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Articles / IoT / Arduino

LED Candle Light with Timer

5.00/5 (4 votes)
25 Feb 2019CPOL1 min read 12.6K  
LED candle light with timer

LEDTimedCandle

I did a lot of research on battery powered LED candle lights circuits and code and was unable to find a time controlled LED candle light.

As I have some ATTiny13 left, I decided to use this little chip. As I want the LED to do a candle light for about 4 hours and then stay off for another 20 hours, I need one timer and counter. Another timer/PWM is needed to imitate a candle flickering. But the ATTiny13 has only one timer. On the ATTiny13, you can either use the timer or PWM.

PHP
// watchdog interrupt
ISR (WDT_vect)
{
  sec8_counter++;

#ifdef USE_HEART_BEAT_LED  
  //flash heart beat LED
  digitalWrite(LED2, HIGH);
  delay(1);
  digitalWrite(LED2, LOW);
#endif
  
  if(sec8_counter>=HOUR_INTERVAL){
    sec8_counter=0;
    if(bLedIsOn==1){
      on_hours++;
      if(on_hours>=MAX_ON_HOURS){
        bLedIsOn=0; //switch to OFF mode
        off_hours=0;
      }
    }else{
      off_hours++;
      if(off_hours>=MAX_OFF_HOURS){
        bLedIsOn=1; //switch to ON mode
        on_hours=0;
      }
    }
  }
  wdt_reset();
}  // end of WDT_vect

Fortunately, the ATTiny has also a Watchdog timer that can be used to call an interrupt function. The watchdog runs with a separate 128kHz clock, independent from the CPU clock. The largest timeout is 8 seconds. So I need to count this 450 times to have one hour.

PHP
void loop ()
{
  //sleep 20 hours and work 4 hours
  noInterrupts();
  if(bLedIsOn==1){
    doCandle();
  }else{
    digitalWrite (LED, LOW); //ensure LED is OFF
   goToSleep ();
  }
  interrupts();
}  // end of loop

The code makes the ATTiny13 sleep for another 8 seconds or light the LED. The ON phase is 4 hours and the sleep phase will be extended to 20 hours. The sequence starts with the ON phase, when power is applied. In the ON phase I measure about 3mA and in the OFF phase, the circuit needs 300µA.

Image 1

The circuit is documented in the Arduino code file. Running the ATTiny13 at lower clock than 9.6MHz did not change the power usage. But I switched to the 1.2MHz internal clock and disabled BOD (auto power down for low power) to get a longer runtime with two or three AA batteries.

https://github.com/hjgode/LEDTimedCandle/tree/master

CREDITS to all who share their knowledge, especially:

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)