MicroPython ESP32开发：脉宽调制（PWM）

脉宽调制（PWM）是一种在数字引脚上获得人工模拟输出的方法。它通过快速将引脚从低电平切换到高电平来实现。与此相关的参数有两个：切换频率和占空比。占空比的定义是，与单周期（低电平加高电平时间）的长度相比，引脚高电平的时间有多长。最大占空比是指引脚一直处于高电平状态，最小占空比是指引脚一直处于低电平状态。

• 包含全部 16 个 PWM 通道和 8 个定时器的综合示例：

from machine import Pin, PWM
try:
    f = 100  # Hz
    d = 1024 // 16  # 6.25%
    pins = (15, 2, 4, 16, 18, 19, 22, 23, 25, 26, 27, 14 , 12, 13, 32, 33)
    pwms = []
    for i, pin in enumerate(pins):
        pwms.append(PWM(Pin(pin), freq=f * (i // 2 + 1), duty= 1023 if i==15 else d * (i + 1)))
        print(pwms[i])
finally:
    for pwm in pwms:
        try:
            pwm.deinit()
        except:
            pass

输出为：

PWM(Pin(15), freq=100, duty=64, resolution=10, mode=0, channel=0, timer=0)
PWM(Pin(2), freq=100, duty=128, resolution=10, mode=0, channel=1, timer=0)
PWM(Pin(4), freq=200, duty=192, resolution=10, mode=0, channel=2, timer=1)
PWM(Pin(16), freq=200, duty=256, resolution=10, mode=0, channel=3, timer=1)
PWM(Pin(18), freq=300, duty=320, resolution=10, mode=0, channel=4, timer=2)
PWM(Pin(19), freq=300, duty=384, resolution=10, mode=0, channel=5, timer=2)
PWM(Pin(22), freq=400, duty=448, resolution=10, mode=0, channel=6, timer=3)
PWM(Pin(23), freq=400, duty=512, resolution=10, mode=0, channel=7, timer=3)
PWM(Pin(25), freq=500, duty=576, resolution=10, mode=1, channel=0, timer=0)
PWM(Pin(26), freq=500, duty=640, resolution=10, mode=1, channel=1, timer=0)
PWM(Pin(27), freq=600, duty=704, resolution=10, mode=1, channel=2, timer=1)
PWM(Pin(14), freq=600, duty=768, resolution=10, mode=1, channel=3, timer=1)
PWM(Pin(12), freq=700, duty=832, resolution=10, mode=1, channel=4, timer=2)
PWM(Pin(13), freq=700, duty=896, resolution=10, mode=1, channel=5, timer=2)
PWM(Pin(32), freq=800, duty=960, resolution=10, mode=1, channel=6, timer=3)
PWM(Pin(33), freq=800, duty=1023, resolution=10, mode=1, channel=7, timer=3)

• 平滑频率变化示例

from time import sleep
from machine import Pin, PWM

F_MIN = 500
F_MAX = 1000

f = F_MIN
delta_f = 1

p = PWM(Pin(5), f)
print(p)

while True:
    p.freq(f)

    sleep(10 / F_MIN)

    f += delta_f
    if f >= F_MAX or f <= F_MIN:
        delta_f = -delta_f

• 平滑占空比变化的例子：

rom time import sleep
from machine import Pin, PWM

DUTY_MAX = 2**16 - 1

duty_u16 = 0
delta_d = 16

p = PWM(Pin(5), 1000, duty_u16=duty_u16)
print(p)

while True:
    p.duty_u16(duty_u16)

    sleep(1 / 1000)

    duty_u16 += delta_d
    if duty_u16 >= DUTY_MAX:
        duty_u16 = DUTY_MAX
        delta_d = -delta_d
    elif duty_u16 <= 0:
        duty_u16 = 0
        delta_d = -delta_d

**注意：**无需指定Pin.OUT模式。对于传递给PWM构造函数的每个引脚，通道都会被内部初始化为PWM模式一次。

以下代码是错误的：

pwm = PWM(Pin(5, Pin.OUT), freq=1000, duty=512)  # Pin(5) 为PWM模式
pwm = PWM(Pin(5, Pin.OUT), freq=500, duty=256)  # Pin(5) 为输出模式, PWM关闭

应使下面的代码替代：

pwm = PWM(Pin(5), freq=1000, duty=512)
pwm.init(freq=500, duty=256)