/*

There is a tactile switch and LED connected to Arduino Nano. The LED is off initially.

Depending on switch press, the LED blinks in following way.

1st Switch press: LED blinks at frequency of 0.5 Hz.

2nd Switch press: LED blinks at frequency of 1 Hz.

3rd Switch press: LED blinks at frequency of 2 Hz.

4th Switch press: LED turns off. Reset the Switch Press Counter. Repeat.

*/

#include "TimerOne.h"

#define RESET 0 // Constant for flags

#define SET !RESET // Constant for flags

#define SWITCH_PIN 3 // Defining switch input pin as pin 3 of Arduino Nano because it has interrupt available

#define LED_PIN 13 // Defining output for LED blinking as pin 13 of Arduino Nano because LED is at pin 13 on board

#define REFERENCE_TIME 1000000 // 1000000 us that is 1 second of reference time is set based on which different

                               // constants are set

#define SWITCH_DEBOUNCE_FREQUENCY 20 // 50 ms time that is 20 Hz frequency is set for testing valid switch input

#define TIMER_ONE_INTERRUPT_TIME 10 // Timer 1 interrupt occurance time in us

#define SWITCH_DEBOUNCE_TIME_LIMIT (REFERENCE_TIME / SWITCH_DEBOUNCE_FREQUENCY) / TIMER_ONE_INTERRUPT_TIME // Switch // debounce time limit count for correct switch press detection

#define LED_PIN_TOGGLE_TIME_TWO_Hz (REFERENCE_TIME / 2) / TIMER_ONE_INTERRUPT_TIME // Output LED toggle time count 

// for 2 Hz of blinking

#define LED_PIN_TOGGLE_TIME_ONE_Hz REFERENCE_TIME / TIMER_ONE_INTERRUPT_TIME // Output LED toggle time count for 1 Hz // of blinking

#define LED_PIN_TOGGLE_TIME_HALF_Hz (REFERENCE_TIME * 2) / TIMER_ONE_INTERRUPT_TIME // Output LED toggle time count // for 0.5 Hz of blinking

#define LED_PIN_OFF digitalWrite(LED_PIN, LOW) // Switching LED Off

#define LED_PIN_TOGGLE digitalWrite(LED_PIN, !digitalRead(LED_PIN)) // Toggling LED 

uint16_t switch_pressed_counter = 0;

uint32_t led_pin_toggle_counter = 0; // Counter for LED blinking which, when reaches to specific limit based on 

// operation, resets 

uint8_t led_blink_frequency_counter = 0; // Counter for deciding the LED Blinking frequency, which resets after 

// being greater than 3

bool switch_current_state = HIGH; // Variable that stores the current state of the digital input pin 3 by reading 

// its value, set to HIGH because HIGH indicates the switch is open 

bool switch_previous_state = HIGH; // Variable used for switch debouncing correction, set to HIGH because HIGH

// indicates the switch is open

bool switch_interrupt_flag = RESET; // Flag that is polled in the Timer ISR to decide whether the switch is pressed

bool switch_pressed_flag = RESET; // Once the switch_interrupt_flag becomes TRUE, this flag becomes TRUE and gets

// reset to FALSE after SWITCH_DEBOUNCE_TIME_LIMIT

void timer_one_isr(void)

{

    if(switch_interrupt_flag == SET) // Falling Edge detected at Pin 3

    {

        switch_interrupt_flag = RESET; // Resetting the switch interrupt flag

        switch_current_state = digitalRead(SWITCH_PIN); // Reading Switch Pin 3 and storing  

        if(switch_current_state == LOW) // The state of the Pin 3 has to be LOW to proceed further 

        {

            switch_pressed_flag = SET; // Flag is set to correct switch debounce

            switch_previous_state = switch_current_state; // Reference is stored to check switch debounce later 

        }     

    }

    if(switch_pressed_flag == SET) // Polling the flag to re-enter for cofirming correct switch input entry 

    // everytime till SWITCH_DEBOUNCE_TIME_LIMIT is reached

    {

        switch_pressed_counter++; // Increment the counter till SWITCH_DEBOUNCE_TIME_LIMIT    

        if(switch_pressed_counter >= SWITCH_DEBOUNCE_TIME_LIMIT) // SWITCH_DEBOUNCE_TIME_LIMIT is achieved

        {

            switch_current_state = digitalRead(SWITCH_PIN); // Reading Switch Pin 3 and storing

            if(switch_current_state == switch_previous_state) // Comparing the reading with the stored 

                                                              // reference value

            {

                led_blink_frequency_counter++; // Switch press is valid and hence increment a counter 

                                               // the value of which decides the frequency of LED Blinking

            }

            switch_pressed_flag = RESET; // Reset the flag

            switch_previous_state = HIGH; // Reset the reference value to HIGH because HIGH indicates 

                                          // the switch is open

            switch_current_state = HIGH; // Reset the current reading value to HIGH because HIGH indicates 

                                         // the switch is open

            switch_pressed_counter = 0; // Reset the counter

        }

    }

    switch(led_blink_frequency_counter) // Taking the counter in switch statement - it has values 0, 1, 2 and 3

    {

        case 1:

            led_pin_toggle_counter++; // Incrementing the counter till LED_PIN_TOGGLE_TIME_HALF_Hz 

                                      // that makes LED Blinking Time 2000 ms

            if(led_pin_toggle_counter >= LED_PIN_TOGGLE_TIME_HALF_Hz) // Counter has reached the value

                                                                      // LED_PIN_TOGGLE_TIME_HALF_Hz

            {

                led_pin_toggle_counter = 0; // Resetting the counter

                LED_PIN_TOGGLE; // Toggling the LED

            }

            break;

        case 2:

            led_pin_toggle_counter++; // Incrementing the counter till LED_PIN_TOGGLE_TIME_ONE_Hz 

                                      // that makes LED Blinking Time 1000 ms

            if(led_pin_toggle_counter >= LED_PIN_TOGGLE_TIME_ONE_Hz) // Counter has reached the value                                                                                     // LED_PIN_TOGGLE_TIME_ONE_Hz

            {

                led_pin_toggle_counter = 0; // Resetting the counter

                LED_PIN_TOGGLE; // Toggling the LED

            }

            break;

        case 3:

            led_pin_toggle_counter++; // Incrementing the counter till LED_PIN_TOGGLE_TIME_TWO_Hz 

                                      // that makes LED Blinking Time 500 ms

            if(led_pin_toggle_counter >= LED_PIN_TOGGLE_TIME_TWO_Hz) // Counter has reached the value        

                                                                   // LED_PIN_TOGGLE_TIME_TWO_Hz

            {

                led_pin_toggle_counter = 0; // Resetting the counter

                LED_PIN_TOGGLE; // Toggling the LED

            }

            break;

        default:

            led_pin_toggle_counter = 0; // Resetting the counter

            led_blink_frequency_counter = 0; // Resetting the counter

            LED_PIN_OFF; // Switching the LED Off

            break;

    }        

}

void switch_input_isr(void)

{

    switch_interrupt_flag = SET; // flag is set as FALLING Edge is detected

}

void setup() 

{

    pinMode (SWITCH_PIN , INPUT_PULLUP); // Pin 3 as Digital Input with internal pull up because 

                                         // the switch is placed in such a way that when pressed, 

                                         // Pin 3 connects to ground 

    pinMode(LED_PIN, OUTPUT); // Pin 13 which connected to the On-Board LED is set as output pin

    LED_PIN_OFF; // Switching LED Off as initialization

    Timer1.initialize(TIMER_ONE_INTERRUPT_TIME); // Initializing Timer 1 with 

                                                 // Timer overflow time as TIMER_ONE_INTERRUPT_TIME

    Timer1.attachInterrupt(timer_one_isr); // Taking 'timer_one_isr' as ISR

    attachInterrupt(digitalPinToInterrupt(SWITCH_PIN),switch_input_isr,FALLING); // Setting the digital input

                                                                                 // interrupt at Pin 3 

                                                                                 // with the mode 

                                                                                 // set for FALLING Edge

    TIMSK1 = _BV(TOIE1); // sets the timer 1 overflow interrupt enable bit

}

void loop() 

{

}