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Fix bounce_time debouncing for brief signals in DigitalInputDevice#137

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pjbRPF merged 11 commits into
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copilot/fix-bounce-time-sound-sensor
Nov 28, 2025
Merged

Fix bounce_time debouncing for brief signals in DigitalInputDevice#137
pjbRPF merged 11 commits into
devfrom
copilot/fix-bounce-time-sound-sensor

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Copilot AI commented Nov 25, 2025 •
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bounce_time parameter doesn't work with sensors that produce brief pulses (e.g., sound sensors). Setting bounce_time=1 prevents detection entirely instead of debouncing multiple rapid triggers.

Root Cause

Original implementation blocks in a loop waiting for signal stability for the entire bounce period:

# Original code - waits for signal to stop changing
stop = ticks_ms() + (bounce_time * 1000)
while ticks_ms() < stop:
    if p.value() != last_state:
        stop = ticks_ms() + (bounce_time * 1000)  # Reset timer on any change
        last_state = p.value()

For brief pulses (sound sensor HIGH for 50ms with bounce_time=1):

  • Interrupt fires, signal is HIGH
  • Loop waits for 1 second of stability
  • Signal returns to LOW within 100ms
  • After 1 second of LOW being stable, code sees: initial_state (LOW) == final_state (LOW)
  • No callback fired

Changes

Replaced blocking stability check with timestamp-based debouncing:

  • Track _last_callback_ms instead of blocking
  • Fire callback immediately if enough time passed since last callback
  • Always update _state to track reality, but suppress callbacks within bounce period
  • Non-blocking: interrupt handler returns immediately
# New approach - timestamp-based
time_since_last_callback = current_time_ms - self._last_callback_ms
if bounce_time is None or time_since_last_callback >= (bounce_time * 1000):
    self._state = new_state
    self._last_callback_ms = current_time_ms
    # Fire callback
else:
    self._state = new_state  # Update state, suppress callback

Result: First pulse fires callback, subsequent pulses within bounce_time are ignored. Works for both mechanical bounce (buttons) and brief signals (sensors).

Original prompt

This section details on the original issue you should resolve

<issue_title>bounce_time not working when using with DigitalInputDevice</issue_title>
<issue_description>Describe the bug
When using a sound sensor (like this one: Sound Sensor) as an DigitalInputDevice everything is working as expected. But since you will get a dozen signals from one hand clap, you might use bounce_time=1. But then no signal is detected at all.

To Reproduce
Steps to reproduce the behaviour:

  1. Install a sound sensor on Pin 15.
  2. Run the code below.
  3. Nothing ist detected.
  4. No error is detected.
from picozero import DigitalInputDevice
from time import sleep

sound_sensor = DigitalInputDevice(15, bounce_time = 1)

def detected():
    print("Sound detected!")
    
sound_sensor.when_activated = detected

while True:
    sleep(1)

Expected behaviour
You whould expect, that "Sound detected" ist getting printed exactly one time after a noise like a hand clap.

System information:

  • OS: Windows
  • Development environment: Thonny
  • picozero version: 0.42

Additional context
Everythong is working when you don't add bounce_time. But now you will get printed "Sound detected" several times.
</issue_description>

<agent_instructions>Fix</agent_instructions>

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Copilot AI and others added 4 commits November 25, 2025 16:09
@pjbRPF
Fix bounce_time implementation for DigitalInputDevice
2755a54 
Co-authored-by: pjbRPF <104009652+pjbRPF@users.noreply.github.com>
@pjbRPF
Improve bounce_time implementation to be non-blocking
d12e6f9 
Co-authored-by: pjbRPF <104009652+pjbRPF@users.noreply.github.com>
@pjbRPF
Clarify variable naming and add documentation for debounce logic
6212a7a 
Co-authored-by: pjbRPF <104009652+pjbRPF@users.noreply.github.com>
@pjbRPF
Add detailed comments explaining debounce logic
ab463d7 
Co-authored-by: pjbRPF <104009652+pjbRPF@users.noreply.github.com>
Copilot AI changed the title [WIP] Fix bounce_time issue with DigitalInputDevice Fix bounce_time debouncing for brief signals in DigitalInputDevice Nov 25, 2025
Copilot AI requested a review from pjbRPF November 25, 2025 16:22
@pjbRPF pjbRPF marked this pull request as ready for review November 25, 2025 16:42
@pjbRPF pjbRPF requested a review from MarcScott as a code owner November 25, 2025 16:42
@pjbRPF pjbRPF changed the base branch from main to dev November 28, 2025 11:22
@pjbRPF pjbRPF merged commit 9d03da0 into dev Nov 28, 2025
@pjbRPF pjbRPF deleted the copilot/fix-bounce-time-sound-sensor branch November 28, 2025 13:30
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bounce_time not working when using with DigitalInputDevice

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@MarcScott @pjbRPF @grega