Hardware debounce using RC filter and correct GPIO configuration on MCU side

Question

I need a quick way of adding some de-bouncing to a button in hardware. I am aware that ultimately the software should really do it, but for now I came up with this, saw it somewhere on internet:

Does it make sense? I would say GPIO node is HIGH when the button is not pressed, and it will be LOW when button is pressed.

In that case, what should be the configuration on MCU side? Obviously the pin should be configured as INPUT, but the question is should I enable any pull-up or pull-down resistors internally in the MCU?

Should the trigger be POS EDGE or NEG EDGE or HIGH or LOW? I am a bit confused about all the different possibilities.

Answer 1

Do not enable any pull up / down resistors inside the mcu, and the switch will generate a trailing edge when depressed, so if you want to trigger your event when the switch is depressed you configure for “Neg edge”. “Low” may also work but depending on how the interrupt works it may continuously retrigger when the button is held - review level sensitive vs edge sensitive interrupts for more information.

Answer 2

In my opinion you should not go for external hardware to fix your problem. Don't fix your software with hardware.

Assumption:

You want to read a simple tactile button as HMI. Just use some debouncing code in the main - no interrupts required.

#define ReadIO() {.....}
uint8_t ButtonState = 0;

bool debounce() {
  static uint16_t state = 0;
  state = (state<<1) | ReadIO() | 0xfe00;
  return (state == 0xff00);
}

main void(void){

    //Setup

    //Endless
    while(1){

        if (debounced()) {
           //Do action
        }
    }
}

You can now directly connect your switch to the port. Use the internal pulldown. No external components required.

Vcc->switch (normally open)->port (with internal pulldown)