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I have an AT-Tiny (trinket) and I want to trigger LED on for 30 seconds every 24 hours. I'm using the timer library as follows

timer.setInterval(86400000, toggleit());

void toggleit()
{
  turnLightOn();
  delay(6000);
  turnLightOff();               
}

How accurate will this be, if it's off by a few minutes each day that's fine, but will this drift over time? Also does it make a difference if I'm running it in 8 or 16 bit mode?

  • Just measure how long it actually take. Then change 86400000 to a lower or higher value, depending on whether it took more of less that 24 hours to re-flash the led. You could still get some drift, depending mostly on the temperature, but probably accurate enough in your case. – Gerben Nov 22 '16 at 9:18
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The on-chip systemclock is not very accurate. You can calibrate it to some degree but it also depends on the temperature and load of the MCU. You will need a high quality quartz oscillator as external clock source to reduce it. But it will still have a drift. Switching from 8-bit to 16-bit won't make a difference.

In your case an RTC sounds like the way to go.

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