Arduino timer interrupt

Frugal Timer1 interrupt support for Arduino R3 NANO and R3 UNO

Important

Maximum interval between interrupts is 4193 ms

Info (PrincOps)

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• Set TIMER1_COMPA_vect interrupt vector to the correponding ISR (Interrupt Service Routine)

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• Set WGM12 bit of register TCCR1B for CTC (Clear Timer on Compare match) mode
  TCCR1B |= (1 << WGM12);

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• Set CS10 and CS12 bits of register TCCR1B for prescaler = 1024
  TCCR1B |= (1 << CS12) | (1 << CS10);

Use (1<<CS11) for prescaler = 8, (1<<CS10)|(1<<CS11) for prescaler = 64, (1<<CS12) for prescaler = 256 as shown above

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• Set OCIE1A bit of register TIMSK1 to enable Timer1 TCI (Timer Compare Interrupt) mode
  TIMSK1 |= (1 << OCIE1A);

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Usage

The timer_interrupt_demo.ino example is a sensor control that uses interrupts and keeps the previous (true or false) reading while hesitating/flickering and only changes it when stable.

Timer interrupt occurs every 10 ms in the example below

Tip

Note the use of static variables for the slow job

#include "timer_interrupt.h"

#define TIMER_INTERRUPT_MS 10
#define SLOW_GATE          11
#define A_LONG_TIME (60L*1000/TIMER_INTERRUPT_MS)
// One minute here, may be many days long

// =============================================================================
// The timer interrupt service routine (ISR)
SET_TIMER_ISR({
  // Do the fast job(s) here, once every 10 ms

  // A slow job
  // Toggle SLOW_GATE pin once per minute
  static unsigned long slow_counter = 0;
  if (++slow_counter >= A_LONG_TIME)
  {
    slow_counter = 0;
    static bool slow_status = false;
    slow_status = !slow_status;
    digitalWrite(SLOW_GATE, slow_status ? HIGH: LOW);
  }
});

// =============================================================================
void setup()
{
  pinMode(SLOW_GATE, OUTPUT);
  // The rest of the setup

  INIT_TIMER_INTERRUPT(TIMER_INTERRUPT_MS);
}

// =============================================================================
void loop()
{
  // The rest of the logic     
}