(power down mode)
http://interface.khm.de/index.php/lab/experiments/sleep_watchdog_battery
Use timer1 on Atmega
http://www.electronicsblog.net/exampl...-bit-hardware-timer-for-digital-clock
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http://search.digikey.com/scripts/DkS....dll?Detail&name=ATMEGA168A-AU-ND