Can Atmega328P weak itself up from sleep mode every 24 hours without RTC or other components.I am planing to log DHT11 results to SD card for a month outdoors and it should be powered from 2200mAh battery for over a month.If it is really necessary I have 5-6 of DS1307 but I don't think they can wake up arduino.Sorry if I'm asking at wrong place
Use a DS3231
Put the controller to sleep, wake up now and the check the time.
If it is time, record the data.
power savings:
I would use the DS3231 to wake up the 328p once each day.
Good thing is that I'll be making a PCB for it with just crystal,2x22pf capacitors,microcontroller,DHT11,N-channel mosfet for turning DHT11 on and off,and pulldown resistors for mosfet.I think it should draw less current than original arduino.Also I just came up with idea of adding SIM900 on a PCB insead of SD card,so my DHT11 readings can be sent directly to my phone.Maybe i should leave microcontroller working all the time and running simple "RTC" program and when it thinks 24 hours have passed turn on SIM900 and make sure time is good and send a reading,then turn SIM900 off.What do you think,is that good idea?