Fading LEDs and Trying PWM Drivers along with the Linux sysfs

General Discussion
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1

I have a PWM Driver and I was testing it for fading a LED.

#!/usr/bin/python3
 
from time import sleep
import signal
import sys
 
from pwm_driver import Pwm
 
LED = Pwm(path="/sys/class/pwm/pwmchip0/pwm0/", enabled=False, period=100000, duty_cycle=85000)
 
Duty = 0
low  = 0.8 # Smallest angle (in ms)
hi   = 2.4 # Largest angle (in ms)
pos  = 1.5 # Current position, about middle ms)
step = 0.4 # Step size to next position
 
try:
    LED.enabled=True
    while True:
        pos += step    # Take a step
        if(pos > hi or pos < low):
            step *= -1
        Duty = LED.duty_cycle
        Duty = str(pos)
        print('pos = ' + str(pos) + ' duty_cycle = ' + Duty)
        (LED.duty_cycle)
        sleep(0.2)
except KeyboardInterrupt:
    LED.enabled=False
    pass
 
# Trying to fade a LED
# This is from your (@zmatt) PWM driver written a while back and some code from docs.beagleboard.org

The driver allows for setting (path=’/sys/class/pwm/pwmchip0/pwm0/”, enabled=False, period=100000, duty_cycle=85000) and I was using the above code to handle this effort.

Does anyone see an error or how the above code from the driver may or may not work as intended?

2

That is where I got the code for the back and forth motion…

3

Why do you only want to set LED.enabled = False, when the user presses Ctrl+C ? Surely that should be in a finally: so it’s put back after any Exception at all, no matter what type it is. The pass is pointless too.

try:
    ...
except KeyboardInterrupt:
    LED.enabled=False
    pass

Does activating the PWM driver really only need LED.enabled = True, not some method call?

What’s the point in reassigning Duty, and the duplicating str(pos)? I don’t really understand the point of pos at all, other than the code’s best guess at what LED is doing. Isn’t there anything available in the pwm_driver API to introspect LED to get definitive information from?

If the sleep was explcitly related to step, that would at least make more sense as a time tracker.

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4

No…LED is made by me to call it later. Pwm is the class.

There is no point in reassigning Duty. I just figured it would make it easier. True and False for .enabled is how the code works that is being called.

while True:
    pos += step    # Take a step
    if(pos > hi or pos < low):
        step *= -1
    duty_cycle = str(round(pos*1000000))    # Convert ms to ns
    # print('pos = ' + str(pos) + ' duty_cycle = ' + duty_cycle)
    f.seek(0)
    f.write(duty_cycle)
    time.sleep(ms/1000)

That is some original code from the docs. pages: Motors — BeagleBoard Documentation

So, I could in fact add the sleep(ms/1000) code back to the source but I figured I could get away without it.

5

Also. I found this lib for PWM along with other peripheral accessing. See here: GitHub - linux4sam/mpio: Microchip Peripheral I/O Python Package · GitHub

Right now, I may be able to get it to work but came across some issues after changing the library up some.

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