I've been developing a web interface for a simple raspberry pi project. It's only turning lights on and off, but I've been trying to add a dimming feature with PWM.
I'm using modWSGI with Apache, and RPi.GPIO for GPIO access. For my prototype I'm using (3) SN74HC595's in series for the LED outputs, and am trying to PWM the OE line to dim the lights.
Operating the shift registers is easy, because they hold the outputs in between updates. However, for PWM to work the GPIO.PWM instance must stay active between WSGI sessions. This is what I'm having trouble with. I've been working on this for a few days, and saw a couple similar questions here. But nothing for active objects like PWM, only simple counters and such.
My two thoughts are:
1) Use the global scope to hold the PWM object, and use PWM.ChangeDutyCycle() in the WSGI function to change brightness. This approach has worked before, but it seems like it might not here.
Or 2) Create a system level daemon (or something) and make calls to that from within my WSGI function.
For anyone looking at this in 2020:
I changed mod_wsgi to single thread mode. I'm not sure if it's related to Python, mod_wsgi, or bad juju, but it still would not last long term. After a few hours the PWM would stop at full off.
I tried rolling my own PWM daemon, but ultimately went with the pigpio module (is Joan on SE?). It's been working perfect for me.
Object persistence in WSGI