I have decided to create temperature sensors in my house.
I use an Arduino Pro mini, with NRF24L01+ radio and a DS18B20 temperature sensor.
Everything works on 3.3V with a 18650 Li-ion battery, that I want to last for about a year on a single charge.
Basically, each sensor reads the temperature, transmits data to a receiver, and sleeps for a minute, then repeats the process.
The first problem is that the battery delivers a voltage that depends on the remaining capacity and can go up to 4.2 V. How do I down-regulate it to 3.3V?
Here are my questions, in the descending order of importance:
1) I heared about “Buck-Boost” voltage regulators (example) and low-dropout linear regulators (example). But do they consume any current if my sensor is in sleep mode most of the time and consumes only a few µA? So, what solution do I have that will only consume about a few µA in stand-by mode?
2) How can I detect a low battery condition? I'd like to be able to send a "low battery" signal to my receiver.
3) Can I power everything off after a grace period when I detect that battery is low?
I think that I need some kind of voltage regulation, because I already tried without, and the NRF24L01+ module isn't working properly with a fully-charged Li-Ion battery that delivers 4.2V (well-above the required 3.3V).
Thank you for your suggestions!