Dimmer and breathing LED (PWM)

Parts in this circuit

Wiring, pin by pin

Red = 5 V, orange = 3.3 V, black = GND, other colours = signals. “Pin” is the position on the 40-pin header; the GPIO number is what the code uses. Power the Pi from a 5.1 V supply and wire with the power off.

Python code (gpiozero)

from gpiozero import PWMLED
from time import sleep

led = PWMLED(18)

for step in range(0, 11):            # 0, 1, ... 10
    led.value = step / 10            # 0.0 to 1.0
    print("Brightness", step * 10, "%")
    sleep(0.3)

for step in range(10, -1, -1):       # back down
    led.value = step / 10
    print("Brightness", step * 10, "%")
    sleep(0.3)

print("Now let it breathe")
led.pulse(fade_in_time=1.5, fade_out_time=1.5)   # runs in the background
sleep(60)

The same program with RPi.GPIO

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
pwm = GPIO.PWM(18, 1000)        # 1 kHz PWM on GPIO18
pwm.start(0)                    # 0 % duty cycle

try:
    while True:
        for duty in range(0, 101, 5):
            pwm.ChangeDutyCycle(duty)
            print("Duty", duty, "%")
            time.sleep(0.1)
        for duty in range(100, -1, -5):
            pwm.ChangeDutyCycle(duty)
            print("Duty", duty, "%")
            time.sleep(0.1)
finally:
    pwm.stop()
    GPIO.cleanup()

How the code works

• PWM turns the pin on for a part of each cycle. 50 % duty means on half the time, so the LED looks half as bright.
• led.value goes from 0.0 (off) to 1.0 (full).
• pulse() fades in and out by itself in the background.

Parts to buy

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