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.
Output a Pulse Width Modulated signal on a given pin.
Note
The exact frequencies possible depend on the specific microcontroller. If the requested frequency is within the available range, one of the two nearest possible frequencies to the requested one is selected.
If the requested frequency is outside the range, either (A) a ValueError may be raised or (B) the highest or lowest frequency is selected. This behavior is microcontroller-dependent, and may depend on whether it’s the upper or lower bound that is exceeded.
In any case, the actual frequency (rounded to 1Hz) is available in the frequency property after construction.
Note
The frequency is calculated based on a nominal CPU frequency. However, depending on the board, the error between the nominal and actual CPU frequency can be large (several hundred PPM in the case of crystal oscillators and up to ten percent in the case of RC oscillators)
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.
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)
Deinitialises the PWMOut and releases any hardware resources for reuse.
No-op used by Context Managers.
Automatically deinitializes the hardware when exiting a context. See Lifetime and ContextManagers for more info.
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.
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. However, an output glitch may occur during the adjustment.
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