Raspberry Pi: Push-button + Two(2) LEDs that Toggle

2026-03-26 4 minute read 0 Comments #raspberry pi

Got another simple project here for you!

This project is about adding an additional LED light to the Raspberry Pi: Push-button + One(1) LED post, and having the push-button toggle the LED lights. I used one red and one blue LED.

The desired result, toggle on/off of the two LEDs with the push of a button; if the red light is on then the blue is off, and vice versa.

Let's see how this goes...

What You Will Need

This project builds directly on the push-button + one LED project. You will need the same setup with one addition:

A Raspberry Pi with Pi Cobbler and breadboard
Two LEDs — I used one red and one blue
One push-button
Resistors (220Ω for each LED)
Jumper wires

The GPIO pin assignments for this project:

Pin 4 (SWITCH_IN) — push-button input
Pin 25 (RED_LED) — red LED output
Pin 24 (BLUE_LED) — blue LED output

The Challenge: Button Bouncing

With this project, I learned I need to have a better understanding around detecting events with the GPIO. I found myself modifying “bouncetime” to achieve the desired result, but it is not optimal.

Button bounce is a real hardware phenomenon. When you press a mechanical button, the physical contacts don’t make a clean single connection — they “bounce” and rapidly open and close many times before settling. Without debouncing, each press can register as multiple events. The RPi.GPIO library’s bouncetime parameter (in milliseconds) tells the library to ignore further events for that duration after the first event fires. I set it to 900ms here, which is quite long — you press the button once and have to wait nearly a second before the next press registers.

With the code below, there are times when the lights do not toggle or the light remains on.

Any ideas what I am doing wrong? Let me know in the comment section below.

#!/usr/bin/env python

import RPi.GPIO as GPIO
import time

def on_callback(channel):
    GPIO.output(channel, GPIO.input(4))

def off_callback(channel):
    GPIO.output(channel, False)

GPIO.setmode(GPIO.BCM)
RED_LED = 25
BLUE_LED = 24
SWITCH_IN = 4
GPIO.setup(SWITCH_IN, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(RED_LED, GPIO.OUT, initial=GPIO.LOW)
GPIO.setup(BLUE_LED, GPIO.OUT, initial=GPIO.LOW)
GPIO.add_event_detect(SWITCH_IN, GPIO.RISING, bouncetime=900)


led = BLUE_LED
nled = RED_LED
run = 1
while (run != 0):
    try:
        if GPIO.event_detected(4):
            print led
            led = BLUE_LED if (led == RED_LED) else RED_LED
            nled = RED_LED if (nled == BLUE_LED) else BLUE_LED

            on_callback(led)
            off_callback(nled)

        pass
    except KeyboardInterrupt:
        run = 0
        GPIO.cleanup()
        print 'KeyboardInterrupt caught'
        break
GPIO.cleanup()
print 'EXITED!'

Also available here, raspi-push-button-led-toggle.

What I Learned

Despite the inconsistent behavior, this project taught me several valuable lessons about GPIO event detection:

Bouncetime is Tricky

The bouncetime=900 value was arrived at through trial and error. Too short and the button registers multiple events per press; too long and the button feels unresponsive. A more robust solution uses software debouncing: track the time of the last event and ignore events that arrive too quickly.

GPIO.RISING vs GPIO.BOTH

In the one-LED project I used GPIO.BOTH to detect both button presses and releases. Here I switched to GPIO.RISING — this triggers only when the button goes from LOW to HIGH (i.e., when pressed), which maps more cleanly to the “toggle on press” behavior I wanted.

Event Detection vs Polling

The polling approach from the first project (while (run != 0): if GPIO.event_detected(4):) has a race condition: if a button press happens between iterations of the while loop, you can miss it. GPIO.add_event_detect with a callback solves this, but mixing both methods (as the code attempts) causes issues — you can use one or the other, not both.

A Cleaner Approach with gpiozero

On modern Raspberry Pi OS, the gpiozero library handles debouncing and toggling elegantly:

from gpiozero import LED, Button
from signal import pause

red = LED(25)
blue = LED(24)
button = Button(4, bounce_time=0.1)

red.on()   # Start with red on
blue.off()

def toggle():
    if red.is_lit:
        red.off()
        blue.on()
    else:
        red.on()
        blue.off()

button.when_pressed = toggle

pause()

This version handles debouncing automatically (via bounce_time=0.1 — 100ms), is more readable, and does not have the polling/event-detection conflict.

Python 3 Note

The original code uses Python 2 print syntax (print led). In Python 3, this should be print(led). The GPIO library itself works fine in Python 3 — just update the print statements and install dependencies with pip3.