Control LED light

[Ala]

hey there

I have a project where I need to control light of a LED and dim it. usually we use TIMER PWM GENERATION. for example in CubeMX I set a pin to TIMx CHy and by choosing "PWM Generating CHy" I can easily control LED light using PWM signal.

but in my case this LED pin has no TIM Channel connected to it. what should I do to dim the LED?

[Ahmet Yasin CİVAN]

You can use GPIO with delay loops.

[Ala]

sure! but this occupies CPU and also is not efficient.

is there a way to generate an internal PWM signal and control LED with it?

[Nikita91]

Set a timer as timebase at 1000Hz, and in the ISR toggle the LED GPIO.

This will generate your "PWM"

You should be able to manage about 16 light levels

[Ala]

this one sounds great! but it affects the entire process, as ISR happens fast, though I might end up doing such...

[Nikita91]

You can set the timer to 500Hz, and the ISR is quite short.

[Javier1]

So you need to implement a softpwm.

There is three ways:(that i can think of now)

• software bitbang (toglegpio;delay;togglegpio),Process intensive, not scalable, huge jitters.
• interrupt based bitbang (as @Nikita91​ )said , less process intensive, jitter depends of the interrupt priority.
• DMA based GPIO bitbang, lesser processor intensive, very scalable, a bit more complex and memory hungry.

If your system can spare those interrution times i would choose the second option.

I had to implement a bunch of pins at the same time and my system couldnt spare lots of processing time so i had to do the third option

https://www.hackster.io/javier-munoz-saez/all-pins-as-pwm-at-the-same-time-baremetal-stm32-1df86f

[Javier1]

You could also use the DAC if that function is available in your pin (overkill)

[gbm]

You may use 2 channel DMA to GPIO BSRR triggered by timer update and compare; set on update, reset on compare. The only quirk is to prevent outputting active level at timer update when duty is equal to 0.