I am new to the electronics world and trying to figure out how to choose the battery for the circuit.
The circuit consists of an ATMega328P-PU, a DS2321 RTC and a PIR motion detector sensor. It needs 5 volts to operate normally.
Initially, when a button is pressed the circuit has access to power input which automatically starts the RTC, sets the time and powers the PIR sensor through a transistor for a specific duration. During which, the sensor is trying to detect motion (with small delay) and lights up an LED for a duration different than the former. After the detection period is over, the controller enters in deep power down state until a trigger from the RTC wakes it up and from there the controller cycles between detection and sleeping state.
By implementing the above, i was able to reduce power consumption as much as i could.
The circuit for the controller already has a 5V voltage regulator which I can use to power the whole circuit, however, my problem is here, as i am not supposed to go below 5V, i have to use a higher voltage as input but as you guys are pointing out: using a voltage regulator will eat up the battery and then the battery size won't even matter. Thank you for pointing it out since i didn't know about regulators, i only compared schematics and decided accordingly.
If i measure the current draw of the circuit and its in the milliAmps range then would it be safe to use voltage regulator with a drop out voltage of 3-6V?
I updated this post to ask help about choosing a regulator without dramatically compromising the circuit's power consumption.
Sorry for the inconvenience.