pulseio – Support for pulse based protocols

The pulseio 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 pulseio
import time
from board import *

pwm = pulseio.PWMOut(D13)
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.

class pulseio.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 fade:

import pulseio
import board

pwm = pulseio.PWMOut(board.D13)     # output on D13
pwm.duty_cycle = 2 ** 15            # Cycles the pin with 50% duty cycle (half of 2 ** 16) at the default 500hz

PWM at specific frequency (servos and motors):

import pulseio
import board

pwm = pulseio.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 pulseio
import board
import time

pwm = pulseio.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(self) → None

Deinitialises the PWMOut and releases any hardware resources for reuse.

__enter__(self) → PWMOut

No-op used by Context Managers.

__exit__(self) → None

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

class pulseio.PulseIn(pin: microcontroller.Pin, maxlen: int = 2, *, idle_state: bool = False)

Measure a series of active and idle pulses. This is commonly used in infrared receivers and low cost temperature sensors (DHT). The pulsed signal consists of timed active and idle periods. Unlike PWM, there is no set duration for active and idle pairs.

Create a PulseIn object associated with the given pin. The object acts as a read-only sequence of pulse lengths with a given max length. When it is active, new pulse lengths are added to the end of the list. When there is no more room (len() == maxlen) the oldest pulse length is removed to make room.

Parameters

  • pin (Pin) – Pin to read pulses from.

  • maxlen (int) – Maximum number of pulse durations to store at once

  • idle_state (bool) – Idle state of the pin. At start and after resume the first recorded pulse will the opposite state from idle.

Read a short series of pulses:

import pulseio
import board

pulses = pulseio.PulseIn(board.D7)

# Wait for an active pulse
while len(pulses) == 0:
    pass
# Pause while we do something with the pulses
pulses.pause()

# Print the pulses. pulses[0] is an active pulse unless the length
# reached max length and idle pulses are recorded.
print(pulses)

# Clear the rest
pulses.clear()

# Resume with an 80 microsecond active pulse
pulses.resume(80)
maxlen :int

The maximum length of the PulseIn. When len() is equal to maxlen, it is unclear which pulses are active and which are idle.

paused :bool

True when pulse capture is paused as a result of pause() or an error during capture such as a signal that is too fast.

deinit(self) → None

Deinitialises the PulseIn and releases any hardware resources for reuse.

__enter__(self) → PulseIn

No-op used by Context Managers.

__exit__(self) → None

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

pause(self) → None

Pause pulse capture

resume(self, trigger_duration: int = 0) → None

Resumes pulse capture after an optional trigger pulse.

Warning

Using trigger pulse with a device that drives both high and low signals risks a short. Make sure your device is open drain (only drives low) when using a trigger pulse. You most likely added a “pull-up” resistor to your circuit to do this.

Parameters

trigger_duration (int) – trigger pulse duration in microseconds

clear(self) → None

Clears all captured pulses

popleft(self) → int

Removes and returns the oldest read pulse.

__bool__(self) → bool
__len__(self) → int

Returns the current pulse length

This allows you to:

pulses = pulseio.PulseIn(pin)
print(len(pulses))
__getitem__(self, index: int) → Optional[int]

Returns the value at the given index or values in slice.

This allows you to:

pulses = pulseio.PulseIn(pin)
print(pulses[0])
class pulseio.PulseOut(carrier: PWMOut)

Pulse PWM “carrier” output on and off. This is commonly used in infrared remotes. The pulsed signal consists of timed on and off periods. Unlike PWM, there is no set duration for on and off pairs.

Create a PulseOut object associated with the given PWMout object.

Parameters

carrier (PWMOut) – PWMOut that is set to output on the desired pin.

Send a short series of pulses:

import array
import pulseio
import board

# 50% duty cycle at 38kHz.
pwm = pulseio.PWMOut(board.D13, frequency=38000, duty_cycle=32768)
pulse = pulseio.PulseOut(pwm)
#                             on   off     on    off    on
pulses = array.array('H', [65000, 1000, 65000, 65000, 1000])
pulse.send(pulses)

# Modify the array of pulses.
pulses[0] = 200
pulse.send(pulses)
deinit(self) → None

Deinitialises the PulseOut and releases any hardware resources for reuse.

__enter__(self) → PulseOut

No-op used by Context Managers.

__exit__(self) → None

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

send(self, pulses: ReadableBuffer) → None

Pulse alternating on and off durations in microseconds starting with on. pulses must be an array.array with data type ‘H’ for unsigned halfword (two bytes).

This method waits until the whole array of pulses has been sent and ensures the signal is off afterwards.

Parameters

pulses (array.array) – pulse durations in microseconds