pwmio – Support for PWM based protocols

The pwmio module contains classes to provide access to basic pulse IO.

All classes change hardware state and should be deinitialized when they are no longer needed if the program continues after use. To do so, either call deinit() or use a context manager. See Lifetime and ContextManagers for more info.

For example:

import time
import pwmio
import board

pwm = pwmio.PWMOut(board.LED)
pwm.duty_cycle = 2 ** 15
time.sleep(0.1)

This example will initialize the the device, set duty_cycle, and then sleep 0.1 seconds. CircuitPython will automatically turn off the PWM when it resets all hardware after program completion. Use deinit() or a with statement to do it yourself.

For the essentials of pwmio, see the CircuitPython Essentials Learn guide.

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class pwmio.PWMOut(pin: microcontroller.Pin, *, duty_cycle: int = 0, frequency: int = 500, variable_frequency: bool = False)

Output a Pulse Width Modulated signal on a given pin.

Create a PWM object associated with the given pin. This allows you to write PWM signals out on the given pin. Frequency is fixed after init unless variable_frequency is True.

Note

When variable_frequency is True, further PWM outputs may be limited because it may take more internal resources to be flexible. So, when outputting both fixed and flexible frequency signals construct the fixed outputs first.

Parameters
  • pin (Pin) – The pin to output to

  • duty_cycle (int) – The fraction of each pulse which is high. 16-bit

  • frequency (int) – The target frequency in Hertz (32-bit)

  • variable_frequency (bool) – True if the frequency will change over time

Simple LED on:

import pwmio
import board

pwm = pwmio.PWMOut(board.LED)

while True:
    pwm.duty_cycle = 2 ** 15  # Cycles the pin with 50% duty cycle (half of 2 ** 16) at the default 500hz

PWM LED fade:

import pwmio
import board

pwm = pwmio.PWMOut(board.LED)  # output on LED pin with default of 500Hz

while True:
    for cycle in range(0, 65535):  # Cycles through the full PWM range from 0 to 65535
        pwm.duty_cycle = cycle  # Cycles the LED pin duty cycle through the range of values
    for cycle in range(65534, 0, -1):  # Cycles through the PWM range backwards from 65534 to 0
        pwm.duty_cycle = cycle  # Cycles the LED pin duty cycle through the range of values

PWM at specific frequency (servos and motors):

import pwmio
import board

pwm = pwmio.PWMOut(board.D13, frequency=50)
pwm.duty_cycle = 2 ** 15  # Cycles the pin with 50% duty cycle (half of 2 ** 16) at 50hz

Variable frequency (usually tones):

import pwmio
import board
import time

pwm = pwmio.PWMOut(board.D13, duty_cycle=2 ** 15, frequency=440, variable_frequency=True)
time.sleep(0.2)
pwm.frequency = 880
time.sleep(0.1)
duty_cycle :int

16 bit value that dictates how much of one cycle is high (1) versus low (0). 0xffff will always be high, 0 will always be low and 0x7fff will be half high and then half low.

Depending on how PWM is implemented on a specific board, the internal representation for duty cycle might have less than 16 bits of resolution. Reading this property will return the value from the internal representation, so it may differ from the value set.

frequency :int

32 bit value that dictates the PWM frequency in Hertz (cycles per second). Only writeable when constructed with variable_frequency=True.

Depending on how PWM is implemented on a specific board, the internal value for the PWM’s duty cycle may need to be recalculated when the frequency changes. In these cases, the duty cycle is automatically recalculated from the original duty cycle value. This should happen without any need to manually re-set the duty cycle.

deinit() None

Deinitialises the PWMOut and releases any hardware resources for reuse.

__enter__() PWMOut

No-op used by Context Managers.

__exit__() None

Automatically deinitializes the hardware when exiting a context. See Lifetime and ContextManagers for more info.