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
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.
-
__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
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.
-
__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.
-
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
-
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)
-
__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 anarray.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