class PWM – pulse-width modulation#

The PWM class outputs a pulse-width-modulated signal on a Pin. It is the modern, cross-port API for PWM; on STM32 OpenMV cams it wraps the underlying pyb.Timer channel machinery, so each PWM instance ties up one timer channel.

Example usage:

from machine import PWM, Pin

# 50 Hz PWM on a header pin with a 12.5 % duty.
pwm = PWM(Pin("P7"), freq=50, duty_u16=8192)

pwm.duty_u16(32768)            # change duty to 50 %
pwm.init(freq=5000, duty_ns=5000)  # re-init at 5 kHz, 5 us pulse
pwm.duty_ns(3000)              # 3 us pulse

pwm.deinit()

Constructors#

class machine.PWM(dest: Pin | int, *, freq: int | None = None, duty_u16: int | None = None, duty_ns: int | None = None, invert: bool = False)#

Construct a PWM object driving dest (a Pin on OpenMV cams). The keyword arguments are equivalent to calling init() immediately after construction:

  • freq – PWM frequency in Hz.

  • duty_u16 – duty cycle as a ratio duty_u16 / 65535.

  • duty_ns – pulse width in nanoseconds.

  • invert – if True, invert the output polarity.

At most one of duty_u16 / duty_ns may be passed at a time. Setting freq may affect other PWM instances that share the same underlying timer (true on STM32 – every channel of a given TIM runs at the same frequency).

Methods#

init(*, freq: int | None = None, duty_u16: int | None = None, duty_ns: int | None = None) → None#

Reconfigure the PWM output. Only arguments supplied are updated; the others retain their previous values. See the constructor for the meaning of each argument.

deinit() → None#

Disable the PWM output and release the timer channel it occupied.

freq() → int#
freq(value: int, /) → None

Get or set the PWM frequency.

With no argument, return the current frequency in Hz.

With a single value argument, set the frequency to that value in Hz. May raise ValueError if the frequency is outside the range achievable by the underlying timer.

duty_u16() → int#
duty_u16(value: int, /) → None

Get or set the duty cycle as an unsigned 16-bit value in the range 0 – 65535.

With no argument, return the current duty.

With a single value argument, set the duty cycle to value / 65535 of the period. 0 is always low, 65535 is always high.

duty_ns() → int#
duty_ns(value: int, /) → None

Get or set the pulse width directly in nanoseconds.

With no argument, return the current pulse width.

With a single value argument, set the high-time of each cycle to value nanoseconds. Useful for servo-style outputs where the pulse width is the meaningful quantity rather than the duty ratio.

Limitations#

  • PWM frequency and duty resolution are interdependent on every hardware timer: at high frequencies, fewer counter steps fit in a period and so fewer low bits of duty_u16 are meaningful.

  • The achievable PWM frequency depends on the timer’s clock source and prescaler. STM32 TIM2 / TIM5 are 32-bit on most parts (and TIM3 / TIM4 as well on the STM32N6), giving wider frequency and duty ranges; the remaining timers are 16-bit. See the relevant MCU reference manual for the exact ranges.

  • On STM32 multiple PWM channels on the same TIM share a frequency. Setting freq() on one instance changes the output of every other channel attached to that TIM.