Raspberry Pi - Button - Debounce
When a button is pressed or released, or when a switch is toggled, newbies often assume that its state is simply changed from LOW to HIGH or HIGH to LOW. In reality, this is not the case. Due to mechanical and physical characteristics, the state of the button (or switch) may be toggled between LOW and HIGH multiple times. This phenomenon is known as chattering. Chattering can cause a single press to be read as multiple presses, leading to malfunction in certain applications.
The method to prevent this problem is referred as debouncing or debounce. This tutorial instructs you how to do it when using the button with Raspberry Pi. We will learn though the below steps:
- Raspberry Pi code without debouncing a button.
- Raspberry Pi code with debouncing a button.
- Raspberry Pi code with debouncing for multiple buttons.
Hardware Preparation
Or you can buy the following sensor kits:
| 1 | × | DIYables Sensor Kit (30 sensors/displays) | |
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
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Additionally, some of these links are for products from our own brand, DIYables.
Additionally, some of these links are for products from our own brand, DIYables.
Wiring Diagram
This image is created using Fritzing. Click to enlarge image
Let's take a look at the differences between Raspberry Pi code WITH and WITHOUT debounce, as well as their respective behaviors.
Reading Button with Debounce
Detailed Instructions
- Create a Python script file button_debounce.py and add the following code:
"""
This Raspberry Pi code was developed by newbiely.com
This Raspberry Pi code is made available for public use without any restriction
For comprehensive instructions and wiring diagrams, please visit:
https://newbiely.com/tutorials/raspberry-pi/raspberry-pi-button-debounce
"""
import RPi.GPIO as GPIO
# Set the GPIO mode to BCM
GPIO.setmode(GPIO.BCM)
# Define the GPIO pin for your button
BUTTON_PIN = 16
# Define debounce time in milliseconds
DEBOUNCE_TIME_MS = 200 # 200 milliseconds
# Set the initial state and pull-up resistor for the button
GPIO.setup(BUTTON_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP)
# Initialize the button state and previous state
button_state = GPIO.input(BUTTON_PIN)
prev_button_state = button_state
# Define a function to handle button presses
def button_callback(channel):
global button_state
button_state = GPIO.input(BUTTON_PIN)
# Add an event listener for the button press
GPIO.add_event_detect(BUTTON_PIN, GPIO.BOTH, callback=button_callback, bouncetime=DEBOUNCE_TIME_MS)
try:
# Main loop
while True:
# Check if the button state has changed
if button_state != prev_button_state:
if button_state == GPIO.HIGH:
print("Button released")
else:
print("Button pressed")
prev_button_state = button_state
except KeyboardInterrupt:
# Clean up GPIO on exit
GPIO.cleanup()
- Save the file and run the Python script by executing the following command in the terminal:
python3 button_debounce.py
- Press and hold the button for a few seconds, then release it.
- Check the terminal for the results.
PuTTY - Raspberry Pi
Button pressed
Button released
As you can observe, you only pressed and released the button once. Raspberry Pi detects it as a single press and release, thus eliminating any unnecessary noise.
Raspberry Pi Button Debounce for Multiple Buttons
"""
This Raspberry Pi code was developed by newbiely.com
This Raspberry Pi code is made available for public use without any restriction
For comprehensive instructions and wiring diagrams, please visit:
https://newbiely.com/tutorials/raspberry-pi/raspberry-pi-button-debounce
"""
import RPi.GPIO as GPIO
# Set the GPIO mode to BCM
GPIO.setmode(GPIO.BCM)
# Define the GPIO pins for your buttons
BUTTON_PIN_1 = 14
BUTTON_PIN_2 = 15
BUTTON_PIN_3 = 18
# Define debounce time in milliseconds
DEBOUNCE_TIME_MS = 200 # 200 milliseconds
# Set the initial state and pull-up resistor for the buttons
GPIO.setup(BUTTON_PIN_1, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(BUTTON_PIN_2, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(BUTTON_PIN_3, GPIO.IN, pull_up_down=GPIO.PUD_UP)
# Initialize the button states and previous states for all buttons
button_state_1 = GPIO.input(BUTTON_PIN_1)
button_state_2 = GPIO.input(BUTTON_PIN_2)
button_state_3 = GPIO.input(BUTTON_PIN_3)
prev_button_state_1 = button_state_1
prev_button_state_2 = button_state_2
prev_button_state_3 = button_state_3
# Define a function to handle button presses
def button_callback_1(channel):
global button_state_1
button_state_1 = GPIO.input(BUTTON_PIN_1)
def button_callback_2(channel):
global button_state_2
button_state_2 = GPIO.input(BUTTON_PIN_2)
def button_callback_3(channel):
global button_state_3
button_state_3 = GPIO.input(BUTTON_PIN_3)
# Add event listeners for the buttons
GPIO.add_event_detect(BUTTON_PIN_1, GPIO.BOTH, callback=button_callback_1, bouncetime=DEBOUNCE_TIME_MS)
GPIO.add_event_detect(BUTTON_PIN_2, GPIO.BOTH, callback=button_callback_2, bouncetime=DEBOUNCE_TIME_MS)
GPIO.add_event_detect(BUTTON_PIN_3, GPIO.BOTH, callback=button_callback_3, bouncetime=DEBOUNCE_TIME_MS)
try:
# Main loop
while True:
# Check if the button states have changed and print when they do
if button_state_1 != prev_button_state_1:
if button_state_1 == GPIO.HIGH:
print("Button 1 released")
else:
print("Button 1 pressed")
prev_button_state_1 = button_state_1
if button_state_2 != prev_button_state_2:
if button_state_2 == GPIO.HIGH:
print("Button 2 released")
else:
print("Button 2 pressed")
prev_button_state_2 = button_state_2
if button_state_3 != prev_button_state_3:
if button_state_3 == GPIO.HIGH:
print("Button 3 released")
else:
print("Button 3 pressed")
prev_button_state_3 = button_state_3
except KeyboardInterrupt:
# Clean up GPIO on exit
GPIO.cleanup()
The diagram that illustrates the wiring for the code mentioned:
This image is created using Fritzing. Click to enlarge image