https://learn.sparkfun.com/tutorials/reducing-arduino-power-consumption/all
Leo..
Yup,
Reducing the voltage, does have a catch though. Reducing the system voltage too much, without reducing clock speed, could make the microcontroller start to behave strangely. The RedBoard, Uno, and 5V Pro Mini all use a 16MHz crystal. Looking at the datasheet for the 328P, we can see that at 3.3V, the recommended maximum frequency is around 13MHz. The relationship between clock speed and system voltage is the reason our 3.3V Pro Mini uses a 8MHz clock instead of 16MHz.
Tom... 
Pardon, but I simply wish to stress important points.
Here is my "stock" answer to this:
The clear blunder is not comprehending what the "Vin" or "RAW" terminal [b]is[/b]. The regulator on the Arduino UNO/ Nano/ Pro Mini/ Mega2560/ Leonardo/ Pro Micro has very little heatsink, so will not pass very much current (depending on the input voltage and thus, how much voltage it has to drop) before it overheats and (hopefully reversibly) shuts down. It is essentially little more than a **novelty** provided in the very beginning of the Arduino project when "9V" power packs were common and this was a practical way to power a lone Arduino board [i]for initial demonstration purposes[/i]. And **even then** it was limited because an unloaded 9 V transformer-rectifier-capacitor supply would generally provide over 12 V which the regulator could barely handle.
Now while some "clones" such as the "RoboRed" and more sophisticated Arduinos do incorporate an actually functional switchmode regulator, it should simply be ignored on the older designs. 
Nowadays, 5 V regulated switchmode packs are arguably the most readily available in the form of "Phone chargers" and switchmode "buck" regulators to regulate down from 12 V or other available voltages are cheap on eBay or Aliexpress so these can be fed into the USB connector or (more appropriately) 5 V pin to provide adequate power for most applications. Unfortunately, many tutorials or "instructables" are seriously outdated or misleading and have not been updated to reflect the contemporary situation.
If powering directly from batteries, as long as the battery pack cannot exceed 5.5 V, this must be connected to the 5 V pin.
*3.3V pin
I was just giving my "stock" reply. On a Pro Mini it is generically labelled "VCC" as the PCB is exactly the same for 3.3 V 8 MHz and 5 V 16 MHz.
This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.