Arduino uno battery

Projects General Guidance
1

Hi everyone,

I have some doubts about what battery use for Arduino. I have one soil moisture sensor connected to arduino and I need a battery that last 3 months. The programm gets sensor data 2 times a day and have to send the data via GPRS module to a server. Considering that I only have to "wake up" the Arduino twice a day, what is the best option?

Thanks in advance :wink:

P.S: sorry for my English...

2

Are you able to power down a lot of the electronics? Like the GPRS module? If not, the battery choice will be difficult as the non-sleeping parts (all but the microcontroller - voltage regulator, USB interface, voltage autoswitcher, power-on LED, GPRS module, sensor) will all drain the battery anyway.
A better plan would be a standalone microcontroller that can connect to everything else and control the connections to power. When going into sleep mode, bring all control lines low, turn off power to the devices using P-channel mosfets, and then go into power down sleep mode. Upon wakeup, bring up power, then bring up the control lines.
That will keep the devices from receiving power thru the control lines and damaging the IO lines. Many parts have limits where the IO lines are not to go more than 0.5V above VCC and 0.5V below Gnd to keep power from entering the device thru the IO lines.

3

Well use of a soil moisture sensor would tell me using a solar charger might be an option (unless you are doing mushroom farming or something similar). Adafruit sells solar chargers, and lipo battery chargers that allow the battery to be charged from solar while powering the Arduino. I'm sure there are other places that have a solar setup, I'm just familiar with the adafruit catalog. Note, I do not own the solar charger, though I do use their lipo batteries.

Nick Gammon has written a tutorial on how to make your microprocessor much more memory efficient, including sleep modes, etc. http://www.gammon.com.au/power. His example of a bare bones processor reading the temp. every so often ran for at least 5 months on just 3 rechargeable AA batteries.