Rising edge interrupt triggering multiple times on STM32 Nucleo

Question

I am using the STM32 NUCLEO-F401RE microcontroller board.

I have a speaker programmed to change frequency by a set amount when the joystick is pushed up/down. My issue is

Answer 1

Mechanical switch bounce is a feature of all mechanical switches to a lesser or greater extent. It is often necessary to implement "debouncing" in software especially if the switch is directly driving an interrupt as in this case.

A quick Google search for software denounce techniques yields some rather poor techniques IMO. I seen it done poorly more times than well unfortunately.

I suggest that in the switch ISR you start (or restart in the event of a "bounce") a hardware timer for a period of say 20ms or so (longer than the switch bounce time, but shorter than the time you could possibly to genuinely release the switch). Then in the timer ISR, you test the state of the switch and change the frequency accordingly:

Pseudocode:

void upISR()
{
    debounceTimerRestart() ;
}

void downISR()
{
    debounceTimerRestart() ;
}

void debounceTimerISR()
{
    debounceTimerStop() ;

    tDirection dir = getJoystickDir() ;
    swithc( dir )
    {
        case UP :
        {
            increaseFrquency() ;
        }
        break ;

        case DN :
        {
            decreaseFrquency() ;
        }
        break ;
    }
}

What this does is trigger a timer interrupt shortly ("debounce time") after the switch stops bouncing. Note the timer is "single-shot" not periodic.

Below I present an enhancement at @BenVoigt's suggestion (in comments). I am keeping it separate to make it clear it was his work. The above will generally work, but if you have a particularly poor switch the following would resolve issues, and at little cost, so you may as well:

void debounceTimerISR()
{
    debounceTimerStop() ;

    static tDirection previous_dir = CENTRE ;
    tDirection dir = getJoystickDir() ;

    // If the state changed...
    if( previous_dir != dir )
    {
        previous_dir = dir ;

        switch( dir )
        {
            case UP :
            {
                increaseFrquency() ;
            }
            break ;

            case DN :
            {
                decreaseFrquency() ;
            }
            break ;
        }
    }
}