I am trying to create an alarm that wakes up at a certain time and does a series of instructions. To set the times that it wakes up, I am going to use the headphone of an Android device to send serial data to the MCU about what time(s) to wake up. I will simply plug it in, make the transfer and unplug the jack. Then the time is set on the MCU. The transfer will also sync the time to set the timer appropriately.
I can set a timer interrupt with a prescaler to give me 4s on each interrupt. Then use 2 bytes as secondary counter of some sort. That would give me 72 hours that I could wait and I only need 24 since I can reset when the day ends.
So my question comes when the device is reset. I can save the current time in the EEPROM and then read it on load but how much overhead does that have on current use? I want the battery to last as long as possible.
My question may need to be elaborated on but I was wondering if there was a better way or if I am going about this the correct way.