i want to make a quick experiment and i need a view tipps to start. the idea is to place a photoresistor on the outside of a package and send it to someone by mail. in the inside of the box there is a arduino board with an sd card, which logs the values from the photoresistor every 5 seconds or so. and want to log the data on the sd card, just to see how much light my package gets during the trip. i want to use following tutorials to do so:
how long could i log data? can someone make a guess when the battery is empty? i dont know how to save data with an arduino without a sd card, and otherwise is the data save on the arduino board or will it be deleted when the battery is empty? i guess the package is sent in 2 days will the battery last so long? i also have an li-ion battery from my iphone but it just has 3.7 v and i read it is not save to use same because discharged. does the arduino board need much current? how to save much energie with good code? more batterys result in more power, but not in a longer overall battery life?