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SGROU.1
SGROU.1
Associate III
January 21, 2021
Question

Output compare to turn on a LED

  • January 21, 2021
  • 5 replies
  • 1730 views

Hello,

I am working on a STM32F723E-Disco,

I am learning the use of timers and their functionalities.

In particular, I try to use the output compare.

What I'm trying to do is to use the output compare to turn on a LED when the output compare is triggered.

I don't know where to start, I don't see any examples of what I want to do on the internet.

Do you have any examples, help please?

Thanks

This topic has been closed for replies.

5 replies

KnarfB
KnarfB
Super User
January 21, 2021

There are samples included in the firmware. windoes location: %USERPROFILE%\STM32Cube\Repository\STM32Cube_FW_F7_V1.16.0\Projects\STM32F746ZG-Nucleo\Examples\TIM, alsoavail. online. Not precisely for your board, bt close.

hth

KnarfB

Ozone
Ozone
Principal
January 21, 2021

Be sure to compare the LED current requirement with the limits of the GPIO pin you intend use for driving it.

SGROU.1
SGROU.1Author
Associate III
January 22, 2021

0693W000007CGszQAG.pngThanks for your answers.

I looked at the samples provided by STM32, having also STM32F429, I used it for my tests. It helped me a lot, I think I succeeded.

However, I have a second question,

is it possible that when the output compare is triggered, the PIN of the timer of my channel goes directly to the LED?

Because for the moment, I have configured the TIMER channels directly on the LED PIN.

On my STM429, I can't select any timer going to my LED pin (attached image), how can I make the channel timer corresponding to my output compare to be linked to this pin ?

I don't know if you see what I want to do, I hope so.

Thanks you,

KnarfB
KnarfB
Super User
January 22, 2021

If you leave the LED pins (PG13 PG14) in the Reset_State (no Output) you may safely connect a wire from the timer channel output pin to the LED pin to make the LED blinking.

If you don't like wires and timing is not very critical, you can enable a timer OC interrupt and toggle the LED from the interrupt handler in software.

Note that OC is only a short pulse (unless you use Toggle on Match mode). You may also look into PWM mode for dimming a LED.

SGROU.1
SGROU.1Author
Associate III
January 22, 2021

To be honest, I don't really like wires.

So if I want to turn on the LED by the software, I put my LED in GPIO_OUTPUT.

Then in my output compare callback function : "HAL_TIM_OC_DelayElapsedCallback", I check if the channel of my timer is equal to HAL_TIM_ACTIVE_CHANNEL_X, if it returns true, it enters my condition and turns on my LED.

That's how I see the program, but this one doesn't work, is there something I didn't understand? 

void HAL_TIM_OC_DelayElapsedCallback(TIM_HandleTypeDef *htim){
 
	if(htim->Channel == HAL_TIM_ACTIVE_CHANNEL_1){
		HAL_GPIO_WritePin(LD3_GPIO_Port, LD3_Pin, GPIO_PIN_SET);
	}
}

Yes I use the toggle on match mode.

Yes I have already succeeded for dimming a led with the PWM mode.

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