Demonstration code for several things at the same time

Projects General Guidance
4

I prefer using switch statements for may state variables rather than ifs, even if there's only two states something can be in. I find it easier to follow than trying to match an else with the right if to find out what's going on, especially if they're nested.

So instead of:

void updateLed_A_State() {

  if (led_A_State == LOW) {
    if (currentMillis - previousLed_A_Millis >= led_A_Interval) {
       led_A_State = HIGH;
       previousLed_A_Millis = currentMillis;
    }
  }
  else {
    if (currentMillis - previousLed_A_Millis >= blinkDuration) {
       led_A_State = LOW;
       previousLed_A_Millis = currentMillis;
    } 
  }    
}

I prefer:

void updateLed_A_State()
{
  switch( led_A_State )
  {
    case LOW:
      if (currentMillis - previousLed_A_Millis >= led_A_Interval)
      {
        led_A_State = HIGH;
        previousLed_A_Millis = currentMillis;
      }
    
    case HIGH:
      if (currentMillis - previousLed_A_Millis >= blinkDuration) 
      {
        led_A_State = LOW;
        previousLed_A_Millis = currentMillis;
      }
    default:
      ;
  }
}

I also prefer a different bracketing style to yours, but that's neither here nor there.