Hi all,
I want to do a temperature and humidity Bluetooth sensor. I have all the code working, but the current battery usage is very high. I read the posts about cutting the 3v3 jumper, but before doing that (and not being able to program the arduino any more), I wanted to ask how to make this arduino sleep between readings.
Assume I want to read the sensors once every 5 seconds and then send the readings over bluetooth. How do I use as few power as possible (to extend the battery life)? I couldn't find a deep sleep library for this model. Are there also considerations in the usage of bluetooth to extend the battery life as well?
On the other hand, I wanted to know what kind of battery can I use. I guess a 3.7v lipo battery is too high, but if it is possible to use please correct me (I would love to have rechargable batteries). If it is not possible, should I use two 1.5v regular batteries in parallel? After I cut the 3v3 jumper I understand I should power the arduino on the 3v3 pin instead of vin, am I right?
Thanks in advance for your help, and sorry for packing so many questions in a single post 
I'm investigating to make a datalogger with BT connection. I want to record rain gauge data, temperature... I'm looking at several possibilities. I excluded the Nano 33 BLE due to too high power consumption (see this). BT chip capabilities are also very partially supported. It may be an issue to reduce power drain.
Right now, I'm considering using the Adafruit ItsyBitsy nRF52840. It should have a deep sleep power consumption below 100 µA (it is using a AP2112 low dropout linear regulator with 55 µA quiescent current).
One may also have a look at the nRF52840 dongle. Current should be below 20 µA. You will have to switch to another development tool.
Considering the battery, you may consider LiFePO4 that have a voltage near 3.3 V, at least at room temperature. Self discharge of 3%/month is not an issue. Capacity of 1.2 A.h for a 18650 one. With a current of 100 µA, it will stay up for more than one year.
Do you really need to read and send data each 5 s?
Thanks for the information, I guess I should consider changing the board as you suggested. The board is not only power hungry but also the heat produced by it makes the temperature and humidity sensor readings basically useless.