PWM

Using PWM in RPi.GPIO

To create a PWM instance:

p = GPIO.PWM(channel, frequency)

To start PWM:

p.start(dc)   # where dc is the duty cycle (0.0 <= dc <= 100.0)

To change the frequency:

p.ChangeFrequency(freq)   # where freq is the new frequency in Hz

To change the duty cycle:

p.ChangeDutyCycle(dc)  # where 0.0 <= dc <= 100.0

To stop PWM:

p.stop()

Note that PWM will also stop if the instance variable 'p' goes out of scope.

An example to blink an LED once every two seconds:

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(12, GPIO.OUT)

p = GPIO.PWM(12, 0.5)
p.start(1)
input('Press return to stop:')   # use raw_input for Python 2
p.stop()
GPIO.cleanup()

An example to brighten/dim an LED:

import time
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(12, GPIO.OUT)

p = GPIO.PWM(12, 50)  # channel=12 frequency=50Hz
p.start(0)
try:
    while 1:
        for dc in range(0, 101, 5):
            p.ChangeDutyCycle(dc)
            time.sleep(0.1)
        for dc in range(100, -1, -5):
            p.ChangeDutyCycle(dc)
            time.sleep(0.1)
except KeyboardInterrupt:
    pass
p.stop()
GPIO.cleanup()