Arduino: Debounced Switch (ISRs only, no polling)

debounced_switch_interrupt.ino

/*
HOOK-UP: NORMALLY OFF
---------------------
Connect one pin of the push-button or toggle switch to pin D5.
Connect a 10K pull-down resistor between the above pin and GND.
Connect the other pin of the push-button or toggle switch to 5V.

HOOK-UP: NORMALLY ON
--------------------
Connect one pin of the push-button or toggle switch to pin D5.
Connect a 10K pull-up resistor between the above pin and GND
(or use the Arduino's weaker ~20-50K internal pull-up resistor
by setting pin D5 to INPUT_PULLUP mode).
Connect the other pin of the push-button or toggle switch to GND.

LED INDICATOR
-------------
This code example uses the built-in LED on the Arduino's 
digital pin D13 as an indicator for the push-button or
toggle switch state changes.
*/

#include <avr/wdt.h>                                    // collection of watchdog timer handling functions

void setup() {
    bitClear(DDRD, DDD5);                               // pinMode(5, INPUT);  
//  bitClear(DDRD, DDD5); bitSet(PORTD, PORTD2);        // pinMode(5, INPUT_PULLUP); (for internal pull-up resistor setup)
    bitSet(DDRB, DDB5);                                 // pinMode(13, OUTPUT);
    noInterrupts();                                     // disable global interrupts (cli);
        bitWrite(PORTB, PORTB5, bitRead(PIND, PIND5));  // digitalWrite(13, digitalRead(5));     
//      bitWrite(PORTB, PORTB5, !bitRead(PIND, PIND5)); // digitalWrite(13, !digitalRead(5)); (for pull-up resistor setup with normally off mode)
        bitSet(PCMSK2, PCINT21);                        // specify interupt on pin D5
        bitSet(PCIFR, PCIF2);                           // clear any outstanding interrupts for D8 - D13
        bitSet(PCICR, PCIE2);                           // enable pin change interrupts for D8 - D13
        bitClear(MCUSR, WDRF);                          // clear watchdog timer interrupt flag to allow clearing of WDE (2nd operation below)
        WDTCSR = (1 << WDCE) | (1 << WDE);              // enter watchdog timer configuration mode
        WDTCSR = (1 << WDIE) | (1 << WDP1);             // set watchdog timer overflow interrupt (without system reset) to 64mS
    interrupts();                                       // enable global interrupts (sei);
}

void loop() {}

ISR(PCINT2_vect) {                                      // pin change interrupt service routine for pin D5
    wdt_reset();                                        // start measuring fixed time interval (64mS) after which watchdog timer ISR is automatically triggered
    GPIOR1 = bitRead(PIND, PIND5);                      // digitalRead(5) and store value in the second General Purpose I/O register
//  GPIOR1 = !bitRead(PIND, PIND5);                     // !digitalRead(5) and store (inversed) value in the second General Purpose I/O register (for pull-up resistor setup with normally off mode)
}

ISR(WDT_vect) {                                         // watchdog timer interrupt service routine for switch debouncing
    if (GPIOR1 == bitRead(PIND, PIND5)) {               // verify new state presists by compering value of the second General Purpose I/O register with current state of pin D5
//  if (GPIOR1 != bitRead(PIND, PIND5)) {               // verify new state presists by compering (inversed) value of the second General Purpose I/O register with current state of pin D5 (for pull-up resistor setup with normally off mode)
        bitWrite(PORTB, PORTB5, GPIOR1);                // digitalWrite(13, GPIOR1);
        bitSet(PCIFR, PCIF2);                           // clear any outstanding interrupts for D8 - D13
    }
}

/*

Reference: http://gammon.com.au/interrupts

ISR (PCINT0_vect) {
  // handles pin change interrupts for D8 - D13
}

ISR (PCINT1_vect) {
  // handles pin change interrupts for A0 - A5 
}

ISR (PCINT2_vect) {
  // handles pin change interrupts for D0 - D7
}

void setup () { 
  // pin change interrupt (example for D9)
  PCMSK0 |= bit (PCINT1);  // want pin 9
  PCIFR  |= bit (PCIF0);   // clear any outstanding interrupts
  PCICR  |= bit (PCIE0);   // enable pin change interrupts for D8 - D13
}

 ARDUINO PIN INTERRUPT VECTOR MAPPING
--------------------------------------
D0    PCINT16 (PCMSK2 / PCIF2 / PCIE2)
D1    PCINT17 (PCMSK2 / PCIF2 / PCIE2)
D2    PCINT18 (PCMSK2 / PCIF2 / PCIE2)
D3    PCINT19 (PCMSK2 / PCIF2 / PCIE2)
D4    PCINT20 (PCMSK2 / PCIF2 / PCIE2)
D5    PCINT21 (PCMSK2 / PCIF2 / PCIE2)
D6    PCINT22 (PCMSK2 / PCIF2 / PCIE2)
D7    PCINT23 (PCMSK2 / PCIF2 / PCIE2)
D8    PCINT0  (PCMSK0 / PCIF0 / PCIE0)
D9    PCINT1  (PCMSK0 / PCIF0 / PCIE0)
D10   PCINT2  (PCMSK0 / PCIF0 / PCIE0)
D11   PCINT3  (PCMSK0 / PCIF0 / PCIE0)
D12   PCINT4  (PCMSK0 / PCIF0 / PCIE0)
D13   PCINT5  (PCMSK0 / PCIF0 / PCIE0)
A0    PCINT8  (PCMSK1 / PCIF1 / PCIE1)
A1    PCINT9  (PCMSK1 / PCIF1 / PCIE1)
A2    PCINT10 (PCMSK1 / PCIF1 / PCIE1)
A3    PCINT11 (PCMSK1 / PCIF1 / PCIE1)
A4    PCINT12 (PCMSK1 / PCIF1 / PCIE1)
A5    PCINT13 (PCMSK1 / PCIF1 / PCIE1)

*/