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b491967bbd
The methods duty_u16() and duty_ns() are implemented to match the existing docs. The duty will remain the same when the frequency is changed. Standard ESP32 as well as S2, S3 and C3 are supported. Thanks to @kdschlosser for the fix for rounding in resolution calculation. Documentation is updated and examples expanded for esp32, including the quickref and tutorial. Additional notes are added to the machine.PWM docs regarding limitations of hardware PWM.
116 lines
3.7 KiB
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116 lines
3.7 KiB
ReStructuredText
.. _esp32_pwm:
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Pulse Width Modulation
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======================
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Pulse width modulation (PWM) is a way to get an artificial analog output on a
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digital pin. It achieves this by rapidly toggling the pin from low to high.
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There are two parameters associated with this: the frequency of the toggling,
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and the duty cycle. The duty cycle is defined to be how long the pin is high
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compared with the length of a single period (low plus high time). Maximum
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duty cycle is when the pin is high all of the time, and minimum is when it is
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low all of the time.
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* More comprehensive example with all 16 PWM channels and 8 timers::
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from machine import Pin, PWM
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try:
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f = 100 # Hz
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d = 1024 // 16 # 6.25%
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pins = (15, 2, 4, 16, 18, 19, 22, 23, 25, 26, 27, 14 , 12, 13, 32, 33)
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pwms = []
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for i, pin in enumerate(pins):
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pwms.append(PWM(Pin(pin), freq=f * (i // 2 + 1), duty= 1023 if i==15 else d * (i + 1)))
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print(pwms[i])
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finally:
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for pwm in pwms:
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try:
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pwm.deinit()
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except:
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pass
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Output is::
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PWM(Pin(15), freq=100, duty=64, resolution=10, mode=0, channel=0, timer=0)
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PWM(Pin(2), freq=100, duty=128, resolution=10, mode=0, channel=1, timer=0)
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PWM(Pin(4), freq=200, duty=192, resolution=10, mode=0, channel=2, timer=1)
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PWM(Pin(16), freq=200, duty=256, resolution=10, mode=0, channel=3, timer=1)
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PWM(Pin(18), freq=300, duty=320, resolution=10, mode=0, channel=4, timer=2)
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PWM(Pin(19), freq=300, duty=384, resolution=10, mode=0, channel=5, timer=2)
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PWM(Pin(22), freq=400, duty=448, resolution=10, mode=0, channel=6, timer=3)
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PWM(Pin(23), freq=400, duty=512, resolution=10, mode=0, channel=7, timer=3)
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PWM(Pin(25), freq=500, duty=576, resolution=10, mode=1, channel=0, timer=0)
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PWM(Pin(26), freq=500, duty=640, resolution=10, mode=1, channel=1, timer=0)
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PWM(Pin(27), freq=600, duty=704, resolution=10, mode=1, channel=2, timer=1)
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PWM(Pin(14), freq=600, duty=768, resolution=10, mode=1, channel=3, timer=1)
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PWM(Pin(12), freq=700, duty=832, resolution=10, mode=1, channel=4, timer=2)
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PWM(Pin(13), freq=700, duty=896, resolution=10, mode=1, channel=5, timer=2)
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PWM(Pin(32), freq=800, duty=960, resolution=10, mode=1, channel=6, timer=3)
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PWM(Pin(33), freq=800, duty=1023, resolution=10, mode=1, channel=7, timer=3)
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* Example of a smooth frequency change::
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from utime import sleep
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from machine import Pin, PWM
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F_MIN = 500
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F_MAX = 1000
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f = F_MIN
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delta_f = 1
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p = PWM(Pin(5), f)
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print(p)
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while True:
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p.freq(f)
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sleep(10 / F_MIN)
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f += delta_f
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if f >= F_MAX or f <= F_MIN:
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delta_f = -delta_f
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See PWM wave at Pin(5) with an oscilloscope.
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* Example of a smooth duty change::
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from utime import sleep
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from machine import Pin, PWM
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DUTY_MAX = 2**16 - 1
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duty_u16 = 0
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delta_d = 16
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p = PWM(Pin(5), 1000, duty_u16=duty_u16)
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print(p)
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while True:
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p.duty_u16(duty_u16)
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sleep(1 / 1000)
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duty_u16 += delta_d
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if duty_u16 >= DUTY_MAX:
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duty_u16 = DUTY_MAX
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delta_d = -delta_d
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elif duty_u16 <= 0:
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duty_u16 = 0
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delta_d = -delta_d
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See PWM wave at Pin(5) with an oscilloscope.
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Note: the Pin.OUT mode does not need to be specified. The channel is initialized
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to PWM mode internally once for each Pin that is passed to the PWM constructor.
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The following code is wrong::
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pwm = PWM(Pin(5, Pin.OUT), freq=1000, duty=512) # Pin(5) in PWM mode here
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pwm = PWM(Pin(5, Pin.OUT), freq=500, duty=256) # Pin(5) in OUT mode here, PWM is off
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Use this code instead::
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pwm = PWM(Pin(5), freq=1000, duty=512)
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pwm.init(freq=500, duty=256)
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