抖动的情况？即使对代码进行了一定的时延优化，仍然会受到影响。现在，我们可以使用PCA9685模块来驱动舵机。

PCA9685是一种常用的PWM（脉冲宽度调制）驱动器芯片，通常用于控制舵机、电机和其他需要精确控制的设备。该芯片可以通过I2C总线与微控制器或单片机通信，以实现对多路PWM信号的生成和控制。

16路PWM输出：PCA9685可以同时控制最多16路PWM输出，每路输出的占空比都可以独立设置，但16路PWM频率一样。

12位分辨率：PCA9685提供了12位分辨率的PWM输出，可以实现精细的输出控制。

内部振荡器：芯片内部集成了振荡器，可以产生稳定25MHz的时钟信号，无需外部晶振。

可编程频率：可以通过配置寄存器来设置PWM输出的频率，范围从24Hz到1526Hz。

I2C接口：使用标准的I2C串行总线接口与主控设备通信，方便集成到各种微控制器系统中。

输出驱动能力：每路PWM输出都具有较强的驱动能力，可以直接驱动舵机或其他负载。

接线

1. PCA9685绿端VCC和GND要和电池的正负极相连。
2. PCA9685控制端的GND和VCC和树莓派的3.3v（pin1）和GND（pin9）相连。
3. PCA9685的SCL和SDA和树莓派的SCL0（pin5）以及SDA0（pin3）相连。

安装PCA9685驱动

adafruit/Adafruit_CircuitPython_PCA9685: Adafruit CircuitPython driver for PCA9685 16-channel, 12-bit PWM LED & servo driver chip. (github.com)

在树莓派终端输入：

pip3 install adafruit-circuitpython-pca9685

或者输入：

sudo pip3 install adafruit-circuitpython-pca9685

如果只是想下载虚拟环境到你当前的项目里可以：

mkdir project-name && cd project-name
python3 -m venv .venv
source .venv/bin/activate
pip3 install adafruit-circuitpython-pca9685

安装Motor驱动

adafruit/Adafruit_CircuitPython_Motor: Helpers for controlling PWM based motors and servos (github.com)

在树莓派终端输入：

pip3 install adafruit-circuitpython-motor

或者输入：

sudo pip3 install adafruit-circuitpython-motor

如果只是想下载虚拟环境到你当前的项目里可以：

mkdir project-name && cd project-name
python3 -m venv .venv
source .venv/bin/activate
pip3 install adafruit-circuitpython-motor

测试程序

# SPDX-FileCopyrightText: 2021 ladyada for Adafruit Industries
# SPDX-License-Identifier: MIT

import time
import board
from adafruit_motor import servo
from adafruit_pca9685 import PCA9685

i2c = board.I2C()  # uses board.SCL and board.SDA
# i2c = busio.I2C(board.GP1, board.GP0)    # Pi Pico RP2040

# Create a simple PCA9685 class instance.
pca = PCA9685(i2c)
# You can optionally provide a finer tuned reference clock speed to improve the accuracy of the
# timing pulses. This calibration will be specific to each board and its environment. See the
# calibration.py example in the PCA9685 driver.
# pca = PCA9685(i2c, reference_clock_speed=25630710)
pca.frequency = 50

# To get the full range of the servo you will likely need to adjust the min_pulse and max_pulse to
# match the stall points of the servo.
# This is an example for the Sub-micro servo: https://www.adafruit.com/product/2201
# servo7 = servo.Servo(pca.channels[7], min_pulse=580, max_pulse=2350)
# This is an example for the Micro Servo - High Powered, High Torque Metal Gear:
#   https://www.adafruit.com/product/2307
# servo7 = servo.Servo(pca.channels[7], min_pulse=500, max_pulse=2600)
# This is an example for the Standard servo - TowerPro SG-5010 - 5010:
#   https://www.adafruit.com/product/155
# servo7 = servo.Servo(pca.channels[7], min_pulse=400, max_pulse=2400)
# This is an example for the Analog Feedback Servo: https://www.adafruit.com/product/1404
# servo7 = servo.Servo(pca.channels[7], min_pulse=600, max_pulse=2500)
# This is an example for the Micro servo - TowerPro SG-92R: https://www.adafruit.com/product/169
# servo7 = servo.Servo(pca.channels[7], min_pulse=500, max_pulse=2400)

# The pulse range is 750 - 2250 by default. This range typically gives 135 degrees of
# range, but the default is to use 180 degrees. You can specify the expected range if you wish:
# servo7 = servo.Servo(pca.channels[7], actuation_range=135)
servo7 = servo.Servo(pca.channels[0])

# We sleep in the loops to give the servo time to move into position.
for i in range(180):
    servo7.angle = i
    time.sleep(0.03)
for i in range(180):
    servo7.angle = 180 - i
    time.sleep(0.03)

# You can also specify the movement fractionally.
fraction = 0.0
while fraction < 1.0:
    servo7.fraction = fraction
    fraction += 0.01
    time.sleep(0.03)

pca.deinit()

参考资料

Introduction — Adafruit motor Library 1.0 documentation (circuitpython.org)

Introduction — Adafruit PCA9685 Library 1.0 documentation (circuitpython.org)