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2. Pulse Width Modulation

Pulse width modulation (PWM) is a way to get an artificial analog output on a digital pin. It achieves this by rapidly toggling the pin from low to high. There are two parameters associated with this: the frequency of the toggling, and the duty cycle. The duty cycle is defined to be how long the pin is high compared with the length of a single period (low plus high time). Maximum duty cycle is when the pin is high all of the time, and minimum is when it is low all of the time.

• More comprehensive example with all 16 PWM channels and 8 timers:

  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
  

  Output is:

  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)
  

• Example of a smooth frequency change:

  from utime 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
  

  See PWM wave at Pin(5) with an oscilloscope.

• Example of a smooth duty change:

  from utime 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
  

  See PWM wave at Pin(5) with an oscilloscope.

Note: the Pin.OUT mode does not need to be specified. The channel is initialized to PWM mode internally once for each Pin that is passed to the PWM constructor.

The following code is wrong:

pwm = PWM(Pin(5, Pin.OUT), freq=1000, duty=512)  # Pin(5) in PWM mode here
pwm = PWM(Pin(5, Pin.OUT), freq=500, duty=256)  # Pin(5) in OUT mode here, PWM is off

Use this code instead:

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