• tested on Raspberry Pi 3 Model B V1.2
• Raspbian 10 (buster) x64

Python Libary for Hardware PWM on Raspberry Pi using Linux kernel driver and /sys interface

This is a python library that allows control of the limited number of PWM pins available on most Raspberry Pi hardware. It does via a Linux kernel PWM driver that comes with recent kernels (at least version 4.9).

Using it to, for example, control servo motors leads to very smooth control, which I wasn't able to get with RPi.GPIO on a Raspberry Pi Zero W.

Enabling PWM driver:

1. Edit /boot/config.txt and add the following: dtoverlay=pwm-2chan
2. Reboot
3. Check that driver is loaded: lsmod | grep pwm_bcm
   1. Output should be something like pwm_bcm2835 2711 0

Using code:

Place syspwm.py in the same directory as your code, and include it like from syspwm import SysPWM

Abstract example

        from time import sleep
        import atexit
        SLEE=3
        FREQ=20

        #pwm0 is GPIO pin 18 is physical pin 12
        pwm = SysPWM(0, FREQ)
        atexit.register(pwm.disable)
        pwm.enable()

        while True:
                pwm.set_duty_cycle(0.3)
                print 0
                sleep(SLEE)
                pwm.set_duty_cycle(0.5)
                print 90
                sleep(SLEE)
                pwm.set_duty_cycle(0.9)
                print 180
                sleep(SLEE)

I learned the /sys interface for hardware PWM from http://www.jumpnowtek.com/rpi/Using-the-Raspberry-Pi-Hardware-PWM-timers.html