I need an answer fast.I want to make a keyboard class to handle a few buttons attached to my arduino. I want to use interrupts.The problem is I have to use the same interrupt function for all my buttons(it would beimpractical to create a routine for each button).So inside the routine I must know at least what pin fired the interrupt. How can I solve this?(I belive it can be solved by changing some registers but that would be too complicated).PS:there are only two buttons(pins 2 and 3 are enough)

Edit: Isn't possible to create/call an interrupt routine inside a class? (I know that the routine actually doesn't exist initially because the object of the class type wasn't created). Can this be done?

class Keyboard{
    struct btn{
      boolean pressed;
      uint32_t pressTime;
    btn button1;

    void int_handler(){

  • 1
    Keyboard::int_handler() must be static. – Edgar Bonet Apr 12 '17 at 21:08

You only have two external interrupts on the Uno, so a simple solution would be to call an "intermediate" routine, which remembers the button number. eg.


Those two functions could then call your main function passing down 2 or 3 depending on which one was called.


void int_handler2 ()
  int_handler (2);

void int_handler3 ()
  int_handler (3);

If you have more switches than that you can use pin-change interrupts. The typical way of detecting which one fired is to see which bits are different this time, compared to last time.

See my page about interrupts.

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  • Yes.I believe I'm gonna use the same old-functions to handle the interrupts.Thanks for the link! – sergiu reznicencu Apr 12 '17 at 21:32

I solved this in a more..compressed way. I already store the state of the buttons(pushed down or up-that is if they set their connected pin to 0 or 1).So I can have a single routine called by the microcontroller and then inside it decide what pin changed states(clever):

#define btn1Pin 2
#define btn2Pin 3

class Timer{
uint32_t Timer::start_time;
class KeyboardBtn{
    const static byte clicksDelay=255;
    struct btn{
      byte state=1;   //(0-keyDown / 1-keyUp) 2-Click 
      byte pin;
      Timer clickLapse;
    volatile static btn buttons[2];

      attachInterrupt(digitalPinToInterrupt(btn1Pin),keyPress,CHANGE );
      attachInterrupt(digitalPinToInterrupt(btn2Pin),keyPress,CHANGE );
    static void keyPress(){
      //digitalRead ==1 then button up
      for(int i=0;i<2;i++){
        if(bitRead(buttons[i].state,0)==digitalRead(buttons[i].pin)) continue;
        //i is the switched button
    byte stateChanged(byte key){
volatile KeyboardBtn::btn KeyboardBtn::buttons[2];

KeyboardBtn btn;
void setup() {

void loop(){
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