Button Debouncing with ESP32

What is Button Bouncing?

  • When a button is pressed or released, it does not change its state instantaneously.
  • Due to mechanical and physical issues, the button may rapidly fluctuate between HIGH and LOW states before stabilizing.
  • This phenomenon is known as "button bouncing".

What is Button Bouncing?

Illustrating Button Bouncing

  • A MicroPython script with an ISR demonstrates button bouncing on an ESP32 by incrementing a counter on pin 32 for each falling edge.
from machine import Pin
import time

# Initialize global counter
counter = 0

# Define the interrupt service routine
def isr(pin):
    global counter
    counter += 1
    print('Button pressed count:', counter)

# Setup the button input and attach the ISR
button = Pin(32, Pin.IN, Pin.PULL_UP)
button.irq(trigger=Pin.IRQ_FALLING, handler=isr)

# Run an infinite loop to keep the program running
while True:
    time.sleep(1)  # sleep to reduce CPU usage

Illustrating Button Bouncing

  • With this script, when the button is pressed, you'll observe the counter incrementing multiple times due to bouncing.

Why is Debouncing Important?

  • Without debouncing, a single button press could be interpreted as multiple presses, causing unexpected behavior.
  • Debouncing ensures that a single press is only registered once.

Debouncing Techniques

  • Software debouncing
  • Hardware debouncing

Software Debouncing with MicroPython

  • A simple way to implement software debouncing is to use a delay.
  • Check the button state, wait for a short period, then check the state again.
  • If the state is the same, the button press is considered valid.

Software Debouncing Example

from machine import Pin
import time

button = Pin(32, Pin.IN)

def debounce(pin):
    # initial state
    state = pin.value()
    # wait for 20 milliseconds
    time.sleep(0.02)
    # check state again
    return state if pin.value() == state else None

while True:
    button_state = debounce(button)
    if button_state is not None:
        print('Button state:', button_state)

Software Debouncing Example

from machine import Pin, Timer  # Import necessary classes from the machine module
import time  # Import the time module

# Initialize global variables
button = Pin(32, Pin.IN, Pin.PULL_UP)  # Initialize pin 32 as a pull-up input
counter = 0  # Counter to keep track of button presses
irq_isenable = True  # Flag to indicate whether IRQ is enabled

def isr(pin):  # ISR function to handle button presses
    global counter, irq_isenable  # Access global variables
    if irq_isenable:  # Check if IRQ is enabled
        print(f'Button pressed, IRQ disabled, starting timer')
        counter += 1  # Increment the counter
        print('Button pressed count:', counter)
        timer.init(mode=Timer.ONE_SHOT, period=200, callback=enable_irq)  # Start a one-shot timer
        print(f'Timer start {timer}')
        irq_isenable = False  # Disable IRQ

def enable_irq(timer):  # Function to re-enable IRQ
    global irq_isenable  # Access global variable
    irq_isenable = True  # Re-enable IRQ
    print('Timer expired, IRQ re-enabled')

# Attach ISR
button.irq(trigger=Pin.IRQ_FALLING, handler=isr)  # Attach ISR to handle falling edge triggers

# Set up the one-shot timer
timer = Timer(0)  # Initialize a Timer object

print("Program Start")  # Print program start message
# Run an infinite loop to keep the program running
while True:
    time.sleep(1)  # Sleep to reduce CPU usage

Hardware Debouncing Example

Recap

  • Button bouncing is a common issue that can cause unexpected behavior.
  • Software debouncing is a simple and effective method to handle button bouncing.
  • The MicroPython code provided demonstrates a basic debouncing technique using a delay.

ESP32 Button Bounce

By wschen

ESP32 Button Bounce

Learn about button debouncing with ESP32. Discover what button bouncing is and why debouncing is important. Explore software and hardware debouncing techniques with MicroPython. Get practical examples for software debouncing.

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