pwm.py

A simple Python class to work with the Linux PWM kernel driver.

Written for the Raspberry Pi and the hardware pwm timers, but should work with other SOCs.

Requires that a PWM kernel driver is loaded appropriately which on the RPi normally means a dts overlay.

Instructions for building and loading an appropriate dts for the RPi can be found here.

I'm using a custom Yocto built O/S where pwm overlays are installed by default.

Here is a simple interactive example using the PWM class

root@rpi3:~# python3
Python 3.5.2 (default, Nov 22 2016, 06:54:46)
[GCC 6.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

Import the PWM class from pwm.py

>>> from pwm import PWM

Create an instance of the class for the PWM0 timer

>>> pwm0 = PWM(0)

Call export() before first use

>>> pwm0.export()

Setup a 1 ms period, 25% duty cycle pulse (period and duty_cycle units are nanoseconds)

>>> pwm0.period = 1000000
>>> pwm0.duty_cycle = 250000

Start the pwm timer

>>> pwm0.enable = True

Change the duty cycle to 50%

>>> pwm0.duty_cycle = 500000

Turn off the timer

>>> pwm0.enable = False

Create an instance for the PWM1 timer

>>> pwm1 = PWM(1)
>>> pwm1.export()

Setup a servo-like pulse with a 50 ms period and 2 ms duty_cycle

>>> pwm1.period = 50000000
>>> pwm1.duty_cycle = 2000000
>>> pwm1.enable = True

Set the servo pulse to 2.5 ms

>>> pwm1.duty_cycle = 2500000

Set the servo pulse to 1.5 ms

>>> pwm1.duty_cycle = 1500000

Back to 2.0 ms

>>> pwm1.duty_cycle = 2000000

Turn it off

>>> pwm1.enable = False

Unexport both timers

>>> pwm0.unexport()
>>> pwm1.unexport()
>>> quit()