Raspberry Pi Push Button Input with Hardware and Software Debouncing

This experiment implements a reliable push‑button input for a Raspberry
Pi.
The design combines hardware debouncing with software debouncing
to produce stable digital input signals.

The circuit output connects to a Raspberry Pi GPIO pin that reads 0 V
(LOW) and 3.3 V (HIGH).

Components

Required hardware:

  • Raspberry Pi board (any version). Example used: Raspberry Pi 3
    Model B
  • Tactile push button
  • Resistors:
    • 1 kΩ
    • 10 kΩ
  • Capacitor: 0.1 µF (100 nF)
  • Schmitt Trigger IC: SN74HC14N
  • Breadboard
  • Jumper wires (female‑to‑male)

Button Driver Circuit

2222.png

The circuit output connects to a Raspberry Pi GPIO input.

The Raspberry Pi provides:

  • 3.3 V for logic HIGH
  • GND for logic LOW

These supply rails are sourced directly from the Pi.

GPIO Connection

22222.png

Key detail:

  • Button output → Pin 12
  • Pin 12 → BCM GPIO 18

The software must reference GPIO 18.

Power Considerations

The Raspberry Pi 3.3 V and 5 V rails come directly from the
power adapter.

The official Raspberry Pi adapter provides up to 2.5 A, which is
sufficient for small external circuits.

However:

  • Always calculate current draw
  • Verify component limits
  • Avoid overloading the Pi power rails

Software Implementation

Several languages support Raspberry Pi GPIO control.
Python is commonly used due to its readability and mature libraries.

Example implementation using RPi.GPIO.

#!/usr/bin/python

import RPi.GPIO as GPIO
import time

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)

BTN_PIN = 18

# Configure input
GPIO.setup(BTN_PIN, GPIO.IN)

def btn_callback(channel):
    if GPIO.input(BTN_PIN):
        print("Button was pressed.")

input("Press Enter when ready
>")

# Detect rising and falling edges
GPIO.add_event_detect(
    BTN_PIN,
    GPIO.BOTH,
    callback=btn_callback,
    bouncetime=100
)

try:
    while True:
        time.sleep(1)

except KeyboardInterrupt:
    GPIO.cleanup()

GPIO.cleanup()

Hardware Debouncing

Mechanical buttons produce rapid voltage oscillations when pressed
or released.
These oscillations create false transitions.

The hardware debounce circuit:

  • Filters noise
  • Smooths voltage transitions
  • Produces a stable digital signal

Why Use a Schmitt Trigger

The SN74HC14N Schmitt trigger further stabilizes the signal.

It uses hysteresis, meaning:

  • One threshold for LOW → HIGH
  • Another threshold for HIGH → LOW

This prevents rapid toggling caused by noisy signals and slow voltage
transitions.

Software Debouncing

The GPIO library also implements software debouncing.

Mechanism:

  • Multiple reads of the GPIO input
  • Each read separated by the configured bounce time
  • State change is confirmed only if the signal remains stable

Example logic for detecting a rising edge:

0 V → 3.3 V → 3.3 V

Each read occurs 100 ms apart.

Short spikes (e.g., 3.0 V for 30 ms) are ignored.

Choosing a Bounce Time

Bounce duration depends on the mechanical properties of the button.

Typical values:

  • 50--100 ms

Empirical testing is recommended to determine the optimal value.

Result

The circuit produces a stable push‑button input for Raspberry Pi
GPIO.

This pattern is reusable for:

  • User input interfaces
  • Control panels
  • Embedded interaction systems

Future circuits can reuse this button interface as a reliable input
module.