frequencyio – Support for frequency based protocols


This module is not available in SAMD21 builds. See the Module Support Matrix - Which Modules Are Available on Which Boards for more info.

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 frequencyio
import time
from board import *

frequency = frequencyio.FrequencyIn(D13)
frequency.capture_period = 15

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

class frequencyio.FrequencyIn(pin: microcontroller.Pin, capture_period: int = 10)

Read a frequency signal

FrequencyIn is used to measure the frequency, in hertz, of a digital signal on an incoming pin. Accuracy has shown to be within 10%, if not better. It is recommended to utilize an average of multiple samples to smooth out readings.

Frequencies below 1KHz are not currently detectable.

FrequencyIn will not determine pulse width (use PulseIn).

Create a FrequencyIn object associated with the given pin.

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

  • capture_period (int) – Keyword argument to set the measurement period, in milliseconds. Default is 10ms; range is 1ms - 500ms.

Read the incoming frequency from a pin:

import frequencyio
import board

frequency = frequencyio.FrequencyIn(board.D11)

# Loop while printing the detected frequency
while True:

    # Optional clear() will reset the value
    # to zero. Without this, if the incoming
    # signal stops, the last reading will remain
    # as the value.
capture_period :int

The capture measurement period. Lower incoming frequencies will be measured more accurately with longer capture periods. Higher frequencies are more accurate with shorter capture periods.


When setting a new capture_period, all previous capture information is cleared with a call to clear().


Deinitialises the FrequencyIn 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.


Pause frequency capture.


Resumes frequency capture.


Clears the last detected frequency capture value.

__get__(self, index: int)int

Returns the value of the last frequency captured.