Hi Ladies and Gents
I recently decided that I will investigate the Arduino Sleep Library and see how long I can get an Arduino to run of a single N size1.5v Battery. Yes ! of a 1.5V battery. if you are interested here is what you will need.
1) N size battery
2) N size battery Holder
3) 1v- 3.3v Step up convert ( I used sparkfun unit https://www.sparkfun.com/products/10967 )
4) Pro Mini 3.3v version ( https://www.sparkfun.com/products/11114 )
the code is written in such a way that when in sleep mode the current drawn is around 4.7 uA and when active around 7mA. but to this we need to do a couple of things to insure that not extra power is wasted on regulators and leds.
Step 1: Arduino Pro Mini Modifications
Depending on the Version/ Supplier of your Arduino pro mini board there a few mods needs to be made.
If you bought your pro mini board from spark-fun then you are lucky , there is only one solder jumper that needs to be removed to disable the on-board power regulator.
In the photo you will see there a 3 modes marked, de-solder Mod "1" and you are done , this disables the power regulator and drops the current consumption to around 380 uA in normal operation before the sleep code is uploaded
Other version of the board
In the photo attached you need to remove the on-board power led by de-soldering it .the LED is marked "3" and cut a trace on the board to disable the power regulator. see other photo for the trace that needs to be cut.
Once this is done.
You are one step closer ! this is all the hardware modifications that needs to be done.
Step 2: Wiring Setup
The Photo attached illustrate the minimum wiring required to make your Arduino work. my project made use of a cheap china data radio connected to pin 11 and pin 9 for power but you can update the code as you desire.
Step 3: Code
This is the code currently running on my board.
This code wakes up every hour and reads a analog value on pin A3 and transmits the value over a data link to a remote station. ( you can remove this code and replace with what ever you want to do upon wake-up.)
the code has comments that explains everything the code does and should be easy to modify as you require.
All battery life predictions that follow is just that predictions and should not be taken as factual but it should give you a good idea of expected battery life.
N size battery is around 900mah capacity.
At 4.5uA of consumption in sleep mode and 7mA in active mode the maths looks as follows.
Lets say you use the device once a day for 1 sec before going back to sleep
you would expect the battery to last 126000 hours total.
126000 - 30% for efficiency losses = 88200 hours.
88200 hours at 1.5v before the step up converter. so divide 88200 by 2 because our device runs at 3.3v
you get 44100 hours effective battery life.
that is 1837 days !!!
NOTE: I know there is better ways of doing this and longer times can be achieved by running at 1.8v but since most sensors run at either 3.3v or 5v I prefer to stick to 3.3v for now and using a N size battery makes the project very small size and the project stays small.